Jan 2024

Question 1

1.3. Give 3 differences between the structure of the gas exchange systems of insects and mammals. (3)

Answer 1

any 3 of:
1. Many tracheae: one trachea
2. No alveoli/no bronchioles/has tracheoles: alveoli / bronchioles / no tracheoles
3. (Many) spiracles: no spiracles
4. Direct to tissues: via blood/capillaries

Question 2

1.4. State 1 advantage & 1 disadvantage of the gas exchange system of an insect when compared to a mammalian gas exchange system. (2)

Answer 2

Advantage
1. Gas exchange direct with muscle/tissue/cells or
No need for a circulatory system (to transport gases)

Disadvantage
2. Limits (insects) size or Takes up a lot of space

Question 3

2.4. Suggest 1 advantage & 1 disadvantage of using the sequence of amino acids in cytochrome c (a protein) to classify species. (2)

Answer 3

Advantage:
1. Same/similar amino acid sequence in all individuals of the same species or cytochrome c is present in all species (so you can compare eukaryotes)

Disadvantage:
2. Cannot be used on extinct species/prokaryotes or Amino acid sequences not as accurate as using DNA / mRNA sequences or Other proteins may differ more (than cytochrome c) so differences not seen

Question 4

3.5. In the osmosis exp., the student leaves the cylinders of potatoes in the sucrose solutions for 24 hours. Why? (1)

Answer 4

The mass of the cylinders will become constant (after 24 hours)

Question 5

3.6. In the osmosis exp involving potatoes and sucrose solution conc., explain why you have to seal each test tube with a bung. (2)

Answer 5

1. Prevents evaporation / loss of water / solvent from the sucrose solution overnight
2. Increasing the conc / decreasing the water potential

Question 6

5.1. Aromatase is an enzyme needed for reproduction in many animals.
Describe how mRNA is synthesised from the aromatase gene. (5)

Answer 6

any 5:
1. DNA splits / separates / unzips / hydrogen bonds break
2. Correct reference to DNA helicase/an enzyme (to separate DNA strands)
3. Complementary sequence / base-pairing
4. Reference to promoter or stop / start codons
5. Make mRNA via RNA polymerase
6. mRNA detaches from the DNA
7. Introns / junk / non-coding RNA spliced out

Question 7

5.3. Aromatase is an enzyme needed for reproduction in many animals.

mRNA produced from the aromatase gene: U A A G C G

mRNA produced from the inserted DNA: A U U C G C

Suggest how the inserted DNA prevents aromatase production. (3)

Answer 7

1. mRNA (transcribed) from inserted gene binds to mRNA (transcribed) from aromatase gene
2. Aromatase mRNA cannot bind to ribosome
3. (Complementary) tRNA molecules cannot bind

Question 8

6.3. Describe the process of crossing over. (2)

Answer 8

(1) Description of crossing over e.g. (non-sister) chromatid in each (homologous) pair twist / cross over around each other

2. Chromatid breaks and rejoin to chromatid on homologous chromosome or DNA / alleles have been exchanged between homologous chromosomes

Question 9

7.3. A small number of human cells may be left at the scene of a crime. When examining cells from the scene of a crime, scientists often examine mitochondrial DNA instead of nuclear DNA. Why? (1)

Answer 9

More copies (of the same gene) so more likely to be able to detect it

Question 10

7.4. “There is a clear record of distant maternal evolution in mitochondrial DNA because it only originates from the mother, and its DNA code changes less frequently than in nuclear DNA.”
The DNA code changes less frequently in mitochondrial DNA compared to nuclear DNA. Why? (2)

Answer 10

(1) DNA from mitochondria does not undergo independent
assortment / crossing over
(2) (Random) fertilization does not occur / idea of not combining DNA of 2 individuals