IB Biology SL Theme B: Form and function questions

Answer: C. In the figure, P joins separate α-glucose monomers into a starch polymer, while Q separates the polymer into monomers. Joining monomers by condensation releases water; hydrolysis uses water to break the polymer apart. Coiling and branching make the polymer compact, while its large molecular size makes it relatively insoluble.

A: reverses the direction of the two processes, so it assigns polymer breakdown to P and polymer building to Q.
B: identifies the processes correctly but reverses their water balance.
D: swaps the structural explanations: coiling and branching account for compactness, while large molecular size accounts for relative insolubility.

Remember: condensation builds glucose polymers and releases water; hydrolysis breaks them down and uses water.

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: D. The concentration of X is lower outside the cell, so inward movement is against its concentration gradient. P transports X but not Y, showing selectivity, and its activity depends on ATP. It therefore acts as a selective pump using ATP for active transport.

A: Confuses active transport with facilitated diffusion, which does not use ATP to move particles against a concentration gradient.
B: Reverses the observed direction of X transport.
C: Treats P as non-selective, although it transports X but not Y.
Remember: pumps use ATP to move specific particles against concentration gradients.

Answer: D. Organelles are discrete cell subunits adapted to perform specific functions; the plasma membrane is classified as an organelle.

A: treats the cytoplasm, which is not an organelle, as a discrete subunit.
B: confuses the cytoskeleton with an organelle; it is not classified as one.
C: treats the cell wall as an organelle, although it is not classified as one.
Remember: the plasma membrane is an organelle, but the cell wall, cytoskeleton and cytoplasm are not.

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. Inspiratory reserve volume is the additional volume that can be inhaled after a normal inspiration.

A: confuses the additional inhalation with tidal volume, the volume moved during a normal breath.
C: reverses the direction; expiratory reserve volume is additional air exhaled after a normal expiration.
D: treats the additional volume as vital capacity, which is the volume moved between maximum inspiration and maximum expiration.
Remember: inspiratory reserve is measured beyond the end of a normal inspiration.

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: B. Hot deserts are characterized by high temperatures and very low rainfall, so the stated climate makes a hot desert likely.

A: adds II by treating high temperature alone as sufficient for tropical forest, despite the very low rainfall.

C: includes II, which requires high rainfall, and III, which is characterized by low temperatures.

D: accepts both tropical forest and tundra; the low rainfall excludes the former, and the high temperatures exclude the latter.

Remember: use both temperature and rainfall to distinguish biomes.

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.