▶️ Answer/Explanation
(a) haemoglobin
Explanation: Haemoglobin is the protein found in red blood cells that binds with oxygen to form oxyhaemoglobin, enabling the transport of oxygen from the lungs to tissues throughout the body.
(b) platelets
Explanation: Platelets are small cell fragments in the blood that play a crucial role in blood clotting by forming a plug at the site of injury and releasing chemicals that promote clot formation.
(c)(i) 9.3%
Working:
Initial diameter = 7.5 μm
Final diameter = 8.2 μm
Increase = 8.2 – 7.5 = 0.7 μm
Percentage increase = (0.7 / 7.5) × 100 = 9.333…% ≈ 9.3% (to 2 significant figures)
(c)(ii)
Explanation: The 1.8% salt solution has a lower water potential than the red blood cells. This causes water to move out of the cells by osmosis, across the partially permeable membrane, from an area of higher water potential (inside the cell) to lower water potential (the salt solution). As a result, the cells shrink, decreasing their mean diameter from 7.5 μm to 6.0 μm.
(c)(iii) The water potential of the red blood cells is the same as the 0.9% salt solution.
Explanation: When the water potential inside and outside the cell is equal, there is no net movement of water across the cell membrane. This isotonic condition means the cells neither gain nor lose water, so their diameter remains unchanged.
(d) Red blood cells do not have a rigid cell wall.
Explanation: In pure water, red blood cells take in water by osmosis and burst (lyse) because they lack a cell wall to prevent over-expansion. Plant cells have a rigid cell wall that resists the inward pressure of water, preventing bursting and instead making the cell turgid.
(e) Any two from:
- Transport of ions/sucrose (translocation)
- As a reactant in photosynthesis
- As a solvent for metabolic reactions
- Maintaining turgidity of cells (support)
- Medium for enzyme reactions
Explanation: Water is essential in plants for various functions. It acts as a transport medium in the xylem and phloem, is a raw material in photosynthesis, provides structural support through turgor pressure, and serves as a solvent for biochemical reactions.
Question
(a) Fig. 2.1 shows the transfer of materials between blood and tissues.
(i) Complete Table 2.1 by:
• stating the names of the fluids
• writing yes if the fluid contains red blood cells or no if the fluid does not contain
red blood cells.
(ii) State the name of the process by which oxygen is transferred from fluid B to the cells.
(iii) Explain why cells need oxygen.
(b) Describe the functions of arterioles in the skin.
(c) Describe the functions of lymph nodes in the lymphatic system.
(d) Lacteals are part of the lymphatic system.
(i) State where in the body lacteals are found.
(ii) Describe the role of lacteals.
Answer/Explanation
Answer:
(a) (i)
(ii) diffusion ;
(iii) (aerobic) respiration ;
for the release of energy ;
for a (named) metabolic process ;
(b) 1 deliver / supplies, blood / oxygen / glucose (from arteries) to,capillaries / shunt vessels ;
2 controls blood flow, through capillaries / to the surface of the skin ;
3 by vasoconstriction / vasodilation ;
4 ref to (arteriole) muscle contraction / relaxation ;
5 ref to maintenance of body temperature / homeostasis
/ description of ;
(c) contains lymphocytes (which produce antibodies) ;
filters the lymph ;
ref. to immunity / defends against disease / ref. to destruction of
(named) pathogens ;
(d) (i) small intestine / villi ;
(ii) fat, absorption / transport ;