2.4 Plasma membranes

Question 1

What are membranes made of?

Answer 1

Phospholipid bilayer

Question 2

What is the name of the model that forms the basis of our understanding of membranes today?

Answer 2

Fluid-mosaic model

Question 3

What are the 2 types of membrane proteins?

Answer 3

intrinsic and extrinsic

Question 4

What are intrinsic proteins and name 2 examples?

Answer 4

• transmembrane proteins that are embedded through both layers of a membrane
• channel proteins
• carrier proteins

Question 5

What type of membrane protein are glycoproteins?

Answer 5

intrinsic proteins

Question 6

What do glycoproteins play a role in?

Answer 6

cell adhesion and as receptors for chemical signals

Question 7

What do glycolipids play a role in?

Answer 7

cell markers or antigens

Question 8

What are extrinsic proteins and name an example?

Answer 8

• Extrinsic proteins are present on one side of the bilayer

- cholesterol

Question 9

What are the factors affecting membrane structure and permeability?

Answer 9

• temperature

- solvents

Question 10

What is diffusion?

Answer 10

The net/overall movement of particles from a region of higher concentration to a region of lower concentration

Question 11

Does diffusion occur between different concentrations of different substances?

Answer 11

no it only occurs between different concentrations of the same substance

Question 12

What are the 2 factors that affect the rate of diffusion?

Answer 12

• temperature

- concentration gradient

Question 13

What affects the rate at which molecules/ions diffuse across a membrane?

Answer 13

• surface area

- thickness of membrane

Question 14

What is facilitated diffusion?

Answer 14

the movement of molecules down a concentration gradient via protein channels or carrier proteins

Question 15

What is active transport?

Answer 15

the movement of molecules/ions into or out of a cell from a region of lower concentration to a region of higher concentration

Question 16

What is bulk transport?

Answer 16

a form of active transport that involves large molecules

Question 17

What is endocytosis?

Answer 17

the bulk transport of material into cells

Question 18

What are the 2 types of endocytosis?

Answer 18

• phagocytosis (solids)

- pinocytosis (liquids)

Question 19

What is exocytosis?

Answer 19

The bulk transport of material out of cells

Question 20

What is osmosis?

Answer 20

the diffusion of water across a partially permeable membrane

Question 21

Define water potential

Answer 21

the pressure exerted by water molecules as they cooled with a membrane/contained (measured in units of pressure)

Question 22

Do all solutions have positive or negative water potentials?

Answer 22

negative

Question 23

What is hydrostatic pressure?

Answer 23

the diffusion of water into a solution leads to an increase in volume of this solution and if in a closed system, this results in an increase in pressure

Question 24

What is cytolysis?

Answer 24

when an animal cell is placed in a solution with a higher water potential than that of the cytoplasm so the cell-surface membrane breaks and the cell bursts

Question 25

What is crenation?

Answer 25

when an animal cell is placed in a solution with a lower water potential than that of the cytoplasm so water is lost via osmosis down the water potential gradient which causes a reduction in the volume of the cell and the cell surface membrane ‘puckers’

Question 26

What happens when the water potential of an external solution is higher than inside a plant cell?

Answer 26

The cell swells and becomes turgid

Question 27

What happens when the water potential of an external solution is lower than inside a plant cell?

Answer 27

Plasmolysis