to increase the antibody production (to a level that protects the person against the disease)
Second injection is given when (the person still infected and) his antibodies has dropped below immunity level, (therefore he needs antiserum injection against the disease)
Adabi 2011
3 (a) Describe the role played by each of the following in maintaining the circulation of blood in the human body.
˗ The heart is a muscular organ with two distinct valves, the left side receives and pumps out oxygenated blood, the right side receives and pumps out oxygenated, the right side receives and pumps out deoxygenated blood
˗ Rhythmic contractions of the heart help pump blood into the pulmonary and systemic circulations
˗ The blood is pump into the systemic circulation at a lower pressure because the lungs are situated close to the heart
˗ The heart rate changes according to the body’s requirements
˗ Example, strenuous activity causes the heart rate to increase Blood vessel:
˗ Arteries are vessels that are thick-walled, containing muscle and elastic tissue within the walls
˗ Arteries are capable of peristaltic movement which pushes blood further along the arteries: this is important for arteries that supply tissues that are distant from the heart
˗ Veins are vessels with thinner walls and they have valves
˗ The pressure of blood in veins is very low, thus the presence of valves aid the flow of blood towards the heart
˗ Capillaries have wall which are one-cell thick and permeable. This allow the exchange of material between the blood and body cells.
Muscle of the limb:
˗ Large veins are located between the muscles of limbs
˗ The constriction of muscles squeeze the veins
˗ Blood in the veins are forced to move in one direction only (towards the heart)
(b) Diagram 3.1 shows a red blood cell structure. One of the major function of blood is the transport of oxygen.
Diagram 3.1
Describe how the structure of red blood cells is adapted to perform this function.
[4 marks]
˗ The biconcave disc provides a large surface area to volume ratio
˗ This increases the rate of gaseous exchange
˗ The absence of a nucleus provides more space to store haemoglobin
˗ The flexible and elastic membrane of a red blood cell allows it to squeeze through narrow capillaries
(c) Diagram 3.2 shows that the blood circulatory systems of an amphibian and a human.
Amphibian Human
Diagram 3.2
Based on the diagram compare both circulations.
[4 marks]
Similarities:
˗ Both are closed circulation systems
˗ Both are double circulatory system Differences:
Amphibian Human
Have three chambers in the heart Have four chambers in the heart There is some mixing of the oxygenated
and deoxygenated blood in the ventricle (incomplete circulatory system)
There is no mixing of the oxygenated and deoxygenated blood in the ventricle (complete circulatory system)
38 TIMES 2011
4 (a) Diagram 4.1 shows the movement of water from the roots to the leaves and out to the atmosphere.
Diagram 4.1
Based on Diagram 6.1, describe the movement of water from roots to the leaves.
[10 marks]
Root pressure
˗ The cell sap of root hair (usually) hypertonic to the surrounding soil solution
˗ Water diffuses into the root by osmosis.
˗ (As they absorb more water by osmosis), a cell sap becomes more dilute compared to neighbouring cells.
˗ Water (therefore) moves to these adjacent cells which become more diluted themselves, so
˗ osmosis continues across the cortex
˗ (At the same time), ions from the soil are actively secreted into the xylem vessels and this causes osmotic pressure to increase
˗ Water flows continuously into the xylem and this create a pressure known as root pressure
˗ Root pressure gives an initial upward force to water and mineral ions in the xylem vessels
Capillary action
˗ Water moves up through the xylem in the stems by capillarity (with is the upward movement of a
˗ fluid in a narrow bore tube)
˗ Capillary action is due to combined force of cohesion (water molecule have attraction for each
˗ other) and adhesion (water molecules are attracted to the side of the vessels)
˗ Water molecule form a continuous water column in the xylem vessel (due to cohesion and adhesion force enable water to move up along the xylem vessels)
˗ (As water is pulled upwards) the cohesion of water (which is due to hydrogen bonding holds the
˗ water molecule together) prevent the water column in the xylem breaking apart
˗ (At the same time) the adhesion of the water (to the wall of the xylem vessel and tracheids) prevents gravity from pulling the water down the column
39
˗ called transpiration pull
˗ The transpiration pull draws water from the xylem in the leaves/stems/roots.
˗ The continuous flow of water through the plant is known as the transpiration stream (b) Diagram 4.2 shows part of the blood circulatory system and the lymphatic system in the
human body.
Diagram 4.2
(i) Explain the differences between the composition of fluid P and fluid Q.
[4 marks]
˗ Fluid Q/lymph has a larger numbers of lymphocyte compare to fluid P/blood
˗ lymphocyte is produced by the lymph nodes in lymph system
˗ Fluid Q/lymph has lower contents of oxygen compare to fluid P/blood
˗ oxygen has been used up by the cell
(ii) Describe how fluid Q is formed from blood until it is brought back into the blood circulatory system.
[6 marks]
˗ (When the blood flows from arteries into capillaries)there is higher hydrostatic pressure at the arterial end of the capillaries
˗ (This high pressure) forces some plasma to pass through the capillary walls into the intercellular spaces (between the cells)
˗ Once the fluid leaves the capillary walls, it is called interstitial/tissue fluid // The interstitial fluid fills the spaces between the cells and constantly bathes the cells
˗ 90% of the interstitial fluid diffuses back into blood capillary
˗ 10% of the interstitial fluid that has not been reabsorbed into the bloodstream goes into the lymph capillaries. (Once inside the lymph capillaries) the fluid is known as lymph.
˗ The lymph capillaries unite to form larger lymphatic vessels.
˗ From the lymphatic vessels, lymph eventually passes into the thoracic duct/the right lymphatic duct.
˗ The thoracic duct empties its lymph into the right subclavian vein. (Hence, lymph drains back into the blood).