IB Biology HL Theme B: Form and function questions

Answer: A. Lipids dissolve in non-polar solvents and are only sparingly soluble in aqueous solvents, so the observed pattern is consistent with a lipid. A glycerol molecule linked by condensation to three fatty acids forms a triglyceride; a phospholipid has two fatty acids and a phosphate group.

B: recognizes the solubility pattern but confuses the three-fatty-acid product with a phospholipid.
C: identifies the triglyceride but mistakes it for a phospholipid and omits the matching solubility evidence.
D: accepts the correct statements but also labels the product a phospholipid, despite its specified composition.

Remember: three fatty acids form a triglyceride; two fatty acids and a phosphate group form a phospholipid.

Answer: A. Removing the extracellular carbohydrate chains lowered adhesion from 82% to 46% and correct recognition from 91% to 52%. The paired decreases support a role for these structures in both processes.
B: accounts for the decrease in recognition but overlooks the decrease in adhesion.
C: accounts for the decrease in adhesion but overlooks the decrease in recognition.
D: reverses the relationship: removal decreased both responses, rather than increasing them.
Remember: membrane carbohydrate chains can contribute to cell adhesion and cell recognition.

Answer: D. Arteries have a thicker wall relative to lumen diameter than veins. The wall-thickness-to-lumen-diameter ratios are P: 150/1000 = 0.15, Q: 30/300 = 0.10, R: 40/800 = 0.05 and S: 80/400 = 0.20. S has the greatest relative wall thickness.

A: chooses P by comparing absolute wall thickness alone; its wall is 150 µm, but its ratio is 0.15.
B: chooses Q by using the smallest lumen diameter alone rather than comparing wall thickness relative to diameter.
C: chooses R by reversing the criterion and selecting the smallest wall-to-lumen ratio.
Remember: identify an artery by its relatively thick wall, not by absolute wall thickness alone.

Answer: C. Arthropods have exoskeletons, while vertebrates have endoskeletons. Arthropod muscles attach to the inner surface of the exoskeleton, whereas vertebrate muscles attach to bones. When muscles contract, the skeleton provides anchorage and acts as a lever to move the appendage.
A: reverses which group has an exoskeleton and which has an endoskeleton.
B: places the arthropod muscle attachment on the outer, rather than inner, surface of the exoskeleton.
D: reverses the roles: the skeleton acts as the lever, while muscles provide the force.
Remember: skeletons provide muscle anchorage and act as levers during movement.

Answer: A. Biome distribution is associated with patterns of temperature and rainfall. Consistently high values for both are characteristic of tropical forests; similar abiotic conditions can favor similar communities through convergent evolution.
B: selects hot desert from the high temperature but overlooks the consistently high rainfall.
C: classifies rainfall as biotic; it is an abiotic factor that helps determine biome distribution.
D: matches the high rainfall but overlooks the consistently high temperature.
Remember: terrestrial biome distribution reflects both temperature and precipitation.