biological membranes

Question 1

what are 3 functions of the plasma membranes?

Answer 1

cell communication
recognition by other cells
barrier between cell and its environment (partially permeable)

Question 2

what are 3 functions of membranes within cells?

Answer 2

form vesicles to transport substances between different areas of the cell
site of chemical reactions
control which substance can enter and leave the organelle eg RNA in nucleus via nuclear membrane

Question 3

what do channel proteins allow into the phospholipid bilayer?

Answer 3

they allow small or charged particles through by forming pores

different channel proteins facilitate the diffusion of different charged particles

Question 4

what do carrier proteins do?

Answer 4

they transport large molecules and ions across the membrane by active transport and facilitated diffusion

different carrier proteins facilitate the diffusion of different molecules

Question 5

what do proteins act as?

Answer 5

receptors for molecules in cell signalling

Question 6

what is the role of glycoproteins and glycolipids?

Answer 6

they stabilise the membrane by forming hydrogen bonds with surrounding water molecules

where drugs, hormones and antibodies binds

act as receptors for cell signalling

they are antigens

Question 7

how is a messenger molecule detected?

Answer 7

it binds to the receptor on the cells cell membrane

Question 8

why can messenger molecules only bind to specific receptor proteins?

Answer 8

its because the receptor proteins have a specific shape and only messenger molecules with a complementary shape can bind to them

Question 9

what 2 factors affect membrane permeability?

Answer 9

temperature and the solvent

Question 10

define diffusion

Answer 10

is the net movement of particles from an area of high concentration to an area of lower concentration down a conc gradient

passive process

Question 11

which molecules can diffuse through cell membranes?

Answer 11

small,non polar molecules such as oxygen and carbon dioxide and water as even though its polar it is small enough to fit between phospholipids

Question 12

which 4 factors does the rate of diffusion depend on?

Answer 12

the conc gradient-higher-faster rate of diffusion

thickness of exchange surface-thinner (shorter distance)

surface area-larger

temperature-warmer, the faster it is

Question 13

define active transport

Answer 13

uses energy to move molecules and ions across plasma membranes against a conc gradient, this process involves carrier proteins

Question 14

describe endocytosis

Answer 14

a cell surrounds a substance with a section of its plasma membrane

the membrane then pinches off to form a vesicle inside the cell containing the ingested substance

requires ATP

Question 15

describe exocytosis

Answer 15

vesicles containing substances such as hormones, digestive enzymes etc pinch off from the sacs of golgi apparatus and moves towards the plasma membrane

the vesicles fuse with the plasma membrane and release their contents outside the cell.

ATP IS USED

Question 16

define osmosis

Answer 16

the diffusion of water molecules across a partially permeable membrane down a water potential gradient

Question 17

what has the highest water potential?

Answer 17

pure water

Question 18

define water potential

Answer 18

the potential of water molecules to diffuse out of or into a solution

Question 19

define hypotonic solution in terms of animal cells

Answer 19

solution with a high water potential than the cell

net movement of water molecules is into the cell, cell bursts

Question 20

define isotonic solution in terms of animal cells

Answer 20

solution with the same water potential as the cell

water molecules pass into and out of the cell in equal amounts. the cell stays the same

Question 21

define hypertonic solution in terms of a hypertonic solution

Answer 21

solution with a lower water potential than the cell

net movement of water molecules is out of the cell. the cell shrinks

Question 22

what happens to a plant cell in a hypotonic solution

Answer 22

vacuole swells and the vacuole and cytoplasm push against cell wall. the cell becomes turgid, swollen

Question 23

what happens to a plant cell in a hypertonic solution

Answer 23

cell becomes flaccid , the cytoplasm and membrane pull away from the cell wall, the cell becomes plasmolysis

Question 24

what happens to a plant cell in a isotonic solution

Answer 24

cell stays the same