Unit 3 Exam Questions

Question 1

Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and surrounding tissue.

Answer 1

-Single cell thick so reduces diffusion distance
-small diameter so short diffusion distance
-narrow lumen so reduces flow rate so more time for diffusion
- red blood cells in contact with wall so more time for diffusion

Question 2

Describe the cohesion- tension theory of water transport in the xylem

Answer 2

1. Water lost from leaf because transpiration
2. Lowers water potential in mesophyll
3. Water pulled up by xylem
4. Water molecules stick together by H bonds
5. Water column
6. Adhesion of water to walls of xylem

Question 3

A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why.

Answer 3

Short diffusion pathway

Question 4

Explain how efficient gas exchange is ensured by the dissociation curve for the fetus being to the left of the dissociate curve for the woman.

Answer 4

Fetal haemoglobin has a greater affinity for oxygen so it loads oxygen from mother’s haemoglobin.

Question 5

One theory of translocation states that organic substances are pushed from a high pressure in the leaves to a low pressure in the roots. Describe how a high pressure is produced in the leaves.

Answer 5

Water potential becomes lower so water enters phloem by osmosis so increased volume so increased pressure.

Question 6

Describe the mass flow hypothesis for the mechanism of translocation in plants

Answer 6

1. Leaf sugars actively transported into phloem
2. By companion cells
3. Lowers water potential of sieve cells
4. Increased pressure causes mass movement
5. Sugars used in roots for respiration

Question 7

Explain the role of the heart in the formation of tissue fluid.

Answer 7

Contraction of ventricles forces water out of blood capillaries

Question 8

What is the function of the coronary arteries?

Answer 8

Carry oxygen TO the heart muscle

Question 9

Explain how changes in the shape of haemoglobin result in the S- shaped oxyhaemoglobin dissociation curve for HbA.

Answer 9

First oxygen binds to Hb causing change in shape which allows more O2 to bind easily.

Question 10

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

Answer 10

-Pressure gradient
-Valves prevent backflow

Question 11

Explain how the structures of the walls of arteries, veins and capillaries and arterioles are related to their functions.

Answer 11

Artery=
- Thickest wall so carry blood at high pressure
-Most elastic tissue so maintains pressure
-Most muscle so maintains pressure

Vein=
-Thin wall doesn’t need to withstand pressure

Capillary=
-Thin wall for diffusion
-Endothelium so short diffusion pathway

Arterioles=
can constrict to regulate blood flow

Question 12

Explain four ways in which the structure of the aorta is related to its function.

Answer 12

-Elastic tissue to allow stretching
-Muscle for contraction
-Thick wall withstands pressure
-Semi lunar valve prevents backflow