1 CELL STRUCTURE

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• Draw and label low power plan diagrams of tissues and organs (including a transverse section of stems, roots and leaves)

• Describe and interpret drawings and photographs of typical animal and plant cells as seen using the light microscope

• Describe and interpret drawings and photographs of typical animal and plant cells as seen using the electron microscope, recognizing:– rough and smooth endoplasmic reticulum,– Golgi apparatus, – mitochondria, – ribosomes, – lysosomes, – cell surface membrane, – centrioles, – nucleus and microvilli, – chloroplasts, cell wall, – vacuole, – tonoplast and plasmodesmata

Organization of cells

• Cell• Tissue (e.g. palisade tissue, blood, …)• Organ (e.g. leaf, heart, …)• Organ system (e.g. circulatory system)• Organism (e.g. bufo bufo – common toad)

LOW POWER PLAN DRAWINGS

• Shows distribution of tissues but not details of individual cells

• How to draw a low power plan diagram?• https://www.youtube.com/watch?v=t3FuoBoE

9XE

Rules for biological drawings

• Always use a pencil, not a pen!• Don’t use shading• Use clear, continuous lines• Use accurate proportions and observation –

not a text book version• Label all tissues and relevant structures• Identify parts correctly• Use a ruler for label lines

Low-power drawings

• Don’t draw individual cells• Draw all tissues completely enclosed by lines• Draw a correct interpretation of the

distribution of tissues• A representative portion may be drawn

High-power drawing

• Draw only a few representative cells• Draw the cell wall of all plant cells• Don’t draw the nucleus as a solid blob

Task: draw low-power plan

CELL• Robert Hook – English scientist, in 1665

examined cork, he called the pore-like structures CELLS

• Cell is the fundamental unit of all living things• CELL THEORY– The basic unit of structure and function of all living

organisms is the cell (Schleiden - botanist and Schwann – zoologist) 1838 and 1839

– All cells arise from pre-existing cells by cell division (Virchow) 1855

CELL BIOLOGY AND MICROSCOPY

• The light microscope– Uses light as a source of radiation– Golden age in 19th century – new branch of

biology = CYTOLOGY• The electron microscope– Uses electrons and source of radiation

CELL STRUCTURE AS SEEN UNDER THE LIGHT vs. ELECTRON MICROSCOPE

UNITS O MEASUREMENT IN CELL STUDIES

• The basic unit of measurements is METRE (m)

• Magnification– The number of times larger an image is, compared

with the real size of the object

– Observed size – what you can measure with a ruler– Actual size – the real size, the size of a cell before it’s

magnified

• Resolution– The ability to distinguish between two separate

points– If two points cannot be resolved, they will be seen

as one point– In practice – the amount of detail that can be seen

– the greater the resolution, the greater the detail– Max for light microscope is 200 nm

THE ELECTROMAGNETIC SPECTRUM

• Light travels in waves with variable lengths• Different lengths are in our brain translated

into different colors• The whole range of different wave lengths is

called = electromagnetic spectrum

• The limit of resolution is about one half the wavelength of the radiation used to view the specimen

• If an object is smaller than half the wavelength of the radiation used to view it, it cannot be seen separately from nearby objects

(ribosomes can never be seen under the light microscope as their diameter is 25 nm)

• If an object is transparent, it will allow waves to pass through it and therefore needs to be stained before it can be seen

THE ELECTRON MICROSCOPE

• Uses radiation of shorter wavelength than light – electrons (negatively charged particles which orbit the nucleus of an atom)– Free electrons behave like electromagnetic

radiation– They have very short wavelength– Thanks to the negative charge they can be easily

focused using electromagnets– Resolution of 0.5 nm can be obtained

• Transmission electron microscope (TEM)– The beam of electrons is passed through the

specimen before being viewed – Only those electrons that are transmitted are seen– This allows to see thin sections and inside of cells

• Scanning electron microscope (SEM)– The electron beam is used to scan the surface of

structures and only the reflected beam is observed

– Three dimensional appearance is obtained

• Disadvantages of electron microscopes:– Electron beam has to be projected onto a

florescent screen– The resulting picture is like an X-ray photograph– The electron beam and the specimen and the

screen must be in vacuum and therefore all specimens must be dehydrated – only dead material can be examined

ULTRASTRUCTURE OF AN ANIMAL CELL

• Ultrastructure = detailed structure of a cell as revealed by the electron microscope

http://www.biology4all.com/resources_library/source/62a.pdf

NUCLEUS

• The largest cell organelle• Surrounded by – nuclear envelope

• Two membranes• Outer layer is continuous with the endoplasmic

reticulum• Has small openings called NUCLEAR PORES that allow

and control exchange between the nucleus and cytoplasm

(entering substances: proteins, ATP, hormones Leaving substances: mRNA, ribosomes)

• Chromatin – loosely coiled chromosomes that contain DNA organized into functional units = genes– Genes control the activities of the cell and

inheritance

• FUNCTION– Controls all the cell’s activities and cell division– Nucleolus inside the nucleus makes ribosomes

ENDOPLASMIC RETICULUM (ER)

