Marck Scheme Answers

Question 1

What is the difference between active and passive immunity? (1)

Answer 1

Active immunity is slower

Question 2

Why is a mixture of venoms from several snakes of the same species used to make an antivenom? (1)

Answer 2

There may be a different form of antigen/toxin within one species

Question 3

Why is an animal observed when injected with a newly tested antivenom/antibody (1)

Answer 3

To ensure that the animal does not suffer from the venom/vaccine

Question 4

What are B-cells and how are they produced? (1)

Answer 4

B-cells are specific to venom/antigens and are produced by mitosis

Question 5

Describe the gross structure of the human gas exchange system and how we breathe in and out (5)

Answer 5

• Trachea, bronchi, bronchioles, alveoli
Breathing in
• Diaphragm contracts and external intercostal muscles contract
• Volume increases and pressure decreases in the thoracic cavity
Breathing out
• Volume decreases and pressure increases in the thoracic cavity
• Diaphragm relaxes and internal intercostal muscles contract

Question 6

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhemoglobin (2)

Answer 6

• Increases/more oxygen dissociation/unloading
• By decreasing the blood (pH)

Question 7

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (7)

Answer 7

• Micelles contain salts and fatty acids/monoglycerides
• Make fatty acids/monoglycerides (more) soluble (in water)
• Bring/release/carry fatty acids/monoglycerides to cell/lining (of the ileum)
• Maintain higher concentration of fatty acids/monoglycerides to cell/lining (of the ileum)
• Fatty acids/monoglycerides absorbed by diffusion
• Triglycerides reformed in cells
• Vesicles move to cell membrane

Question 8

Explain how an arteriole can reduce the blood flow into capillaries (2)

Answer 8

• Muscle contracts
• Narrow lumen reduces blood flow

Question 9

Suggest and explain why the combined actions of Endopeptidases and Exopeptidases are more efficient than exopeptidases on their own (3)

Answer 9

• Endopeptidases hydrolyse internal peptide bonds
• Exopeptidases remove amino acids/hydrolyse (bonds) at end
• More ends or increase in surface area (for absorption)

Question 10

Explain why the addition of a respiratory inhibitor stops the absorption of amino acids (4)

Answer 10

• No/less ATP produced
• Sodium (ions) not moved (into/out of cell)
• No diffusion gradient for sodium (to move into cell with amino acid)
• No concentration gradient for sodium (to move into cell with amino acid)

Question 11

Name the process by which oxygen reaches the cells inside the body of small, thin animals (1)

Answer 11

SIMPLE diffusion

Question 12

Suggest why means are used in investigations (3)

Answer 12

• For comparison
• To see effect of variables
• Takes into account outliers/anomalous results

Question 13

One of the severe disabilities that results from emphysema is that walking upstairs becomes difficult.

Explain how a low FEV1 (the volume of air a person can breathe out in one second) value can cause this disability (4)

Answer 13

• Less carbon dioxide removed
• Less oxygen uptake in the blood
• Less aerobic respiration/ATP
• More anaerobic respiration

Question 14

Some people produce a much higher ventricular blood pressure than normal. This can cause tissue fluid to build up outside the blood capillaries of these people.

Explain why (3)

Answer 14

• More fluid forced/filtered out of the capillary/blood due to high pressure
• Less return of fluid (into capillary/blood) due to pressure
• Lymphatic system cannot drain away all excess fluid

Question 15

Some drugs used to reduce high ventricular blood pressure cause widening of blood vessels.

Suggest how widening of blood vessels can reduce ventricular blood pressure (3)

Answer 15

• Larger lumen/volume of blood vessels
• Reduces blood pressure in the blood vessels
• Less friction/ resistance in the blood vessels

Question 16

Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse (3)

Answer 16

• Mouse is smaller so it has a larger surface area to volume ratio
• More/faster heat loss
• Faster rate of heat loss/ metabolism

Question 17

Give two ways in which the structure of starch is different from cellulose (4)

Answer 17

• Starch contains alpha glucose
• Starch is helical and not straight
• Starch contain 1,6 branching
• Has no microfibrils

Question 18

Suggest one way in which sieve tubes are adapted for mass transport (Application and knowledge) (2)

Answer 18

• No/few organelles/very little cytoplasm/ more room/large vacuole/thick walls
• So easier/more flow to resist pressure

Question 19

Describe how a high pressure is produced in the leaves (Application) (3)

Answer 19

• Water potential becomes lower as sugar enters the phloem
• Water enters the phloem by osmosis
• Increased volume of water causes increased pressure

Question 20

What is the difference between active transport and facilitated diffusion in terms of proteins (knowledge)(1)

