Biological Membranes

Question 1

what is the roles of membranes within cells and at the surface of cells

Answer 1

• partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles
• sites of chemical reactions
• sites of cell communication (cell signalling).

Question 2

describe the fluid mosaic model

Answer 2

a bilayer of phospholipid molecules with proteins scattered , some embedded some floating in the bilayer

Question 3

how does temperature affect membrane stability?

Answer 3

If temperature increases further, the phospholipid bilayer may lose its mechanical stability (it may melt) and the membrane becomes even more permeable.

Eventually, the proteins in the membrane will denature.

This will further damage the structure of the membrane and it will become completely permeable.

Question 4

how does solvents affect membrane permeability?

Answer 4

Solvents such as alcohol dissolve fatty substances.

As the concentration of alcohol increases, the membrane is more likely to dissolve.

Question 5

roles and functions of phospholipids

Answer 5

. form a barrier that limits movement of some substances into and out of the cell, or into and out of the organelles, so the membrane is partially permeable.

Question 6

roles and functions of cholesterol

Answer 6

. It inhibits movement of the phospholipids, reducing the fluidity of the membrane. It also holds the phospholipid tails together, for mechanical stability.

Question 7

roles and functions of glycoproteins and glycolip

Answer 7

. The carbohydrate group on the protein or lipid molecule always has a specific shape and is used to recognise the cell — to identify it as ‘self’ or ‘foreign’. Antigens on cell surfaces are usually glycolipids or glycoproteins. (cell signaling)

Question 8

roles and functions of proteins

Answer 8

. enzymatic activity and cell signalling.

Question 9

what can some proteins form?

Answer 9

• pores that allow the movement of molecules that cannot dissolve in the phospholipid bilayer * carrier molecules that allow facilitated diffusion
• active pumps

Question 10

what are the passive ways of transporting substance?

Answer 10

facilitated, simple diffusion and osmosis

Question 11

What is simple diffusion?

Answer 11

The net movement of particles from an area of high concentration to an area of low concentration and is a passive process

Question 12

What is facilitated diffusion?

Answer 12

The passive movement of a particle across a cell membrane via a channel protein or carrier protein

Question 13

what is osmosis?

Answer 13

the net movement of water molecules across a partially permeable membrane.

Water molecules move down their water potential gradient

Question 14

how does temperature affect rate of diffusion?

Answer 14

a higher temperature gives molecules more kinetic energy. At higher temperatures the molecules move faster, so the rate of diffusion increases.

Question 14

how does concentration affect rate of diffusion?

Answer 14

more molecules on one side of a membrane (or less on the other) increases the concentration gradient. This increases the rate of diffusion

Question 15

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

Answer 15

small molecules or ions can move more quickly than larger ones. Therefore, they diffuse more quickly than larger ones.

Question 16

how does the thickness of the membrane affect rate of diffusion?

Answer 16

a thick barrier creates a longer pathway for diffusion, so diffusion is slowed down by a thick membrane.

Question 17

how does surface area affect rate of diffusion?

Answer 17

diffusion across membranes occurs more rapidly if there is a greater surface area.

Question 18

what is active transport?

Answer 18

Active transport involves the movement of molecules using metabolic energy in the form of ATP. It can move molecules against their concentration gradient and uses membrane-bound proteins that change shape to move the molecules across the membrane.

Question 19

what is bulk transport?

Answer 19

the movement of molecules through a membrane by the action of vesicles.

Question 20

what is endocytosis?

Answer 20

the formation of vesicles by the plasma membrane, which moves molecules into the cell.

Question 21

What is exocytosis?

Answer 21

the fusion of vesicles with the plasma membrane, which moves molecules out of the cell.

Question 22

what happens in an isotonic solution (animal cells)

Answer 22

. water potential is equal between cell and solution

. no net movement of water

. normal cells

Question 22

what happens in a hypertonic solution (plant cells)

Answer 22

. cells have a higher water potential than solution

. net movement of water out

. shrivelled cells , plasmolysed

Question 22

what happens in a hypertonic solution (animal cells)

Answer 22

. cells have higher water potential than solution

. net movement of water out

. shrivelled cells

Question 23

what happens in a hypotonic solution (animal cells)

Answer 23

. cells have a lower water potential than solution

. net movement of water in

. cells swell, may burst

Question 24

what happens in a hypotonic solution (plant cells)

Answer 24

. cells have a lower water potential than solution

. net movement of water in

. cells swell, turgid

Question 25

what happens in an isotonic solution (plant cells)

Answer 25

. water potential is equal both inside and outside cell

. no net movement of water

. normal cells, flaccid