Which statements are correct reasons for how animals cool down in hot environments using latent heat of vaporisation of water?
- Some animals lie down and roll in wet soil.
- Fish move into deeper water.
- Some animals lick their fur to make it wet.
- Some animals breathe quickly with a wet tongue hanging out of their mouth.
▶️ Answer/Explanation
Ans: C
1,3,4 involve water evaporation (cooling mechanism). Fish moving deeper (2) relates to temperature gradients, not evaporation. Thus correct options are 1 (wet soil evaporation), 3 (fur wetting), and 4 (panting).
An investigation was carried out into the effect of four different treatments on the permeability of the cell surface membranes and tonoplasts of beetroot cells. Beetroot cell vacuoles contain a red pigment. This pigment cannot diffuse through the tonoplasts or cell surface membranes.
1 cm³ cubes were cut from beetroot tissue and washed in running water for 20 minutes to remove any pigment released from damaged cells.
Two cubes were then placed in each of the four test-tubes containing different contents and observed for five minutes.
Which row shows a correct explanation for the observation recorded for one of the treatments?
▶️ Answer/Explanation
Ans: B
Ethanol dissolves membrane lipids, causing pigment release (red color). Acid (A) would denature proteins but also likely damage membranes. Cold water (C) wouldn’t denature proteins, and hot water (D) primarily affects protein structure, not just lipids. Thus, B provides the correct explanation.
The diagram shows the mean dimensions of an epithelial cell in micrometres (µm).
Which row shows the surface area to volume ratio of the epithelial cell and how the surface area to volume ratio of the cell would change if the cell width doubled?
▶️ Answer/Explanation
Ans: C
Surface area = 2(2×3 + 2×8 + 3×8) = 92 µm². Volume = 2×3×8 = 48 µm³. Ratio = 92:48 ≈ 23:12. When width doubles (4 µm), new ratio = 136:96 ≈ 17:12, which is smaller. Thus, C (23:12, decreases) is correct.
The diagram shows part of a cell surface membrane.
Which row correctly identifies the molecules labelled 1 and 2?
▶️ Answer/Explanation
Ans: C
In the cell membrane, glycoproteins (1) are proteins with carbohydrate chains attached, extending from the surface. The phosphate heads (2) of phospholipids form the outer layer of the membrane bilayer. Glycolipids (D) would have lipid tails, and lipoprotein (B) isn’t a standard membrane component. Thus, C is correct.