Cell Facts and Tissues (rev 3-10) Cells are the smallest structural and functional unit of life All cells are surrounded by a thin, outer membrane called

Cell Facts and Tissues (rev 3-10)

Cells are the smallest structural and functional unit of life• All cells are surrounded by a thin, outer membrane called

the plasma membrane (PM).– This separates the cell from interstitial fluid which

bathes the outside of the cell.• On the inside of the cell is a gel-like fluid called

cytoplasm. This contains specialized structures called organelles and the nucleus, a small circular body.

The Plasma Membrane • Forms the outer boundary of the cell

– Composed of 2 layers of fat molecules called phospholipids and another kind of fat molecule called cholesterol

Cell Facts & Tissues-BIO 006 1

Cell Facts & Tissues-BIO 006

• The plasma membrane (PM) keeps the cell whole and intact– It serves as a gateway (entrance) between the fluid

inside and outside the cell– It identifies a cell as belonging to one particular

person; the cell’s surface proteins act as identification tags (each person has different surface proteins)

Cytoplasm: composed of a gel-like fluid called cytosol

– Lies between the PM and the nucleus– Contains Organelles: structures with specialized

functions which are located in the cytoplasm.• Also contains a nucleus.

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Nucleus:

• Controls every organelle in the cytoplasm and the cell reproduction process because it contains the genetic code—instructions for making proteins, which in turn determine cell structure and function

• directs all functions of the cell.

Structural features:

• Outer surface is a double-layered nuclear membrane, also called nuclear envelope.

• Contains 46 chromosomes which contain DNA, the genetic code

Figure 3.19a3


Organelles

Ribosomes: tiny particles found throughout the cell; responsible for making enzymes and other protein compounds– Made up of 2 tiny subunits mostly made up of a

special kind of RNA— called ribosomal RNA – Ribosomes may be attached to the Endoplasmic

Reticulum– Free floating ribosomes produce proteins for use

by the cell

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Endoplasmic reticulum (ER) is a system of membranes forming a network of connecting sacs and canals that wind back and forth through a cell’s cytoplasm. – manufactures proteins and chemical compounds

produced by the cell.– The sacs and canals carry proteins and other

substances through the cytoplasm of the cell from one area to another.

Types: rough and smooth• Rough ER: areas where the surface is dotted with

ribosomes– Rough ER receives, from the ribosomes, and

transports newly made proteins • Smooth ER: Areas without ribosomes

– These areas synthesize chemicals and make new cell membrane

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Golgi Apparatus

• Group of flattened sacs• Called the chemical processing and packaging

center because it collects chemicals from the smooth ER in vesicles

Mitochondria: • Provide most of the power for cellular work;

nicknamed the cell’s “power plant”• Enzymes found in the mitochondria use oxygen

to breakdown glucose to release energy

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Lysosomes • contain digestive enzymes that digest food compounds

as well as other substances.– Can destroy microbes

Centrioles: used in cell division

Cilia: fine, hairlike extensions on the free surface of some cells; are capable of movement

Flagella: is a single projection from the cell surface; is

larger than cilia; “tails” of sperm cells are the only example of flagella in humans

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Movement of Substances through Cell Membranes

• Occurs through passive or active transport• Energy is required only for active transport and

is obtained from adenosine triphosphate or ATP– ATP is produced in the mitochondria

• Passive transport processes do not require added energy and result in movement “down a concentration gradient”

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• Solution terms

– Solute is a substance that dissolves into another substance

– Solvent is a substance in which other substances are dissolved



Passive Transport

• Transports a molecule without requiring the cell to use any energy; requires that there be a difference in concentration between 2 areas, called a concentration gradient.

