Cell Structure - sciencemania.net bio 11 unit1.pdf · lates everything that enters and exits a cell, the nucleus controls all of ... structure manages a different cell ... 2 Cell

U N I T UN C H A P T E R 2

Cell Structure and Function

36

By the end of this unit, you will be able to:

� describe how organelles and othercell components carry out variouscell processes and explain howthese processes are related to thefunction of organs (2.3Investigation 1, Investigation 2)

� describe the fluid mosaic structureof cell membranes (2.2)

� illustrate and explain importantcellular processes, including theirfunctions in the cell, the ways inwhich they are interrelated, andthe fact that they occur in all livingcells (2.1, 2.2, 2.3)

� identify new questions andproblems stemming from the studyof metabolism in plant and animalcells (2.3)

� explain how scientific knowledgeof cellular processes is used intechnological applications (2.2, 2.3)

� analyze ways in which societalneeds have led to technologicaladvances related to cellularprocesses (2.2)

SPECIFICEXPECTATIONS

FIGURE 2.1 The diagram of a plant cell indicates the importance of the cell wall,choroplasts and central vacuole. These are all structures that are not present in animal cells

Cells

What do you remember about cells? You have probably looked at cells underthe microscope in previous science classes. Sketch a diagram of a cell frommemory. Include structures in your drawing and label them. Compare yourdrawing with those of other students. Were you reminded of some organellesyou had forgotten by looking at others’ drawings?

37

All living things are made of cells, but despite the amazing diversity of lifeon earth — everything from microscopic bacteria to giants squids to hu-

mans — all cells contain similar basic parts. Each part or structure has aspecific job or function to perform. For instance, the cell membrane regu-lates everything that enters and exits a cell, the nucleus controls all of thecell’s activities, and vesicles transport materials from place to place withina cell. If any structure fails, the operation of the entire cell is compromised.For example, when a basic cell structure called a lysosome malfunctions ina human cell, about thirty other diseases collectively known as lysosomaltransport diseases.

In this chapter, you will be introduced to cells and basic cell theory. Youwill study the relationship between surface area and volume, which explainswhy cells are so small. You will learn to differentiate between the two basictypes of cells: prokaryotic and eukaryotic. You will investigate the types ofstructures mentioned above as well as other important cell structures suchas the endoplasmic reticulum, golgi complex, and mitochondria. You will–examine how each structure manages a different cell function. As you proceedthrough the chapter, you will gain an understanding of some of the serioushealth problems that result when any one of the cell’s structures malfunctions.

D i s c o v e r i n g B i o l o g y

CHECKPOINT

Make a chart to list whatyou know about cell struc-tures and how they func-tion.

Structure Function

38 U N I T 1 Ce l lu la r Funct ions

Cells had been observed since the 1600s,when Robert Hooke made his first ob-servations of cells in cork, but their im-portance as the basic unit of life was notrealized until the 1800s when the celltheory was developed from the workof many scientists. Schleiden, Schwann,and Virchow each made a proposal thatcontributed to the development of thetheory. Schleiden was the first to observethat all plant tissue was composed ofcells; Schwann soon extended the ob-servation to animal tissue and then toall living tissue. Later, Virchow extendedthe theory by adding that all cells couldarise only from other cells. Virchow’scontribution laid to rest the theory ofspontaneous generation.

Even today, the cell theory is thefoundation used by biologists to try tounderstand life on Earth. The moderncell theory states:

• All living things are composed ofcells.

• Cells are the basic units of living or-ganisms.

• All cells come from pre-existing cells.

Cell Size and Shape Most plant and animal cells are similarin size—they are very small, rangingsomewhere between 10 and 100 µm. Inthis chapter you will be seeing actualphotos taken through a microscope ofcells and cell structures. These photosare called photomicrographs.

Why are most cells small? There aregood reasons. A cell needs a constantsupply of energy and a method to riditself of waste products. Cells obtain en-ergy and get rid of waste productsthrough their cell or plasma membrane.It is therefore better for a cell to have the

2.1 A Background to Cell StructureKey Understandings

When you have completed this section, you will be able to: � explain the cell theory� describe the relationship between surface area and volume� understand why cells are small

MATHL INK

Remember the formulas:a) Volume of a cube = s3

b) Surface area of a cube = 6s2

FIGURE 2.2 From left to right Schleiden, Schwann, and Virchow. Each contributedto the cell theory, in 1838, 1839, and 1858 respectively.

WEBL INK

Robert Hooke, Antonie vanLeuwenhoek, and HenriDutrochet contributed to thecell theory. Research the roleof each of these scientists andprepare a written report tosummarize your information.Begin your research atwww.pearsoned.ca/biology11.

C H A P T E R 2 Cel l S t ruc tu re and Funct ion 39

maximum membrane surface area pos-sible, while at the same time minimiz-ing the distance within the cell thatimportant molecules have to travel.Minimizing distance also minimizes thetime taken for cell processes. With thisin mind, it is easy to show mathemati-cally why it is better for cells to be small.

FIGURE 2.4 Little and big. The size of various objects.

FIGURE 2.3 Hidden life. Microscope enlarge-ments of the point of a pin show living organ-isms, bacteria, present on an object that wemight think unsuitable for supporting life.a) �85; b) �425; c) �2100)

blue whale

human

chicken egg

frog egg

plant andanimal cells

cell nucleus

most bacteria

mitochondria

smallest bacterialarge virus

proteins

lipids

atoms

100 m

10 m

1 m

10 cm

1 cm

1 mm

100 µm

10 µm

1 µm

100 nm

10 nm

1 nm

0.1 nm

1 meter (m) = 1.09 yards1 centimeter (cm)1 millimeter (mm)1 micrometer (µm)1 nanometer (nm)

= 10–2 (1/100) meter (1 cm = 0.4 inch)= 10–3 (1/1000) meter= 10–6 (1/1,000,000) meter= 10–9 (1/1,000,000,000) meter

Section 2.1 Review


As you can see in Table 2.1, smallercells, such as those on the right, bene-fit from a much larger surface area tovolume ratio than do larger cells. In re-ality, no cells are perfect cubes or

spheres and a great variety of shapesexist. For example, human nerve cellscan be very long, but to maintain a highenough surface area to volume ratio tosurvive, they are very slender.

INFOBIT

Although most cells are aboutthe same size, there are excep-tions: Mycoplasma (at approxi-mately 0.2 µm in diameter) isthe smallest cell yet discoveredand the single-celledAcetabularia sp. (at 5–7 cm) isone of the largest cells.

Understanding Concepts

1. Biologists accept that life begins at thecellular level of organization. Providetwo pieces of evidence to support thisview.

2. What is the normal size range for mostcells? Explain why it is an advantagefor cells to be small.

3. Calculate the volume and surface areaof 512 cubes with sides of 0.25 cm.

Applying Inquiry/Communication Skills

4. Two different types of cells have the fol-lowing dimensions. Cell #1 is 2 mm� 2 mm � 8 mm and cell #2 is 1 mm� 2 mm � 16 mm.

a) Calculate the volumes of cell #1 and#2. How do they compare?

b) Calculate the surface areas of thetwo cells. How do they compare?

c) Calculate the surface area to vol-ume ratio for the two cells. How dothese values compare?

d) What do the values in c) tell youabout the importance of cell shape?

Use this information to explain hownerve cells can be very large (up to1 m in length).

5. Cells were observed as early as 1665.Since that time, important new dis-coveries about the cell have occured.Research and construct a time-line ofobservation and discovery.

6. Assume you are a 19th-century re-porter assigned to explain the impor-tance of the discovery of cells and thecell theory. Write a supported para-graph to tell your readers why suchdiscoveries are important to them.

Making Connections

7. An understanding of cells informs andaffects everyone.

a) Explain how the cell theory relatesto other living organisms besideshumans, e.g., to a dog or anamoeba.

b) Describe four ways that cells haveaffected your life.

Refer to page 59,Investigation 2

I n v e s t i g a t i o n

One (2 � 2 � 2)-cm cube Eight 1-cm cubes Sixty-four 0.5-cm cubes

Surface Area (cm2) 24 48 96

Volume (cm3) 8 8 8

Surface Area to Volume Ratio 3:1 6:1 12:1

TABLE 2.1 The Effect of Size per Cube Side on Surface Area and Volume


2.2 Cell StructuresKey Understandings

When you have completed this section, you will be able to: � distinguish between prokaryotic and eukaryotic cells� describe how cell structures manage various cell functions� explain the fluid mosaic structure of membranes

There is no such thing as a typical cell,but all cells can be classifed accordingto certain characteristics. Every organ-ism must be either a prokaryote or a eukaryote.Prokaryotic cells lack internalcompartments and membrane-bound organelles, and these organisms are all

unicellular. Bacteria and other similarcells of the kingdoms Archaebacteria andEubacteria are the only prokaryotes. Allother cells are eukaryotic and have amembrane-bound nucleus and or-ganelles. Eukaryotes may be single-celled or multicellular and include all

FIGURE 2.5 Comparison ofprokaryotic and eukaryoticcells. Prokaryotes, theArchaebacteria, andEubacteria are single-celledorganisms. Eukaryotes maybe single- or multicelled andinclude protists, fungi, plants,and animals.

Prokaryotes Eukaryotes

DNA

Size

Organization

Metabolism

Organelles

in “nucleoid” regionwithin membrane-bound nucleus

usually smaller

usually larger

usually single-celled often multicellular

may not need oxygen usually need oxygen to exist

no organelles membrane-bound organelles

O2O2

O2 O2 O2

O2

O2

protists, fungi, plants, and animals.Protists are organisms like Amoeba andParamecium.

Eu is a Greek word meaning “good.”Therefore eukaryotes have a “good” orreal nucleus as well as other cell struc-tures. Eukaryotic cells are divided intocompartments by membranes. These dif-ferent compartments have specific func-tions and are called organelles. Each typeof organelle has its own unique function.Throughout the rest of this chapter youwill learn about the structure and func-tion of the various cell organelles.

Cell (Plasma) MembraneThe cell membrane is the only thing be-tween a cell and its outside environment.It has a crucial role to play in the life ofa cell: it must control what enters andleaves the cell. The cell membrane must

allow a sufficient number of foodmolecules, such as glucose, to pass inand must also allow for the prompt re-moval of waste products, such as car-bon dioxide. Without this control the cellwill die.

The cell (or plasma) membrane ismade of a double layer of phospholipidmolecules called the phospholipid bi-layer. Because it is too small a structureto be seen clearly with a microscope, sci-entists have developed a model to ex-plain what they think it looks like. Thismodel is known as the fluid mosaicmodel. The term “fluid” is used becausethe phospholipid molecules and proteinsthat make up the membrane are freeto drift around in fluid motion. The term“mosaic” is used to describe the positionof the protein molecules. The moleculesare placed randomly and there is no set pattern.


WORDORIGIN

Prokaryote is from a mixtureof Latin and Greek; the LatinPro, meaning “before,” andkaryote from the Greek karyon,meaning “kernal”—a referenceto the appearance of the nu-cleus through early micro-scopes. The combination of thetwo terms indicates thatprokaryotes originated beforecell structures such as the nucleus evolved.

FIGURE 2.6 Theplasma membrane

proteins

integralprotein

peripheralprotein

cytoskeleton

cholesterolphospholipids

THE PLASMA MEMBRANE

1

1

2 3

2 3

a.

a.

b.

b.

A double or “bilayer” of phospholipid molecules, with their hydrophilic “heads” facing outward, toward the watery environment that lies both inside and outside the cell, and their hydrophobic “tails” pointing inward, toward each other.

Cholesterol molecules that act as a patching substance and that help the cell maintain an optimal level of fluidity.

Structural support, often when attached toparts of the cell’s scaffolding, or “cytoskeleton.”

Recognition. Binding sites on some proteins can serve to identify the cell to other cells, suchas those of the immune system.

Proteins, which are integral, meaning bound to the hydrophobic interior of the membrane, or peripheral, meaning not bound in this way. Membrane proteins serve four main functions:


The phospholipid bilayer is com-posed of two rows or layers of phos-pholipid molecules. The hydrophilicheads of the phospholipids are found onthe outside and inside of the mem-brane facing the watery environmentlocated both inside and outside a cell.

The hydrophobic fatty acid tails fromeach layer face one another in the mid-dle of the membrane (Figure 2.7). If youdisorganize a membrane, the phospho-lipid molecules will return to their orig-inal arrangement because of theirreaction to water. The polarheads will

As it turns out, environmentallyharmful substances that would killmost organisms—such as crude oil,gasoline, diesel fuel, and other or-ganic pollutants—serve as a sourceof food for other organisms. It is the

discovery that certain bacteria andfungi thrive upon pollutants thatforms the basis for what is known as“bioremediation technology.” Thereare about 1000 species of bacteriaknown to have the ability to breakdown toxins and/or pollutants for useas their food source. They then re-lease far less damaging waste prod-ucts themselves.

Bacteria produce enzymes thatbreak down waste materials into sub-stances that they can more readily di-gest. As the bacteria digest these

wastes, they produce more enzymesto break down more waste. The cyclecontinues until all the waste materialis gone. Then the bacteria eitherbecome inactive and/or die from star-vation. Companies that specialize inthis form of biotechnology grow andstudy many types of micro-organ-isms, so that they know which typeof organism can be used to effectivelyclean up a certain type of industrialwaste.

Waste Not, Want Not

glycocalyx

sugarchains

c.

c. d.

d.

4

4

The glycocalyx. Sugar chains that attach to communication or recognition proteins, serving as their binding sites. The glycocalyx can also lubricate cells and act as an adhesion layer for them.

Communication. Receptor proteins, protruding out from the plasma membrane, can be the point of contact for signals sent to the cell via traveling molecules, such as hormones.

Transport. Proteins can serve as channels through which materials can pass in and out of the cell.


orient toward the watery environmentwhile the non-polar lipid tails will mixwith other non-polar molecules.

The protein molecules embedded inthe membrane are called integral or in-trinsic proteins. They have differentfunctions. Some serve as special carri-ers or transport channels for moleculesthat are either too large or too hy-drophilic to pass through the phospho-lipid bilayer. The transport proteinsallow these molecules to enter the cell.Other membrane proteins have sugarchains attached to them. These carbo-hydrate and protein combinations,known as glycoproteins, act as attach-ment sites for molecules that need to

enter or carry a message to the cell. Theyare highly specific to each individual andhelp the cells of your immune system torecognize your body cells while alsoidentifying foreign cells in your body sothat they can be destroyed.

Cholesterol is also found within cellmembranes. Its function is to help keepthe membrane fluid at the relatively highbody temperatures of most mammals.At low temperatures cholesterol keepsthe phospholipids apart. This keepsthe membrane fluid. At higher temperatures (around 37ºC) it attractsthe phospholipids and stabilizes themembrane.

