June 2017

Question 1

1.2. Describe one method scientists could use to find out if Nereiphylla paretti & nereiphylla rubiginosa are 2 separate species (2)

Answer 1

(1) mate them // sequencing of DNA // immunological testing
(2) do not give fertile offspring // shows differences in DNA // shows different patterns / proteins

Question 2

2.3. Give 3 examples of human activity that reduce biodiversity. For each example, explain how the activity reduces biodiversity. (3)

Answer 2

(1) deforestation => loss of habitat / food sources
(2) selective breeding => reduction of gene pool
(3) farming => reduction in habitat types / food types

Question 3

6.1. Exp= effect of pH on activity of catalase.
The students controlled the temp. by placing the boiling tube in a beaker of water at 25°C. Explain why it was necessary to control the temp. (2)

Answer 3

(1) change of temp = change RoR
(2) pH should be the only variable

Question 4

7.1. The red blood cells in the capillaries differ in shape. Suggest one reason for this. (1)

Answer 4

(1) squashed out of shape in narrow capillaries

Question 5

8.1. Describe chemical tests you could do to show that a sample of fruit juice contains reducing sugar and contains non-reducing sugar (3)

Answer 5

(1) reducing sugar: heat with benedict’s –> red ppt
(2) then boil supernatant in acid
(3) neutralise and repeat benedict’s test –> red ppt

Question 6

8.2. In chromatography exp, suggest reasons for each of the steps in the method: (4)
1. The origin line was drawn on the paper in pencil not ink.
2. The level of the solvent surface in the tank was at least 2 cm below the origin
3. A very small vol. of fruit juice was added to the origin and dried before adding more fruit juice
4. When the paper was removed from the tank, the position of the solvent front was marked immediately.

Answer 6

1. Ink would dissolve in solvent / carried up the paper by solvent
2. Sugars aren’t carried up the paper / would spread sideways on paper
3. To give better separation / spots would overlap more if larger area
4. Solvent evaporates so front vanishes / to measure Rf

Question 7

9.5. The predicted length of human cytochrome c is 813 amino acids. The actual length of a molecule of human cytochrome c is 104 amino acids. Explain why it’s much shorter. (2)

Answer 7

(1) non-coding sequences / introns
(2) are cut out / removed

Question 8

9.6. The synthesis of cytochrome c takes place on ribosomes.
In human cells, most ribosomes occupy a fixed position. In bacterial cells, the ribosomes aren’t in a fixed position.
What causes this difference? (1)

Answer 8

(1) ribosomes are attached to the ER