transport across cell membrane

Question 1

describe phospholipids

Answer 1

hydrophilic heads of both layers point to the outside of the CSM attracted to the water on both sides, hydrophobic tails of both layers point into the centre of the CSM, repelled by water on both sides

Question 2

what are the functions of the CSM proteins?

Answer 2

provide support, act as carriers for substances, to help cells stick together, act as receptors

Question 3

what are extrinsic proteins?

Answer 3

on the surface but only partly embedded, they give mechanical support to the cell/act as receptors for molecules such as hormones

Question 4

what are intrinsic proteins?

Answer 4

completely span membrane, act as carriers to transport material across the CSM, others can be enzymes

Question 5

what are glycolipids?

Answer 5

cell surface receptors for hormones and neurotransmitters, allow cell-cell recognition, helps cells attach to each other

Question 6

what does cholesterol do?

Answer 6

adds strength/rigidity to the CSM by pulling the fatty acid tils of the phospholipids together, reduces membrane fluidity at high temps, prevents water leakage from the cell

Question 7

why is the arrangement of the CSM referred to as the fluid mosaic model?

Answer 7

the phospholipids can move relative to one another, the proteins can vary in size and shape like the tiles in a mosaic

Question 8

what factors affect diffusion?

Answer 8

concentration gradient, length of diffusion pathway, surface area, temperature

Question 9

definition of diffusion

Answer 9

movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached

Question 10

how to work out diffusion rate

Answer 10

surface area x concentration difference divide by lenth of diffusion pathway

Question 11

what prevents molecules from passing through the CSM?

Answer 11

not lipid soluble, very large, polar

Question 12

what is facilitated diffusion?

Answer 12

diffusion made easier by the use of channel and carrier proteins that span the CSM

Question 13

what are protein channels?

Answer 13

protein pores that open or close to control the passage of selective ions e.g. sodium/potassium

Question 14

what are carrier proteins?

Answer 14

take substances from one side of the membrane to the other

Question 15

how does the number of proteins in the CSM limit the rate of diffusion?

Answer 15

proteins become saturated and can’t support any more molecules

Question 16

what happens to the permeability of the CSM in very cold temperatures?

Answer 16

phospholipids don’t have much energy and can’t move much so they’re tightly packed together, making the membrane rigid. proteins denature, increasing permeability as proteins lose structure and function. ice crystals form, pierce through membrane making it highly permeable

Question 17

what happens to the permeability of the CSM in warm temperatures?

Answer 17

phospholipids can move around, not as tightly packed together - membrane is partially permeable. as temp increases the phospholipids move more as they have more energy, increases the permeability

Question 18

what happens to the permeability of the CSM in hot temperatures?

Answer 18

phospholipid bilayer starts to break down/melt and membrane becomes more permeable. water inside the cells expands, putting pressure on the membrane. proteins denature so can’t control what enters/leaves the cell - increases permeability

Question 19

definition of osmosis

Answer 19

water moves from an area of high water potential to low water potential across a semi-permeable membrane until equilibrium is reached

Question 20

water potential of pure water

Answer 20

zero

Question 21

what is water potential measured in?

Answer 21

kilo-pascals (KPa)

Question 22

what is water potential?

Answer 22

a measure of how easy it is for water to move

Question 23

what happens with animal cells are placed in a higher water potential?

Answer 23

red blood cells - absorb water by osmosis when placed in water as it has a higher water potential. has a very thin CSM that can’t stretch to a great extent, so CSM breaks, bursting the cell and releasing its contents…. HAEMOLYSIS

Question 24

how do animal cells stop haemolysis from happening?

Answer 24

they usually stay in a liquid which has the same WP as the cell

Question 25

what happens when a plant cell becomes turgid?

Answer 25

placed in pure water they absorb water by osmosis has it has a higher WP. protoplast swells and presses on cell wall - cell wall only capable of limited expansion so pressure builds up on it that resists the entry of more water.

Question 26

what happens with animal cells are placed in a lower water potential?

Answer 26

water leaves by osmosis and the cell shrinks, becoming shrivelled

Question 27

why does incipient plasmolysis happen in plant cells?

Answer 27

when it’s placed in a solution with equal/lower WP - water leaves cell by osmosis and the vol of the cell decreases. a stage is reached when the protoplast no longer presses on the cell wall and begins to pull away from it

Question 28

why does plasmolysis happen in plant cells?

Answer 28

when water leaves via osmosis, the further loss of water causes the cell contents to shrink further and the protoplast pulls even more (completely) away from the cell wall

Question 29

definition of active transport

Answer 29

when molecules move from an area of low concentration to an area of high concentration against the concentration gradient across a semi-permeable membrane - requires energy in the form of ATP

Question 30

how is ATP produced?

Answer 30

via aerobic respiration by mitochondria

Question 31

how does ATP help substances across the membrane?

Answer 31

with the release of energy from the ATP molecule, the shape of the channel protein changes to allow it through, it then goes back to normal and repeats again