IB Biology HL Theme B: Form and function questions

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: 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.