Dr. Harry Jennings of the NationalResearch Council has contributed toa medical breakthrough—the pro-duction of the first fully synthetic

(human-made) vaccine. Dr. Jenningshas spent 24 years developing a vac-cine to prevent a disease known asgroup B meningitis. Meningitis is adisease caused by bacteria that killsabout 40 people a year in Canada—about half of whom are infants—andoften leaves the survivors with braindamage that causes mental retarda-tion and blindness.

Dr. Jennings’s research resultedin the making of a combination car-bohydrate-protein molecule that re-sembles the cell membrane

glycoprotein chains of the meningitisbacteria very closely. As a result, cellsfrom your immune system think thatthe meningitis bacteria has invadedyour body and produce antibodies tofight the bacteria. However, since thecarbohydrate-protein vaccine isharmless, you gain protection againstmeningitis without risk of becomingill. Human trials for this vaccine arecurrently under way, and if success-ful, it should become available forpublic use soon.

Membrane Glycoprotein Chains Play a Key Role

in the Fight AgainstDisease

FIGURE 2.7 Thephospholipid bilayer.A double layer or bi-layer of phospholipidsform the plasmamembrane. The hy-drophobic tails formthe interior of themembrane, while thehydrophilic headspoint toward the wa-tery environment in-side and outside thecell.

wateryextracellularfluid

waterycytosol

hydrophilic

hydrophobic

hydrophobic moleculespass through freely

hydrophilic moleculesdo not pass through

freely

hydrophilic

polarhead

nonpolartails

a Phospholipid molecule b Phospholipid bilayer

+

–

N

P


Cell WallCell walls are not found in animal cells,but they are found in Archaebacteria,bacteria, some protists, fungi, and plantcells. Plant cell walls are mainly madeof the polysaccharide cellulose. Cellwalls are much stronger and thickerthan cell membranes, and in plants pro-vide structural support to the cell. It isbecause of cell walls that trees are ableto grow to such enormous heights andthat wood, composed of cell walls withlignin attached, is as strong as it is.

1. Take a party balloon and blow it up until it bursts.2. Cut a length from the leg of some pantyhose.3. Take the same type of balloon as used in Step 1 and put it inside the length of

pantyhose.4. Blow up the balloon as far as possible. Try to make it burst.5. Observe the result.

The material of the pantyhose acts like the cell wall and prevents the balloon frombursting. This is due to the cross-linking of fibres that makes the pantyhose verystrong. In a similar way the cell wall prevents the cell membrane in a plant cellfrom bursting. Compare this to the animal cell shown in Figure 3.7, page 71

D i s c o v e r i n g B i o l o g y A Model of the Cell Wall

FIGURE 2.8 Strength fromcell walls

a) Cell walls play a role in bothliving and dead cells. Here theymake up part of the bark.(�240)

b) A tree can reach enormousheights because of the strengthof the wood, which is mostlymake up of lignified cell walls.

a)b)

Caution: Do not do this activity if you have a latex allergy unless you are sure the balloonsare non-latex balloons.


INFOBIT

Cell without a nucleusMature red blood cells areunique; they no longer have anucleus! These oxygen-carry-ing cells actually expel theirnuclei to make more room foroxygen in the cell. This hastwo important results. Lackingthe instructions contained inthe nucleus, red blood cellscannot reproduce themselvesand so new red blood cells areformed in bone marrow in-stead. Also, DNA testing ofblood actually uses the DNA inthe disease-fighting whiteblood cells. No nucleus meansno DNA, so the red blood cellscannot be used.

FIGURE 2.9 The nucleus. In eukaryoticcells the DNA remains in the nucleus.Compounds pass into the nucleusthrough nuclear pores. The nucleolus specializes in the production of ribosomalRNA, a substance found in the ribosomes.(Transmission electron micrograph� 4400)

WEBL INK

Penicillin no longer functionseffectively as an antibiotic forsome people. Research whythis is so, as well as three alternative antibiotics that canbe prescribed. Summarize yourinformation in a summary paragraph and data table, including the name and description of the alternative.Begin your research atwww.pearsoned.ca/biology11.

Cell Walls and Antibiotics Antibiotics aremedicines that kill bacteria. Many scien-tific discoveries are the result of hours ofresearch and countless setbacks. Otherdiscoveries appear to occur quite by ac-cident. The discovery of penicillin, the firstantibiotic by Alexander Fleming in 1928is one example of a seemingly acciden-tal discovery. Fleming discovered that oneof his Petri plates growing bacteria hadbeen contaminated with mould, a type offungus. Fleming noticed that no bacteriawere able to grow around the area of themould. Rather than throw the plate away,Fleming investigated the mould further.His studies revealed that a chemical it

produced was highly effective in killingbacteria. The mould was later identifiedto be a species of Penicillium.

The discovery of penicillin is an example of how observation can lead tofurther experimentation. Fleming wasworking against the background of latenineteenth-century studies in microbi-ology by Pasteur and others that had indicated an effect of mould on bacterial growth. He had himself alreadydiscovered other substances that causedbacteria to burst. So he was able to appreciate the importance of an appar-ently chance observation and to carrythe scientific process forward in his experiments.

Today it is known that penicillinworks by preventing the formation ofbacterial cell walls. This leads to thedeath of the bacteria. Since eukaryoticcells, including human cells, do not havecell walls, penicillin targets only the invading bacteria for destruction and not

nucleolus

nuclearenvelopeDNA

inner membrane

outer membrane

nuclear pore

DNA

mRNA

http://www.pearsoned.ca/

Section 2.2 Review


the cells of the infected person. Countlesslives have been saved by penicillin sinceits discovery. The discovery of penicillinopened the door for the successfulsearch for many more antibiotics.Antibiotics must always be prescribedand taken with care. For example, somepeople are allergic to penicillin.

NucleusThe nucleus is the genetic control cen-tre of the cell. It is usually sphericalin shape and is often the most easilyseen structure when cells are viewedthrough a light microscope. The nu-cleus houses the cell’s DNA. In eu-karyotes, the DNA is combined withproteins into a fine, thread-like struc-ture called chromatin. Occasionally,just before cell division occurs, thechromatin condenses to form chromo-somes. Chromosomes are also visiblethrough a light microscope. Becausethe nucleus is a large structure that iseasily stained and readily visible underthe light microscope, it was one of thefirst cell structures to be studied. In1882 the German scientist WalterFlemming discovered chromatin as wellas the stages of cell division (mitosis).

The nucleus is separated from therest of the cell by the nuclear envelope,a double membrane with many nucleo-spores in it to allow materials to pass inand out of the nucleus (Figure 2.9). Alsowithin the nucleus is the nucleolus.Under the light microscopes the nucle-olus appears dense. It is composed ofDNA, granules, and fibres, and is the lo-cation where other cell structures calledribosomes are made. The dense-ap-pearing material contains many copiesof the region of the DNA that determinesthe formation of the RNA in ribosomes.

CytoplasmThe cytoplasm in eukaryotic cells includesthe interior of the cell between the nu-clear envelope and the cell membrane.Once thought to be composed mainly offluid, the cytoplasm has been revealedby electron microscopy to be a highly or-ganized area. Approximately one half ofthe space in the cytoplasm is taken up byother organelles. The other half of the cy-toplasm is the liquid portion known asthe cytosol. The cytosol contains a con-centrated mix of ions and molecules suchas enzymes, amino acids, ATP, and car-bohydrates.


1. What three cell structures do most cellshave in common?

2. Describe the structure and function ofa) the cell membraneb) the nucleusc) the cytoplasm

3. Explain why the fluid mosaic modelis used to describe the appearance ofthe cell membrane.

4. Describe the differences betweenprokaryotes and eukaryotes. Relatethese differences to their distributionon Earth.


5. Imagine that your cell membranes sud-denly became cell walls made of cellu-lose. List three possible effects of thischange.

Making Connections

6. In what ways did the discovery of peni-cillin impact society?

7. Prepare a cost/benefit analysis on theuse of bioremediation in cleaning theenvironment.


The activities in eukaryotic cells are or-ganized in ways that can be comparedto the body as a whole. Using the anal-ogy of the body’s organ systems, struc-tures that perform specialized functionsin cells are called organelles. Your di-gestive system breaks down food mate-rials into substances accessible to otherparts. There are organelles called lyso-somes, that are powerful in digestivefunctions within each cell. As your bloodsystem acts to transport the products ofdigestion, so the cell’s vacuoles and vesi-cles store and/or transport substanceswithin the cell. Just as your body has asystem of blood vessels, the cell hasmembranous transportation channelscalled the endoplasmic reticulum. Themitochondria in the cell use oxygen to

produce ATP, the energy molecule of thecell. In the process of cell respiration,carbon dioxide is produced and is ex-creted through the cell membrane. Thisprocess is similar to the way that yourrespiratory system supplies oxygen andremoves carbon dioxide

Advances in MicroscopyOur understanding of cells and theirfunctions has increased dramatically dueto improvements in microscopy. The de-signing of the microscope began with thework of Dutch lens makers in the 1500s.Until about 50 years ago scientists wererestricted to using light microscopes.Clear colour images of living tissue orprepared and stained non-living tissue,can be obtained using the light micro-scope. However, there are limits to theresolving power—the ability to distin-guish between two closely positioned ob-jects. Also magnification is limited toabout 1000�.

The transmission electron micro-scope (TEM) was invented in 1938 byCanadian scientists James Hillier andAlbert Prebus, and perfected by John L. Watson to a point where it was use-ful for biological research. As the namesuggests, electron microscopes use abeam of electrons instead of rays of lightto produce an image. The two types ofelectron microscopes, scanning electronmicroscopes (SEMs) and transmissionelectron microscopes (TEMs), work indifferent ways and for different pur-poses. TEMs send a beam of electronsthrough a thinly sliced sample of an object and produce a finely detailed viewof parts of its inner structure. The sci-

2.3 Cytoplasmic Organelles

Key Understandings

When you have completed this section, you will be able to: � describe how cell organelles manage various cell functions� relate cell functions to the functions of organs

FIGURE 2.10 Transmission electron micrograph of important nuclear structures.The arrows indicate nuclear pores. A vesicle (V) approaches the nucleus.

WORDORIGIN

Vesicle from the Latin vesicula, meaning “little blad-der or container.”

Endoplasmic from the Greekendon, meaning “within” andplasm, derived from the term“cytoplasm.”

V

entist must re-create the three-dimen-sional relationships of the various struc-tures. SEMs scan the outer surface of anobject and produce pictures that lookthree-dimensional. Scanning TunnellingMicroscopes (STMs), see section 1.3, areone of the latest advances in microscopetechnology and provide a three-dimen-sional view of molecules.

Vacuoles and VesiclesVacuoles and vesicles are both contain-ers, bags made of membrane, filled withwater and dissolved molecules. Vacuolesare found mainly in plant cells and areused for storage of starch molecules orwater and to give support to the cell.They are surrounded by a single-layeredmembrane called a tonoplast. Vesiclesare used for transporting materialsthroughout the cell rather than for stor-age and keep the different parts of thecell in contact.

RibosomesRibosomes are dense-looking dark gran-ules located on the surface of parts of theendoplasmic reticulum and floating withinthe cytoplasm. They are made of a com-bination of RNA and protein, and are thesites where amino acids are assembledinto proteins (protein synthesis).

Endoplasmic ReticulumThe endoplasmic reticulum is a seriesof interconnected small tubes (tubules)made of membranes that branch outfrom the nuclear envelope. Part of the en-doplasmic reticulum has ribosomes at-tached to it. The ribosomes give theendoplasmic reticulum in this location arough-looking appearance; therefore, thisportion is known as the rough endoplas-mic reticulum. The rough endoplasmicreticulum is where protein synthesistakes place at the ribosomes, particularlythe synthesis of those proteins for use outside the cell (Figure 2.11, 2.12b).Additional membranes are also manu-factured on the rough endoplasmic retic-

ulum, in response to the need for mem-branes by other organelles.

The smooth endoplasmic reticu-lum lacks ribosomes and takes its namefrom its resulting smooth-looking ap-pearance (Figure 2.12a). The function ofthe smooth endoplasmic reticulum is tomake lipids—including phospholipidsand steroids. It also serves as a storagesite for calcium ions.


roughendoplasmic reticulum

nuclearenvelope

ribosomes

cisternae

cisternalspaces

FIGURE 2.11 The rough endoplasmic reticulum: where proteins take shape.Polypeptide chains made at the ribosomes drop into the cisternal space of the roughendoplasmic reticulum. The chain then folds up into its protein shape and may undergoprocessing; for example, the addition of a side chain of carbohydrate. The protein is thensurrounded by a vesicle and transported to the Golgi complex. (Micrograph � 90 500)

FIGURE 2.12 The endoplasmic reticulum. a) The smooth endoplamsic reticulumlacks ribosomes: it is involved in the synthesis of lipids and carbohydrates. b) Therough endoplasmic reticulum has attached ribosomes where proteins are synthe-sized.

ribosomes

membraneswithout ribosomes

cisternalspaces


Golgi Complex (Apparatus)Named after the Italian scientist who dis-covered them, Golgi complexes are nu-merous and important to the operationof the cell. They consist of flattenedstacks of membrane, whose function isto receive, modify, and transport pro-teins produced by the endoplasmic retic-ulum. If the destination of the protein isoutside of the cell, the Golgi packagesit into a membrane-bound vesicle andsends it to the cell membrane for exportout of the cell.

LysosomesBoth the Golgi complex and the endo-plasmic reticulum produce lysosomes.Lysosomes are membrane-bound sacs

that make compartments in the cell toallow digestion. They contain hydrolyticenzymes and have a variety of roles.In unicellular organisms, lysosomes maybe used to digest food, while certaintypes of human white blood cells (neu-trophils and macrophages) use them todestroy invading bacteria.

Lysosomes are also used to breakdown damaged organelles within a cell.For example, human brain cells that sur-vive from birth until death but haveorganelles such as mitochondria and ribosomes, usually less than one monthold. The cells themselves are, with thehelp of the lysosomes, breaking downold organelles while continually formingnew ones.

INFOBIT

DNA segments coding forfluorescent molecules from ajellyfish were fused with DNAcoding for proteins of the Golgiapparatus so that these proteinswould become fluorescent too.Scientists were then able tofollow the movement of theseproteins in the cell. Scientistsbelieve that these proteinswere immobilized in the Golgicomplex. Other proteins moveout of the Golgi complex andhead to the part of the cellwhere they will carry out theirspecific function. It remains amystery why some proteins arenot transported.

cisternae

cisternalspaceGolgi

complex

to cytosol for exportout of cell

1. Side chains are edited(sugars may be trimmed,phosphate groups added).

2. Vesicle formedfor protein transport.

to plasma membrane

vesicle

from RER

P P

FIGURE 2.13 The Golgicomplex. Vesicles from therough endoplasmic reticulumfuse with the Golgi mem-brane. Side chains may bemodified as the proteinpasses through the cisternaeof the Golgi complex. The protein is then encased invesicles for further transportinside or outside the cell.


