Biological Membranes

Question 1

What is the plasma membrane for, on the surface of the cell?
separates..
regulates..
contain's..
has..
signals..
site...

Answer 1

separates cell’s components from external env.
regulates transport of materials in/out
contain enzymes involved in metabolism
has antigens so immune system recognises it
signals to other cells by chemicals/ has receptors
site of chemical reactions

Question 2

What is the plasma membrane for, within the cell?
separates..
mitochondria membrane..
chloroplast membrane..
epithelial cell membrane..

Answer 2

separates organelle contents from cytoplasm
in mitochondria, folded membrane increases SA for reactions
in chloroplasts, thylakoid (inner membrane) contains chlorophyll for photosynthesis
in epithelial cells, digestive enzymes on membrane to catalyse breakdown of sugar

Question 3

Fluid mosaic model

Answer 3

proteins embedded in sea of phospholipids, bilayer more dynamic, interact with env.

Question 4

Proteins in the membrane can do 3 things

Answer 4

have pores to act as channels for charged ions
be carriers, change shape to carry specific molecules across
be attached to carriers, act as enzymes, antigens, receptor site

Question 5

What regulates fluidity? and what else does it do?

Answer 5

Cholesterol

regulates mechanical stability, resists temperature change

Question 6

thickness of membrane

Answer 6

5-10nm

Question 7

carbohydrate chains attached to lipids/proteins?

Answer 7

glycocalyx

Question 8

What is a passive process?

Answer 8

uses only kinetic energy, not ATP of the cell

Question 9

What happens when molecules are evenly dispersed (in terms of diffusion)?

Answer 9

no net diffusion, in equilibrium

Question 10

What molecules can diffuse?

What can’t pass through the bilayer?

Answer 10

small molecules (oxygen, CO₂)
fat-soluble molecules because dissolve in lipid bilayer (steroid hormones) 
water because it is polar so insoluble in bilayer, but passes through aquaporins which are channel proteins

Question 11

What is facilitated diffusion?

What happens with glucose?

Answer 11

when polar molecules are insoluble so diffuse through water-filled protein channels in the membrane
Glucose is too large for the water-filled channels so bind to transmembrane carrier proteins which open to allow it through.

Question 12

How do carrier proteins work?

Answer 12

they combine reversibly with certain solute molecules or ions and have region that allows hydrolysis of ATP to release energy so carrier proteins act as an enzyme.
The energy changes the carrier protein’s conformation and so carries ions to the other side.

Question 13

What if molecules are too large to pass through membrane?

Answer 13

bulk transport (uses energy)
endocytosis/exocytosis

Question 14

eating by sells, solid matter, is…

Answer 14

phagocytosis

Question 15

ingesting liquids is

Answer 15

pino(endo)cytosis

Question 16

What happens when solute molecules turn into charged ions?

Answer 16

they exert more effect on the relative number of water molecules because dissociating creates more solute particles. Large non-polar molecules like glucose have less effect because there are less particles.

Question 17

Water potential is…

Answer 17

the measure of tendency of water molecules to diffuse from one region to another

Question 18

What is cytolysis?

Answer 18

in animal cells, if lots of water enters, the cell will swell up and burst because the plasma membrane breaks.

Question 19

What is turgid?

Answer 19

in plants, the cell becomes swollen but the cell wall prevents it from bursting.

Question 20

What is crenated?

Answer 20

when water leaves an animal cell and shrivels

Question 21

What is plasmolysed?

Answer 21

when water leaves a plant cell, the cytoplasm shrinks and the membrane pulls from the cell wall. The metabolism can’t proceed because the cell is dehydrated.

Question 22

What is flaccid?

Answer 22

a plant tissue with plasmolysed cells.

Question 23

What do organic solvents do to cell membranes?

Answer 23

damage them because they dissolve lipids.

Question 24

What happens to membranes when temperature drops?
saturated..
proportions..
cholesterol..
fish and microorganisms..

Answer 24

• saturated fatty acids compress.
• proportions of saturated and unsaturated fatty acids in the cell membrane determine its fluidity. Unsaturated fatty acids compress so kinks in tails push adjacent phospholipid molecules away and maintains fluidity.
• cholesterol buffers the effect of low temperature by preventing the reduction in fluidity. It prevents phospholipid molecules packing close
• fish and microorganisms change the composition of fatty acids in membranes in response to low temp.

Question 25

What happens to membranes when temperature increases?

phospholipids. .
permeability. .
membrane. .
increased. .
cholesterol. .

Answer 25

• phospholipids have more kinetic energy so move more and fluidity increases which affects infolding of plasma membrane during phagocytosis
• permeability increases
• membrane embedded proteins’ position and function is affected. alters the rate of reactions of enzymes
• increased fluidity changes the ability of cells to signal with chemicals (exocytosis)
• cholesterol buffers effect of high temp by reducing increase in fluidity