Unit 3- MT in Animals =)

Question 1

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

Answer 1

• contraction of ventricles produces high hydrostatic pressure
• water (& some dissolved substances) forced out of the capillaries

Question 2

Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system.
Suggest how a blockage in the lymphatic system could cause lymphoedema. (1)

Answer 2

EXCESS tissue fluid builds up (∵ cannot be reabsorbed)

Question 3

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

Answer 3

Loss of water/ friction against capillary lining

Question 4

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 4

• water has left the capillary
• proteins in blood too large to leave
• ↑ conc. of proteins in blood (∴ ↓ Ψ)

Question 5

Give one way blood plasma is different from tissue fluid. (1)

Answer 5

1. ↑ proteins
2. ↑ glucose/ a.a./ O2
3. ↓ urea/ CO2

Question 6

In children, some diets may result in a low concentration of protein in blood plasma. This can cause the accumulation of tissue fluid.
Explain the link between a low concentration of protein in blood plasma and the accumulation of tissue fluid. (3)

Answer 6

• ↓ Ψ gradient ∵ Ψ in capillary not as low
• ↑ tissue fluid formed at the arteriole end
• ↓ water absorbed in capillary by osmosis

Question 7

Tissue fluid is formed from blood at the arteriole end of a capillary bed.
Explain how water from tissue fluid is returned to the circulatory system. (4)

Answer 7

1. plasma proteins remain in blood
2. creates Ψ gradient (↓ Ψ of blood)
3. water moves in by osmosis
4. returns by lymphatic system

lymph reenters the bloodstream through veins located close to the heart

Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries (if not x reabsorption of water into capillaries)

Question 8

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

Answer 8

• muscle contracts
• constrict lumen

Question 9

In a healthy person, blood moves in one direction as it passes through the heart.
Give two ways in which this is achieved. (2)

Answer 9

• valves to prevent backflow
• pressure gradient

Question 10

Name the blood vessel carrying blood at the lowest blood pressure. (1)

Answer 10

Vena cava

Question 11

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

Answer 11

• haemoglobin ↓ affinity for O2–> ↑ dissociation
• for aerobic respiration in muscles/ anaerobic resp delayed/ ↓ lactate

Question 12

Explain how having higher affinity for oxygen is an adaptation of the seal’s myoglobin for diving. (1)

Answer 12

• allows a. resp when diving
• provides O2 when haemoglobin unloaded (delays an. resp./ lactate production)

Question 13

Explain how the bicuspid valve maintains a unidirectional flow of blood. (2)

Answer 13

• when pressure in atrium > ventricle –> valve opens
• ventricle > atrium –> closes

Question 14

The thickness of the aorta wall changes all the time during each cardiac cycle.
Explain why. (3)

Answer 14

• wall stretches ∵ ventricle contracts
• recoils ∵ relaxes
• maintains smooth flow

Question 15

There is a greater percentage reduction in blood flow to the diaphragm than to the lungs during a dive.
Explain the advantage to a diving seal of blood continuing to flow to the lungs. (1)

Answer 15

some O2 still in lungs–>enter blood

Question 16

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

Answer 16

• binding of 1st O2 changes tertiary structure of haemoglobin
• creates another binding site (/uncovers another haem group for binding)
• allows ↑ O2 to bind

Question 17

Why does speed of flow of blood decreases from the aorta to the capillaries? (1)

Answer 17

↑ total cross-sectional area of blood vessels (↑ friction)

Question 18

Explain how the structure of capillaries is related to their function. (2)

Answer 18

1. walls are one-cell thick–> ↓ diffusion distance
2. narrow lumen–> ↓ rate of flow –> ↑ time for diffusion
3. gaps between cells–> ↑ rate of diffision out of vessel

Question 19

In one cardiac cycle, the volume of blood flowing out of the heart along the pulmonary artery is the same as the volume of blood returning along the pulmonary vein.
..
Explain why the volumes are the same although the speed of flow in the artery is greater than in the vein. (1)