Researchers now think that lyso-somes may also play a role in the age-ing process. Apparently lysosomescannot digest all of the outdated mate-rial in a cell. As these compounds ac-cumulate within the lysosomes overtime, they cause a decrease in cell func-tions such as is associated with ageing.

Lysosomes in Human Disease A missingor defective enzyme in lysosomes causes

a number of human diseases known aslysosomal storage diseases. Among themis Tay-Sachs disease, a hereditary con-dition that results in deterioration of thebrain. When working correctly, the en-zyme involved breaks down excess fatin the brain. Without this enzyme, fat isallowed to build up in the lysosomesstored within the brain cells. This causesincreasing, irreversible damage, and even-tually leads to death at around age five.

FIGURE 2.14 Lysosomes:cellular recycling.

When a lysosome fuses with aworn-out organelle, its enzymesbreak the organelle down intosmall molecules that can be re-turned to the cytosol and usedelsewhere. Lysosomes expelmaterials that they cannot di-gest from the cell. In unicellu-lar organisms lysosmes alsodigest food particles for use inthe cell.

WEBL INK

Research lysosomal storagediseases. Compile a list of thetypes of disease, the specificcauses, and the treatmentsavailable. Begin your researchat the Pearson Education Website at www.pearsoned.ca/biology11

worn-outorganelle

lysosome

digestiveenzymes

fusion

digestion

moleculesrecycled tomake neworganelles

small moleculesreturned tocytosol

wastes expelledfrom cell

CELLULAR RECYCLINGRefer to page 58,Investigation 1




Other diseases such as gangliosido-sis, Sly syndrome, and Hurler syndromeare caused by other defective lysosomalenzymes. There are approximately 30human diseases in total involving mal-functioning lysosomal enzymes. Thenumber of diseases caused by improp-erly working lysosomes clearly indicatesthe importance of this structure to thecell.

Lysosomes are also responsible forchanges in whole organisms. Examplesof tissues digested by lysosomes are thetail of a tadpole, any unwanted tissueduring insect metamorphosis, and tissuethat exists between the fingers in thehuman embryo, giving them a webbedappearance.

Interaction between living organisms can show their physiology1. Prepare and observe a slide of a live Paramecium culture under

the low power objective of a microscope.2. Obtain a small sample from a yeast solution that has been

treated with an indicator that changes colour as the acidity ofthe solution changes. Transfer a small drop of the yeast solu-tion to the edge of the slide using a toothpick.

3. Observe the Paramecium through the microscope for five min-utes and record your observations.What changes did you observe in the Paramecium? What or-ganelles did you see at work within the Paramecium?

Watching a Paramecium’s Organelles


Dr. Vett Lloyd is a professor of cell bi-ology at Dalhousie University inHalifax, Nova Scotia. Her cell biologyresearch has focused on lysosomestorage and transport diseases.Children with these diseases experi-ence a lot of pain and eventually dieof cancer, usually in late childhood.“What happens in these sick childrenis that the lysosomes inside their cellsdo not work properly,” says Lloyd.

One of the roles of lysosomes isto help your immune system to de-stroy cancer cells. If a cell in yourbody turns cancerous, your immunesystem sends out a killer cell that en-gulfs the cancer cell. Powerful en-zymes inside the immune cell’s

lysosomes then destroy the cancercell. The lysosomes in the sick chil-dren, however, lack these enzymes.

Normally, enzymes are deliveredto the lysosomes in tiny cargo pack-ets called vesicles. Unfortunately, inthe children, the vesicles get lost. Itis as if the post office has lost thepackage because the wrong addresswas written on it. “The enzymesdon’t get into the lysosomes so thelysosomes don’t work, and if the lyso-somes don’t work the immune sys-tem cells cannot kill the cancer cells,”says Lloyd.

Her first big breakthrough camea number of years ago when she dis-covered fruit flies that were dyingfrom the same lysosome problem thatwas killing human children. Lloyd isnow using the fruit flies to help herin her studies. The big advantage ofusing fruit flies is that you can testthe safety and effectiveness of newdrugs on them before you give thedrugs to children. She believes thefruit fly’s cells will provide the

answers that will eventually lead toa cure to this group of dreaded child-hood diseases.

Vett Lloyd, CellBiologist

FIGURE 2.15 Dr. Vett Lloyd studies lyso-somal storage and transport diseases.

Caution: Wash your hands after handling living cultures.


MitochondriaMitochondria (singular: mitochondrion)are found in both plant and animalcells. These organelles play a vital role inenergy-transforming activities. Mito-chondria are composed of an outer mem-brane, an inner membrane organizedinto folds called cristae, and an inner liq-uid solution known as the matrix.

The mitochondrion is the site of cel-lular respiration in eukaryotic cells. Theprocess of cellular respiration involvesextracting energy from food moleculessuch as glucose and using that energy tomake ATP. In the process CO2 is pro-duced, to be later exereted by the cell.

ChloroplastsThese green organelles, found only incells of plants and some protists (likealgae), are responsible for producingfood for most of the life on Earth. Theorganelles produce food by the processof photosynthesis. Photosynthesisenables plants and some protists to con-vert the energy of sunlight into chemi-

FIGURE 2.16 Mitochondria. Mitochondria convert the energy contained in thechemical bonds in food into a form more easily used by the cell, the ATP molecule.

Mitochondria contain their own DNA,separate from the DNA in a cell’s nu-cleus. Unlike nuclear DNA, which isinherited from both parents, mito-chondrial DNA (known as mtDNA),is inherited along maternal lines—orin other words, from your mother.

This unique form of inheritance isuseful for scientists because it allowsthem to study human evolution usingchanges in the structure of molecules.Because mtDNA is passed frommother to offspring it is fairly easy totrace its course through a population.For example. although you had eightgreat-grandparents, you inheritedyour mtDNA from only one of them(your mother’s grandmother on hermother’s side). It is also possible toanalyze mtDNA from sources such asteeth and bones—often still availableeven from ancient human remains.

Because DNA is known to changenaturally over time (or mutate), at a

fairly constant rate, researchers areable to compare modern mtDNA withthat from early human remains anddetermine how related certain pop-ulations may be. For example, sci-entists recently compared the mtDNAof prehistoric human bones found ina cave in Wales with mtDNA fromvolunteers throughout Europe. Totheir surprise, the closest match wasfound belonging to a man living in anearby Welsh town. This proved thatthe man was a direct descendantfrom the cave person and that theman’s ancestors had lived in thatarea of Wales for at least 30 000years!

A Unique Gift from Your Mom, and Her Mom...

mitochondrion

food oxygen

watercarbon dioxide

ATP

outer membrane

inner membrane


cal energy in the form of carbohydrates.Chloroplasts have a double mem-

brane surrounding them and also havean internal membrane system contain-ing light-capturing molecules of chlorophyll. The internal membranesare interconnected and frequently forma stack of pancake-shaped structurescalled grana (singular: granum). A thickfluid, the stroma, that contains enzymesand other molecules, occupies the re-mainder of the space in a chloroplast(Figure 2.17).

Chloroplasts are the best known ofa diverse group of organelles called plastids that occur only in plants andalgae, and some other protists. As wellas photosynthesis in chloroplasts, plas-tids store nutrients and give colour tomany cells by storing pigment.

The Endosymbiotic Theory Did you knowthat you have ancient bacteria living inyour cells? According to Dr. LynnMargulis, a professor of botany at theUniversity of Massachusetts, you do.Early in her career she developed theendosymbiotic theory, proposing that

mitochondria and chloroplasts wereonce free living cells; bacterial cells andalgal cells, respectively. She proposesthat about 1.4 billion years ago, thesebacterial and algal cells found a betterlife living inside other cells. There is ev-idence to support this theory. For ex-ample, mitochondria and chloroplastsreproduce on their own, separately fromthe rest of the cell. They contain theirown DNA and ribosomes. Both mito-chondria and chloroplasts are about thesame size as bacteria.

Margulis’s theory took a long timeto gain acceptance. Many scientists re-jected the concept when it was proposedin the early 1960s. However, Margulispersevered in her investigations, slowlyaccumulating more evidence for her hy-pothesis and more supporters amongher colleagues.

An accidental discovery by Dr.Kwang Jeon added strong support toMargulis’s theory. Jeon found that amongamoebas infected with bacteria, somesurvived the infection while still har-bouring up to 40 000 bacteria livinginside of them. Even more remarkably,

sugar (food) oxygen

watercarbon dioxide

minerals

outer membrane

inner membrane

FIGURE 2.17 The chloroplast. Surrounded by a double membrane, chloroplasts arethe sites of photosynthesis. Chloroplasts enable plant and some protist cells to usethe energy of sunlight to transform water, carbon dioxide, and a few minerals intofood materials that sustain most of the life on Earth. Micrograph: � 13 000

MicrotubulesIntermediate filamentsMicrofilaments

10 nm7 nmMain function: changes in cell shape

Main function: maintenance of cell shape Main functions: maintenance

of cell shape, movement of organelles, cell mobility (cilia and flagella)

25 nm


he also found, upon trying to remove thebacteria from their hosts, that theamoeba could no longer live without thebacteria. Jeon, then, proved that it ispossible for an organism to becomedependent on an invading organism, andthat, rather than have the bacteria de-stroy the amoeba, it was possible forthem to co-exist.

CytoskeletonThe cell membrane gives very little sup-port to an animal cell. Plant cells have acell wall to support their shape. However,animal cells are able to maintain theirshape due to the cytoskeleton: a sup-portive network of fine protein fibres.These protein fibres, the microfilaments,intermediate filaments, and microtubulesare shown in Figure 2.18. Besides of-fering support to the cell, the cytoskele-ton helps anchor the organelles within

the cytoplasm and may also play a rolein relaying messages back and forth be-tween the cell membrane and the inte-rior of the cell.

Cilia and FlagellaCilia and flagella are made of fine pro-tein fibres that function to providemovement to some cells. The most ob-vious difference between them is theirlength: flagella are long; cilia are short.Also cilia may be very numerous andcover the cell while flagella are few innumber. Many protist cells use thesestructures for locomotion: Parameciumis covered with tiny cilia that beat in acoordinated fashion to propel it throughthe water, Euglena moves by way of itstwo whip-like flagella located at theanterior. Human sperm cells are able tomove due to the presence of a single flagellum (Figure 2.19).

FIGURE 2.18 The cytoskeleton. Three types of fibresform the cytoskeleton: microfilaments, about 7 nm; in-termediate filaments, about 10 nm ; and microtubules,about 25 nm.

WORDORIGIN

Endosymbiosis from theGreek symbiosis, meaning “liv-ing together” and endo, mean-ing “within.” When combined,the two words nicely representendosymbiosis, meaning “oneorganism living inside another.”

INFOBIT

Many of our sensory structuresmay have evolved from cilia.The basic cilia-like form isfound in: the light-sensitiveportions of our eye; the fibreslocated in our noses that allowus to sense smells; and the tinyhairs of our internal ear thatare used to help us maintainour balance.

Section 2.3 Review


1. What are organelles?

2. How do lysosomes function to digestmaterials?

3. Describe the location of the endoplas-mic reticulum. Make a table to showthe differences in appearance and func-tion between the rough and smoothendoplasmic reticulum.

4. Explain the function of the Golgi com-plex (apparatus).

5. The table below shows the observa-tions made of three different cells.Determine as much as you can abouteach type of cell. For example, arethe cells prokaryotic or eukaryotic;plant or animal?

6. If scientists were able to remove mito-chondria or chloroplasts from cells andturn them into free functioning organ-isms once more, would this help, hin-der, or have no effect upon Dr. Lynn

Margulis’s endosymbiotic theory?Explain.

Making Connections

7. A patient being treated for a form ofcancer known as leukemia, had hisspleen removed—a common treatmentfor this type of cancer. Soon re-searchers discovered that the man’sspleen cells produced a protein that ac-tually helped fight the cancer. The re-searchers patented the cells and thepatient—upon discovering that his cellswere being used this way—sued for ashare of the profits but eventually lostthe lawsuit. Do you think the re-searchers were correct in their use ofthe cells without obtaining the patient’sconsent? Do you think the patient wastreated fairly? How would you havevoted if you were on a jury decidingthis issue? Provide the reasons behindyour decision.


Cell wall Cell membrane Chloroplasts Mitochondria Nucleus

Cell A Yes Yes Yes Yes Yes

Cell B No Yes No Yes Yes

Cell C Yes Yes No No No

FIGURE 2.19 Functions of microtubules

a) Electron micrograph of protist cell covered with hair-like cilia for locomotion.

b) Human sperm cell; notice the long flagellum on the sperm cell.

Analyzing the Issue

BACKGROUND INFORMATION

CaseCase Study

Stem cells and their potential uses in the treatment ofdisease are the focus of heated social controversy. Thereare two types of stem cells, those that are totipotent (thatis, make all cell types), and those that are tissue restricted(that is, make one type of tissue only). Totipotent cells(sometimes called embryonic stem cells) have beenthought to provide a way to treat diseases likeParkinson’s, juvenile diabetes, and Alzheimers by re-generating tissue.

Many people believe that using the stem cells fromhuman embryos for research and medical purposes ismorally wrong. Others believe that it is the responsibil-ity of the medical community to use whatever knowledgethey possess in their research to decrease human suf-fering. They feel society has an obligation to do the re-search required for the people who are living with thesediseases.

Dr. Mickie Bhatia, Scientist at The John P. RobartsResearch Institute in London, Ontario, has discoveredthat when adult blood stem cells are given a protein pre-sent during human blood development earlier in life,theseblood stem cells will grow and reproduce in a similarmanner to embryonic blood stem cells. If these bloodstem cells could be induced to form other types of tissue,such as neural or muscle cells, these adult cells couldprovide a potential alternative to the use of totipotentembryonic stem cells in the treatment of disease. Will thecontroversy continue? Wherever ethics come into a ques-tion, there will most likely always be differing opinions.

1. What are the ethical perspectives relating to the con-troversy about stem cell research?

2. What additional factors influence society’s response tostem cell research? Explain.

3. Propose what impact Dr. Bhatia’s discovery may haveon attitudes toward stem cell research and treatmentwith stem cells.

4. Research stem cells and their use in the treatment ofParkinson’s disease.

5. Prepare a risk-benefit analysis to summarize your find-ings. Write a position paper to address the followingquestion. If faced with a degenerative or potentially fataldisease, should a person be able to refuse medical helpbecause of his or her own moral principles if that helpis available to them?

