IB Biology SL Theme C: Interaction and interdependence 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 cell’s metabolic reactions must occur quickly enough to support its activities. Which role of enzymes provides this benefit?

Show answer and explanation

Answer: D. Enzymes are catalysts that increase the rates of reactions. Faster metabolic reactions can support the activities of the cell.

A: confuses catalysis with increasing the supply of reactants. B: treats enzymes as an energy source rather than catalysts. C: treats enzymes as reactants that are converted into products.

Remember: enzymes increase reaction rates without being used up.

Researchers cultured equal numbers of animal cells with equal supplies of glucose and amino acids, under the same conditions and with oxygen available. For this investigation, enzyme S catalyses condensation reactions that join glucose monomers into glycogen. In a separate test using enzyme S alone, the activity of S was lower when compound X was present.

After 2 hours, mean measurements per culture were:

Treatment	Glucose removed from medium (mg)	Glycogen accumulated (mg)	Protein accumulated (mg)	CO2 released (mg)
Without X	50	18	8	14
With X	50	6	8	22

CO2 released was recorded as an indicator of respiration.

(a)

Define metabolism and explain why many different enzymes are required in cells.

[3]

(b)

For each reaction, state whether it is anabolic or catabolic.

Amino acids joined by condensation to form a protein
Glucose monomers joined by condensation to form glycogen
Protein hydrolysed into amino acids during digestion
Glucose oxidized during respiration

[4]

(c)

A researcher claims that X affects glycogen formation but has no effect on metabolism elsewhere. Evaluate this claim using the enzyme test and all the measurements in the table. State one limitation of the evidence.

[9]

Question 3

Multiple choiceHard1 mark

The schematic shows solute transfer between equal-sized compartments and two interconversions of ATP. Which interpretation correctly describes the energy transfers?

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Answer: D. The solute moves from a compartment with fewer particles to an equal-sized compartment with more particles, so it moves against the concentration gradient and requires energy. At X, ATP is hydrolysed to ADP and phosphate, releasing energy that can drive this transport. At Y, ATP is synthesized from ADP and phosphate, which requires an energy input.
A: reverses the energy changes for both ATP hydrolysis and ATP synthesis.
B: correctly identifies energy release at X but reverses the energy requirement for ATP synthesis.
C: correctly identifies the energy input for ATP synthesis but treats ATP hydrolysis as requiring energy input.
Remember: ATP hydrolysis releases energy; ATP synthesis requires energy.

Question 4

Multiple choiceEasy1 mark

When an impulse reaches a neuron terminal, the presynaptic membrane depolarizes and neurotransmitter is released. Which ion movement acts as the intracellular signal for this release?

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Answer: C. Depolarization of the presynaptic membrane causes Ca²⁺ uptake into the neuron. Ca²⁺ acts as a signalling chemical inside the neuron and promotes neurotransmitter release. A: confuses K⁺ efflux, associated with repolarization, with the signal for neurotransmitter release. B: confuses Na⁺ influx, associated with depolarization, with the ion that signals release. D: reverses the direction: Ca²⁺ enters rather than leaves the presynaptic neuron. Remember: Ca²⁺ entry at the presynaptic membrane signals neurotransmitter release.

Question 5

Paper 2Easy5 marks

A healthy adult’s pineal gland secretes melatonin. The table shows relative melatonin secretion over 24 hours. A student walks along a narrow beam while catching a ball.

Time	Relative melatonin secretion / arbitrary units
08:00	2
14:00	1
20:00	5
02:00	9
08:00 next day	2

(a)

Describe the pattern of melatonin secretion shown in the table.

[1]

(b)

Explain how this pattern helps establish a cycle of sleeping and waking.

[2]

(c)

State two roles of the cerebellum in the student’s movements.

[2]

Question 6

Multiple choiceEasy1 mark

The diagram shows the inputs used by four organisms that synthesize carbon compounds. Which organism is an autotroph?

Show answer and explanation

Answer: C. An autotroph uses an external energy source to synthesize carbon compounds from simple inorganic substances. Organism C receives external light energy and its sole carbon-containing input is CO₂, a simple inorganic substance.

A: treats glucose, an organic carbon source, as a simple inorganic substance.
B: treats amino acids, which are organic, as a simple inorganic carbon source.
D: treats starch, an organic carbon source, as a simple inorganic substance.
Remember: autotrophy depends on the source of carbon, not only on the energy source.

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