IB Biology SL Theme D: Continuity and change 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.

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Question 1

Multiple choiceEasy1 mark

A particular gene is inactive in a non-dividing somatic cell. Which description is consistent with the gene having been switched off at the first stage of gene expression?

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Answer: A. The first stage of gene expression is transcription. When transcription is switched off, no new RNA is transcribed from the gene; using DNA as a template does not change its base sequence.

B: assumes that switching off transcription alters the DNA sequence.
C: confuses switching off transcription with continued transcription while a later stage is inactive.
D: assumes the DNA template is consumed or destroyed rather than used without changing its sequence.

Remember: transcription changes gene expression, not the DNA base sequence.

Question 2

Multiple choiceEasy1 mark

During budding in yeast, a small bud receives much less cytoplasm than the larger cell. Which distribution of mitochondria is expected when the cells separate?

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Answer: D. Cytokinesis can divide cytoplasm unequally, but each daughter cell must receive at least one mitochondrion. The larger cell may receive more mitochondria, but neither cell can receive none. A: assigns all mitochondria to the larger cell, leaving the bud without one. B: reverses that allocation, leaving the larger cell without one. C: assumes mitochondria can be made anew rather than inherited from pre-existing mitochondria. Remember: Unequal cytokinesis does not mean either daughter can lack mitochondria.

Question 3

Multiple choiceEasy1 mark

The figure compares equal-volume samples; each dot represents the same dissolved solute. Which statements are correct?

I. A plant cell in medium P gains water and develops turgor pressure.
II. In medium Q, the plasma membrane pulls away from the cell wall because water enters the plant cell.
III. IV solution R is isotonic to blood-cell contents and is suitable because it causes no net water movement across cell membranes.

Which statements are correct?

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Answer: B. The equal-volume samples show that P has a lower solute concentration than the plant-cell contents, so water enters and turgor pressure develops. Q has a higher solute concentration, so water leaves and the plasma membrane pulls away from the cell wall (plasmolysis). R has the same solute concentration as the blood-cell contents, so it is isotonic and causes no net water movement.

A: omits III; equal concentrations in R indicate an isotonic solution suitable for intravenous use.
C: omits I; the lower solute concentration in P causes water to enter the plant cell.
D: reverses water movement in Q; water leaves the cell, rather than entering it.
Remember: hypotonic media cause water entry; hypertonic media cause plasmolysis.

Question 4

Multiple choiceEasy1 mark

A student traces the route taken by sperm in a male reproductive system diagram. Which structure carries sperm from the epididymis towards the urethra?

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Answer: A. The sperm duct carries sperm from the epididymis towards the urethra.

B: confuses the later passage through which semen leaves the body with the duct that carries sperm from the epididymis.
C: identifies a site of sperm production rather than the structure that transports sperm from the epididymis.
D: confuses a gland that contributes fluid to semen with a sperm-transporting duct.
Remember: sperm travel from the epididymis through the sperm duct towards the urethra.

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