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

Difficulty

Easy Medium Hard

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 2Easy6 marks

A student exposes equal samples of the same enzyme to different conditions for 10 minutes. The student then measures the activity of each sample at pH 7 and 25 °C.

Conditions during exposure	Relative enzyme activity afterwards (% of untreated control)
pH 7, 25 °C (untreated control)	100
pH 7, 80 °C	8
pH 2, 25 °C	12

(a)

State three features of polypeptide chains that allow a wide variety of polypeptides to exist.

[3]

(b)

Use the results in the table.

(i)

Identify the exposure condition that resulted in the lowest enzyme activity.

[1]

(ii)

State the term for the change in protein structure that can be caused by high temperature or extreme pH, and state one effect of this change on enzyme function.

[2]

Question 3

Multiple choiceEasy1 mark

Solutes X and Y each have lower concentrations outside a cell than inside. Membrane protein P transports X into the cell, but not Y; this movement stops when ATP is unavailable. Which description best explains P’s action?

Show answer and explanation

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.

Question 4

Multiple choiceEasy1 mark

Following ultracentrifugation, a researcher tests separated cell components to relate their structures to their functions. Which component should be classified as an organelle?

Show answer and explanation

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.

Question 5

Multiple choiceEasy1 mark

During a spirometry investigation, a student takes a normal breath in and then inhales as much additional air as possible. Which lung volume is represented by the additional volume measured?

Show answer and explanation

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.

Question 6

Paper 2Easy2 marks

A student uses a spirometer to measure the volume of air exhaled during three normal breaths.

Breath	Volume of air exhaled / dm³
1	0.46
2	0.50
3	0.54

(a)

Determine the mean tidal volume.

[1]

(b)

State one change in the diaphragm during inspiration.

[1]

Question 7

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]

Question 8

Multiple choiceEasy1 mark

A terrestrial region has high temperatures throughout the year and very low rainfall in every month. Which statement(s) identify a biome likely to develop there?

I. A hot desert
II. A tropical forest
III. A tundra

Show answer and explanation

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.

Question 9

Paper 2Easy5 marks

A field team records five plant forms in a tropical forest.

Plant	Observation
P	A tree grows until its crown reaches the canopy.
Q	A woody vine rooted in the soil climbs a tree trunk.
R	A plant grows on a branch of a tree.
S	An epiphyte grows on a host tree and later surrounds its trunk.
T	A small herb grows on the shaded forest floor.

(a)

Identify the plant forms represented by Q and R.

[2]

(b)

Identify the plant forms or strategies represented by P, S and T.

[3]

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