Answer 19

larger lumen –> ↑ vol carried

Question 20

Name two substances which are at a higher concentration in the blood at arteriole end than in the blood at venule end. (1)

Answer 20

1. O2
2. glucose
3. minerals
4. a.a.
5. f.a.
6. glycerol

Question 21

Explain what causes the rate of blood flow to be slower in capillaries than in other vessels. (2)

Answer 21

• smaller diameter
• ↑ s.a. in contact w/ blood –> ↑ friction

Question 22

a. Which type of blood vessel has most elastic tissue in its wall? (1)
b. How does this elastic tissue help to smooth out the flow of blood in the blood vessel? (2)

Answer 22

a. artery
b. > stretch to accommodate ↑ vol of blood (when ↑bp)
> recoils when vol of blood ↓ (bp↓)

Question 23

Explain why there is a net loss of water from a capillary at the arterial end. (2)

Answer 23

• hydrostatic pressure
• larger than pressure of Ψ gradient

Question 24

The total volume of fluid that passes from the capillaries to the surrounding tissue fluid is normally greater than the volume that is reabsorbed into them.
Describe what happens to this extra fluid. (2)

Answer 24

• removed by the lymphatic system
• returned to blood

Question 25

The scientists calculated the cardiac output of the volunteers before and after the exercise programme. In some volunteers, their cardiac output stayed the same, even though their resting heart rate decreased. **Explain how their cardiac output could stay the same even when their resting heart rate had decreased.** (2)

Answer 25

- **cardiac output = stroke vol x heart rate** - ↑ sv (so ↓ rate needed for same output)

Question 26

The rise and fall in blood pressure in the aorta is greater than in the small arteries. Suggest why. (3)

Answer 26

- **aorta is close to ventricle** (where pressure is high ∵ contractions) - elastic tissues - stretch + recoil

Question 27

Although the speed of blood flow in an arteriole is greater than speed of blood flow in a capillary, blood does not accumulate in the arterioles. Explain why. (1)

Answer 27

- ↑ capillaries than arterioles - ↑ **cross-sectional area**

Question 28

Other than causing slow blood flow, explain one advantage of capillaries being narrow. (2)

Answer 28

1. **short pathway** betw. blood + outside of capillary 2. ↑ **s.a.** of blood in **contact** w/ capillary walls 3. **fast exchange** (diffusion)

Question 29

What factor limits the minimum internal diameter of the lumen of a capillary? (1)

Answer 29

**size**/ diameter of **blood cell**

Question 30

A principle of homeostasis is the maintenance of a constant internal environment. An increase in the concentration of carbon dioxide would change the internal environment and blood pH. **Explain the importance of maintaining a constant blood pH.** (3)

Answer 30

- **haemoglobin sensitive to pH** - changes tertiary structure/ shape - **↓ O2 binds**

Question 31

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. (2)

Answer 31

- ↑ lumen - ↓ pressure - ↓ friction

Question 32

Explain a property of iron ions that enables these ions to carry out their role in red blood cells. (2)

Answer 32

1. **charged** 2. binds w/ O2 --> oxyhaemoglobin

Question 33

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 33

1. ↑ salt ↓ Ψ of tissue fluid 2. ↓ water returns to capillary by osmosis (venule end) // - ↑ salt ↑ bp - ↑ fluid pushed out of capillary (arteriole end)

Question 34

A high concentration of sodium in the blood can affect blood volume and cause hypertension. Use your knowledge of water potential to suggest how high sodium concentrations in the medicines taken could affect blood volume. (3)

Answer 34

- Na+ ↓ Ψ of blood - water enters blood **by osmosis** - ↑ vol

Question 35

EPO is another performance-enhancing drug. It can increase the haematocrit (the percentage of red blood cells in blood). A heart attack is caused by a lack of glucose and oxygen being delivered to cardiac muscle via the coronary arteries. The overuse of EPO can increase the risk of a heart attack. Suggest how. (2)

Answer 35

- **blood thickens** - cause blockages in coronary arteries