Ethics and Stem CellResearch

� Defining the Issue

� Developing Assessment Criteria

� Researching the Issue

� Analyzing Data and Information

� Proposing a Course of Action

� Justifying the Course of Action

� Communicating Your Proposal

Decision-Making Skills


FIGURE 2.20

Characteristics of Cells

Investigation 1 (Section 2.3)

Cells are the basic units of structure and functionfor all living things. All cells fall into one of two majordivisions—prokaryotic or eukaryotic. How might youclassify an unknown cell? You will determine the dif-ferences through an examination of prepared slides.You will then use these differences to help you clas-sify a test specimen.

ProblemWhat differences can be observed between prokary-otic and eukaryotic cells?

Materials(per group)

� microscope� prepared slides of prokaryotic and eukaryotic cells

Procedure1. Set up your data table in your notebook in a man-

ner similar to Table 2.2.

2. Obtain a microscope.

3. Obtain a prepared slide to examine.

4. In the data table, write the name of the specimenyou are examining. Sketch its shape. Place a checkmark under the cell structures you are able toidentify on this slide. Examine the slide under low,medium, and high power to help you locate asmany cell structures as possible.

5. Based on your observations, decide if each cellis a prokaryote or a eukaryote.

6. In your notebook, draw and label the appearanceof the specimen under high power.

7. Repeat steps 3–6 for the other prepared slides pro-vided by your teacher.

8. Repeat steps 3–6 for an unidentified prepared slideprovided by your teacher.

9. Once you have finished the lab, return all of theequipment to its proper place.

Analyzing and Interpreting1. Based on your observations, do all cells have a

common shape? Explain your answer.2. Under which magnification can you see the dif-

ferent structures?3. What cell structures were common to all cells?

Concluding and Communicating4. What cell structures are found only in eukary-

otic cells?5. Explain how you decided on the cell type of the

unknown specimen.6. Why do different types of cells have different

shapes and sizes?

Extending7. The procedure of DNA fingerprinting relies on ex-

tracting DNA from the nucleus of a cell in orderto identify a suspect. Explain why DNA finger-printing will not work if DNA is extracted from ablood sample that contains only red blood cells.

8. Prokaryotes have no nuclear membrane but con-tain DNA in the cell. How can these cells carry outcell activities without a nuclear membrane?

Cell Specimen Shape Cell Structures Prokaryotic or Eukaryotic?

Cell

Wal

l

Cell

Mem

bran

e

Nuc

leus

Nuc

lear

Env

elop

e

Cyto

plas

m

Vacu

oles

Plas

tids

� Initiating and Planning

� Applying Technical Skills

� Using Tools, Material, Equipment

� Conducting and Recording

� Analyzing and Interpreting

� Concluding and Communicating

Inquiry Skills


TABLE 2.2 Characteristics of cells

CAUTION: Observe proper technique with the microscopeand slides to ensure safe handling of equipment.








Inquiry Skills

Estimating an Object’s Size with the Microscope


�

FIGURE 2.21 Set-upfor measuring the di-ameter of the field ofview.

While it may be interesting and informative to viewobjects under a microscope, it often difficult toknow the actual size of the object being observed.Magnification causes us to lose our perspective onsize. In this lab you will learn how to estimate thesize of an object by comparing it with something youalready know—the diameter of the field of view.

ProblemHow is the compound microscope used to estimatethe size of microscopic specimens?

Materials(per group):

� microscope� transparent metric ruler� prepared slides

Procedure1. Obtain a microscope and place a transparent met-

ric ruler on the stage so that it covers about halfof the stage, as shown in Figure 2.21.

2. Observe the ruler under low power. Adjust the po-sition of the ruler so that its view is similar toFigure 2.22.

3. Move the millimetre ruler so that you are mea-suring the diameter (width) of the low power fieldof view from left to right.

4. Measure the diameter of the low power field tothe nearest tenth of a millimetre. Record this mea-surement in your notebook.

5. Use a ratio to calculate the diameter of the highpower field (the magnification of objectives is in-versely proportional to the field size).

6. Record the high-power field diameter in mi-crometres. Show your work.

7. Estimate the size of objects you view under the microscope by comparing them with the diameter of the field of view. For example, if anorganism takes up one-half of a field of viewthat is 500 µm in diameter, then its size is aboutone-half of 500 µm, or 250 µm.

8. Obtain prepared slides of various organisms andpractise estimating their lengths and/or widths.Record the name of the organism or structure youare viewing and its estimated size in µm in thedata table.

9. Return you microscope and slides to their properstorage locations once you have finished this ac-tivity.

FIGURE 2.22 Adjust the position of the ruler so that youcan measure the diameter of the field of view.

High-power field diameter

low-powerfield diameter

high power magnification

low powermagnification

�


Analyzing and Interpreting1. Set up a data table similar to Table 2.3 in your

notebook.

For calculation, see the equation given in proce-dure step 5.

2. Gather the necessary information to completeTable 2.3 and copy it into your notebook. Copyand complete Table 2.4 in your notebook.

Concluding and Communicating3. How many micrometres are in one millimetre?4. How many micrometres are in one metre?5. Describe what happens to the field of view when

you switch from the low power magnification tothe high-power magnification.

6. How many times is the magnification increasedwhen you change from the low power lens tothe high power lens?

7. How many times is the field diameter decreasedwhen you change from the low power lens tothe high power lens?

8. Approximately 400 bacteria fit across the fieldof view of the low-power lens. What is the esti-mated size of one bacterium?

9. Approximately six of certain species of protist canfit across the high-power field of vision. What isthe size of one protist?

10. If a microscope has a low-power magnification of100X, a high power magnification of 450X, anda low-power field diameter of 1800 micrometres,what is the high power field diameter in mi-crometres?

11. If 16 protists fit across a low-power field of viewwhose field diameter is 4800 micrometres, whatis the approximate size of each protist?

12. You have determined the field size of the low andhigh-power objective lenses. How do you thinkyou would calculate the field diameter of themedium-power lens?

Extending13. Make a wet-mount slide of a protist culture.

Choose one protist and observe it under low andhigh power. Estimate its length in micrometres.

Name of object Estimate of object’s size

Field Field diameterMagnification in mm

Low power

From measurement:

High power

From measurement:

(continued)

TABLE 2.3 Size of Field Diameters

TABLE 2.4 Size of Objects

Key Terms

CHAPTER SUMMARY


cell membranecell theorycellulosecell wallchloroplastscholesterolchromatin

chromosomesciliacytoplasm cytoskeletoncytosolendoplasmic reticulumeukaryote

flagella fluid mosaic modelGolgi complex

(apparatus)lysosomemitochondrianucleus

nuclear envelopenucleolusorganellephotosynthesisphospholipid bilayerprokaryoteribosome

rough endoplasmicreticulum

smooth endoplasmicreticulum

surface areavacuolevesicle

2.1 An Introduction to Cells � Cells are the basic units of life and are present in

all living things.� Cells come only from pre-existing cells.� Cells are small so that they can maximize their sur-

face area.� An increased surface area helps cells obtain energy

and rid themselves of waste products through theircell membranes.

2.2 Cell Structures� Prokaryotic cells lack a nucleus and other mem-

brane-bound organelles.

� Eukaryotic cells have specialized structures calledorganelles.

� The phospholipid-containing cell membrane sepa-rates the cell from the environment.

� In eukaryotes the volume inside the cell membraneis divided into nucleus, cytoplasm, and organelles.

2.3 Cytoplasmic Organelles� Organelles are structures located within the cyto-

plasm that perform specialized functions for the cell.� Cell organelles include vacuoles and vesicles, ribo-

somes, smooth and rough endoplasmic reticulum,Golgi complex, lysosomes, mitochondria, chloro-plasts, cytoskeleton, cilia, and flagella.

Cell Organelles in Plant and Animal Cells

Essential Understandings

1. Revisit the Checkpoint on page 37 and review your chartlisting the structures and functions of cells. Revise yourchart based on what you learned in this chapter.

2. Construct a concept map to show the relationship be-tween the following key terms: Cell Theory, prokaryote,eukaryote, organelle, cytoplasm, cell membrane, and nu-cleus.

3. Prepare an analogy to describe the structures and func-tions of the cell to an elementary school class. Suggestillustrations or models to support your presentation.

4. Reflect on your learning. Explain why theories like theCell theory are important to the process of scientific discovery.

Consolidate Your Understanding

Name Location Function

Cell (Plasma) membrane Surrounds cytoplasm Regulates what enters and leaves the cell Nucleus Within nuclear envelope Contains the DNA Cytosol Cytoplasm Fluid containing organelles and important molecules such as proteins Vacuoles and vesicles Cytoplasm Vacuoles store food or water; vesicles transport molecules Ribosomes Rough endoplasmic reticulum Site of protein synthesis

Free-floating in cytoplasm Rough endoplasmic reticulum Cytoplasm Processing of proteins Smooth endoplasmic reticulum Cytoplasm Lipid synthesis Golgi complex Cytoplasm Processing and packaging of protein Lysosomes (in animal cells only) Cytoplasm Digestion of molecules, bacteria, or damaged organelles Mitochondria Cytoplasm Produce ATP from energy released from glucoseCytoskeleton Cytoplasm Maintains cell shape and helps hold organelles in place Cilia and flagella Outside cell membrane Permits cell movement Cell wall (in plant cells only) Outside cell membrane Provides shape and support for the cell Chloroplasts (in plant and some Cytoplasm Use energy of sunlight to produce carbohydrates (photosynthesis)protist cells only)

CHAPTER 2 REVIEW



1. The genetic control centre of the cell is the a) nucleusb) cytoplasmc) mitochondriond) lysosome

2. The structure of the cell between the nucleus and cellmembrane is called the a) mitochondrionb) cytoskeletonc) chloroplastd) cytoplasm

3. Which of the following organisms have prokaryotic cells?a) humansb) bacteriac) fungid) plants

4. As the surface area of a cell increases, the volume of thecella) increases as much as the surface areab) does not changec) decreasesd) none of these

5. Cells that need a large amount of energy would usuallycontain many a) mitochondriab) chloroplastsc) vesiclesd) Golgi complexes

6. Organisms whose cells do not contain a nucleus are calleda) prokaryotesb) eukaryotesc) plantsd) fungi

7. Which structure is the site of protein synthesis?a) nucleusb) lysosomec) smooth endoplasmic reticulumd) ribosome

8. Where in a cell would you expect to find the cytoskeleton?a) within the nucleusb) within a mitochondrionc) within the cytoplasmd) between the cell membrane and the cell wall

9. Under a microscope a cell was found to contain many mi-tochondria, chloroplasts, a nucleus, a cell wall, cytoplasm,as well as other organelles. This cell is most likely aa) bacterial cellb) human cellc) plant celld) none of these

10. Which of the following structures is not involved in cellsupport or movement?a) cytoskeletonb) cell wallc) ciliad) lysosome

11. Sketch a typical animal cell to show all of the struc-tures and organelles it is likely to contain. Do the samefor a typical plant cell.

12. Which structures are found in plant cells but not in an-imal cells?

13. Explain the difference between the nucleolus and nucleus.

14. Living cells are sometimes compared to factories. Explainwhat part of a cell may match the function of each ofthese: security guard, shipping centre, power plant, fac-tory manager, and storage tank.

15. Sketch a diagram of the cell membrane and identifythe structures present. Using your diagram as a refer-ence, explain why the term “fluid mosaic model” is ap-propriate to describe the cell membrane as we know it.

16. Prepare a speech for a meeting of cell biologists. The titleof your speech is to be: It is better for organisms to bemade of many small cells than a few large ones. Prepareyour speech for this meeting.

17. Compare the information obtained from transmissionelectron microscope and scanning electron microscopeimages.

18. How did the evidence accumulated by Dr. Kwan Jeonsupport the endosymbiotic theory?

19. Make a flow chart to show the way that bacteria may beused to break down waste materials.

20. Explain why secretory cells like the thyroid gland cellsmight be expected to have an active Golgi complex?



21. Draw a diagram of three cells with the same volume butdifferent surface areas.

22. a) Complete the following chart in your notes to performa mathematical comparison of surface area (S.A.) andvolume (V) for a hypothetical cube-shaped cell.

b) Plot a graph of your calculated values for the indexversus the dimensions of the cube-shaped cell. Plotthe index on the vertical axis.

c) Describe the shape of your graph.d) Now relate this mathematical relationship to the op-

eration of a cell as it increases in size. Why mustthe majority of cells ultimately divide using mitosis?

23. Copy the graph below onto a separate piece of paper.Add data points to the graph for cubes with sides of 2 cm, 3 cm, 4 cm, and 5 cm. (In order to do this, youwill need to first calculate the surface area for each ofthe cubes, and then calculate the surface area to volumeratio.) Complete the graph and indicate what informa-tion can be obtained from the graph.

24. Prepare a concept map illustrating how the ribosomes,rough endoplasmic reticulum, Golgi complex, and cellmembrane may function together.

25. Robert Hooke coined the term cells while looking at deadcork cells through his homemade microscope. Some yearsearlier, Dutch tailor Antonie Van Leuwenhoek observeda number of different living specimens using microscopesof his own design, but did not describe cells. Why do youthink this is so?

26. Liver cells have hundreds of mitochondria, while fat cellshave only a few. Why do you think there is such a dif-ference between the two cells in the number of mito-chondria? Provide reasons for your answer.

27. When a specialized white blood cell defends your bodyagainst bacteria many cell systems are involved in theprocess. Set up a T-chart to show the organelles involvedand their functions in defense of the body.

Making Connections

28. Scientists believe that originally all life on Earth con-sisted of prokaryotic cells and that eukaryotic cellsevolved later. Based on what you know about the dif-ferences between the two cell types, explain why thisview does or does not make sense.

29. a) Explain why an understanding of cell processes is essential to the development of vaccines.

b) How might this understanding have impact onCanada’s health system and allocation of resources?

Dimensions Surface Volume S.A.: Index = of “cube” Area (cm3) Volume S.A./Vcell (cm) (cm2) (ratio)

05 × 0.5 × 0.5

1.0 × 1.0 × 1.0

1.5 × 1.5 × 1.5

2.0 × 2.0 × 2.0

2.5 × 2.5 × 2.5

3.0 × 3.0 × 3.0

6

5

4

3

2

1

1 2 3 4 5Length of cube side (cm)

Surfa

ce a

rea/

volu

me

Cell Transport

C H A P T E R 3

64

Many cellular functions involve the transport of materials in, out, andthrough cells. Cells, particularly those in multicellular organisms, are

surrounded by a complex and constantly changing liquid environment con-sisting of many dissolved molecules: gases such as oxygen, compounds suchas glucose, ions such as sodium, and chemical messengers such as pro-

By the end of this chapter, you will be able to:

� describe how organelles and othercell components carry out variouscell processes and explain howthese processes are related to thefunction of organs (3.1, 3.2, 3.4)

� describe the fluid mosaic structureof cell membranes and explain thedynamics of passive transport andthe processes of endocytosis andexocytosis of large particles (3.1,3.2, 3.3, 3.4, Investigation 1)

� design and carry out an investiga-tion on cellular function, controllingthe major variables (Investigation 2)

� present informed opinions on ad-vances in cellular biology and pos-sible applications through relatedtechnology (3.1, 3.3)

� analyze ways in which societalneeds have led to technological ad-vances related to cellular pro-cesses (3.3)

SPECIFICEXPECTATIONS

FIGURE 3.1 Colour enhanced scanning electron microscope image of a lymphocyte,natural killer cell attacking a cancer cell (orange).

