2.5-Membranes

Question 1

What is the fluid mosaic model?

Answer 1

A model for the bilayer membrane - fluidity based on the movement of the lipids, and the mosaic comes from the embedded proteins in the layer.

Question 2

Types of active transport?

Answer 2

Bulk Transport
Endocytosis
Exocytosis

Question 3

What are carrier proteins?

Answer 3

Proteins that bind to specific molecules and use ATP to open and close on the other side of the membrane

Question 4

What are channel proteins?

Answer 4

Proteins that have a water-filled channel down the centre to allow polar molecules/molecules insoluble in lipids to dissolve in this and pass through the membrane

Question 5

What affects rate of diffusion?

Answer 5

Size of molecule 
Polarity
Kinetic energy
Diffusion distance
Surface area

Question 6

What is facilitated diffusion?

Answer 6

A process that uses carrier or channel proteins to allow the diffusion of molecules too large to pass through the bilayer or unable to dissolve in the lipids

Question 7

Role of the membrane at the surface of cells?(5)

Answer 7

Separates cell components from external environment
Regulates transport in and out
Contains enzymes involved in specific metabolic pathways
Has antigens for protection against immune system
Releases signalling chemicals
Site of chemical reactions

Question 8

Roles of membrane within cells?

Answer 8

Separate organelle contents from cell cytoplasm

Inner membranes of chloroplasts house chlorophyll for photosynthesis

Question 9

What is a glycoprotein?

Answer 9

A carbohydrate chain attached to a protein molecule

Question 10

What is the carbohydrate molecule on glycoproteins, and what do they do?

Answer 10

Glycocalyx - these are very hydrophilic and attract water with dissolved solutes for transport into the cell

Question 11

What is the thickness of the cell membrane?

Answer 11

Between 5 and 10 micrometres

Question 12

Why are some membranes composed differently?

Answer 12

Because the cells have different functions - for example, mitochondria have a higher protein concentration because they transport more ions, while root hair cells have more carrier proteins to transport nitrate ions from the soil

Question 13

What is a passive process?

Answer 13

One that uses the kinetic energy of the molecules and not ATP

Question 14

What is endocytosis?

Answer 14

A process where substances are moved into the cell - the membrane wraps around this and forms a vesicles inside the cell. This process requires ATP

Question 15

What is exocytosis?

Answer 15

A process where substances are transported out of the cell in a pinocytotic vesicle, pulled along the cytoskeleton filaments by motor proteins. They fuse with the plasma membrane and release contents outside. The process is active

Question 16

Components of the membrane?

Answer 16

Phospholipids
Cholesterol 
Proteins
Glycolipids
Glycoproteins

Question 17

Role of cholesterol?

Answer 17

Helps maintain fluidity of membrane, for example when temperature increases they keep lipids apart

Question 18

Effect of solvents on membrane?

Answer 18

Cause the membrane to break down/ destroys it as they dissolve lipids

Question 19

Effects of high temperature on membranes?

Answer 19

Increases fluidity as lipids have more energy to move around, cause enzyme to denature, proteins to change shape and switch places
Increased permeability

Question 20

What binds to membrane-bound receptors?

Answer 20

Drugs and hormones

Question 21

Define osmosis

Answer 21

The movement of water from a dilute to concentrated solution down the water potential gradient across a partially permeable membrane

Question 22

Effects of water on plant cells?

Answer 22

Too much water (in a solution of high water potential) causes the cell to become turgid as it swells.
Too little water causes the cell to become plasmolysed- cell membrane pulls away from cell wall

Question 23

Effect of water on animal cells?

Answer 23

Too much causes it to swell and burst - cytolysis

Too little causes it to shrink and shrivel up - crenation.

Question 24

Describe the transport of sodium and potassium ions

Answer 24

(3) sodium ions bind to a specific site on the pump protein, ATP binds to it and is hydrolysed to provide energy.
(2) potassium ions bind to their specific site, and the protein changed shape so the sodium ions are outside and the potassium inside

Question 25

What effect does low temperature have on membranes?

Answer 25

Saturated fatty acids become compressed, but because there are also unsaturated the kinks in these maintain some fluidity
Proportions of these help it
Cholesterol prevents them packing together too tightly

Question 26

What do glycolipids and glycoproteins do? (4)

Answer 26

Stabilise membrane by forming hydrogen bonds with surrounding water molecules
Sites where drugs, hormones and antibodies bind
Receptors for cell signalling
Antigens

Question 27

How do cells communicate with one another?

Answer 27

One cell releases a messenger molecule e.g a hormone
This travels e.g via blood to another cell
The molecule is detected by the cell as it binds to a receptor on the membrane