cell membranes and transport

Question 1

what is the function of the cell membrane?

Answer 1

controls what enters and leaves the cell (selectively permeable)
cell-to-cell recognition/signalling
chemical reactions (enzymes)

Question 2

what is cell recognition?

Answer 2

a cell’s ability to distinguish one type of neighbouring cell from another

Question 3

what are the various components found in a cell membrane?

Answer 3

extrinsic/intrinsic (e.g. channel & carrier) proteins, glycoproteins, glycolipids, cholesterol and the phospholipid bilayer

Question 4

what is the function of the phospholipid bilayer?

Answer 4

controls what can enter/leave the cell by acting as a selectively permeable barrier.

Question 5

what is the function of extrinsic proteins?

Answer 5

extrinsic proteins are found on the surface of the bilayer. they provide structural support and form recognition sites

Question 6

what is the function of intrinsic proteins?

Answer 6

intrinsic proteins span the membrane. they act as carriers, transport water-soluble substances across the membrane, or allow for active transport of ions by forming channels.

Question 7

what is the function of cholesterol in the cell membrane?

Answer 7

cholesterol makes the membrane more rigid/stable. it is found in animal cells only

Question 8

what is the function of glycoproteins/glycolipids?

Answer 8

contain projections (a carbohydrate chain attached to the protein/lipid) which are involved in cell-to-cell recognition or function as hormone receptors

Question 9

what are all the glycoproteins/lipids together called?

Answer 9

glycocalyx

Question 10

why is the model of cell membrane structure known as a fluid mosaic?

Answer 10

‘fluid’ -> parts can move laterally
‘mosaic’ -> many components of different shapes/sizes
‘model’ -> the current theory

Question 11

how do lipid-soluble and non-polar molecules move through the membrane?

Answer 11

they can move directly across the membrane by dissolving in the fatty acid tails

Question 12

how do water-soluble molecules and ions move through the membrane?

Answer 12

they have to cross the membrane via intrinsic carrier or channel proteins

Question 13

how does the concentration gradient affect the rate of diffusion?

Answer 13

the greater the concentration gradient, the greater the rate of diffusion

Question 14

how does cell membrane thickness affect the rate of diffusion?

Answer 14

the shorter the diffusion pathway, the more molecules can diffuse in a given time period

Question 15

how does temperature affect the rate of diffusion?

Answer 15

the higher the temperature, the higher the kinetic energy of the particles, so the higher the rate of diffusion

Question 16

how does lipid solubility affect the rate of diffusion?

Answer 16

lipid-soluble molecules are non-polar and diffuse faster than larger molecules, which are polar

Question 17

how does the size of the molecule affect the rate of diffusion?

Answer 17

smaller molecules diffuse faster than larger molecules

Question 18

how does the membrane surface area affect the rate of diffusion?

Answer 18

the larger the surface area, the faster the rate of diffusion (more space for molecules to diffuse)

Question 19

what is simple diffusion?

Answer 19

the net movement of molecules/ions from an area of high concentration to an area of low concentration (down the conc. gradient) across a membrane

Question 20

name some examples of simple diffusion

Answer 20

small and non-polar molecules e.g. oxygen, carbon dioxide, vitamin A and vitamin D

Question 21

is simple diffusion an active or passive process?

Answer 21

passive (no energy required)

Question 22

what is the difference bewtween facilitated and simple diffusion?

Answer 22

facilitated diffusion involves transport proteins (carrier/channel), whereas simple diffusion does not

Question 23

what is facilitated diffusion?

Answer 23

the net movement of large and/or charged molecules from a high concentration to a low concentration through a transport protein

Question 24

what limits the rate of facilitated diffusion?

Answer 24

the number of transport proteins

Question 25

what are the characteristics of channel proteins?

Answer 25

-the pores are lined with polar groups -channels can open/close depending on cell needs

Question 26

how do carrier proteins work?

Answer 26

molecules attach to a binding site. the carrier protein then changes shape to release the molecule on the other side of the membrane

Question 27

what is active transport?

Answer 27

the transportation of molecules against the concentration gradient (low->high) using transport proteins. only carrier proteins are used as they can change shape and push molecules across the membrane.

Question 28

is active transport an active or passive process?

Answer 28

active (requires ATP to move molecules against conc. gradient)

Question 29

what is co-transport?

Answer 29

a type of facilitated diffusion by which two substances are simultaneously transported across a membrane by the same carrier protein

Question 30

name an example of co-transport

Answer 30

sodium-glucose co-transport

Question 31

what is endocytosis?

Answer 31

the bulk transport of substances into a cell

Question 32

is endocytosis an active or passive process?

Answer 32

active (requires ATP to change shape of cell membrane)

Question 33

what are the two different types of endocytosis?

Answer 33

phagocytosis (solid particles moving into a cell) pinocytosis (liquids moving into a cell)

Question 34

what is exocytosis?

Answer 34

the bulk transport of substances out of the cell

Question 35

is exocytosis an active or passive process?

Answer 35

active (requires ATP to change shape of cell membrane)

Question 36

why can CO2 and O2 move into a membrane by simple diffusion?

Answer 36

they are small and non-polar so dissolve in fatty acid tails

Question 37

why does an increase in temperature increase the permeability of the membrane?

Answer 37

the kinetic energy of the phospholipids/proteins increases, so the membrane loses structure. therefore molecules can pass through more easily so the membrane is more permeable. high temperatures also cause the membrane proteins to denature leaving gaps where molecules can pass through.

Question 38

how do non-polar solvents increase the permeability of the membrane?

Answer 38

non-polar solvents (e.g. ethanol) force through into the fatty acid tail layer, so the membrane starts to lose structure, allowing more molecules to pass through. therefore, the membrane becomes more permeable.

Question 39

which factors affect the rate of active transport and endo/exocytosis?

Answer 39

-amount of ATP/rate of respiration -oxygen availability (needed for aerobic respiration) -respiratory inhibitors e.g. cyanide (stops respiration -> no ATP produced -> no active transport)

Question 40

name some examples of phago/pinocytosis

Answer 40

phagocytosis- pathogens being engulfed by lymphocytes pinocytosis- fat/lipid droplets being absorbed

Question 41

name an example of endo/exocytosis

Answer 41

proteins made inside a cell e.g. enzymes