• Extensive system of membranes running through the cytoplasm

• It is continuous with the outer membrane of the nuclear envelope

• Two types:– Rough ER – it is covered with many tiny ribosomes

visible as black dots• Forms and extensive system of flattened sacs spreading in

sheets throughout the cell• Proteins produced by ribosomes enter the sacs and move

through them• Ribosomes – consist of two subunits (small and large); 80S- they are the site of protein synthesis; - can be found free in cytoplasm or on the rough ER- very small – 25 nm in diameter- made of RNA (ribonucleic acid) and protein

– Smooth ER» Lacks ribosomes» Makes LIPIDS and STEROIDS such as

cholesterol, oestrogen and testosterone

GOLGI APPARATUS

• Stack of flattened sacs• The stack is formed as the vesicles bud off from

the ER; are further broken down to form Golgi vesicles

• Function:– Collects, processes and sorts molecules (proteins)– Golgi vesicles transport these either to another part

of the cell or out of the cell– Golgi vesicles are used to make lysosomes

LYSOSOMES

• Spherical sacs, surrounded by a single membrane with no internal structure

• 0.1 – 0.5 μm in diameter• Contain digestive (hydrolytic) enzymes• Function:– Responsible for the breakdown of unwanted

structures (old organelles, bacteria in lymphocytes)

MITOCHONDRIA

• Around 1μm in diameter• Various shapes (often sausage)• Contain ribosomes (smaller than those in cytoplasm,

70S), circular DNA molecules – endosymbiont theory• Surrounded by two membranes (an envelope)– Inner membrane – folded to form CRISTAE which project

into the interior solution called MATRIX• Function:– Carry out aerobic respiration – they make ATP– Involved in the synthesis of lipids

CELL SURFACE MEMBRANE

• Extremely thin (about 7nm)• Has three layers• Semipermeable = partially permeable• Controls exchange between the cell and its

environment

MICROVILLI

• Finger-like extensions of the cell surface membrane

• Typical of epithelial cells• Increase the surface area of the cell surface

membrane (absorption in guts)

CENTRIOLES

• 2 centrioles just outside the nucleus• Lye close together at right angles to each other• Not found in plant cells!• = hollow cylinder about 0.4 μm long formed of

short microtubules– Tiny tubes made of protein = tubulin– Used as a starting point for growing the spindle

microtubules for nuclear division

ULTRASTRUCTURE OF A PLANT CELL

• He only structure commonly found in animal cell which is absent from plant cell is the centriole

• Plant cells posses cell wall, large permanent vacuoles and chloroplasts

CELL WALL

• Outside the cell surface membrane• Rigid thanks to the fibres and cellulose• Gives the cell a definite shape and prevents the

cell from bursting • May be reinforced with extra cellulose or lignin• Freely permeable• Plasmodesmata – fine strands of cytoplasm which

pass through the walls of neighbouring cells

VACUOLES

• Large, permanent, central• Surrounded by a membrane = tonoplast– Controls exchange between the vacuole and the

cytoplasm• Fluid inside a vacuole – solution of mineral salts,

sugars, oxygen, carbon dioxide, pigments, enzymes including waste products

• Help to regulate the osmotic properties of cells; pigments give color to the different flower parts

CHLOROPLASTS

• Relatively large organelles; green thanks to chlorophyll (green pigment)

• Granum – small structures inside chloroplast; responsible for light absorption during photosynthesis– Consist of stacks of membrane-bound sacs called

thylakoids

PROKARYOTIC CELLS

• Cells with no true nucleus• Organisms – PROKARYOTES – mainly bacteria• Average diameter of cell is 0.5-5 μm• DNA is circular and lies free in the cytoplasm; it is

naked• Ribosomes 70S• No ER• Very few organelles; no double membranes• Cell wall present; strengthened with murein

• Organisms made of eukaryotic cells = EUKARYOTES– Animals, plants, fungi and unicellular eukaryotes

called PROTOCTISTS

TISSUES AND ORGANS

• Unicellular organisms (e.g. bacteria)• Multicellular organisms– Greater independence from the environment– Functions of the organisms are divided among

groups of cells– Structurally and functionally specialized cells are

grouped into TISSUES

A TISSUE

• Is a collection of cells, together with any intercellular secretion produced by them, that is specialized to perform one or more particular functions

• The cells may be of the same type (e.g. parenchyma) or they may be of mixed type (e.g. blood, bones,…)

• The study of tissues is called HISTOLOGY

• Messophyll- Tissue made up of many similar cells, all with the same

function

• Epidermis– A protective layer one cell thick– May be covered with waxy cuticule which is

waterproof and protects the organ from drying out and infection

– Pores called stomata– Extensions called root hairs

• Parenchyma– Thin-walled cells used as packing tissue– The cells are very active and can be used for many

functions– Forms cortex in roots and stems and the pith in

stems– Palisade mesophyll and spongy mesophyll

• Endodermis– Like the epidermis one cell thick– Surrounds the vascular tissue in stem and roots

• Pericycle– A layer of cells just inside the endodermis and

next to the vascular tissue– In roots one cell thick and new roots can grow

from this layer– In stems – is formed from a tissue called

sclerenchyma• Xylem and phloem

AN ORGAN

• Is a part of the body which forms a structural and functional unit and is composed of more than one tissue

• Leaf, stem, root, brain, liver, kidney

A SYSTEM

• Is a collection of organs with a particular function: secretory, excretory, reproductive, …

• E.g. vascular system