Module 2 - Cell membranes and transport

Question 2

3 marks

Explain why phospholipids can form a bilayer but triglycerides cannot.

Answer 2

• Phospholipid both hyrdophillic and hydrophobic
• Triglycerides only hydrophillic
• Hydrophillic phosphate head attracted to water

Question 3

The movement of substances across cell membranes is affected by membrane structure. Describe how.

Answer 3

1. Phospholids only allows non-polar, lipid-soulube molecules diffuse across phospholipid bilayer
2. Phospholipid bilayer prevent diffusion of water- solube, polar molecules across membrane
3. Carrier proteins allow active transport
4. Carrier proteins and channel proteins allow facilitated diffusion
5. Cholestrol affects rigidty/ fluidity

Question 4

5 marks

Name and describe five ways substances can move across the cell-surface membrane into a cell.

Answer 4

1. Simple diffusion of small/non-polar molecules down a concentration gradient
2. Facilitated diffusion down a concentration gradient via protein carrier and channel
3. Osmosis of water down a water potential gradient
4. Active transport against a concentration gradient via protein carrier using ATP
5. Co-transport of 2 different substances using a carrier protein

Question 5

2 marks

Suggest and explain 2 ways the cell-surface membranes of the cell lining the uterus may be adapted to allow rapid transport of nutrients

Answer 5

1. Memrane folded so large SA
2. Large number of protein channels/ carriers for FD
3. Large number of carrier proteins for active transport
4. Large number of protein channels/ carriers for co-transport

Question 6

5 marks

Name and describe five ways substances can move across the cell-surface membrane into a cell.

Answer 6

1. Simple diffusion of small, non-polar molecules down a concentration gradient
2. Facilitated diffusion down a concentration gradient via carrier or channel protein
3. Osmosis of water down a water potential gradient
4. Active transport against a concentration gradient via protein carrier using ATP
5. Co-transport of 2 different substances using a carrier protein

Question 7

3 marks

Describe the processes of facilitated diffusion and active transport

Answer 7

1. Movement of polar/charged molecules
2. Facilitated diffusion movement down a concentration gradient via carrier/channel protein
3. Active transport movement against a concentration gradient via carrier protein using ATP

Question 8

3 marks

Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane as two dark lines.

Answer 8

1. Membrane has phospholipid bilayer
2. Stain binds to phosphate / glycerol
3. On inside and outside of membrane