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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Multiple choice Written

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Question 1

Paper 2Hard16 marks

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 2

Paper 2Medium16 marks

Researchers cultured equal numbers of the same type of animal cell under identical conditions, supplying a different carbon compound to each group. They measured the rates of ATP synthesis and oxygen uptake.

Carbon compound supplied	ATP synthesis rate (relative units min⁻¹ per 10⁶ cells)	Oxygen uptake rate (µmol min⁻¹ per 10⁶ cells)
None added	2.0	1.0
Glucose	8.0	4.0
Fatty acids	6.0	5.0

(a)

Calculate the percentage increase in ATP synthesis rate when glucose is supplied compared with when no carbon compound is added. Show your calculation.

[3]

(b)

State which of glucose or fatty acids gives the higher ATP synthesis rate, and state the difference between their rates.

[2]

(c)

Explain how energy from cell respiration can be transferred to active transport through the interconversion of ATP and ADP.

[4]

(d)

Distinguish between gas exchange and cell respiration.

[2]

(e)

A student claims that oxygen uptake is a direct measure of the rate of ATP synthesis. Evaluate this claim using the data, and identify two limitations of the evidence.

[5]

Question 3

Paper 2Medium16 marks

An electrical impulse was initiated at a point on the axon of a neuron. Detectors recorded the time at which the impulse reached different distances along the same axon. Figure 1 shows the results. Times and distances were recorded to the nearest 0.1 ms and 0.1 cm, respectively.

(a)

State what forms the cell body of a neuron, and give two differences between an axon and dendrites.

[3]

(b)

Use Figure 1 for parts (i) and (ii).

(i)

Describe the relationship between distance from the stimulation point and time of detection shown in Figure 1.

[2]

(ii)

Determine the average speed of the impulse along the axon. Give your answer in m s⁻¹.

[3]

(c)

Use the best-fit line in Figure 1 to estimate the time at which the impulse would be detected 7.0 cm from the stimulation point.

[2]

(d)

Explain how the arrangement of a neuron’s fibres can enable it to conduct impulses over long distances and along multiple branches.

[3]

(e)

A student concludes that Figure 1 proves that all neurons conduct electrical impulses at the same speed. Evaluate this conclusion using Figure 1.

[3]

Question 4

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 5

Paper 2Medium16 marks

A group of 100 people with HIV was followed from the time their infection was confirmed. Researchers recorded the mean count of a particular type of lymphocyte and the percentage of participants who had at least one opportunistic infection.

Years after HIV infection was confirmed	Mean lymphocyte count (cells per μL)	Participants with at least one opportunistic infection (%)
0	900	2
3	690	6
6	420	24
9	180	50

(a)

Calculate the percentage decrease in mean lymphocyte count between year 0 and year 9.

[3]

(b)

Describe the changes in both measurements between year 0 and year 9, using the data.

[4]

(c)

Identify the type of lymphocyte infected by HIV and state what HIV does to these cells.

[2]

(d)

Explain how the decline in these lymphocytes can lead to AIDS.

[3]

(e)

Explain two mechanisms by which HIV can be transmitted in body fluids: one involving blood and one during sexual intercourse.

[4]

Question 6

Paper 2Medium16 marks

Two rabbit populations were monitored in separate fenced grassland enclosures, each with an area of 2.0 ha. The enclosures had similar vegetation and water supplies. At year 0, each enclosure contained 20 rabbits. From year 1 onwards, supplementary food was added to enclosure B each year; no supplementary food was added to enclosure A. Other management was kept the same.

Year	Rabbits in enclosure A	Rabbits in enclosure B
0	20	20
1	39	44
2	55	67
3	65	85
4	70	96
5	69	101
6	71	99

(a)

Calculate the approximate rabbit population density at carrying capacity in enclosure A. Give your answer with a unit.

[2]

(b)

Describe the changes in rabbit population size in enclosures A and B over the seven years.

[3]

(c)

Define carrying capacity and give two examples of resources that may limit it.

[3]

(d)

Explain how competition for limited resources affects a rabbit population as it approaches carrying capacity.

[4]

(e)

Use the data to explain what the comparison between enclosures A and B suggests about the effect of food availability on carrying capacity. State one limitation of this comparison.

[4]

Question 7

Paper 2Medium3 marks

A bacterial culture was grown in darkness in a medium in which carbon dioxide was the only source of carbon. The same amount of iron was supplied in each culture, but in different forms. All other conditions were identical.

Form of iron supplied	Change in bacterial biomass after 48 hours
Iron(II) compounds	Increase
Iron(III) compounds	No increase

(a)

Classify these bacteria as photoautotrophs or chemoautotrophs.

[1]

(b)

Explain how the bacteria can produce carbon compounds in the condition where biomass increased. Refer to both the carbon source and the energy source.

[2]

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