Transport In Humans

Question 1

Function of RBCs

Answer 1

1. Contains haemoglobin —> enables RBCs to transport O2
2. RBCs are circular, flattened biconcave discs—>increases surface area to volume ratio—>efficient rate of diffusion
3. Does not possess a nucleus—>able to carry more haemoglobin—> more O2

Question 2

Clotting mechanism of blood

Answer 2

1. When blood vessels are damaged, damaged tissue and blood platelets release thrombokinase(enzyme)
2. Thrombokinase and calcium ions convert prothrombin into thrombin
3. Thrombin converts fibrinogen into fibrin threads
4. Fibrin threads entangle blood cells and the whole mass forms a clot—>seals the wound, preventing the entry of microorganisms.

Question 3

Pathway of blood

Answer 3

Heart—>artery—>arterioles—>capillaries—>Venules—> veins

Question 4

Why does the artery has thick elastic muscular walls?

Answer 4

1. Having thick walls to withstand the immense pressure of the blood as it is pumped out by the heart.
2. The elastic walls helps to push the blood along the artery

Question 5

Structure and function of vein

Answer 5

Presence of semi-lunar valves helps to prevent black flow of blood

Question 6

How are substances transferred between capillaries and tissue cells?

Answer 6

1. Dissolved food substances and oxygen diffuse from the blood in the blood capillaries into the tissue fluid then into the cells.
2. Metabolic waste products diffuse from the cells into the tissue fluid and then through the blood capillary walls into the blood.
3. The blood transports these to the excretory organs for removal

Question 7

Describe the cardiac cycle

Answer 7

1. The atria contract, forcing blood into the relaxed ventricles.
2. After a short pause , the ventricles contract. The high pressure in the ventricles causes the tricuspid valve and the bicuspid valve to close to prevent the back flow of blood into the atria. This produces the ‘lub’ sound.
   The high pressure in the ventricles also forces the semi-lunar valves to open. Blood flows from the right ventricle into the pulmonary arch and the left ventricles into the aortic arch.
3. As the ventricles contract, the atria relax. The right atrium receives blood from the interior vena cava and the anterior vena cava while the left atrium receives blood from the pulmonary veins.
4. The ventricles then relax. The fall in pressure of the ventricles causes the semi-lunar valves to close to prevent the black flow of blood from the 2 arches into the ventricles. This produces the ‘dub’ sound. The increase in pressure of the atria forces the tricuspid valve and the bicuspid valve to open.
   The atria contract again and the whole cycle repeats.

Question 8

Contraction of the ventricles is called the ventricles systole

Answer 8

Relaxation of the ventricles is called the ventricular diastole

Question 9

Describe coronary heart disease

Answer 9

1. Fatty substances may be deposited on the inner surface of the coronary arteries
2. This narrows the linen of these arteries and increases blood pressure.
3. The increased blood pressure may injure the inner surface of the coronary artery when blood flows through it.
4. When it is injures, blood clots will form on the inner surface of the coronary artery. This may cut off the supply of blood to the heart muscles.
5. The heart muscles may die due to the lack of oxygen thus resulting in a heart attack

Question 10

Preventive measures against coronary heart disease

Answer 10

1. Polyunsaturated plant fats should substitute animal fats as they do not stick to the inner surface of the arteries.
2. Proper stress management helps to reduce the risk of a heart attack.
3. Regular physics exercise has long-term benefits by strengthening the heart and maintain the elasticity if the arterial walls.