C2.1 Chemical signalling questions for IB Biology

39 questions on Chemical signalling, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.

IB Biology
Part of C Interaction and interdependence
HL only

Questions by paper and level

Paper	Questions
Paper 1A	21
Paper 1B	6
Paper 2	12
Every paper	39

Counted on 10 November 2026

Questions to try

Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.

Question 1 · BIO-01045Paper 1A · 1 mark

Which feature of a receptor allows it to respond to only one type of signalling chemical?

A
It is a phospholipid embedded in the plasma membrane
B
It converts its ligand into a product at the binding site
C
Its binding site has a shape and chemical properties complementary to one ligand
D
It is present in the plasma membrane of every cell in the body

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Question 2 · BIO-01065Paper 1B · 10 marks

The marine bacterium Vibrio fischeri produces light (bioluminescence). In experiment 1, three flasks of liquid medium were inoculated with V. fischeri and kept at 25 °C. Every 2 hours a sample was taken from each flask to measure the cell density and the light emitted (luminescence). The table shows the means of the three flasks.

Time / h	Mean cell density / 10⁷ cells cm^-3	Mean luminescence / arbitrary units
0	0.1	2
2	0.4	3
4	1.6	5
6	5.2	40
8	12.0	650
10	18.5	2400
12	20.1	2600

In experiment 2, a culture at low density (1.6 × 10⁷ cells cm^-3) was divided between two flasks. Synthetic autoinducer dissolved in a solvent was added to one flask, and the same volume of solvent alone was added to the other. Luminescence was measured 30 minutes later. The bar chart shows the means of four repeats (error bars show ± 1 standard deviation).

Bar chart: mean luminescence after 30 min was 5 ± 2 arbitrary units with solvent only and 380 ± 45 with autoinducer added, in low-density V. fischeri cultures.

(a)
Identify the independent variable in experiment 2.
1 mark
(b)
Calculate the luminescence per 10⁷ cells cm^-3 at 4 h and at 10 h in experiment 1.
2 marks
(c)
Describe the relationship between cell density and luminescence in experiment 1.
2 marks
(d)
Explain why solvent alone was added to the second flask in experiment 2.
2 marks
(e)
Explain the results of experiments 1 and 2 in terms of quorum sensing.
3 marks

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Question 3 · BIO-01070Paper 2 · 6 marks

Cells detect signalling chemicals using receptor proteins.

(a)
State the term used for a signalling chemical that binds to a receptor.
1 mark
(b)
Distinguish between transmembrane receptors and intracellular receptors.
3 marks
(c)
Explain why only certain cells in the body respond to a particular hormone.
2 marks

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Question 4 · BIO-01046Paper 1A · 1 mark

The marine bacterium Vibrio fischeri emits light only when its population density is high. What explains this?

A
The autoinducer released by each cell reaches a threshold concentration only when many cells are present, so genes for light production are transcribed
B
Each cell emits light at every population density, but the light is only bright enough to be seen when many cells are close together
C
At high population density the cells are short of oxygen, which switches on the genes for light production
D
Nutrients run out at high population density, so each cell uses the energy released by light production to survive

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Question 5 · BIO-01066Paper 1B · 9 marks

Muscle cells grown in culture were incubated for 20 minutes with insulin at five concentrations, either without or with a drug that inhibits the tyrosine kinase activity of the insulin receptor. The rate of uptake of glucose by the cells was then measured. Each treatment was carried out on five dishes of cells. The error bars show ± 1 standard deviation.

Grouped bar chart: without inhibitor, glucose uptake rises from 12 at 0 to 52 at 10 and 55 at 100 nmol dm−3 insulin

(a)
State the dependent variable in this investigation.
1 mark
(b)
Calculate the percentage increase in glucose uptake between 0 and 10 nmol dm^-3 insulin without the inhibitor.
1 mark
(c)
Discuss whether there is a significant difference in glucose uptake between 10 and 100 nmol dm^-3 insulin without the inhibitor.
2 marks
(d)
Suggest a reason for the uptake of glucose in the absence of insulin.
1 mark
(e)
Explain the effect of the inhibitor on glucose uptake.
3 marks
(f)
State one variable, other than those already given, that should have been kept constant.
1 mark

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Question 6 · BIO-01071Paper 2 · 8 marks

Animals use a wide range of chemical substances as signalling chemicals.

(a)
Identify the chemical group to which each of these signalling chemicals belongs.
Signalling chemical
Chemical group
Epinephrine
Insulin
Oestradiol
Glycine (a neurotransmitter)
2 marks
(b)
Contrast the ways in which hormones and neurotransmitters reach their target cells.
2 marks
(c)
Suggest reasons for animals using many different chemical substances as signalling chemicals.
2 marks
(d)
Outline the role of cytokines as signalling chemicals.
2 marks

Signalling chemical	Chemical group
Epinephrine
Insulin
Oestradiol
Glycine (a neurotransmitter)

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