Answer 20

• Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins

Question 21

Describe how you would use a microscope to find the mean diameter of triglyceride droplets on a slide (6)

Answer 21

• measure the eyepiece graticule/ scale
• Calibrate the stage micrometer/ object of known size
• Repeats and calculate the mean/
• Use a ruler to estimate the field diameter under the microscope
• How many droplets go across the field
• Repeats and calculate the mean

Question 22

Describe the action of lipase and bile salts on the hydrolysis of triglycerides (3)

Answer 22

• Small droplets have a larger surface area to volume ratio
• More surface for lipase to act on leading to faster digestion of triglycerides
• Fatty acids are produced more quickly so pH will drop more quickly with bile salts

Question 23

In healthy lungs, a gradient is maintained between the concentration of oxygen in the
alveoli and the concentration of oxygen in the lung capillaries.
(i) Describe how ventilation helps to maintain this difference in oxygen concentration (2)

Answer 23

(In alveolus)
- Need the idea of air moving and oxygen concentration
- Brings in air containing a high(er) oxygen concentration;
Neutral: reference to carbon dioxide concentration
Removes air with a low(er) oxygen concentration

Question 24

(ii) Give one other way that helps to maintain the difference in oxygen concentration. (1)

Answer 24

(ii) Circulation of blood / moving blood;

Question 25

How is Haemoglobin formed? (1)

Answer 25

Via condensation reactions

Question 26

Hereditary persistence of fetal haemoglobin (HPFH) is a condition in which production of fetal haemoglobin continues into adulthood. Adult haemoglobin is also produced. People with HPFH do not usually show symptoms. Suggest why. (2)

Answer 26

- Enough adult Hb produced / enough oxygen released / idea that curves / affinities / - Hb are similar / more red blood cells produced;

Question 27

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why. (1)

Answer 27

Loss of water / loss of fluid / friction (against capillary lining)

Question 28

High blood pressure leads to an accumulation of tissue fluid. Explain how. (3)

Answer 28

- High blood pressure = high hydrostatic pressure; - Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary; - (So) more tissue fluid formed / less tissue fluid is reabsorbed.

Question 29

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why. (3)

Answer 29

- Water has left the capillary; - Proteins (in blood) too large to leave capillary; - Increasing / giving higher concentration of blood proteins (and thus wp)

Question 30

Describe the mass flow hypothesis for the mechanism of translocation in plants (4 marks)

Answer 30

- In source/leaf sugars actively transported into phloem - By companion cells - Lowers water potential of sieve cell/tube and water enters by osmosis - Increase in pressure causes mass movement (towards sink/root) - Sugars used/converted in root for respiration for storage

Question 31

explain why the diameter of the branch decreased during the first 12 hours (1)

Answer 31

increase transpiration) produce a higher tension / reduces the pressure in the xylem reducing the diameter / adhesive forces between xylem and water;

Question 32

How does oxygen diffuse into the capillaries (1)

Answer 32

-Down the diffusion gradient

Question 33

Control variables

Answer 33

- Concentration of... - Volume of...... - Temperature

Question 34

Mammals have some cells that produce extracellular proteases. They also have cells with membrane-bound dipeptidases. Describe the action of these membrane-bound dipeptidases and explain their importance (2)

Answer 34

1. Hydrolyse (peptide bonds) to release amino acids; 2. Amino acids can cross (cell) membrane; OR Dipeptides cannot cross (cell) membrane; OR Maintain concentration gradient of amino acids for absorption; OR Ensure (nearly) maximum yield from protein breakdown;

Question 35

At Q on Figure 3 there is a small increase in pressure and in rate of blood flow in the aorta. Explain how this happens and its importance. (2)

Answer 35

1. Elastic recoil (of the aorta wall/tissue); 2. Smooths the blood flow OR Maintains rate of blood flow OR Maintains blood pressure

Question 36

A different student did this investigation. He did not have a colorimeter. Describe a method this student could use to prepare colour standards and use them to give data for the total anthocyanin extracted. (3)

Answer 36

1. Use known concentration of blueberry juice/extract OR Use known concentration of anthocyanin/pigment (solution) OR Use known concentration of (extraction) solvent to be added to blueberries; 2. Prepare dilution series; 3. Compare (results) with colour standards to give score/value/concentration;

Question 37

Particulate matter is solid particles and liquid particles suspended in air. Polluted air contains more particulate matter than clean air. A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue. Explain why death of alveolar epithelium cells reduces gas exchange in human lungs. [3 marks]

Answer 37

1. Reduced surface area; 2. Increased distance for diffusion; 3. Reduced rate of gas exchange;