Observing Osmosis

C H A P T E R 3 Cel l Transpor t 65

FIGURE 3.2 Experimental set-up for observing osmosis.


beakercontainingwater

thistlefunnel

teins. Literally billions of events involving these various molecules must occurdaily to ensure your survival. The cell membrane plays a vital role in theseevents: it regulates what enters and leaves the cell; it ensures the cell receivesa non-stop supply of nutrients from its surroundings; and, at the same time,it steadily allows waste products to pass through it in order to exit the cell.In the transport of large molecules and even other cells into the cells interior,the cell membrane rearranges its structure to form a vesicle.

The membranes of organelles within the cell, such as the mitochondrionand endoplasmic reticulum, must also regulate what substances enter andleave them. And the membrane of some organelles, such as the Golgi com-plex, must not only be able to regulate the passage of molecules, but it mustalso be able to package, send, and receive “shipments” from other organelles.

This chapter will outline the transport methods used to move materialssuch as nutrients, water, and oxygen into cells, and waste products such ascarbon dioxide, out of cells. It will also highlight new information about somedisease states that have their origins in faulty cell processes.

CHECKPOINT

Draw a diagram of the cellmembrane to illustratewhat you know about howthis structure functions.

The movement of water through a selectively permeable membrane is calledosmosis.

1. Draw the apparatus your teacher has set up as a demonstration andrecord the original fluid level on your drawing.

2. Observe the apparatus every 60 s for at least five minutes and record thechange in height of the fluid in the tube.

� How would you explain the change in height of the fluid in the tube?� What is happening to the material on the inside of the tube?


The cell membrane plays an essentialrole in regulating what enters and leavesthe cell. This role depends largely on itsstructure. Because most membranes, in-cluding the cell membrane, allow somesubstances to pass through them, theyare said to be permeable. In addition,because most living membranes are ableto control what passes through them,they are described as being selectivelypermeable.

Both the phospholipid bilayer andthe protein molecules help to control thepassage of materials through the cellmembrane. The construction of the bilayer is unique. The hydrophilic

phosphate heads point toward the liquidenvironments inside and outside the cell.The hydrophobic fatty acid tails makingup the middle of the membrane, prevent some molecules from entering thecell. Because the phospholipids are tightlypacked together, molecules that are toolarge cannot pass through this portionof the membrane. Hydrophilic moleculesthat are not fat-soluble cannot dissolveand pass through the middle fatty acidportion of the membrane. The proteinmolecules embedded in the bilayer pro-vide an entryway for certain smallmolecules that cannot enter through thebilayer portion of the membrane.

FIGURE 3.3 Thecell membrane. Thecell membrane is selectively perme-able. It freely al-lows the passageof fat-soluble sub-stances throughthe lipid bilayer and small non-fat-soluble moleculesthrough the proteinchannels.

3.1 Cell Membrane: Gateway to the CellKey Understandings

When you have completed this section, you will be able to: � relate the fluid mosaic model of membrane structure to the function of membranes � explain the importance of permeability to transportation within and between cells

glycocalyx

sugarchains

cholesterol

phospholipids proteins

The glycocalyx. Sugar chains that attach to communication or recognition proteins, serving as their binding sites. The glycocalyx can also lubricate cells and act as an adhesion layer for them.

Transport. Proteins can serve as channels through which materials can pass in and out of the cell.

Communication. Receptor proteins, protruding out from the plasma membrane, can be the point of contact for signals sent to the cell via traveling molecules, such as hormones.

WORDORIGIN

Permeable from the Latinpermeare, meaning “to passthrough.”

Section 3.1 Review


Membrane proteins have functionsin addition to transporting molecules.Some of the proteins provide structuralsupport to the cell by binding to the protein fibres of the cytoskeleton. Otherproteins have a communication function.They receive chemical messengers sentby other cells. Proteins that have carbo-

hydrate chains attached to them are involved in communication and cellrecognition. These carbohydrote “sugar”chains are called the glycocalyx. Othercells, such as those in your immune sys-tem, use these carbohydrate chains torecognize a cell or a molecule as beingself or being foreign.

For many years the nucleus was con-sidered the exclusive control centreof the cell. However, within the last15 years, scientists such as Dr. TonyPawson at the University of Toronto,have learned that the cell membraneand molecules within the cell, calledprotein kinases, have an equally important role in controlling cell function and allowing the communi-cation between cells that is necessary

for the proper functioning of thewhole organism.

This cell-to-cell communicationfunctions as follows: messengermolecules from other cells (often hor-mones) travel through the blood-stream and then attach to specializedprotein molecules on the outside ofthe membrane of the target cell. Theprotein receptor molecule, whichspans the cell membrane, changes theshape of its “tail” (which sticks intothe cytoplasm). The shape changethen triggers a chain reaction that in-volves protein kinases in the cell.

Protein kinases transmit thecommands of many hormones thatregulate cellular processes such ascell division and specialization. Once

activated by the receptor proteins, thekinases join together like Lego blocksto carry the message to the properlocation within the cell and allow thecell to respond to the command.

The understanding of thismethod of cell-to-cell (called intercellular) and within-cell (calledintracellular) communication hasprovided new insights into a numberof human diseases. For example, sci-entists have learned that many typesof cancers and some types of diabetesare caused by problems with the pro-tein kinase intracellular communica-tion system. New treatments aimedat correcting these problems are cur-rently being tested in clinical trials.

Protein Kinases


1. What is the function of the cell mem-brane?

2. Name and describe the molecules thatmake up the cell membrane.

3. Describe the different types and func-tions of the proteins found in the cellmembrane.

4. Contrast the terms “permeable” and“selectively permeable.”

Making Connections

5. Work with a partner to research therole of protein kinases in cell biology.Investigate their involvement in a par-ticular disease. Present an informed

opinion on the effectiveness of newtreatments based on knowledge aboutprotein kinases.

6. Cholesterol molecules are a normalpart of the cell membranes of mam-mals; however, some people have highlevels of cholesterol in their blood thatcan lead to heart and/or artery disease.Some doctors have suggested that alladults should have their blood choles-terol level tested, and those who haveabnormally high cholesterol levelsshould be given medication or put ona special diet. Research the cost tosociety if the Canadian government im-plemented a plan of this nature. Usea PMI chart to organize the results ofyour research.


Solutes are substances that are dissolvedin fluid to form a solution. The liquid thatthe solutes are dissolved in is referredto as a solvent. Many of the moleculesthat must enter or leave cells, such asglucose, oxygen, and carbon dioxide, aredissolved in water and can thereforebe referred to as solutes. Many solutesmust constantly make their way into andout of cells to ensure cell survival.

DiffusionParticles, even those in solids, are con-stantly and randomly moving. As a result,over time, particles tend to spread them-selves out evenly. Diffusion is the ten-dency of particles to move from an areawhere they are more concentrated, andthere are more random collisions, to anarea where they are less concentrated andhave fewer collisions (Figure 3.5). Wherethere is an equal concentration of parti-cles in all areas equilibrium is achieved.Movement from an area of higher con-centration to one of lower concentrationis known as moving along the concen-tration gradient. Movement along theconcentration gradient is referred to aspassive transport. A common example ofdiffusion occurs when someone is wear-ing a strong cologne or perfume. Althoughthe concentrated source is located on theirbody, the perfume molecules spread bydiffusion to fill the room.

Diffusion is the driving force behindthe movement of many moleculesthrough the cell membrane, includingoxygen, carbon dioxide, alcohol, andsmall lipids. A number of factors deter-mine whether a molecule can enter a cellby diffusion. One of these factors is size.Large molecules cannot squeeze throughthe tightly packed phospholipids easily.Another factor is lipid solubility. If amolecule cannot dissolve in the oily mix-ture created by the membrane fattyacids, it cannot diffuse through the mem-brane. Physical factors such as the sizeof the concentration difference and thedistance the molecule has to travel alsoaffect the diffusion process.

Your lungs rely exclusively on diffu-sion to add oxygen to and remove carbon

3.2 The Movement of Solutes and WaterKey Understandings

When you have completed this section, you will be able to: � describe how organelles and cell components carry out various cell processes such

as transportation� explain the dynamics of diffusion and osmosis

Particles diffuse along the concentration gradient. Add a drop ofdark food colouring to a beaker or glass of cold water and anotherdrop to a beaker of hot water. Observe the changes to the ap-pearance of the water over time.

� What have you just observed in action?

� What comments can you make about the speed of the pro-cess you have just observed?

� How might you test your suggestion?

� When did the process appear to stop?

� Did the molecules become stationary at this time? Why or whynot?

DiffusionD i s c o v e r i n g B i o l o g y

solvent water saltwater

solution

salt

solute



FIGURE 3.4 A solute dissolved by a solvent re-sults in a solution. A small amount of table saltpoured into water results in a solution of sodiumchloride.


dioxide from your blood. The air sacs ofthe lungs, called alveoli, and the spe-cialized blood vessels known as capillaries that surround the alveoli, haveadaptations to speed up the relatively slowprocess of diffusion. For example, bothalveoli and capillaries are only one celllayer thick, providing the shortest distancepossible for the dissolved gases to travelthrough the respiratory membrane. Eachalveolus is surrounded by many capil-laries, thus increasing the surface areafor diffusion to occur. Since the oxygencontent is higher in the freshly breathed-in air of the alveoli than in the deoxy-genated blood of the capillaries, theoxygen travels down this concentrationgradient, leaves the alveoli, and enters thebloodstream. The carbon dioxide movesalong its concentration gradient from theblood and into the alveolar air.

OsmosisOsmosis is a special type of diffusion.It is the diffusion of water through aselectively permeable membrane, such

as the cell membrane. Despite the factthat water moelcules are not lipid solu-ble, they can easily pass through thephospholipid bilayer. This is apparentlybecause they are small enough to fitthrough gaps created by the movingphospholipids. During osmosis, watermolecules always pass from the side ofthe membrane that has a higher concentration of water and less soluteconcentration to the side that has thelower concentration of water and highersolute concentration until equilibrium, ifpossible, is established.

The osmotic conditions of the solu-tions surrounding a cell are given spe-cial names. In a hypertonic solution, thefluid surrounding the cells has a highersolute concentration than the cytoplasmof the cell. As a result, water diffuses outof the cell by osmosis.

In an isotonic solution, the con-centration of solutes in the fluid sur-rounding the cell is the same as it is inthe cell’s cytoplasm; therefore, the so-lute concentrations are at equilibriumand no net movement of water occurs.

a b c

water molecules

dye molecules

FIGURE 3.5 Diffusion. A few drops of red dye added to a beaker of water are initially veryconcentrated in one area. Diffusion, the movement of particles along their concentrationgradient from a region of high concentration to a region of low concentration, occurs until an

equilibrium concentration is produced throughout the solution.

WEBL INK

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In a hypotonic solution, the soluteconcentration of the fluid surroundingthe cell is less than that of the cell’s cytoplasm. As a result, water diffusesinto the cell by osmosis.

Osmosis is a very important processin cells. Freshwater organisms generallyhave a higher solute concentration in-side their cells than outside. As a result,they are constantly taking on more waterby osmosis and have developed mech-anisms to rid themselves of the extra

Cell Size and DiffusionD i s c o v e r i n g B i o l o g y

a

b

salt

solute

solvent

semipermeable membrane

OSMOSIS

The size of a cell affects the rate of diffusion.

Materials

CAUTION: Wear disposable non-latex gloves and safety goggles when using sodium hydroxide. Do not allow sodium hydroxide to come in contact with your skin. If it does,wash it off immediately. Be careful when using sharp instruments.

1. Obtain and measure the dimensions of three different-sized agar blocks.2. Calculate and record the surface area to volume ratio for each block. 3. Place the three blocks of agar in a 300-mL beaker. Add 0.4% sodium hydroxide

solution until it completely covers the blocks. 4. After 8 min, use test-tube holders or tongs to gently remove the agar blocks

from the solution and then blot them dry. Cut each block in half with ascalpel.

5. Use a metric ruler to measure the distance the pink material has diffused intoeach block and record your measurement.

� What was the diffusion distance in each block?� Which block had the greatest amount of pink material in it? Can you identify a

pattern between this answer and the surface area to volume ratios you calculated?

� Calculate the rate of diffusion in mm/min.

• 3 different-sized blocks of agarmade with water containing phenolphthalein

• 0.4% sodium hydroxide solution

• 300-mL beaker• test tube holders or tongs• scalpel • metric ruler

FIGURE 3.6 Osmosis

a) A semi-permeable membrane separates thechamber on the left, containing water, from thechamber on the right to which salt is added.

b)Water flows through the membrane in both directions but there is a net movement of wateralong its concentration gradient into the rightchamber.

Section 3.2 Review


water. Some unicellular organisms suchas Paramecium have contractile vacuolesthat fill up with water and, when full,contract. This squeezes the water out ofthe organism.

You place your body cells in an os-motic situation when you eat or drink.For example, when you drink a lot ofwater, your blood develops a higher concentration of water. If the water en-tered your cells by osmosis, every cell inyour body could be affected. However,your kidneys regulate the water balanceof your blood, so if there is too muchwater in your blood, the kidneys excretemore water in your urine and in this waymaintain equilibrium between yourblood and your cells.

Osmosis also helps the kidneys if youdon’t have enough water in your blood.Portions of the kidney tubules passthrough areas of high solute concen-

tration. This enables the kidneys to reabsorb water back into the blood byosmosis rather than having that waterleave as part of the urine. The abilityto reabsorb water is an important adap-tation of all land animals.

FIGURE 3.7 The effects of solute concentration on cells




1. Differentiate between a solute and asolvent.

2. Define the term “diffusion” and give anexample of diffusion in action.

3. What is meant by the term “concen-tration gradient”?

4. Define “osmosis” and provide an ex-ample of osmosis in action.

5. House plants will wilt if you forget towater them. The stems will becomelimp. However, a few hours after youremember to water them they willappear normal again. Using yourknowledge about the movement ofsolutes and water, explain these observations.

ApplyingInquiry/Communication Skills

6. If a cell whose cytoplasm was about 1%solute concentration were placed in a3% salt solution, what would you expect to happen? Use a diagram toexplain what would happen.

