Mark Scheme

Question 1

What is a homologous pair of chromosomes?

Answer 1

Two chromosomes that carry the same genes

Question 2

What is meant by species richness?

Answer 2

The number of different species within a COMMUNITY

Question 3

Three of the bee species collected in the farmland areas were Peponapis pruinosa, Andrena chlorogaster and Andrena piperi.
What do these names suggest about the evolutionary relationships between these
bee species? Explain your answer.

Answer 3

1. A. Chlorogaster and A. Piperies are more closely related
2. As they have the same genus

Question 4

The scientists tested their null hypothesis using the chi-squared statistical test. After 1 cycle their calculated chi-squared value was 350
The critical value at P=0.05 is 3.841
What does this result suggest about the difference between the observed and
expected results and what can the scientists therefore conclude?

Answer 4

The calculate chi squared value is much higher than critical value so reject null hypothesis
The probability that the differences are due to chance is 5%
Differences are significant

Question 5

Describe the gross structure of the human gas exchange system and how we breathe
in and out. (6)

Answer 5

Trachea, bronchi, bronchi, alveoli (1)
Correct order (1)
Breathing in- diaphragm and external intercostal muscles contract
Causes vol to increase and pressure to decrease in thoracic cavity so air moves down a pressure gradient and into the lungs
Breathing out- diaphragm relaxes and intercostal muscles contract
Causes vol decrease pressure increase in thoracic cavity so air moves out down pressure gradient

Question 6

Describe test for starch

Answer 6

Add iodine
Orange-> blue/black

Question 7

Describe test for reducing sugar

Answer 7

1.Add Benedict’s and heat
2.positive test+blue to green/yellow/orange/red
3.higher concentration of reducing sugar=. More red

Question 8

Describe test for sucrose

Answer 8

1. Negative Benedict’s test=stays blue
   2.add acid and boil
2. Add alkali to neutralise
3. Add Benedict’s and het
4. Positive test = blue to brick red

Question 9

Describe the test for proteins

Answer 9

Add biuret
Positive test= blue to purple

Question 10

Describe the biochemical test for lipids

Answer 10

Dissolve sample in ethanol
Then add distilled water
Milky white emulsion forms

Question 11

What improvements can be made to make a scientific drawing more accurate?

Answer 11

1. No shading
2. No overlapping label lines
   . Magnification should be stated

Question 12

What factors affect transpiration?

Answer 12

Temperature
Humidity
Air movement
Light intensity

Question 13

What does a potometer measure and why?

Answer 13

Measures the rate of uptake of water- proportional to transpiration - water vapour yards to measure

Question 14

Why is the plant cut underwater?

Answer 14

Prevent air from entering the xylem and breaking column of water

Question 15

Why is the potometer filled with water?

Answer 15

Removes air bubbles

Question 16

Why is petroleum jelly used to. Seal joints?

Answer 16

To make them ‘air tight’ so air can’t enter
So water can’t leak out

Question 17

An environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees.

Answer 17

1. Use random sample of seeds (from each population);
2. Use (large enough) sample to be representative of whole population;
3. Indication of what size was measured eg mass;
4. Calculate a mean and standard deviation (for each population);
5. Use the (Student’s) t-test;
6. Analyse whether there is a significant difference between (the means of) the two populations;

Question 18

Role of iron, sodium and phosphate ions (5)

Answer 18

Iron ions
1. Haemoglobin binds/associates with oxygen
OR
Haemoglobin transports/loads oxygen;
Ignore reference to 2+ or 3+ in Fe2+ or Fe3+

AQA Biology A-Level - Inorganic Ions MS PhysicsAndMathsTutor.com
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions
6. Affects osmosis/water potential;
Accept 5. OR 6. – not both
7. Joins nucleotides/in phosphodiester bond/in backbone of
DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
Reject ‘energy produced’
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
Accept for 1 mark,
Sodium ions cause water reabsorption in kidneys OR
Sodium ions establish resting potential (in neurones) OR
Sodium ion diffusion creates action potential