B1.2 Proteins questions for IB Biology

40 questions on Proteins, 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 B Form and function
SL and HL

Questions by paper and level

SL and HL questions are for students at either level. HL only questions cover what only HL students study.

Paper	SL and HL	HL only	All
Paper 1A	9	11	20
Paper 1B	2	3	5
Paper 2	7	8	15
Every paper	18	22	40

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-00253Paper 1A · 1 mark

Which groups are bonded to the alpha (central) carbon atom of every amino acid?

A
An amine group, a carboxyl group, a phosphate group and an R-group
B
An amine group, a hydroxyl group, a hydrogen atom and an R-group
C
An amine group, a carboxyl group, a hydrogen atom and an R-group
D
A carboxyl group, a hydroxyl group, a hydrogen atom and an R-group

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Question 2 · BIO-00273Paper 1B · 9 marks

Students investigated the effect of temperature on egg albumin, a soluble protein from egg white. Test tubes containing 5 cm³ of a 1 % albumin solution at pH 7 were placed in water baths at seven temperatures for 10 minutes, then cooled to room temperature. Denatured albumin forms insoluble clumps that make the solution cloudy, so the cloudiness of each solution was measured as its absorbance in a colorimeter. There were three tubes at each temperature.

Temperature / °C	Absorbance, tube 1 / AU	Absorbance, tube 2 / AU	Absorbance, tube 3 / AU	Mean absorbance / AU
30	0.02	0.03	0.02	0.02
40	0.03	0.02	0.03	0.03
50	0.04	0.05	0.04	0.04
60	0.21	0.26	0.24	0.24
70	0.68	0.74	0.71	X
80	0.89	0.93	0.92	0.91
90	0.94	0.95	0.92	0.94

(a)
Identify the dependent variable in this investigation.
1 mark
(b)
Calculate the value of X.
1 mark
(c)
Describe the effect of temperature on the absorbance of the albumin solution.
2 marks
(d)
State one variable, other than those mentioned, that should have been kept constant.
1 mark
(e)
Explain the change in absorbance between 50 °C and 80 °C.
3 marks
(f)
Suggest how the method could be improved to find more precisely the temperature at which albumin starts to be denatured.
1 mark

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Question 3 · BIO-00070Paper 2 · 15 marks

Many biological processes depend on the specific shapes of molecules.

(a)
Outline how amino acids are linked together to form polypeptides and why an immense variety of polypeptides is possible.
4 marks
(b)
Explain how the structure of the active site of an enzyme determines its specificity and how denaturation affects this.
7 marks
(c)
Describe how the rate of an enzyme-catalysed reaction changes as substrate concentration increases.
4 marks

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Question 4 · BIO-00254Paper 1A · 1 mark

When two amino acids are linked by a condensation reaction, which atoms form the molecule of water that is released?

A
–OH from the carboxyl group of one amino acid and –H from the amine group of the other
B
–OH from the R-group of one amino acid and –H from the R-group of the other
C
–H from the carboxyl group of one amino acid and –OH from the amine group of the other
D
–OH from the carboxyl group of one amino acid and –H from the alpha carbon of the other

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Question 5 · BIO-00274Paper 1B · HL only · 9 marks

Casein is the main protein in cow's milk. At the normal pH of milk (pH 6.6), casein molecules remain dispersed in the water. Students adjusted 100 cm³ samples of skimmed milk to different pH values by adding hydrochloric acid at 20 °C. After 10 minutes, each sample was centrifuged and the solid precipitate was dried and weighed. Four samples were tested at each pH.

Line graph: mean dry mass of precipitate rises from 0.1 g at pH 6.6 to a peak of 2.6 g at pH 4.6, then falls to 0.5 g at pH 3.0. Error bars ±1 SD. — Error bars show ± one standard deviation.

(a)
State the pH at which the mass of precipitate was greatest.
1 mark
(b)
Calculate the percentage decrease in mean mass of precipitate between pH 4.6 and pH 3.6.
1 mark
(c)
Deduce, with a reason, whether the difference in mass of precipitate between pH 4.6 and pH 4.2 is significant.
1 mark
(d)
At pH 6.6, casein molecules carry a net negative charge. Explain, with reference to the R-groups of amino acids, why casein precipitates when the pH of milk is lowered to about 4.6.
3 marks
(e)
Suggest a reason for the decrease in mass of precipitate below pH 4.2.
2 marks
(f)
Identify one variable, other than those mentioned in the method, that should be controlled.
1 mark

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Question 6 · BIO-00278Paper 2 · 7 marks

Proteins are polymers of amino acids.

(a)
Draw a labelled diagram to show the generalized structure of an amino acid.
3 marks
(b)
State the word equation for the formation of a dipeptide.
1 mark
(c)
Draw the structure of a generalized dipeptide, showing the position of the peptide bond.
2 marks
(d)
State the type of reaction that breaks peptide bonds during the digestion of proteins.
1 mark

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