June 2024

Question 1

1.3. The antibiotic penicillin causes some prokaryotic cells to die. Penicillin prevents cell wall formation when the cell divides.
Explain why the lack of a cell wall causes cell death. (3)

Answer 1

1. Water enters the cell via osmosis / diffusion
2. Down a water potential gradient / from a high to a low water potential gradient
3. Cell expands and breaks the cell surface membrane (because no cell wall)

Question 2

1.6. When scientists culture prokaryotic cells in a Petri dish, they incubate the Petri dish at 37 degrees celsius. Why? (2)

Answer 2

1. Optimum temperature for enzyme activity
2. Prokaryotic cells grow quickly / more cell division / involved in synthesis of molecules for new cells

Question 3

4.2. Which molecule in the cell membrane allows the movement of non-polar molecules through the membrane? (1)

Answer 3

Phospholipids

Question 4

4.2. What is function of cholesterol? (1)

Answer 4

Regulates fluidity / stability of the membrane

Question 5

4.2. Which molecule in the cell membrane can be a receptor or a channel? (1)

Answer 5

Protein / glycoprotein

Question 6

4.1. Explain why the membrane is described as a ‘fluid mosaic’ structure. (2)

Answer 6

Fluid
1. Molecules can move / not in a fixed position / membrane can change shape (without breaking)

Mosaic
2. Contains proteins and phospholipids

Question 7

4.3. State 2 functions pf membranes INSIDE cells. (2)

Answer 7

any 2 of:
1. Separates / isolates substances eg enzymes in lysosomes / forms vesicles
2. Controls what enters and leaves organelles
3. Site for attachment eg ribosomes, ATP synthase
4. Allows concentration gradients to form

Question 8

5.2. Blood contains red blood cells that are flexible and have a mean diameter of 7 um. The lumen of a capillary has a radius of approximately 4 um.
Suggest an advantage of the lumen of a capillary being this size. (2)

Answer 8

any 2 of:
1. Same / similar diameter as a red blood cell
2. Slow rate of blood flow
3. More surface area in contact / shorter diffusion distance (for gas exchange)
4. Gives more time for gas exchange

Question 9

5.3. Explain how the haem groups in a haemoglobin molecule are involved in the transport of oxygen. (2)

Answer 9

1. Contains an iron ion/Fe2+
2. Binds reversibly to an oxygen (molecule)

Question 10

7.3. Suggest 2 reasons why different enzymes are able to bind to the same substrate. (2)

Answer 10

1. Shape of the substrate may be complementary to two active sites
2. The active sites might bind to different parts / sides of the substrate

Question 11

6.4. In the equation to find the index of diversity, what is the definition of N (the numerator) and n (the denominator)? (2)

Answer 11

N = Total number of individuals in all species (in the sample)
n = The number of individuals in a / one species (in the sample)