7. Before refrigeration was invented,many foods were preserved by storingthem in salt. Explain why micro-organisms may have a difficult timegrowing on food preserved this way.Compare the advantages of salt preser-vation and refrigeration. Provide twoexamples of foods that are preservedusing salt.

Making Connections

8. Many people suffering from kidneyfailure survive through dialysis treat-ment which artifically cleans theirblood. Most dialysis patients have totravel to a hospital for treatment, al-though new technology is enablingsome patients to have dialysis unitsin their homes.

a) Explain how this technique de-pends on diffusion and osmosis.

b) Analyze the social and economicimpact of a treatment like dialysis.

c) Evaluate home dialysis from the as-pects of patient care, affordability,and the health care system.

HypotonicThe concentration of solutes outside is lower than it is inside the cell.

IsotonicThe concentration of solutes outside the cell is equal to that inside the cell.

HypertonicThe concentration of solutes outside is higher than it is inside the cell.

Very HypotonicThis cell has burst due to the large amount of water entering.

normal cell

Passive transport Active transport

simple diffusion

facilitated diffusion

transportproteins ATP

a b c

TRANSPORT THROUGH THE PLASMA MEMBRANE

phospholipidbilayer

Facilitated DiffusionSome molecules cannot travel throughthe lipid portion of the cell membrane.They may be too large or may be hy-drophilic. Many of these molecules entercells by facilitated diffusion. Facilitateddiffusion occurs when molecules entercells through channels that exist in spe-cial transport proteins that span themembrane (Figure 3.8). Transport pro-teins are specialized to carry only cer-tain molecules into or out of cells.Because they only transport materialsalong the concentration gradient, no en-

ergy from ATP is required for facilitateddiffusion. For this reason facilitated diffusion is a form of passive transport.

Glucose is an example of a moleculethat is too large to travel through the cellmembrane without one of these specialprotein carriers. Since glucose is con-stantly being used inside cells for energyto produce ATP, the concentration ofglucose inside cells is usually lower thanthe concentration of glucose in the fluidsurrounding the cells. Therefore, glucosemoves down the concentration gradientand into the cell by facilitated diffusion.


FIGURE 3.8 Transport through the plasma membrane

a) In simple diffusion, molecules move along their concentration gradient.

b) In facilitated diffusion, molecules move along their concentration gradient but passthrough the membrane with the assistance of a transport protein.

c) In active transport, molecules move against their concentration gradient with theassistance of a transport protein and the use of energy from ATP.

3.3 Protein Carrier-Assisted Transport

Key Understandings

When you have completed this section, you will be able to: � describe how the cell membrane uses proteins to carry out transportation� explain the dynamics of facilitated diffusion� compare the processes of facilitated diffusion and active transport� relate certain disease states to a lack of function of cellular processes� describe how advances in cell biology can be applied through technology


Active TransportSometimes cells need to move moleculesor ions against a concentration gradient.Cells cannot rely on any type of diffusionto do this since diffusion only moves par-ticles from a high concentration to a lowconcentration. Therefore, cells have de-veloped another transport methodknown as active transport to movemolecules or ions against a concentra-tion gradient.

Like facilitated diffusion, active trans-port relies on transport proteins to allowsubstances to pass through the mem-brane. This time, however, the moleculesor ions bind to the proteins and are thenpumped across the membrane. Movingmolecules or ions this way is not without

its cost: active transport requires energyreleased from the breakdown of ATP tomove substances against the concen-tration gradient.

The sodium/potassium (Na+/K+)pump in nerve cells (neurons) is an im-portant example of active transport. Inorder to function properly neurons mustmaintain a higher concentration ofsodium ions outside the cell comparedto inside the cell. They must also main-tain a higher concentration of potassiumions inside the cell compared to outside.In order to maintain this imbalance, spe-cialized transport proteins in neuronspump sodium out of the cell and potas-sium in. See Figure 3.9 for further explanation.

Diabetes is a disease that has a longhistory of death and destruction aswell as a long history of research anddiscovery by Canadian scientists.Diabetes, a disease caused by the in-ability to transport glucose into cells,currently affects about two millionCanadians.

Diabetics are unable to producea protein-based hormone called insulin that binds to transport pro-teins on the cell membrane and allows glucose to enter cells by facilitated diffusion. Without insulin,the cells are unable to take up

glucose. This causes the glucose levelof the blood to increase to danger-ously high levels when the personeats a meal. The symptoms of untreated diabetes include thirst,moodiness, blindness, circulatoryproblems, and unconsciousness lead-ing to death.

The first step in the successfultreatment of diabetes came with Dr.Frederick Banting’s discovery of in-sulin in 1922 while working at theUniversity of Toronto with his col-leagues Best, Collip, and Macleod.Banting and Macleod (who providedlab space and advice to Banting)shared the Nobel Prize in 1923.Identifying and purifying insulin al-lowed diabetics to inject themselveswith insulin after eating. This discov-ery has been called “one of the mostrevolutionary moments in medicine”and has saved the lives of an estimated15 million diabetics worldwide.Biotechnology has assured a plentifulsupply of insulin through techniques

that enable this human protein to bemade by micro-organisms.

Dr. Michael Smith, another NobelPrize winner and Canadian re-searcher at the University of BritishColumbia, contributed to the im-proved treatment of diabetes. In1988, Zymogenetics, a biotechnologyresearch firm he co-founded, used hisNobel Prize–winning technique to im-prove the purity of insulin availablefor treating diabetics. This was another important step toward im-proving the lives of diabetics.

Even more recently, researchersat Kinetek Pharmaceuticals, aVancouver-based biotechnology com-pany, have developed a new treat-ment that may eventually freediabetics from their daily ritual of in-sulin injections. The new treatmentaffects signalling pathways within thecell, between the cell membrane andthe nucleus, and is currently under-going clinical trials.

Diabetes: A Problemwith

Facilitated Diffusion

WEBL INK

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Cystic fibrosis is due to a faulty active trans-port protein Cystic fibrosis is a devas-tating inherited disease that affects aboutone in 2500 Canadian children. The dis-ease, characterized by the buildup ofmucus in the lungs and other organs,slowly destroys lung tissue.

The problem is caused by a faultymembrane-based protein that shouldfunction to actively transport chlorideion out of the cell. Due to the defect, lesschloride ion is released than normal.This results in decreased reabsorptionof sodium ion, dehydration of the mem-branes lining the respiratory and diges-tive passages, and the formation of athick mucus. The abnormal secretionsalso have a reduced ability to kill in-vading bacteria. A cycle of infection andinflammation takes place.

Research on cystic fibrosis over thepast twenty years included the 1989 dis-covery of the gene that causes the de-fect. Improved antibiotics, physiotherapyand concentration on improving nutri-tional health have led to better lunghealth and an increased life span. Heartand lung trasnsplants are also a possi-ble treatment. The estimated mediansurvival age for people born with cysticfibrosis in the 1990s is 40 years.

The cell membrane controls the movement of ions and molecules.The graph below shows the concentration of different ions in-side an animal cell (in green) and outside the cell (in blue). Use the graph and what you have read in the previous sections toanswer the following questions:� Explain which ions are transported into the cell by active

transport.� Explain which ions are transported out of the cell by

active transport.

A Concentration SituationD i s c o v e r i n g B i o l o g y

0

20

40

60

80

100

120

140

160

Sodium Magnesium Chloride Potassium

outsideinside

Conc

entra

tion

(mm

ol.L

-1)

FIGURE 3.10 Concentration of ions inside and outside the cell.

FIGURE 3.9 Active transport: the sodium-potassium pump

extracellularfluid

phospholipidbilayer

sodium ion

potassium ion

cytosol

Na+

Na+

Na+

Na+Na+

Na+

Na+

Na+

Na+

P PPATP ADP

K+

K+

K+

K+

1 Three sodium ions(Na+) from inside thecell bind to a transportprotein.

2 ATP gives up a high-energy phosphate group to bind to the transport protein.

3 The binding of phos-phate causes a shapechange in the protein.The channel opens tothe extracellular fluid;the Na+ binding sitesare lost and the ionsare released outsidethe cell; binding sitesfor potassium ions (K+)are created.

4 Two K+ ions bind to thetransport protein, resulting in the releaseof the phosphategroup from the protein.

5 The loss of the phosphate group returns the protein toits original shape. TheK+ ions are released inside the cell and thetransport protein isready to bind moreNa+ ions.


Simple diffusion, osmosis, and facilitateddiffusion efficiently transport substancesof a small size through the cell mem-brane. However, some situations, for ex-ample, defence against infection, requirethe movement of large particles into thecytoplasm. Others, for example, the se-cretion of hormones, require the removalof large particles from the cell. These sit-uations require the formation of vesiclesand involve some rearrangement of thecell membrane. Proteins and polysac-charides are examples of very largemolecules that need to pass into andout of cells. Because these molecules

are too large to fit through a protein car-rier they must use another method toenter or exit the cell.

EndocytosisMoving material into the cell by endocytosis involves the pinching in of aportion of the cell membrane around thematerial to be transported into the cell.The pinched-in portion eventually breaksfree from the cell membrane and formsa vesicle in the cytoplasm. This allows thematerial within the vesicle to travel to itsfinal destination within the cell.

3.4 Transport Requiring VesiclesKey Understandings

When you have completed this section, you will be able to: � describe the processes of endocytosis and exocytosis of large particles� explain how these processes are related to the function of organs

Section 3.3 ReviewUnderstanding Concepts

1. Provide an example of a molecule thatmust use facilitated diffusion to crossmembranes. Explain why it cannotenter cells by some other means.

2. Describe the process of active trans-port.

3. Explain why active transport requiresenergy in order to function.

4. Construct a table to show the similar-ities and differences between diffusion,facilitated diffusion, and active trans-port.


5. Nerve cells rely on the Na+/K+ pumpin order to function properly.

Investigate why the movement of theseions is required to facilitate nerve cellcommunication to and from your brain.Illustrate, using a diagram of the move-ment of the ions during a nerve im-pulse.

6. Each transport protein is specific to thesubstance it channels across the cellmembrane. Suggest ways that the speci-ficity of the transport protein for themolecule being transported is ensured.

Making Connections

7. Research one of the following: Type Ior Type II diabetes, or juvenile-onset ormature-onset diabetes. Prepare a briefreport, explaining the importance of diet,medication, and lifestyle in the manage-ment of the form of diabetes you havechosen to investigate.


There are three types of endocyto-sis. The first type, called phagocytosisinvolves the movement of largemolecules and sometimes even wholecells into the cell’s interior. Phagocytosisleterally means “cell eating.” Specializedwhite blood cells, known asmacrophages, may phagocytose wholebacteria as part of your body’s defenceagainst disease.

A second type of endocytosis, calledpinocytosis or “cell drinking,” involvesthe transport of liquids into vesicles.From the descriptions and Figures 3.11and 3.12, you can see why phagocytosisand pinocytosis are well named.

The third type of endocytosis isknown as receptor-mediated endocy-tosis (RME), and it is how a number ofnutrients and proteins, such as the hor-mone insulin, enter the cell. DuringRME, the molecule that is to enter thecell binds to special receptor proteins lo-cated on the outside of the cell mem-brane. These receptor proteins movewithin the cell membrane towards otheridentical receptor-molecule complexes.Once enough molecules have gatheredin an area, the cell membrane pinchesin, forming the vesicle that will trans-port these molecules into the cell.

RME is currently the subject of ex-tensive research. One reason for inter-est in RME is that cholesterol molecules

enter cells in this way. Cholesterol, isnecessary for the production of certainsex hormones, and is itself a componentof cell membranes. However, cholesterolcan lead to heart and artery disease iftoo much of it is present in the blood.Normally, due to RME, excess cholesterolin the blood enters liver cells and issafely removed from the blood.

However, some individuals inheritvarying degrees of a disease known ashypercholesterolemia. In this disease,the cholesterol receptors on the liver cellsare either absent or greatly reduced innumber. People who completely lackcholesterol receptors are unable to re-move excess cholesterol from their bloodand may die from heart disease whilestill in childhood. Others who have fewerthan normal receptors are also at risk,but may be treated with a low-fat dietand cholesterol-lowering drugs.Researchers are trying to determine thepossibility of stimulating the action ofliver cell cholesterol receptors as a wayto treat patients with high blood choles-terol levels.

The rearrangement of the cell mem-brane needed for vesicle-formation is anenergy requiring process. All three typesof endocytosis involve vesicle formation.For this reason all three types of endocytosis require energy from thebreakdown of ATP.

WEBL INK

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FIGURE 3.11 Phagocytosis. In phagocytosis, particles including whole bacteria aretaken in by pseudopodia that surround them. The cell membrane of the pseudopodiafuses and forms a vesicle that moves into the cell’s interior.

WORDORIGIN

Endocytosis from the Greek,endon, meaning “within,” andkutos, meaning “vessel orcell.”

vesicle

bacterium(or food particles)

pseudopodium

Phagocytosis


receptors capturedmolecules

coatedpit

vesicle

cytosol

extracellular fluid

plasma membrane

vesicle


ExocytosisExocytosis is the opposite of endocyto-sis and is used to export large moleculesout of the cell (Figure 3.14 on the nextpage). Large molecules such as proteinsare surrounded by a membrane at theGolgi complex and a vesicle is formed.In this vesicle the substances make theirway to the cell membrane where thevesicle membrane joins with the cellmembrane and the large molecules areexpelled from the cell. Exocytosis, likeendocytosis, also requires energy fromthe breakdown of ATP molecules.

Exocytosis, like endocytosis, is acommon process in many cells in our

bodies. Hormones are made within cellsbut act outside of these cells, sometimesat a great distance. For example, spe-cialized cells in the pancreas make theblood-sugar-controlling hormone insulin.Like other hormones, insulin travelsthroughout the body by way of thebloodstream. The process of exocytosiscarries the insulin molecules out of thepancreatic cells and allows them to enterthe blood. In another example, digestiveenzymes, made by specialized cells lin-ing the intestine, are released by the pro-cess of exocytosis into the interior of theintestine where they are used to digestfood materials.

FIGURE 3.12 Pinocytosis. In pinocytosis, the cell membrane sinks in to surroundmolecules in the extracellular fluid. The membrane then fuses to pinch off a vesiclethat can then move within the cell.

FIGURE 3.13 Receptor-mediated endocytosis. Many receptors bind to molecules.The receptors move laterally within the cell membrane, forming a coated pit thatpinches off to form a vesicle.

Pinocytosis

Receptor-mediated endocytosis

Section 3.4 Review



1. Describe the process of endocytosisin its three forms.

2. Outline the similarities and differencesbetween phagocytosis and pinocytosis.

3. Explain the process of exocytosis anddescribe two examples in human cells.

4. Use a T-chart to compare phagocyto-sis and receptor-mediated endocytosis.


5. Cells involved in large amounts of exocytosis, such as pancreatic cells,may seem to run out of cell membranequite quickly if they are constantlysending pieces of it away with exportedmaterials, yet the cell membrane re-mains a fairly constant size. Make ahypothesis about what processes are

needed to keep the cell membrane atthis constant size. Suggest ways to testyour hypothesis.

