Biological Membranes (2.1.5)

Question 1

What does a plasma membrane do?

Answer 1

The plasma membrane is a partially permeable barrier between the cell and its environment. It controls which substances enter and leave the cell.

Question 2

What does a membrane do?

Answer 2

Membranes divide the cell into different compartments and act as a barrier between the organelle and the cytoplasm making different functions more efficient.

Question 3

How do membranes help with transport?

Provide an example.

Answer 3

Membranes can form vesicles.

Proteins are transported in vesicles from Ribosoms to the Golgi Apparatus during protein synthesis.

Question 4

What is the role of the thylakoid membrane in the chloroplast?

Answer 4

Thylakoid membranes keep the components needed for light-dependent reactions of photosynthesis together.

Question 5

How does the structure of the inner membrane of the mitochondrion relate to its function?

Answer 5

The inner membrane is folded to increase surface area which makes chemical reactions more efficient.

Question 6

What cannot pass through the centre of the bilayer?

Answer 6

Water-soluble molecules (ions and polar molecules)

Question 7

What does cholesterol do for the membrane?

Answer 7

It causes phospholipids to pack more closely together making it more rigid and less fluid.

Question 8

How do solvents affect membranes?

Answer 8

Increases permeability by dissolving lipids causing the membrane to lose its structure.

Question 9

How does temperature affect a membrane?

Answer 9

It affects how much the phospholipids in the bilayer move, which affects membrane structure and permeability.

Question 10

Summarise the key temperature ranges and their effects on membrane permeability.

Answer 10

• *Below 0 degrees**
• Phospholipids packed tight. The membrane is rigid.
• Channel and carrier proteins denature
• Permeability increases
• Ice crystals may form and pierce the membrane, further increasing permeability when it thaws

0 - 45 degrees
- Phospholipids can move around. The membrane is partially permeable.
As the heat increases, phospholipids move more because they have more energy.
Permeability increase.

Above 45 degrees
The phospholipid bilayer starts to melt (break down). Becomes more permeable.
The water inside the cell expands puts more pressure on the membrane.
Channel and carrier proteins denature. Permeability increases.

Question 11

Name two messenger molecules and their role.

Answer 11

Glucagon
Released when there is not enough glucose in the blood.
Binds to receptors on liver cells.
Causes the liver cells to break down stores of glycogen into glucose.

FSH
Released by the pituitary gland during the menstrual cycle.
Binds to cells in the ovaries, causing an egg to mature ready for ovulation.

Question 12

Cell signalling

A ______ ______ binds to a ______ on a ______ ______ .

Answer 12

Messenger molecule. Receptor. Target cell.

Question 13

How do drugs work in relation to cell signalling?

Answer 13

Drugs bind to receptors, either triggering a response in the cell or blocking the receptor to prevent it from working.

Question 14

Morphine

______ bind to ______ ______ in the brain which reduce the transmission of pain signals.

______ binds to the same ______ ______ trigging a reduction in pain signals.

Answer 14

Endorphines. Opioid receptors. Morphine. Opioid receptors.

Question 15

Define diffusion.

Answer 15

The net movement of molecules or ions from an area of higher concentration to an area of lower concentration.

Question 16

When does diffusion stop?

Answer 16

When the particles are evenly distributed throughout the liquid or gas.

Question 17

What factors affect the rate of diffusion?

Answer 17

Concentration gradient
The higher it is, the fast the rate.

Thickness of the exchange surface
The thinner the surface, the quicker the rate.

Surface area
The larger the surface area, the faster the rate of diffusion.

Temperature
The warmer it is, the faster the rate of diffusion because particles have more kinetic energy and move faster.

Question 18

Define osmosis.

Answer 18

Osmosis is the diffusion of water molecules across a partially permeable membrane down a water potential gradient.

Question 19

What is water potential?

Answer 19

Water potential is the likelihood of water molecules to diffuse out of or into a solution.

Question 20

Define isotonic.

Answer 20

Two solutions that have the same water potential.

Question 21

Define hypotonic.

Answer 21

A solution that has a higher water potential compared with the inside of a cell.

Question 22

Define hypertonic

Answer 22

A solution that has a lower water potential compared with the inside of a cell.

If an animal cell is placed in a hypertonic solution it will shrink.

Question 23

A plant cell placed in a hypertonic solution might experience what?

Answer 23

Plasmolysis.

Question 24

Why do carrier and channel proteins exist?

Answer 24

To speed up the diffusion of large and charged particles through the phospholipid bilayer.

Question 25

Give an example of a carrier protein.

Answer 25

GLUT1

A carrier protein found in almost all animal cells.

Helps transport glucose across the plasma membrane.

Question 26

How do channel proteins work?

Answer 26

Provide a hydrophilic channel that allows for the diffusion of polar molecules and ions down a concentration gradient.

Question 27

Define endocytosis and describe the process.

Answer 27

The plasma membrane surrounds a substance and then pinches off to form a vesicle.

Question 28

Define exocytosis and describe the process.

Answer 28

Vesicles fuse with the plasma membrane and release their contents.

Question 29

Antihistamines

______ ______ causes the release of a chemical called ______ .

______ binds to receptors that cause inflammation.

______ work by blocking ______ ______, preventing ______.

Answer 29

Cell damage. Histamine. Inflammation. Antihistamines. Histamine receptors. Inflammation.