Unit 3 part 2

Question 1

Fish - Explain two ways in which the structure of fish gills is

Answer 1

1. Many lamellae / filaments so large surface area;
2. Thin (surface) so short diffusion pathway;

Question 2

Absorption - how is the golgi apparatus involved in the absorption of lipids.(3)

Answer 2

1. Modifies / processes triglycerides;
2. Combines triglycerides with proteins;
3. Packaged for release / exocytosis OR Forms vesicles;

Question 3

Absorption – Explain how monosaccharides and amino acids are absorbed into the blood (5)

Answer 3

1. Some by facilitated diffusion (when higher concentration in lumen)
2. Sodium ions actively transported from ileum cell to blood;
3. Maintains / forms diffusion / concentration gradient for sodium to enter cells from gut (and with it, glucose);
4. sodium ions enter cell by facilitated diffusion and bring with it a molecule of glucose by co-transport;
5. Facilitated diffusion of glucose into blood/capillary;

Question 4

Haemoglobin - Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why. (2)

Answer 4

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; Ignore ref. to ‘positive cooperativity’ unqualified Ignore ref. to named bonds Accept conformational shift caused
2. Creates / leads to / uncovers second / another binding site

OR

Uncovers another iron / Fe / haem group to bind to;

Question 5

Explain how changes in the shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin dissociation curve (2)

Answer 5

1. First oxygen binds (to Hb) causing change in shape;
2. (Shape change of Hb) allows more O2 to bind (easily) / greater saturation with O2 OR Cooperative binding;

Question 6

Haemoglobin - Haemoglobin is a protein with a quaternary structure. Explain the meaning of quaternary structure (1).

Answer 6

(Molecule contains) more than one polypeptide (chain)

Question 7

Haemoglobin - Describe the advantage of the Bohr effect during intense exercise. (2)

Answer 7

1. Increases dissociation of oxygen; Accept unloading/ release/reduced affinity for dissociation
2. For aerobic respiration at the tissues/muscles/cells

OR

Anaerobic respiration delayed at the tissues/muscles/cells

OR

Less lactate at the tissues/muscles/cells;

Question 8

Haemoglobin - Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin. (2)

Answer 8

1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2; Accept more readily Accept releases more O2
2. (By) decreasing (blood) pH/increasing acidity;

Question 9

Haemoglobin – Animals living at high altitudes shift to left (3)

Answer 9

1. high altitudes have a low partial pressure of O2;
2. high saturation/affinity of Hb with O2 (at low partial pressure O2);
3. sufficient/enough O2 supplied to respiring cells / tissues;

Question 10

Haemoglobin – why small animals have curved to the right (2)

Answer 10

1. Mouse haemoglobin/Hb has a lower affinity for oxygen

OR

For the same pO2 the mouse haemoglobin/Hb is less saturated

OR

At oxygen concentrations found in tissue mouse haemoglobin/Hb is less saturated; For ‘Hb is less saturated’ accept ‘less oxygen will be bound to Hb’.

2. More oxygen can be dissociated/released/unloaded (for metabolic reactions/respiration); Accept ‘oxygen dissociated/released/unloaded more readily/easily/quickly’

Question 11

Haemoglobin – why curve to the right for more active animals (2)

Answer 11

1. Curve to the right so lower affinity / % saturation (of haemoglobin);
2. Haemoglobin unloads / dissociates more readily;
3. More oxygen to cells / tissues / muscles;
4. For greater / more / faster respiration;

Question 12

Heart & circulation – dissection - three control measures the student must use to reduce the risks associated with carrying and using a scalpel.

Answer 12

1. Carry with blade protected / in tray
2. Cut away from body;
3. Cut onto hard surface;
4. Use sharp blade;
5. Dispose of used scalpel (blade) as instructed;

Question 13

Heart & circulation – dissection. Control measures when packing away (2)

Answer 13

1. Carry/wash sharp instruments by holding handle OR Carry/wash sharp instruments by pointing away (from body)/down; Accept for ‘instruments’, a suitable named example, eg. scalpel
2. Disinfect instruments/surfaces; Accept for ‘instruments’, a suitable named example, eg. scalpel Accept for ‘disinfect’, sanitise OR use antiseptic
3. Disinfect hands OR Wash hands with soap (and water); Accept for ‘disinfect’, sanitise OR use antiseptic
4. Put organ/gloves/paper towels in a (separate) bag/bin/tray to dispose;

Question 14

Heart & circulation - Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs. (3)

Answer 14

1. Renal vein;
2. Vena cava to right atrium;
3. Right ventricle to pulmonary artery;

Question 15

Heart & circulation - Name the blood vessels that carry blood to the heart muscle. (1)

Answer 15

Coronary arteries;

Question 16

Heart & circulation - Calculate Cardiac Output (1)

Answer 16

Cardiac Output = Stroke Volume x Heart Rate

Question 17

Heart & circulation – what causes the semi-lunar valve to close (1)

Answer 17

Because pressure in aorta higher than in ventricle;

Question 18

Heart & circulation – explain how the atrioventricular valve is closed (2)

Answer 18

1. ventricle contracts and volume decreases
2. pressure (ventricle) increases so higher than pressure of left atrium;

Question 19

Heart & circulation - Explain how an arteriole can reduce the blood flow into capillaries. (2)

Answer 19

1. Muscle contracts;
2. Constricts/narrows arteriole/lumen;

Question 20

Heart & circulation - Artery – Structure and Function (5)

Answer 20

1. Elastic tissue to allow stretching/recoil/ smooths out flow of blood/maintains pressure;
2. (Elastic tissue) stretches when ventricles contract OR Recoils when ventricle relaxes;
3. Muscle for contraction/vasoconstriction;
4. Thick wall withstands pressure OR stop bursting;
5. Smooth endothelium reduces friction;

Question 21

Heart & circulation - Explain four ways in which the structure of the aorta is related to its function.

