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CIE iGCSE Co-Ordinated Science B11. Gas exchange in humans Exam Style Questions Paper 3

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Question

(a) Fig. 3.1 is a diagram of the human breathing system.
(i) Identify the parts labelled P and Q in Fig. 3.1.
(ii) On Fig. 3.1 draw a label line and the letter D to identify the diaphragm.
(iii) Complete the sentence to describe aerobic respiration.
Aerobic respiration is the chemical reaction in cells that uses ………………………. to break down nutrient molecules to release energy.
(iv) Some of the energy released by aerobic respiration is used in active transport. State two other uses of the energy released from aerobic respiration in living organisms.
(b) Cystic fibrosis is an inherited condition that affects the gas exchange system.
(i) A person with cystic fibrosis produces thick sticky mucus in their gas exchange system. Their ciliated cells have difficulty moving this sticky mucus.
State one part of the gas exchange system where ciliated cells are found.
(ii) Cystic fibrosis is caused by a recessive allele, f.
        Two people that do not have cystic fibrosis have a child with cystic fibrosis.
    Complete the Punnett square to show why the child has cystic fibrosis.
(iii) Identify if the mother’s genotype in part (b)(ii) is heterozygous or homozygous. Circle the correct answer.
heterozygous       homozygous
Explain your answer.

Most-appropriate topic codes (Cambridge IGCSE Coordinated Sciences 0654):

• Topic B11.1 — Gas exchange in humans (Part (a)(i), (a)(ii), (b)(i))
• Topic B12.1 — Respiration (Part (a)(iii), (a)(iv))
• Topic B16.3 — Monohybrid inheritance (Part (b)(ii), (b)(iii))

▶️ Answer/Explanation

(a)(i) P – rib; Q – alveolus / alveoli
The ribs (P) protect the lungs and move during breathing. Alveoli (Q) are tiny air sacs where gas exchange occurs between air and blood.

(a)(ii) Diaphragm labelled D
The diaphragm is a dome-shaped muscle at the base of the chest cavity that contracts and relaxes to change the volume of the thorax during breathing.

(a)(iii) oxygen
Aerobic respiration requires oxygen as the final electron acceptor in the electron transport chain, allowing complete breakdown of glucose to carbon dioxide and water.

(a)(iv) Any two from: muscle contraction; protein synthesis; cell division; growth; the passage of nerve impulses; the maintenance of a constant body temperature
Energy from respiration is used for many cellular processes including mechanical work, biosynthesis, and maintaining homeostasis.

(b)(i) trachea / bronchi
Ciliated cells line the airways (trachea and bronchi). Their cilia beat to move mucus upwards, removing trapped particles and pathogens.

(b)(ii) Father’s genotype: Ff; Offspring genotypes: FF, Ff, Ff, ff
Both parents must be carriers (Ff) to have a child with cystic fibrosis (ff). The Punnett square shows a 1 in 4 chance of the child inheriting two recessive alleles.

(b)(iii) heterozygous and has two different alleles
The mother’s genotype is Ff, meaning she has one dominant allele (F) and one recessive allele (f), which is the definition of heterozygous.

Question

(a) Fig. 10.1 is a diagram of the gas exchange system in humans.
State the name of the parts labelled A and B in Fig. 10.1.
(b) Table 10.1 compares the composition of two gases in inspired air and expired air.
(i) Calculate the difference between the percentage of gas X in inspired air compared to expired air in Table 10.1.
(ii) Describe the test for gas Y and state the positive result.
(iii) State the name of the chemical reaction that occurs in cells that requires gas X.
(c) The rate of breathing increases during physical activity. State one other change to the pattern of breathing during physical activity.
(d) Pulse rate also increases during physical activity to supply more blood to the muscles. White blood cells are one of the major components of blood.
(i) State two other major components of blood.
(ii) State two functions of white blood cells.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B11.1 — Gas exchange in humans (Parts (a), (b), (c))
• Topic B9.4 — Blood (Part (d))

▶️ Answer/Explanation

(a) A – trachea ; B – diaphragm

The trachea (A) is the airway that carries air from the throat down towards the lungs.
The diaphragm (B) is the sheet of muscle beneath the lungs that contracts and relaxes to help drive breathing movements.

(b)(i) 5%

Gas X (oxygen) makes up 21% of inspired air and 16% of expired air.
The difference is \( 21 – 16 = 5\% \).

(b)(ii) Test: bubble the gas through limewater; Positive result: the limewater turns cloudy

Gas Y is carbon dioxide, which is tested for using limewater (calcium hydroxide solution).
If carbon dioxide is present, the limewater turns from clear to cloudy (milky) due to the formation of insoluble calcium carbonate.

(b)(iii) (Aerobic) respiration

Gas X is oxygen, which is required by cells to carry out aerobic respiration.
During aerobic respiration, oxygen is used to break down glucose to release energy.

(c) Increased depth of breathing

As well as breathing faster during physical activity, a person also breathes more deeply.
This increases the volume of air exchanged with each breath, supplying more oxygen and removing more carbon dioxide.

(d)(i) Any two from: red blood cells; platelets; plasma

Besides white blood cells, blood contains red blood cells, platelets and plasma.
Each of these components has a different role in transport, clotting or carrying blood cells.

(d)(ii) Phagocytosis; antibody production

Some white blood cells (phagocytes) engulf and destroy pathogens by phagocytosis.
Other white blood cells (lymphocytes) produce antibodies that help to destroy or neutralise pathogens.

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