Exam Q

Question 1

Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of
proteins from eukaryotic cells (5 marks)

Answer 1

• DNA in nucleus codes for protein
• rough endoplasmic reticulum produce protein through protein synthesis on the ribosomes
• mitochondria produce ATP for protein synthesis
• Golgi modifies proteins by adding carbohydrates to form glycoproteins
• vesicle transports and fuse with the membrane

Question 2

Describe how you could make a temporary mount of a piece of plant tissue
to observe the position of starch grains in the cells when using an optical
(light) microscope. (4 marks)

Answer 2

1) add a drop of water to the slide
2) obtain a thin section of plant tissue and place on the slide
3) stain with iodine from potassium iodide
4)Lower coverslip with mounted needle

Question 3

Suggest one advantage of end product inhibitor being non competitive rather than competitive

Answer 3

• the levels of the end product does not fluctuate with changes in the levels of substrate
• non competitive inhibitions occurs at a site away from the active site rather than in the active site hence why it is not affected by substrate concentration
• therefore levels of substrate concentration do not affect the inhibition of an enzyme nor the normal level of the end product
• competitive inhibition involves competition for active sites so the inhibitors needs to compete with the substrate for the active site of the enzyme
• a change in the level of substrate will affect how many end product molecules combine with the active site
• so a degree in inhibition and substrate would fluctuate the levels of end products

Question 4

When bread becomes stale, the structure of some of the starch is
changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of
amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could
help to reduce weight gain

Answer 4

1. Less hydrolysis of starch;
   Accept no hydrolysis
2. (To) maltose;
3. (So) less absorption (of glucose)

Question 5

Define the term mutagenic agent

Answer 5

(A factor that) increases (the rate of) mutations

Question 6

Genetic variation within a species is increased during meiosis by crossing over and the independent segregation of homologous chromosomes.
Apart from mutation, explain one other way genetic variation within a species is increased

Answer 6

Random fertilisation;
Accept for ‘gametes’,
2. (Produces) new allele combinations

Question 7

(c) Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.

Answer 7

1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;
   (Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change);
   OR
   Mutation is in an intron (so amino acid sequence may not change);
   Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon.
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;
   (Has positive effect because)
6. Results in change in polypeptide that positively changes the
   properties (of the protein) OR
   Results in change in polypeptide that positively changes a named protein;
   For ‘polypeptide’ accept ‘amino acid sequence’ or ‘protein’.
7. May result in increased reproductive success OR
   May result in increased survival (chances);