Chapter 7 Transport in Humans

Question 1

State and explain 2 ways in which red blood cells are adapted to their function [2] (2011/A3)

Answer 1

Any 2 of the following
• Red blood cells contain haemoglobin which binds reversibly to oxygen.
• The nucleus is absent in the red blood cell, allowing it to carry more haemoglobin, thus increasing its oxygen carrying capacity.
• Red blood cells are biconcave in shape, increasing the surface area to volume ratio to increase the rate of diffusion of gases into the cell.
• Flexible membrane allows red blood cells to change its shape and squeeze through narrow capillaries to carry oxygen to all cells of the body.
• Does not contain mitochondria, so less oxygen is used up by respiration.

Question 2

Describe the role of white blood cells in protecting the body from disease [2] (2011/A3)

Answer 2

Lymphocytes produce antibodies to agglutinate pathogens and neutralise toxins [1] and the phagocytes engulf and ingest pathogens by phagocytosis. [1]

Question 3

State two functions of a Phagocyte [2] (2012/A5)

Answer 3

Phagocytes ingest pathogens/harmful microorganisms and cell debris by phagocytosis [1]
Phagocytes can move out of blood capillaries and destroy foreign tissue bringing about tissue rejection. [1]

Question 4

Describe and explain how blood entering the heart from the body organs reaches the lungs [4] (2015/A4)

Answer 4

1. Blood enters the right atrium of the heart from the body organs via the vena cava. [1]
2. During ventricular and atrial
   diastole, the cardiac muscles of the right ventricle and right atrium are relaxed, tricuspid valves are remained opened as the pressure in the ventricle and atrium is very
   low. There is passive filling of blood into the right atrium and ventrical.[1]
3. During atrial systole, muscles of atrial wall contract, pressure in the right atrium is higher than that in the right ventricle, forcing the tricuspid valve to stay open, so blood from the right atrium is forced into the right ventricle. [1]
4. Muscles of the right ventricle contract during ventricular systole, increasing the pressure in the right ventricle to become higher than that of the right atrium and the tricuspid valve is forced closed to prevent backflow of blood from the right ventricle into the right atrium. [1]
5. When the pressure in the right ventricle becomes higher than that of the pulmonary arteries, the semi-lunar valve is forced open and blood is forced out of the right ventricle into the lungs via the pulmonary arteries [1]

Question 5

State the function of the right semi lunar valve [1] (2015/A4)

Answer 5

Prevents backflow of blood from the pulmonary artery to right ventricle

Question 6

Explain how a blood clot is formed [3] (2016/A1)

Answer 6

1. When blood vessels are damaged, damaged tissues and blood platelets release an enzyme, thrombokinase which converts the protein inactive prothrombin in the blood plasma into active thrombin in the presence of calcium ions. [1]
2. Thrombin catalyses the conversion of soluble fibrinogen to insoluble fibrin threads. [1]
3. Fibrin threads entangle blood cells and whole mass forms a clot or a scab to seal the wound. [1]

Question 7

Sometimes blood clots can form inside a blood vessel and can be carried in the blood to the brain. The arteries in the brain may become blocked by the clot. Suggest how this blood blockage may affect the brain. [3] (2016/A1)

Answer 7

1. As the arteries in the brain become blocked by the clot, less/ no blood flows to the brain cells and the cells do not receive oxygen and glucose, no respiration, no energy released for cellular activities. [1]
2. As a result, brain cells die, [1] which may result in a stroke/ brain damage [1]

Question 8

state the function of the right ventricular muscle tissue [2] (2017/A7)

Answer 8

Cardiac muscle/ heart muscle tissue [1]
Contracts to force blood from L to the lungs due to high pressure and relaxes to allow blood to enter into L. [1]

Question 9

State two functions of blood clotting in humans [2] (2018/A3)

Answer 9

To prevent excessive/further loss of blood/ reduce blood loss [1]
Seals the wound to prevent entry of microorganisms/ pathogens into the blood/body [1]

Question 10

Explain how the drug injected into the rats was transported to the heart muscle [4] (2011/B8)

Answer 10

1. The drug will dissolve in the blood plasma and be transported back to the heart via the vena cava. [1]
2. It returns back to the heart after passing the lungs and gets pumped into the aorta from the left ventricle. [1]
3. It then enters the coronary arteries surrounding the heart muscles [1]
4. where it diffuses out of the blood capillaries into the tissue fluid before diffusing into the muscle cells to block the transmission of nerve impulses. [1]

Question 11

Describe how the breakdown products of excess amino acids are transported in the blood from their site of production to their site of removal from the body.
The names of the blood vessels are not required. [5] (2016/B9)

Answer 11

Production
1. Excess amino acids are converted by liver cells through deamination to produce urea which diffuse from the liver cells into the tissue fluid down the concentration gradient. [1]
Transport
2. The dissolved urea diffuse into the blood capillaries and is transported into the heart by veins and out of the heart via the to the kidneys via an artery. [1]
Processing
3. Urea being small molecules are forced out of the blood by high hydrostatic blood pressure during ultrafiltration at the glomerulus across a partially permeable basement membraneinto the Bowman’s capsule. [1]
Exceretion
4. Urea in the glomerular filtrate then flows along the kidney tubules to the collecting duct and into the ureter to the urinary bladder. [1]
5. and discharged in urine out of the body through the urethra. [1]

Question 12

Describe the role of carbonic anhydride in the Excretion of carbon dioxide

Answer 12

1. Carbon dioxide is a metabolic waste product that is produced by tissue cells. It diffused through the tissue fluid, into the blood plasma and into red blood cells.
2. Carbonic anhydrase is found in red blood cells. It catalyses the conversion of carbon dioxide and water to carbonic acid. [1]
3. Carbonic acid is converted into hydrogencarbonate ions which diffuse out of the red blood cells into the blood plasma and are transported to the lungs. [1]
4. In the lungs, hydrogencarbonate ions diffuse back into red blood cells and are converted back into carbonic acid. Carbonic acidis then converted into water and carbon dioxide by carbonic anhydrase in red blood cells. [1]
5. Carbon dioxide then diffuses out of the blood capillaries into the alveoli and out of the lungs through exhalation. [1]

Question 13

Describe the process that generates pressure in the aorta. [1] (2014/B8)

Answer 13

Contraction of the cardiac muscles of the left ventricle of the heart

Question 14

Describe what causes the fall in blood pressure as the blood passes from the aorta to the vena cava. [1] (2014/B8)

Answer 14

Lumen of vena cava is wider than that of aorta.[1] /Less recoil of walls of vena cava/ loss of pressure due to friction

Question 15

Describe what causes the fall in blood pressure as the blood passes from the aorta to the vena cava. [>1] (Self)

Answer 15

As the aorta divides into smaller arteries and eventually into capillaries, the total cross sectional
area of the blood vessel decreases and friction on the blood increases and thus the pressure falls.
Pressure in the veins continue to fall as veins have a larger lumen than arteries and are less elastic, thus little pressure is exerted by the walls of the vein on the blood to move it along.