Answer 21

1. Elastic tissue to allow stretching / recoil / smoothes out flow of blood / maintains pressure;
2. (Elastic tissue) stretches when ventricles contract OR Recoils when ventricle relaxes;
3. Muscle for contraction / vasoconstriction;
4. Thick wall withstands pressure OR stop bursting;
5. Smooth endothelium reduces friction;
6. Aortic valve / semi-lunar valve prevents backflow.

Question 22

Heart & circulation fish – describe type of circulation in fish (1)

Answer 22

1. Single circulatory system
2. chambers/1 ventricle1 atrium
3. One vein carrying blood towards the heart/ One artery carrying blood away

Question 23

Tissue fluid - Explain how water from tissue fluid is returned to the circulatory system.(4)

Answer 23

1. (Plasma) proteins remain; Accept albumin/globulins/fibrinogen for (plasma) protein
2. (Creates) water potential gradient

OR Reduces water potential (of blood);

3. Water moves (to blood) by osmosis;
4. Returns (to blood) by lymphatic system;

Question 24

Tissue fluid - Explain the role of the heart in the formation of tissue fluid. (2)

Answer 24

1. Contraction of ventricle(s) produces high blood / hydrostatic pressure;
2. (This) forces water (and some dissolved substances) out (of blood capillaries);

Question 25

Tissue fluid - High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid.
Explain how. (2)

Answer 25

1. (Higher salt) results in lower water potential of tissue fluid;
2. (So) less water returns to capillary by osmosis (at venule end); OR
3. (Higher salt) results in higher blood pressure / volume;
4. (So) more fluid pushed / forced out (at arteriole end) of capillary;

Question 26

Tissue fluid - High blood pressure leads to an accumulation of tissue fluid. Explain how. (2)

Answer 26

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

Question 27

Tissue fluid - Formation and reabsorption (8)

Answer 27

1. At arteriole end high hydrostatic pressure/blood pressure;
2. Hydrostatic pressure higher than effect of osmosis;
3. Small molecules/named example eg glucose; water
4. Forces out;
5. Proteins remain in blood/ not removed as they are too large to leave capillary;
6. Increasing/giving higher concentration of blood proteins so proteins lower water potential of blood;
7. Water/fluid moves back into blood;
8. Water moves by osmosis

Question 28

Water - Describe the cohesion-tension theory of water transport in the xylem. (5)

Answer 28

1. Water lost from leaf because of transpiration / evaporation of water (molecules) / diffusion from mesophyll / leaf cells;

OR

Transpiration / evaporation / diffusion of water (molecules) through stomata / from leaves;

2. Lowers water potential of mesophyll / leaf cells;
3. Water pulled up xylem (creating tension);
4. Water molecules cohere / ‘stick’ together by hydrogen bonds;
5. (forming continuous) water column;
6. Adhesion of water (molecules) to walls of xylem;

Question 29

Water - T A potometer measures the rate of
water uptake rather than the rate of transpiration.

Give two reasons why the potometer does not truly measure the rate of transpiration.(2)

Answer 29

1. Water used for support / turgidity; Accept: water used in (the cell’s) hydrolysis or condensation (reactions) for one mark. Allow a named example of these reactions
2. Water used in photosynthesis;
3. Water produced in respiration;
4. Apparatus not sealed / ‘leaks’;

Question 30

Water - Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot. (2)

Answer 30

1. Seal joints / ensure airtight / ensure watertight; Answer must refer to precautions when setting up the apparatus Ignore: references to keeping other factors constant
2. Cut shoot under water;
3. Cut shoot at a slant;
4. Dry off leaves;
5. Insert into apparatus under water;
6. Ensure no air bubbles are present;
7. Shut tap;
8. Note where bubble is at start / move bubble to the start position;

Question 31

Sucrose - Describe the transport of carbohydrate in plants. (5)

Answer 31

1. (At source) sucrose is transported into the phloem/sieve element/tube;
2. By active transport OR By co-transport with H+; Accept co-transport with hydrogen/H ions
3. By companion/transfer cells;
4. Lowers water potential in phloem and water enters by osmosis; Accept pressure gradient? For ‘phloem’ accept ‘sieve element/tube’.
5. (Produces) high (hydrostatic) pressure;
6. Mass flow;
7. Transport from site of photosynthesis to respiring cells OR Transport from site of photosynthesis to storage organ OR Transport from storage organ to respiring cells;

Question 32

Sucrose - Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this
phloem tube.(3)

Answer 32

1. Sucrose actively transported (into phloem);
2. Lowering/reducing water potential OR More negative water potential;
3. Water moves (into phloem) by osmosis (from xylem);

Question 33

Sucrose - Phloem pressure is reduced during the hottest part of the day. Use your understanding of transpiration and mass flow to explain why.(3)

Answer 33

1. High (rate of) transpiration/evaporation;
2. Water lost through stomata OR (High) tension in xylem;
3. (Causes) less water movement from xylem to phloem OR Insufficient water potential in phloem to draw water from xylem;