6. Predict the consequences if your bodycells could not perform a) endocytosisor b) exocytosis.

7. “An amoeba is like a free-livingmacrophage.” Write a supported para-graph to agree or disagree with thisstatement.

Making Connections

8. Recently it has been discovered thatmost cold-causing viruses bind to aprotein on the cell membrane andenter the cell they are about to infectby an endocytosis-like process. Howmight researchers working for a pharmaceutical company utilize this information? Suggest an experimentthat could be performed.

FIGURE 3.14 Movement out of the cell

a) In exocytosis, a transport vesicle moves to fuse with the cell membrane. The cellmembrane rearranges, opens, and releases the contents of the vesicle outside the cell.

b) Material being expelled by exocytosis.

plasma membrane

a b

extracellular fluidprotein

cytosoltransport vesicle


Analyzing the Issue

BACKGROUND INFORMATION

CaseCase Study

Whatever the causes of drug addiction, once addic-tive drugs are introduced into the body, the chem-istry of brain cells is altered. Scientists believe thatmesolimbic dopamine cells, neurotransmitters inthe central nervous system (CNS), control a person’smood. These specialized molecules control commu-nication from one neuron to another.

Some addictive drugs enhance mesolimbicdopamine’s role in the brain, which elevates a per-son’s mood, giving them a “high.” Heroin, for ex-ample, increases the rate at which nerve cells in theCNS release dopamine. As a result, those who useheroin experience a brief feeling of extreme eupho-ria, followed by an extreme “low.” In order to main-tain the same level of response, they must takehigher doses of the drug to achieve the same high.This is due to how the brain cells adapt to the on-going use of the drug.

Scientists believe that, over time, the actual num-ber of dopamine receptors is reduced. As a result,not only does the user require more of the drug morefrequently, but other activities such as being withfriends no longer bring pleasure. This also con-tributes to the frequency and amount of drug usedby the addict.

The turning point for the addict is the decisionto end the addiction. There are a variety of thera-pies available to help combat addiction. Some peo-ple believe that addiction can be overcome withwillpower and strength of personal character. Others

argue that addiction is an illness, and whilewillpower is important in overcoming addiction, ad-diction requires medical treatment. Recent researchindicates that addiction occurs at the cellular levelin the brain.

Understanding the causes of addiction is vitalin developing treatments to help addicts recover.Scientific studies that look at the genetic and socialfactors influencing addiction may hold the key toprevention.

1. Describe the social and economic factors that influencethe search for a cure to drug addiction.

2. Research two different drug therapies, one that focuseson working with the psychology of the addict, and a sec-ond that focuses on using drug treatment. Compare thetwo therapies by preparing a P-M chart. Identify the cir-cumstances under which both would be appropriate.

3. Plan a class debate that focuses on one of these drugtherapies. As a class, identify the question for the focusof the debate. Set the criteria you will follow (e.g., timeallotted to speakers, how many participants will speak).Participants must support their point of view with research data and real examples.

4. When the debate has concluded, evaluate the argumentsthat were presented.

Drug Addiction and the Cell

� Defining the Issue

� Developing Assessment Criteria

� Researching the Issue

� Analyzing Data and Information

� Proposing a Course of Action

� Justifying the Course of Action

� Communicating Your Proposal

Decision-Making Skills

FIGURE 3.14 Drug addiction is often complicated by loneliness.

A Study of Osmosis: Determining the SoluteConcentration of Potatoes


Even though potatoes may no longer be growing ontheir plants, they are still alive, and their cells, like allothers, have selectively permeable cell membranes. Inthis lab you will study osmosis; the diffusion of waterfrom an area of high water concentration to an areaof lower water concentration. You will determinehow osmosis affects potato sections.

ProblemsWhat is the solute concentration of potatoes?

Materials � test tubes� 10-mL graduated cylinder� 2 100-mL beakers� 10-mL, 5-mL, 2-mL pipette� test-tube rack� #5 cork borer� single-edged razor blade or scalpel and handle� ruler� centigram balance/electronic balance� potato� 1 mol•L–1 sucrose solution� distilled water� marker for test tubes� grid paper� paper towels

CAUTION: Work carefully with sharp instruments.

Procedure:Part 1: Preparation of the solutions

Prepare seven test tubes, each with a different soluteconcentration, as follows:

1. Label the tubes #1–7 and place them in a test-tuberack.

2. Using a pipette, add the correct amount of waterto each tube and then the correct amount of 1 mol •L–1 sucrose solution to prepare the intendedsolute concentration for each tube.

TABLE 3.1 Solute Concentration

Part 2: Preparation of the potatoes

Prepare 7 equal-sized potato sections.

1. Set up the data table as shown in Table 3.2.

2. Use a #5 cork borer to bore a section of potato. Cutthe skin off both ends and then use a razor bladeto trim the section to a length of 4 cm.

3. Rinse the sections with distilled water and blot themdry with paper towel.

4. Use a balance to determine the mass of each potatosection. Record this mass, I, in Table 2, and placeeach section in its corresponding test tube; thatis, the first potato section you weigh goes into testtube 1, the second section you weigh goes into testtube 2, and so on.

5. After 24 hours, remove each potato section andgently blot it dry. Record the final mass, F, of eachpotato section in Table 2.

6. Calculate the change in mass for each potato sec-tion as follows:

Test Tube Number 1 2 3 4 5 6

Volume of Water (mL) 10 8 6 4 2 0

Volume of Sucrose (mL) 0 2 4 6 8 10

Solute Concentration (mol.L–1) 0 0.2 0.4 0.6 0.8 1.0







Inquiry Skills


�

cork borer

potato

board

potato section

FIGURE 3.16 Set up for preparation of potato sections

(Final Mass – Initial Mass) = (F – I ) = change in mass.)(If the potato lost mass, this number should be negative.)

7. Calculate the percent change in mass for eachpotato as follows:

= % change in mass

(Any negative signs from step 6 will cause a nega-tive result here, too.)

8. On grid paper, plot the Percent change in mass vs.Solute concentration. Include both negative andpositive numbers (if necessary) on your y axis. Usea line of best fit to represent your data points.

Analyzing and Interpreting1. Determine the solute concentration of the potatoes

by interpolation (Hint: what percent change in masswould you expect if the sucrose solution had thesame solute concentration as the potato section?).

2. Indicate on your graph those solutions that werehypotonic or hypertonic to the potato cytoplasm.

3. Explain your results. For example, explain whysome potato sections gained mass and others lostmass over the 24-hour period.

Concluding and Communicating4. Do you think your experimental results are accu-

rate? Explain why or why not.

5. Describe possible changes to the procedure of thislab that would produce more accurate results.

6. You can restore wilted flowers or vegetables bysoaking them in water. From your knowledge ofosmosis, would it be better to soak them in distilledor tap water? Explain.

Extending7. Explain why it is important for intravenous fluids

to be of the same solute concentration as humanblood.

8. If you prepared a solution with the same solute con-centration as you determined in question one, whatchange in mass would you expect to find from apotato section that had soaked in that solution for24 hours? Explain your answer.

9. Road salt that has been accidentally spilled on grassoften kills the grass. Use the knowledge you havegained in this investigation to help explain why thishappens.

TABLE 3.2

(continued)


Test Tube #

1

2

3

4

5

6

SoluteConcentration

(mol.L–1)

0

0.2

0.4

0.6

0.8

1.0

Initial MassI (g)

Final MassF (g)

Change in Mass(F – I ) (g)

Percent Changein Mass

(F – I ) � 100I� �

F – I� 100

I� �


Investigation 2 (section 3.2)

Your teacher will demonstrate a model of a selec-tively permeable membrane made from simple house-hold materials. The demonstration will consist of asolution of cornstarch added to a plastic bag that isplaced in a beaker of distilled water with 20 drops ofiodine added to it.

ProblemWhat factors or variables might influence diffusion orosmosis in this experimental system?

Experimental Design1. Describe what you observe from the demonstra-

tion.

2. Write a list of the variables that you think might in-fluence the diffusion or osmosis across the mem-brane.

3. Write a hypothesis for how each variable would af-fect the movement of particles.

4. Design a procedure to test the hypothesis about each variable.

5. Have your teacher check your procedure before youproceed with your investigation.

6. Present the results of your investigation in a clearand well-organized manner. Use a data table andgraphs.

Analyzing and Interpreting1. What can you conclude about the plastic bag used

in this experiment?

2. Explain, using your knowledge of diffusion, howthe factors you investigated influenced diffusion orosmosis in this system.

3. How would the rate of diffusion change if some ofthese factors were applied together?

4. Suggest two ways of changing the rate of diffusion.

Concluding and Communicating5. What criteria did you apply to developing your pro-

cedure?

6. Describe which observations you felt provided ev-idence as to how much diffusion or osmosis hadtaken place.

7. Account for any experimental errors that may haveaffected your conclusion.

8. Describe the changes, if any, you would make toyour procedure if you repeated your experiment.

Extending 9. Using what you have learned from this activity, de-

vise a method to get rid of unwanted weeds in thecracks of a driveway.

Effects on Permeability







Inquiry Skills

Key Terms

CHAPTER SUMMARY


active transportdoncentration gradientdiffusionendocytosis

exocytosis facilitated diffusion passive transportpermeable

phagocytosispinocytosisosmosisselectively permeable

sodium potassium pump

1. Revisit the Checkpoint on page 65 and review your di-agram of the cell membrane. Revise your drawing basedon what you learned in this chapter.

2. Construct a concept map to show the relationship be-tween the following key terms: cell membrane, perme-ability, diffusion, molecules, concentration gradient,osmosis, facilitated diffusion, active transport, endocy-tosis, exocytosis, glucose, and proteins.

3. Cellular biologists require a variety of employability skills.Research careers in cellular biology and list what youthink are the five most important skills cellular biolo-gists require. Explain your choices.

4. Reflect on your learning. Evaluate the skills you usedto complete the Investigations in the first three chaptersof the Unit. Begin a database inventory of lab skillsthat you can add to throughout the year.

Summary table

Consolidate Your Understanding

3.1 Cell Membrane: Gateway to the Cell� The cell membrane controls movement of substances

into and out of the cell.

3.2 The Movement of Solutes and Water� Some substances pass through the cell membrane

by diffusion, the movement of a substance from highto low concentration.

� Water enters or leaves cells by the process of os-mosis, the diffusion of water through a selectivelypermeable membrane in response to its concentra-tion gradient.

3.3 Protein Carrier-Assisted Transport� In facilitated diffusion, substances move from re-

gions of high concentration to low concentration bymeans of carrier proteins in the membrane. No en-ergy use is needed.

� In active transport, cells use energy to move sub-stances against their concentration gradients.

� Active transport requires the use of carrier proteinsin the membrane similar to those used in facilitateddiffusion. It requires energy from ATP.

3.4 Transport Requiring Vesicles� Endocytosis without a transport protein occurs in

one of two forms: phagocytosis, the intake of largemolecules or whole cells, and pinocytosis, the intake of liquids.

� Some molecules enter the cell by receptor-mediatedendocytosis involving a membrane transport protein.

� Exocytosis involves the export out of the cell of largemolecules such as proteins.

� Both endo- and exocytosis require energy from ATP.

Essential Understandings

Name of Transport Method Description

Diffusion Movement of molecules from an area of high concentration to an area of low concentration (along a concentration gradient) until equilibrium is established

Osmosis Movement of water along a concentration gradient until equilibrium is established

Facilitated Transport Movement of large or polar molecules through a membrane along a concentration gradient by means of a carrier protein. This method does not require energy from ATP.

Active Transport Movement of molecules through a membrane against a concentration gradient by means of a carrier protein. This method requires energy from ATP.

Endocytosis The cell membrane forms a vesicle around large objects that must enter the cell. This method requires energy from ATP.

Exocytosis A vesicle fuses with the cell membrane to rid the cell of large objects. This method requires energy from ATP.

CHAPTER 3 REVIEW



1. The process in which molecules of a substance otherthan water move from an area of higher concentrationto an area of lower concentration is calleda) osmosisb) diffusionc) selective permeabilityd) active transport

2. Energy from ATP is needed in a) active transportb) diffusionc) facilitated diffusiond) osmosis

3. Materials that cannot diffuse through the cell membranecan be brought into the cell by a) endosymbiosisb) osmosisc) endocytosisd) exocytosis

4. In the fluid mosaic bilayer, the term fluid refers to the a) shifting phospholipids in the cell membraneb) the fluid surrounding the outside of the cellc) the fluid portion of the cytoplasm known as the

cytosold) the liquids that enter the cell by the process of

pinocytosis

5. Protein molecules embedded in the cell membranemay a) function as transport proteins to help molecules

enter and exit cellsb) bind to the cytoskeleton to provide structural

supportc) have carbohydrate chains that are involved in cell

communication attached to themd) all of these

6. Solutes area) fatty acid molecules present in the cell membraneb) substances dissolved in a fluidc) the liquid portion of a solutiond) molecules that can only move against the concen-

tration gradient

7. Molecules that can diffuse through the cell membranearea) smallb) lipid solublec) water solubled) both a and b

8. Endocytosis is used to bring _______________ moleculesinto cells.a) small, lipid solubleb) waterc) larged) oxygen

9. Facilitated diffusion differs from diffusion because in fa-cilitated diffusiona) energy from ATP is requiredb) protein carriers are usedc) molecules move against the concentration gradientd) smaller molecules are transported

10. Active transport differs from facilitated transport, be-cause in active transporta) protein carriers are usedb) energy from ATP is requiredc) molecules are moved against the concentration

gradientd) both b and c

11. Explain why you agree or disagree with the followingstatement: Membranes are the most important struc-tures in cells.

12. What would happen if a solution with a higher concen-tration of water than is in your body cells was added toyour bloodstream? Explain your answer.

13. Write a story entitled: “A Day Without Diffusion.”

14. Explain why the phospholipid “heads” of the cell mem-brane phospholipids are always pointing toward the cy-tosol or the fluid surrounding the outside of the cell, whilethe “tails” are always pointing toward the middle ofthe membrane.

15. Soft drinks and other beverages contain different con-centrations of solutes. Some of these drinks have low so-lute concentrations and, as a result, are a source of waterfor your body cells. Other drinks have a high solute con-centration and can dehydrate your body cells. Which ofthese drinks should be marketed as “thirst quenchers”?Explain your answer.

16. If cell membranes were completely permeable, whateffect would this have on cells?

17. Living yeast cells placed in a particular type of red dye(called Congo red) remain colourless. However, deadyeast cells placed in the same dye turn red. Explainthis observation.

