Cambridge IGCSE · Science - Combined (0653)

Biological molecules: Practice Questions

3 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Biological molecules.

8 questions22 marksFree, no account

Question 1

1 mark

Which chemical elements are found in all fat molecules and all protein molecules?

Question 2

1 mark

A pure sample of a biological polymer is found to contain the elements carbon, hydrogen, oxygen, and nitrogen. Which of the following correctly identifies the smaller molecules used to build this polymer and the result of a chemical test on the original polymer?

Question 3

1 mark

A food sample is tested with several reagents, and the results are listed below:
- Benedict’s solution: remains blue after heating
- Biuret reagent: turns from blue to purple
- Iodine solution: remains orange-brown

Which biological molecules are present in this sample?

Question 4

2 marks

List the four chemical elements that make up all protein molecules.

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Question 5

3 marks

Describe the ethanol emulsion test used to detect the presence of fats and oils, including the appearance of a positive result.

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Question 6

5 marks

A scientist analyzes a polymer and determines it is a protein. Identify the specific monomer units used to build this molecule and list the four chemical elements that must be present in its structure.

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Question 7

4 marks

Biological molecules are the building blocks of life.
(a) List the four chemical elements that are found in all protein molecules.
(b) Large biological molecules are made from smaller subunits. Name the smaller molecules that join together to build:
(i) starch
(ii) fats and oils

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Question 8

5 marks

A student is given an unknown liquid sample and must determine which biological molecules it contains.
(a) Describe how the student should test the solution for reducing sugars and state the color observed for a positive result.
(b) To test for fats, the student uses the ethanol emulsion test. Explain the steps of this test and describe the appearance of a positive result.
(c) The student adds iodine solution to a separate sample of the liquid and it remains orange-brown. State what this observation indicates about the contents of the sample.

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