AP Biology Cell Structure and Function

nucleus

contains nuclear envelope, DNA (spread out w/in this as the threadlike matrix chromatin)

Ribosome

manufactured in the nucleus; consists of RNA molecs and proteins; in the cytoplasm, this assists in the assembly of amino acids into proteins

Endoplasmic Reticulum (ER)

stacks of flattened sacs involved in the production of various materials; appear as a series of maze-like channels in cross section; when ribosomes are present, it creates glycoproteins

Smooth ER

without ribosomes; responsible for various activities, including the synthesis of lipids andhormones

Golgi Apparatus

group of flattened sacs arranged like a stack of bowls; modify and package proteins and lipids into vesicles; vesicles often migrate to and merge with the plasma membrane

Vesicles

small, sphericaly shaped sacs that bud from the outside surface of the Golgi apparatus; often migrate to and merge with the plasma membrane, releasing their contens to the outside of the cell

Lysosomes

vesicles from a Golgi apparatus that contain digestive enzymes; break down food, cellular debris, and foreign invaders such as bacteria; a low pH is favorable;do NOT occur in PLANT cells

Peroxisomes

break down various substances, including hydrogen peroxide (H202), fatty acids, and amino acids; common in liver and kidney cells; in plant cells, these modify by-products of photorespiration

Mitochondria

carry out aerobic respiration (energy-in the form of ATP- is obtained from carbohydrates)

Chloroplasts

carry out photosynthesis

Microtubules

made of protein tubulin; provide support and motility for cellular activites; found in the spindle apparatus

Intermediate filaments

provide support for maintaining the shape of the cell

Microfilaments

made of the protein actin; involved in cell motility; found in muscles cells and in cells that move by changing shapes, such as phagocytes (WBCs attacking bacteria)

Flagella

structures that protrude from the cell membrane; long, few, move in a snakelike motion; 9+2 array; Ex: propels sperm

Cilia

structures that protrude from the cell membrane; short, many, move with a back and forth movement; 9+2 array; Ex: line the resp. tract and sweep away debris

9+2 arrangement

nine pairs (doublets) of microtubulesarranged in a circle surrounding a pair of microtubules

Centrioles

microtubule organizing centers; pair (enclosed in a centrosome) are located outside the nuclear envelope, gives rise to the microtubules that make up the spindle apparatus used during cell division; nine triples of microtubules arranged in a circle; PLANTS LACK THESE

Basal bodies

microtubule organizing centers; at the base of each flagellum and cillium and appear to organize their development; 9 triplets of microtubules arranged in a circle; lower plants (mosses and ferns) with MOTILE sperm have these

transport vesicles

move materials b/w organelles or between organelles and the plasma membrane

food vacuoles

temporary receptacles of nutrients; often merge with lysosomes, whose digesitve enzymes break down the food

Storage vacuoles

in plants store starch, pigments, and toxic substances

central vacuoles

large bodies occupying most of the interior of certain plant cells; when fully filled, they exert turgor pressure on the cell walls, thus maintaining the rigidity in the cell; store nutrients and carry out functions otherwise assumed by lysosomes in animal cells

contracile vacuoles

specialized organelles in single-celled organisms that collect and pump excess water out of the cell

cell walls

found in plants, fungi, protists, and bacteria; develop outside the plasma membrane and provide support for the cell; in plants, it consists mainly of cellulose

extracellular matrix

found in animals in the area b/w adjacent cells; occupied by fibrous structural proteins, adhesion proteins, and polysaccharides; provides mechanical support and helps bind adjacent cells together

anchoring junctions

protein attachments between adjacent ANIMAL cells

Desmosome

kind of anchoring junction; consists of proteins that bind adjacent cells together, providing mech. stability to tissues; associated w/protein filaments that extend into the interior of the cell and serve to hold cellular strucures together

tight junctions

tightly stitched seams b/w ANIMAL cells; completely encircles each cell, producing a seal that prevents the passage of materials b/w cells

Communicating junctions

passageways b/w cells that allow the transfer of chemical or electrical signals

gap junctions

narrow tunnels between ANIMAL cells; consist of connexins (proteins); prevent the cytoplasms of each cell from mixing but allow the passage of ions and small molecs; allow communication b/w cells thru exchange of materials or thru the tranismission of elec. impulses; essentially channel proteins of two adjacents cells that are closely aligned

Plasmodesmata

narrow channels between PLANT cells; a narrow tube of ER surrounded by cytoplasm and the plasma membrane passes thru the channel; material exhange occurs thru the cytoplasm surrounding the demotubule

Selectively permeable membrane

allows onliy specific substances to pass

hypertonic

when there is a higher concentration of solutes

hypotonic

when there is a lower concentration of solutes

isotonic

when there is an equal concentration of solutes

Bulk flow

collective movement of substances in the same direction in response to a force or pressure; Ex: blood moving through a blood vessel

Passive Transport

movement of substances from region sof higher to lower concentrations (DOWN a concentration gradient) and do not require expenditure of energy

Diffusion

net movement of substances from an area of higher concentration to an area of lower concentration; this movment occurs as a result of the random and constant motion characteristic of all molecules, motion that is independent from the motion of other molecs; a state of equilibrium is attained where molecs are uniformly distributed but continue to move randomly

osmosis

diffusion of water molecs across a selectively permeable membrane

turgor pressure

osmotic pressure that develops when water enters the cells of plants and microorganisms

Dialysis

diffusion of solutes across a selectively permeable membrane; when different solutes are separated by a selectively permeable membrane

Plasmolysis

movement of water out of a cell that results in the collapse of the cell

facilitated diffusion

diffusion of solutes or water through channel proteins in the plasma membrane; water can pass thru the plasma membrane w/o the aid of specialized proteins, but aquaporins increase the rate of transfer by this

Countercurrent exchange

diffusion of substances b/w two regions in which substances are moving by bulk flow in opposite directions; Ex: fish gills-the direction of water flow is opposite to the flow of blood in the blood vessels... diffusion of O2 is maximized because the relative motion of the molecs b/w the two regions is increased and because the concen. grad. b/w the two regions remain constant

Active Transport

movement of solutes against a gradient and requires the expenditure of energy (usually ATP); transport proteins in the plasma membrane transfer solutes such as small ions, amino acids, adn monosaccharides across the membrane

Exocytosis

process of vesicles fusing with the plamsa membrane and releasing their contents to the outside of the cell

Endocytosis

captureof a substance outside the ell when the plamsa membrane merges to engulf it; enters the cytoplasm enclosed in a vesicle

Phagocytosis

"cell eating"; undissolved material enters the cell; p.m. wraps around the solid material and engulfs it; ex: WBCs

Pinocytosis

"cell drinking"; dissolved substances enter the cell; p.m. folds inward to form a channel allowing liquid to enter; p.m. closes off the channel, encircling the liquid inside a vesicle

Receptor-mediated endocytosis

specific molecules in the fluid surrounding the cell bind to specialized receptors that conecntrate in coated pits in the p.m.