• Movement is from area of high to area of low concentration or “down” the concentration gradient

• Primary passive transport processes are diffusion and osmosis

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• Diffusion : movement of molecules from one region to another as a result of random movement; – Molecules move from the area of higher

concentration to the area of lower concentration

• molecules scatter themselves evenly throughout a solution


Diffusion


(Passive transport: no energy required)

• Diffusion: movement from area of high concentration to low

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Osmosis is the diffusion of water across a selectively permeable membrane (the solutes cannot cross the membrane) from the region of lower concentration to the area of higher concentration

• Selectively permeable means a membrane will permit some substances to pass through it but not others

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Active transport• Movement of substances is “up the concentration

gradient”— movement from an area of lower to higher concentration

• Requires energy from ATP

• Ion pumps– An ion pump is a protein structure in the cell

membrane• Is called a “carrier”

– Ion pumps use energy from ATP to move substances across cell membranes against their concentration gradients

– Examples: sodium-potassium pump, calcium pump– Some ion pumps work with other carriers so that

glucose or amino acids are transported along with ions

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Na+-K+ Pump

3 sodium ions are pumped out of the cell and 2 potassium ions are pumped in during a pumping cycle of the carrier molecule. ATP is broken down and used for energy to pump the ions

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• Why are passive and active transport important in the human body?

– Hint: how do substances move across the plasma membrane?



Body Tissues• Tissue: group of similar cells that perform a

common function• 4 main kinds of tissues

– Epithelial– Connective– Muscle– Nervous

• Tissues differ from each other in their– Size and shape of cells– Amount and kind of material between the cells– Special functions they perform

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Epithelial Tissue covers the body and lines body cavities– Cells packed closely together

• Can be categorized according to shape:– Squamous (flat)– Cuboidal (cube)– Columnar (tall)

• Can be categorized according to arrangement-layers of cells:– Simple– Stratified

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EPITHELIAL TISSUE• Absorbs

– substances can easily pass through it for exampleabsorption of oxygen into the blood

• Secretes– cells function in clusters and form glands which

make and release substances to help the body work i.e. saliva, digestive juices, and hormones

– cells forms the urine-producing tubules of the kidneys

• Protects tissues– when there are several layers of closely packed

cells, microorganisms can’t get through them – cilia move mucus and protect against entry of

foreign particles into the lung

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• Most abundant tissue in body Most widely distributed tissue in body Multiple types, appearances, and functions

- Connects tissues to each other- Forms a supportive framework for the body

and the organs- Transports substances throughout the body

(blood is a type of connective tissue)- Defends us against microorganisms

Relatively few cells in an intercellular matrix

Connective tissue

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Types of Connective Tissue

• Blood— fluid “tissue”; – function is transportation and protection– cells are suspended in a fluid matrix called plasma.

(Considered a connective tissue because all blood cells derive from earlier stem cells located within bone.)

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Areolar: glue that holds organs togetherMost widely distributed type of connective tissue



Adipose (fat)• specialized to store lipids•Oil filled cells

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Dense Fibrous•Has bundles of collagen fibers arranged in parallel rows•Provides strength and flexibility; does not stretch •example is tendons and ligaments

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Bone• functions in support and protection

•Stores the mineral calcium

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Cartilage•bone will be formed from this type tissue•Matrix is the consistency of firm plastic or a gel

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Muscle tissue:

movement “specialist”; can contract

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Skeletal Muscle•also called striated or voluntary; •attaches to bones; •Has striations• is multinucleated• has long cells

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Cardiac Muscle

• also called striated or involuntary

• forms the walls of the heart

•has intercalated disks; fibers branch

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Smooth

•also called nonstriated, visceral, or involuntary

• found in blood vessel walls and hollow organs

• push food and fluids through body

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Nervous tissueprovides rapid communication between body structures

and control of body functions Consists of 2 types of cells:

Neurons—conducting cells Neuroglia—supportive and connecting cells

Neurons Cell components

o Cell bodyo Axon (one or more) carries nerve impulses

away from cell bodyo Dendrites carry nerve impulses toward the

cell body

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Documents

Cell Facts and Tissues (rev 3-10) Cells are the smallest structural and functional unit of life All cells are surrounded by a thin, outer membrane called