IB Biology SL Theme B: Form and function questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type

Multiple choice Written

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Question 1

Multiple choiceHard1 mark

A plant cell stores starch as represented in the figure. Each hexagon represents one α-glucose monomer; the diagram is schematic and not to scale. Which description correctly identifies P and Q and the structural basis of starch’s storage properties?

Show answer and explanation

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.

Question 2

Paper 2Hard16 marks

Six similar, well-watered potted plants were exposed for 2 h to air at either 40% or 90% relative humidity (RH), with six plants in each condition. Light intensity, temperature and air movement were kept the same. Leaf water loss and xylem pressure potential in the upper stem were measured. Figure 1 shows the experimental arrangement and the individual measurements.

(a)

Using the six measurements in Figure 1B, calculate the mean leaf water loss under each RH condition and the percentage decrease from 40% RH to 90% RH.

[3]

(b)

Using Figure 1C, compare the mean upper-stem xylem pressure potential between the two RH conditions, and relate this comparison to leaf water loss.

[2]

(c)

Explain how water loss from cell walls in the leaf leads to movement of water from roots to leaves in the plant.

[5]

(d)

A student concludes: “Figure 1 proves that xylem tension alone is sufficient to maintain upward water transport; cohesion is unnecessary.”

Evaluate this conclusion using Figure 1 and your knowledge of water transport. Include one limitation of the evidence.

[6]

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