2.1.5 Biological membranes

Question 1

Properties of phospholipids

Answer 1

phosphate - hydrophilic head
fatty acid - hydrophobic tail

Question 2

Function of cholesterol

Answer 2

maintains the fluidity of the membrane

Question 3

Function of glycoproteins

Answer 3

cell signalling, cell adhesion and receptors for neurotransmitters and hormones

Question 4

Function of transport proteins

Answer 4

provides a hydrophilic channel which allows large polar molecules and ions to pass through the membrane

Question 5

Substances that can diffuse naturally through the membrane (simple)

Answer 5

small nonpolar molecules
- steroid hormones (testosterone, oestrogen)
- lipid soluble vitamins
- respiratory gases

small polar molecules (very slow rate)
- water
- urea

Question 6

Factors affecting diffusion rate

Answer 6

temperature
concentration gradient
surface area
pressure
number of carrier proteins (facilitated)

Question 7

Substances that use facilitated diffusion

Answer 7

large polar molecules
(Na+ Cl-)

Question 8

What is active transport

Answer 8

Movement of molecules from an area of low concentration to an area of high concentration, requiring energy released from respiration
- Occurs through specific carrier proteins in the membrane

Question 9

What is endocytosis

Answer 9

taking materials into the cell

Question 10

How does endocytosis work

Answer 10

the cell membrane engulfs materials to form a vesicle which moves into the cytoplasm

Question 11

What is pinocytosis

Answer 11

the uptake of liquid materials

Question 12

What is phagocytosis

Answer 12

the uptake of solid materials

Question 13

What is exocytosis

Answer 13

taking materials out of the cell

Question 14

How does exocytosis take place

Answer 14

vesicles move towards and fuse with the cell surface membrane and are released

Question 15

What is osmosis

Answer 15

movement of water through a partially permeable membrane from a high water potential to a low water potential

Question 16

What is water potential

Answer 16

a measure of the quantity of water compared to solute, measured as pressure created by molecules in kPa

Question 17

What happens to animal cells in a hypertonic solution

Answer 17

• lower water potential than in the cell
  water moves out of the cell
• crenation

Question 18

What happens to animal cells in isotonic solutions

Answer 18

• equal water potential to the cell
• water moves in and out of the cell at equal rates

Question 19

What happens to animal cells in hypotonic cells

Answer 19

• higher water potential than in the cell
  water moves into the cell, causing it to swell and become haemolysed

Question 20

What happens to plant cells in a dilute solution

Answer 20

water moves into the cell
cell becomes turgid

Question 21

What happens to plant cells in a concentrated solution

Answer 21

water moves out of the cell
becomes flaccid
- if solution is very concentrated, the cytoplasm is pulled away from the cell wall
- cell has been plasmolysed

Question 22

How does temperature affect membrane permeability and structure

Answer 22

if temperature increases, the phospholipids will have more kinetic energy and become more fluid
- the membrane loses its structure and begins to break down

• loss of structure increases membrane permeability, meaning particles can pass through easier
• carrier and channel proteins may be denatured

Question 23

How does a solvent affect membrane permeability

Answer 23

• organic solvents will dissolve the phospholipid bilayer
• alcohol solutions damage cells as the non polar alcohol molecules can enter the cell membrane and increases the fluidity and permeability of the membrane

Question 24

What is cell signalling

Answer 24

communication between cells