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: C. The 20 amino-acid types are possible building blocks, but their order and the length of a polypeptide chain can vary. Thus I and III are correct; a chain need not contain every type.

A: accepts variation in order but incorrectly assumes chain length cannot vary.
B: accepts variation in length but assumes amino-acid order is fixed.
D: mistakes the 20 amino acids available for a set that every chain must contain.

Remember: a polypeptide can use a subset of the 20 amino-acid types in different orders and chain lengths.

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. The vacuole confines digestive enzymes with the engulfed particle, separating them from cytoplasmic molecules and reducing unwanted digestion.

A: confuses the vacuole’s role with the increased inner-membrane surface area of mitochondria. B: reverses compartmentalization by spreading the enzymes through the cytoplasm. C: describes a mitochondrial adaptation, not the protective effect of a phagocytic vacuole.

Remember: compartments can keep biochemical processes apart or concentrate their components.

Answer: A. A stem-cell niche can maintain stem cells or promote their proliferation and differentiation; hair follicles are an example of a niche in adult humans.
B: assigns the stem cells’ capacity for continued division and differentiation to the niche.
C: recognizes the niche as a location but wrongly denies its role in maintaining or influencing stem cells.
D: confuses the niche with stem cells, which can differentiate along different pathways.
Remember: distinguish a stem cell’s properties from the function of its niche.

Answer: D. Tidal volume is the change between ordinary expiration and inspiration; inspiratory reserve volume is measured from ordinary inspiration to maximum inspiration; vital capacity is the difference between maximum inspiration and maximum expiration.

• Ordinary breaths range from 2.5 to 3.0 dm³, so tidal volume is 0.5 dm³.
• Inspiratory reserve volume is 5.0 − 3.0 = 2.0 dm³.
• Vital capacity is 5.0 − 1.0 = 4.0 dm³.

A: Confusing inspiratory reserve volume with vital capacity makes the 2.0 dm³ reserve seem to be the capacity. B: Measuring inspiratory reserve from ordinary expiration gives 5.0 − 2.5 = 2.5 dm³. C: Reading the ordinary inspiration peak as tidal volume gives 3.0 dm³ instead of subtracting the expiration level.

Remember: Reserve volumes are measured from the appropriate level of ordinary breathing to a forced maximum.

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.

Answer: B. Photosynthetic nutrition uses light energy to make organic matter from inorganic carbon. Biomass increases only when both light and CO₂ are supplied (+12 mg in 24 h); each other condition gives a decrease. With no organic compounds supplied, this supports photosynthetic nutrition.

A: treats CO₂ as sufficient without light; the dark, CO₂-supplied culture loses biomass.
C: treats light as sufficient without CO₂; the illuminated culture without CO₂ loses biomass.
D: assumes either factor alone is sufficient; both single-factor conditions show biomass loss.
Remember: photosynthetic nutrition uses light energy and an inorganic carbon source.