IB Biology SL Theme B: Form and function questions

Answer: B. Polypeptides with the same amino-acid composition can differ when their amino acids are in a different order. A large pH change or high temperature could cause denaturation, changing protein structure.

A: treats composition as sufficient to identify a polypeptide, overlooking amino-acid order.
C: confuses a change in protein structure with a change in amino-acid sequence.
D: assumes structure cannot change unless the amino-acid order changes.

Remember: amino-acid order distinguishes polypeptides, while denaturation changes protein structure.

Answer: C. Gene G is expressed only where the signal concentration exceeds 6 arbitrary units. Regions W and X have concentrations of 8 and 7, so their cells express gene G and differentiate into type P. Regions Y and Z are below the threshold and differentiate into another type.

A: considers only the region with the highest concentration, overlooking that X also exceeds the threshold.
B: reverses the effect of the signal by assigning type P to regions below the threshold.
D: assumes all regions have the same gene expression and fate despite their different signal concentrations.

Remember: a gradient can lead to different gene-expression patterns and cell fates in an early embryo.

Answer: B. Water loss from leaf-cell walls draws water out of the xylem through the cell walls, increasing tension (making the pressure potential more negative). Cohesion keeps water molecules connected in a continuous column, allowing this tension to draw water upward.

A: reverses the direction of water movement, so it incorrectly predicts reduced tension.
C: has the correct movement and tension but reverses the role of cohesion.
D: gets the water movement right but reverses the pressure change; tension is negative pressure potential.

Remember: transpiration creates tension, while cohesion maintains the continuous water column.

Answer: C. The reference skulls associate a lower molar-area index with omnivory and a higher index with herbivory. The index for Homo floresiensis (1.3) is nearer the omnivorous reference (1.2), while that for Paranthropus robustus (2.3) is nearer the herbivorous reference (2.4).

A: reverses the relationship between the index and the reference diets.
B: correctly associates Paranthropus robustus with the herbivorous reference but assigns the lower-index Homo floresiensis to herbivory.
D: correctly associates Homo floresiensis with the omnivorous reference but assigns the higher-index Paranthropus robustus to omnivory.
Remember: comparisons with observed living species can support, but do not prove, dietary inferences from fossil dentition.