18. In this chapter the structure of the cell membrane wasconsidered in detail. All membranes within cells areessentially the same. What differences would you expectto find among membranes in the interior of the cell?


19. A beaker containing two salt solutions is divided by amembrane. The level of solution is higher on the rightof the beaker than on the left side. The membrane is per-meable only to water. Which side of the beaker originallycontained a hypertonic solution? Explain your answer

20. The graph below shows the relative sizes of somemolecules that can diffuse across a cell membrane.Predict which substances will diffuse across the mem-brane the most quickly, the most slowly, and which willdiffuse across at about the same speed. Explain your an-swers in each case.


21. Design an experiment to test the effect of temperatureon the rate (speed) of diffusion. Use the following mate-rials in your experimental design: food colouring andthree beakers of water. One of the beakers is at roomtemperature, the other is filled with ice-cold water andthe third is filled with hot water. Predict what will hap-pen to the water and include an experimental control.

22. The container in the following diagram has a selectivelypermeable membrane separating two solutions. Assumethat the starch molecules are too large to pass throughthe membrane. What will happen to the water level oneither side of the membrane? Explain your answer.

23. Draw one diagram to illustrate active transport andanother diagram to illustrate facilitated transport. Labelthe diagrams and indicate clearly how the two types oftransport differ.

24. The red blood cell in humans behaves like an osmome-ter. Justify this statement. Use a series of diagrams tosupport your position.

25. Using the information gathered in question 24, discussthe statement: “Human life depends on the integrity ofthe red blood cell membrane.”

26. Design an experiment to determine the water concen-tration of an uncooked French fry. As a hint, remem-ber that potatoes are made of cells with cell membranes,and will either gain or lose water due to osmosis.

.27. Prepare a working model of the cell membrane. Use ma-

terials such as Styrofoam®, marbles, string, thread spools,or other equipment. Label the structures that you are usingto represent the phospholipid bilayer, transport proteins,etc. Add the functions of each structure as well.

28. The inside of your stomach is very acidic. This acid condition is created by some of the cells lining your stom-ach; they pump hydrogen ions into your stomach againstthe concentration gradient.a) What process is involved in creating the acidic en-

vironment of your stomach?b) Research how surrounding cells are protected from

the effects of low pH.c) Predict the result of problems with this protection

mechanism.Write a supported paragraph on the environment of theinside of the stomach.

Making Connections

29. One way of growing crops in particularly dry areas ofthe country, such as the prairie provinces, is to irrigatethe crops. However, the water tends to contain salts thatare left behind in the soil as the water evaporates. Basedon what you know about the movement of salts andwater, explain what might occur as a result. Predict thelong-term economic effects on the area. Propose solu-tions to this problem.

30. Protein kinases, the important molecules of communi-cation within cells, are being heavily researched becauseof the possibility that they can be used to stop the spreadof cancer and treat diseases like diabetes. Propose a wayto prioritize the focus of research on specific diseases.

semi-permeable membrane

20015010050

Relative size of molecules

0

water

oxygen

glycerol

glucose

Subs

tanc

es te

sted alcohol

carbon dioxide

UNIT 1 REVIEW



1. Which is an ionic compound?a) waterb) sugarc) carbond) sodium chloride

2. A disaccharide is an example of a(an)a) lipidb) proteinc) carbohydrated) nucleic acid

3. The monomer of a protein is a(an)a) sugarb) fatty acidc) nucleotided) amino acid

4. Nucleic acids are composed of monomers calleda) amino acidsb) saccharidesc) steroidsd) nucleotides

5. Who was the first person to view and name cells?a) Hookeb) Dutrochetc) Van Leuwenhoekd) Schwann

6. The molecule that forms the bilayer of a cell membrane is called aa) proteinb) lipid membranec) phospholipidd) cholesterol

7. Both mitochondria and chloroplasts containa) vacuolesb) DNAc) endoplasmic reticulumd) cytoskeleton

8. The site where ribosomes are assembled is called the a) mitochondrionb) DNAc) chromosomed) nucleolus

9. The cell membrane is known as selectively permeablebecause ita) allows all substances to enter and exit the cellb) allows some substances to enter and some

substances to exit the cell

c) allows some substances to enter and all substancesto exit

d) allows only some substances to exit and all sub-stance to enter

10. The process that involves substances moving throughthe cell membrane without requiring energy is calleda) endocytosisb) exocytosisc) active transportd) facilitated transport

11. Which compound is the energy providing molecule forthe cell?a) DNAb) RNAc) cholesterold) ATP

12. How many molecules of ATP are produced by aerobiccellular respiration?a) 29b) 2c) 4d) 36 or 38

13. Which process is used by plants to make food?a) fermentationb) respirationc) photosynthesisd) glycolysis

14. 6CO2 + 6 H2O + light energy → a) C6H12O6 + 6O2b) 6O2 + 6CO2c) C6H12O6 + 6H2Od) C6H12O6 + 6CO2

15. Fermentation occurs in the a) presence of ATPb) presence of oxygenc) absence of ATPd) absence of oxygen

16. Distinguish between an acid and a base.

17. Set up a T-chart to compare glycogen and cellulose.

18. Outline at least five effects that would occur if hydro-gen bonds did not form between adjacent watermolecules.

19. Explain the difference between a molecular formula anda structural formula. Give an example of each type offormula. what additional information is available if astructural formula is used.

113

20. The hydrogen bond is particularly important in bio-chemistry. Illustrate this statement with regard to:a) fish in the Canadian winterb) the secondary structure of a proteinc) DNA structure

21. Define dehydration synthesis. Use diagrams to show theimportance of dehydration synthesis in:a) formation of a complex carbohydrateb) formation of a protein

22. Phospholipids contain glycerol bonded to one or two fattyacids and to an organic base that is attracted to water.Explain how this chemical structure is essential to thestructure and function of the cell membrane.

23. Demonstrate the formation of a peptide bond by draw-ing a diagram. Use the structural formulas for glycineand alanine in your diagram.

24. The polypeptide chain formed at the ribosome may notbe ready to function in the cell. Discuss the role of theGolgi apparatus in producing the final, active protein.

25. Set up a T-chart to compare the types of information ob-tained from transmission electron microscopy and scan-ning electron microscopy.

26. Explain why you should not place an unopened bottle ofpop in a freezer.

27. Which molecule is larger, ATP or ADP? Explain how youknow this and why there is a size difference.

28. Compare covalent, ionic and polar covalent bonds.

29. List the components of the cell membrane. Indicate howhydrophilic and hydrophobic properties are importantfor entry of substances through the cell membrane.

30. Draw a diagram to show how the structure of water con-tributes to its properties as a solvent.

31. Define specific heat. Indicate the importance of thespecific heat of water for biological systems.

32. List three similarities and three differences between eu-karyotic and prokaryotic cells.

33. Name and describe the cellular structure that containsdigestive enzymes. Explain the importance of this struc-ture to the cell.

34. Draw a flow chart of protein synthesis.

35. Draw a timeline of observation and discovery during the19th century that led to the development of the Cell

Theory. List the essential characteristics of the cell theory.

36. What would happen if you added 3 mL of cola to 10 mL of water? Predict the movement and distributionof the molecules in the solution.

37. Associate faulty transport mechanisms in the cell withdiseases in humans.

38. Draw a diagram to show the relationship in the cell between ATP and ADP.

39. After glycolysis occurs, what happens to pyruvic acid ifno oxygen is present?

40. What does the term essential represent with respect tonutrients.

41. Set up a concept map to show the relationships betweenaerobic and anaerobic respiration and ATP production,alcoholic fermentation, and lactic acid fermentation.

42. Draw a flow chart to indicate the relationship betweenphotosynthesis and respiration.

43. List three uses humans have made of the process of fermentation.

44. Justify the following statement. “Chemoautotrophs arethe only living organism that do not depend on photo-synthesis to surivive.”

45. Explain how DNA controls the production of proteinsin cells.

46. Explain why photosynthesis and respiration are consid-ered opposite processes.

47. Outline the importance of the cell membrane to the sur-vival of the cell. Explain why it is important for the cellmembrane to be selectively permeable.

48. Describe in detail what would happen to a freshwaterorganism if it were placed in salt water.


49. Some antibiotics act by binding to enzymes of the disease-causing bacteria.a) Draw a diagram to show one way that the antibi-

otic might affect the activity of the enzyme.b) What effect of this binding on the bacteria would

you expect?

UNIT 1 REVIEW


50. Consult the Canada Food Guide or another nutritionalinformation source to determine the recommended con-sumption of saturated and unsaturated fat for a personof your age. Then maintain a dietary journal—a recordof what you eat for five days. Consult reference sourcesto determine your approximated intake of saturated vs.unsaturated fats. What changes, if any, should you maketo your diet in light of your findings. What are thelikely benefits to your health of making a change to theamount of fat you consume?

51. Use a T-chart to show the possible positive and negativeeffects of constructing computer processors and othercircuits out of molecules as opposed to constructing themout of elements as they are currently made?

52. Design an experiment to compare the speed with whichpolar and nonpolar compounds dissolve in water. Non-polar compounds include vegatable oil and sugar. Polarcompounds include acetone and hydrogen chloride.Predict the results of your experiment.

53. Imagine that a Canadian scientist has discovered anew and greatly improved microscope that can greatlyincrease the magnification and resolution of microscopes.What effects might this have on our understanding ofcells?

54. People who have nearly drowned in sea water have tobe kept under medical supervision for several hours afterthey have been revived. Using your understanding of os-mosis, explain why this occurs.

55. Briefly describe a plan that would allow you to observethe effects of water moving into a plant cell by osmosis.

56. The table below shows the different amounts of energyreleased from glucose by two different processes.Compare the amount of energy released for each pro-cess. Explain what has happened to energy that appearsto have been lost.

57. Design an experiment to demonstrate the effects of different amounts of light on plant growth. Write a hypothesis and submit your experimental design to yourteacher before you begin your experiment.

58. Copy and complete the following chart on aerobic andanaerobic respiration.

Fuel Fuel use Efficiency of energy conversion

Glucose burned in laboratory 100%experiment

Glucose metabolized during 40%cellular respiration

Aerobic Anaerobic Respiration Respiration

Substrate

Products

Energy (# of ATP produced)

Nutritional Composition of Selected Foods

Food Proteins (g) Lipids (g) Carbohydrates (g)

breakfast cereal (30 g serving) 1.9 3.0 24

salad dressing (15 mL serving) 0.4 8.5 0.4

chocolate chip cookies (2) 1.9 7.8 17

light cream cheese (30 g serving) 2.2 5.2 1.2

whole wheat bread (1 slice) 2.6 1.0 13.0

fried bacon (1 slice) 2.3 4.0 0.25

margarine (10 g serving) 0 8.0 0.1

boiled egg (1) 6.5 5.8 0.5

orange juice (125 mL) 1.8 0.5 26

carrot (1) 0.5 0.1 4.9

macaroni (250 mL) 2.4 0.3 16.3

The Or ig ins o f the per iod ic law 115

59.Copy and complete the table below. Obtain a sheet ofgrid paper and graph the data.

60. The average human requires 2200 kcal per/day to meettheir energy demands. If a person were to regularly con-sume 2500 kcal what effect would this have on theirbody? Express these values in kilojoules.

61. All human cells metabolize glucose and human bonesactively metabolize calcium. Cancerous cells often me-tabolize at much faster rates than normal cells. Read thesection: Nuclear Medicine: using the knowledge of cellfunctions and technology on page 94 and then describehow you would design further nuclear medicine teststo determine cancer in any body tissue as well as can-cer in bones.

62. Use the table below to answer the following:a) What food in the table has the highest ratio of pro-

teins to lipids? The lowest ratio of proteins to lipids?b) If you were advised by your doctor to eat a low fat

diet, which of the foods listed above should youeat less of?

c) Calculate the number of grams of proteins, lipidsand carbohydrates in the following breakfast: 1 cupof orange juice, 1 boiled egg, 2 slices of fried bacon,2 slices of whole wheat toast, and 10 g of margarine.

Making Connections

63. Stem cell research is based on the principle that somecells are capable of dividing and giving rise to differenttypes of differentiated cells. The object of this researchis to have transplanted stem cells assume the role of es-sential functions missing or lost due to diseases likeAlzheimer’s. Other research studies factors that may pre-vent such diseases. Research dollars are limited.

Set up a PMI chart to investigate support for these twotypes of research. Consider:a) data available currently from the two types of re-

searchb) short-term effects on societyc) ong-term effects on society

64. Research possible chemical-based and biological-basedalternatives to fossil fuels. Set up a PMI chart for eachmethod you research. Include a consideration of:a) the cost of the researchb) the likely time-frame before the alternative fuel is

commercially availablec) effects on the environmentd) effects on the Canadian economy

65. Imagine that you are the director of medical imaging forHealth Canada. Recent research results point strongly tothe possibility of harmful effects on humans through ex-posure to strong magnetic fields. Outline at least five rec-ommendations you would make in this circumstance tohospitals and clinics that are currently using MRI scan-ners. What other medical diagnostic tool may serve toprovide some guidelines for writing your proposal?

66. The function of molecules is often dependent on their three-dimensional shape, which leads to yet another story aboutperformance enhancing drug use by Mark McGwire.Besides using creatine phosphate, during his home-runhitting record breaking season, he was also using an-drostenedione—a legal steroid hormone that is identicalto testosterone except for the placement of a single hy-drogen atom. While other anabolic steroids are bannedfrom use, androstenedione is not. What is your opinion ofMcGwire’s use of this performance enhancing substance?Do you think he should be entitled to keep his record? Ifyou were a personal trainer to a world class athlete, whatwould your advice be regarding the use of androstene-dione? Write a supported paragraph on this topic.

67. Compose a letter to the bottlers of Coca-Cola outliningyour opinion of their use of HFCS sweeteners in theirproducts.

68. You have recently been assigned to the federal govern-ment cabinet position of Minister of Health. Draft a state-ment outlining your official policy on performanceenhancing drugs such as anabolic steroids.

69. Dr. Harry Jennings invented the first synthetic vaccine.Other vaccines may cause the inoculated person to con-tract the disease they are supposed to be protected against.This is a rare occurrence. Synthetic vaccines do not causediseases. Imagine you are a medical researcher. Whatother diseases would you suggest for the development ofsynthetic vaccines? List the reasons for your choices.

70. A number of other mammals have been cloned or ge-netically engineered (had their DNA changed by human-made methods) since Dolly’s production in1997—including ANDi, a monkey that contains an arti-ficially introduced jelly fish gene. Find out about someof the other cloned or engineered mammals and reportback to your class on your findings.

Size of Surface area Volume Surface area(cm) (cm2) (cm3) Cube/volume ratio

1

2

3

4

5

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