Weak Exam Qs

Question 1

Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and
Describe one difference between this feature in the chloroplast and similar ones in the rest of the cell.

Answer 1

Feature 1. DNA
Structural difference 1. not associated with histones / introns in chloroplast DNA;

OR
Feature 2. Chloroplast ribosomes
Structural difference 2. Smaller (70s) than cytoplasmic ribosomes/in cytoplasm.

Question 2

What is meant by genetic diversity? (1)

Answer 2

Number of different alleles of each gene / Different base sequences of each gene

Question 3

Describe a method that could be used to determine the mean percentage cover of algae on a coral reef (3)

Answer 3

1. Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
2. Large number of quadrats;
3. Divide total percentage by number of quadrats/samples/readings;

Question 4

Explain how succession results in a wide variety of fish living on coral reefs (2) Do not include the process of succession in your answer

Answer 4

1. Increase in variety/diversity of species/plants/animals;
   OR
   Increase in number of species/populations;
   [Accept increase in biodiversity or species richness]
2. Provides more/different habitats/niches
   OR
   Provides greater variety/types of food;
   [Ignore shelter/homes/environments.
   Accept less hostile’ (environment)]

Question 5

A new antibiotic is safe to use in humans because it does not inhibit the ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited (1)

Answer 5

1. Antibiotic not completetary to human cells / different tertiary structure.

Question 6

Energy enters most ecosystems through the light-dependent reaction of photosynthesis. Describe what happens during the light-dependent reaction (5)

Answer 6

1. Chlorophyll absorbs light energy;
   [Accept photon for light energy]
2. Excites electrons / electrons removed (from chlorophyll);
   Accept higher energy level as ‘excites’
3. Electrons move along carrier to carrier / electron transport chain releasing energy;
4. Energy used to join ADP and Pi to form ATP;
   [Do not accept P as Pi]
5. Photolysis of water produces protons, electrons and oxygen;
6. NADP reduced BY ELECTRONS / HYDROGEN / electrons and protons; [Accept NADP to NADPH]

Question 7

Scientists investigated the effectiveness of AZA in patients with MDS disease. A total of ___ patients were randomised to receive AZA or conventional drugs.

The control patients were treated with conventional drugs. Give two reasons why (2)

Answer 7

1. The effect of AZA can be compared;
2. It is unethical not to treat (control group)

Question 8

Describe how organisms are grouped in a phylogenetic classification system (2)

Answer 8

1. Hierarchy of (smaller) groups within groups with no overlaps;
2. Grouped according to evolutionary origins/common ancestry

Question 9

WHAT IS THE STRUCTURE OF EVALUATE & SUGGEST Qs?

Answer 9

EVALUATE:
For
Against
Limitations
(4 marks)

SUGGEST:
LESS/MORE (SO LESS/MORE)

Question 10

Suggest why the student soaked the root tips in hydrochloric acid (RP2) (2)

Answer 10

1. To break down links between cells/cell walls / to separate cell walls;
2. Allowing stain to diffuse/pass into cells

Question 11

Other students followed the same method (root tip squash RP) but calculated different mitotic indices. Suggest two explanations why (2)

Answer 11

Any 2 from:

• Cells/roots undergo mitosis at different rates
• Roots are a different age / grown in different conditions
• Root tips from different (garlic) plant/species/bulb
• Other students may have looked at more field of views
• single field of view is not representative of a root tip
• different fields of view from different parts of root tip

Question 12

Describe how a scientist will use information from a colorimeter and her calibration curve to determine the pO2 in a sample of lugworm blood (2)

Answer 12

1. Measure many readings of absorbance (a.u);
2. Interpolate/read across graph to find pO2

Question 13

Apart from temp and pH, give two variables the scientist would have controlled when preparing liquid medium cultures (2)

(Investigating the effect of an increase in the concentration of ammonium chloride on the activity of nitrogenase in bacteria)

Answer 13

Any two from:
- Volume of bacteria culture
- Concentration of (stock) bacteria culture
- Concentration of glucose / respiratory substrate
- Concentration/volume of oxygen/nitrogen

Question 14

Give two measurements the student would have to make to determine the rate of aerobic respiration in seeds in cm^3 hour-1 (2) (respirometer)

Answer 14

1. Distance liquid moves
2. Radius/diameter/lumen of tubing

Question 15

Suggest why the student soaked the root tips in hydrochloric acid (RP2) (2)

Answer 15

1. To break down the cell walls/separate cell walls;
2. To allow the stain to diffuse into cells.

Question 16

Define ‘anaphase’ (1)

Answer 16

Replicated sister chromatids are pulled by spindle fibres to OPPOSITE poles of the cell

Question 17

Other students calculated different mitotic indices with the same method. Suggest two explanations why (2)

Answer 17

Any 2 from:

• Cells/roots undergo mitosis at different rates;
• (garlic) roots are a different age/grown in different conditions;
• (Root tips) from different plants/plant species/garlic bulbs;
• Other students may have looked at MORE field of views;
• Single field of view is not representative of the whole root tip;
• Different fields of view from different root tips.

Question 18

Apart from temperature and pH, give two variables that the scientist would have controlled when preparing liquid medium cultures (2)

(Investigating effect of increasing ammonium chloride concentration on nitrogenase in bacteria)

Answer 18

Any 2 from:

• Volume of bacteria culture
• Concentration of (stock) bacterium culture
• Concentration of glucose/respiratory substrate;
• Volume of oxygen/nitrogen

Question 19

Mature leaves from slow-growing, shade-tolerant plants produce poisonous chemicals that are a defence against being eaten by herbivores.
Suggest how this benefits slow-growing, shade-tolerant plants (2)

Answer 19

• In shade so less/slower rate of photosynthesis;
• Slow-growing so would take a long time to replace (mature leaves);
• (so) Plants can maintain a large SA for photosynthesis

Question 20

Describe how the composition of blood in the pulmonary artery of a fetus is different from the artery of its mother. Give one reason for this difference (2)

Answer 20

• Fetal blood has more O2/less CO2;
• as gas exchange occurs in the placenta (not in the fetus’ lungs)

Question 21

Explain how a fetus is protected against the pathogens that infect its mother during pregnancy. Do not give details of an active immune response in the mother (3)

Answer 21

1. Mother produces specific complementary antibodies (to a pathogen) that are passed into fetal blood via placenta;
2. The pathogen crosses the placenta;
3. Gives passive immunity (in fetus)

Question 22

Suggest why there has been a recent increase in the number of children catching measles (virus) (1)

Answer 22

• Reduced vaccination (of children)
OR virus has mutated

Question 23

Explain why giving children more than one tetanus vaccination develops good immunity against tetanus (2)

Answer 23

• On second infection, more antibodies are produced in blood faster/quicker;
• Production of more memory cells (stay in blood).