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CIE iGCSE Co-Ordinated Science B15.4 Sexual reproduction in humans Exam Style Questions Paper 4

CIE iGCSE Co-Ordinated Science Paper 4 - All Chapters

Question

Organisms are made up of cells, tissues and organs.
(a) The boxes on the left show levels of organisation. The boxes on the right show parts of an organism.
Draw one straight line from each level of organisation to the correct part of the organism.
(b) Fig. 1.1 is a photograph of blood seen under a light microscope.
(i) State the function of the white blood cell labelled in Fig. 1.1.
(ii) State the name of the pigment in red blood cells that binds to oxygen.
(c) Plant leaf cells contain chloroplasts. Red blood cells do not contain chloroplasts.
(i) State the name of the pigment in chloroplasts.
(ii) State two other differences between the structure of a red blood cell and the structure of a plant leaf cell.
(d) Eggs and sperm are specialised cells. Describe how the sperm cell is specialised to:
swim to the egg
penetrate the egg

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

• Topic B2.1 — Cell structure (Part (a), (b)(i), (b)(ii), (c)(i), (c)(ii))
• Topic B15.4 — Sexual reproduction in humans (Part (d))

▶️ Answer/Explanation

(a) Correct matching:

This question tests understanding of biological organisation levels. A lymphocyte is a type of white blood cell, so it is a cell. A ribosome is an organelle found within cells. The lung is a whole organ made of multiple tissues. Intercostal muscles are a type of muscle tissue found between the ribs.

(b)(i) Engulfing pathogens / phagocytosis.

White blood cells (phagocytes) are specialised to engulf and digest pathogens through a process called phagocytosis, helping to defend the body against infection.

(b)(ii) Haemoglobin.

Red blood cells contain haemoglobin, a red pigment containing iron that binds reversibly to oxygen molecules for transport around the body.

(c)(i) Chlorophyll.

Chlorophyll is the green pigment found in chloroplasts that absorbs light energy for photosynthesis.

(c)(ii) Any two from:

  • Red blood cell has no cell wall (plant leaf cell has a cell wall)
  • Red blood cell has no vacuole (plant leaf cell has a large vacuole)
  • Red blood cell has no nucleus (plant leaf cell has a nucleus)

Red blood cells are highly specialised for oxygen transport. They lack a nucleus and most organelles to maximise space for haemoglobin, and they are biconcave discs to increase surface area. Plant leaf cells (palisade mesophyll cells) are specialised for photosynthesis, containing chloroplasts, a cell wall for support, and a large vacuole for maintaining turgidity.

(d) Sperm cell specialisations:

  • Flagellum (tail) to swim to the egg.
  • Enzymes in the acrosome to penetrate the egg.

Sperm cells have a flagellum (tail) containing mitochondria for energy production to enable swimming to the egg. The acrosome at the tip of the sperm head contains digestive enzymes that break down the outer layers of the egg cell, allowing the sperm to penetrate and fertilise it.

Question

(a) Fig. 2.1 is a diagram of the breathing system in humans.
(i) On Fig. 2.1: draw a label line and letter L to identify the larynx, draw a label line and letter B to identify a bronchus.
(ii) Describe two features of the gas exchange surface in humans.
(b)
(i) State the balanced symbol equation for aerobic respiration.
______ + ______ → ______ + ______
(ii) Anaerobic and aerobic respiration occur in the human body.
Describe two ways anaerobic respiration is different from aerobic respiration in the human body.
(c) Fig. 2.2 shows a diagram of the adaptive features of a sperm.
(i) State the function of the part labelled G in Fig. 2.2. 
(ii) Name structure H shown in Fig. 2.2 and state its function.
(iii) The nucleus of the sperm cell is haploid. Describe what is meant by a haploid nucleus.

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

• Topic B11.1 — Gas exchange in humans
• Topic B12.1 — Respiration
• Topic B15.4 — Sexual reproduction in humans

▶️ Answer/Explanation

(a)(i) Larynx labelled L or larynx ; bronchus labelled B or bronchus

The larynx is the voice box located at the top of the trachea, while the bronchi are the two main airways that branch off from the trachea into each lung.

(a)(ii) Any two from:

• large surface area
• thin (surface) / thin wall
• good blood supply
• good ventilation (with air)

These features maximise the efficiency of gas exchange. A large surface area allows more gas to diffuse simultaneously, thin surfaces provide a short diffusion distance, good blood supply maintains concentration gradients, and ventilation ensures fresh air is constantly supplied.

(b)(i) C6H12O6 + 6O2 → 6CO2 + 6H2O
This equation shows glucose being oxidised in the presence of oxygen to produce carbon dioxide and water, releasing energy that is used for life processes.

(b)(ii) Any two from:

• anaerobic does not require oxygen / ORA
• anaerobic produces lactic acid / ORA
• anaerobic releases less energy / ORA
• anaerobic does not produce water or carbon dioxide / ORA

Anaerobic respiration is less efficient than aerobic respiration. It occurs when oxygen is in short supply, resulting in the production of lactic acid and a lower energy yield per glucose molecule.

(c)(i) motility / movement / swimming
The tail (flagellum) of the sperm cell allows it to swim through the female reproductive tract to reach the egg for fertilisation.

(c)(ii) name: acrosome ; function: (contains digestive) enzymes to penetrate the egg
The acrosome is a specialised structure at the tip of the sperm head containing hydrolytic enzymes that break down the outer layers of the egg cell, allowing fusion of the sperm and egg membranes.

(c)(iii) contains a single set of chromosomes
A haploid nucleus contains only one set of chromosomes (23 in humans), unlike diploid cells which contain two complete sets (46 chromosomes). This ensures that when the sperm and egg fuse, the resulting zygote has the correct diploid number.

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