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CIE iGCSE Co-Ordinated Science B7.3 Digestion Exam Style Questions Paper 3

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Question

(a) Fig. 2.1 is a diagram of the human digestive system.
(i) Using letters A–G in Fig. 2.1, identify:
the anus 
the liver 
(ii) Using letters A–G in Fig. 2.1, identify an organ where these processes occur:
absorption 
digestion 
(b) Complete the sentences about digestion.
The breakdown of food into smaller pieces is called …………………… digestion.
This increases the surface area of the food.
The food is then broken down from large …………………… molecules to small …………………… molecules.
This is called …………………… digestion and produces molecules that can be absorbed.
(c) Table 2.1 shows the nutrition label from a bag of rice.
(i) Use Table 2.1 to calculate the percentage of protein in the rice.
(ii) Table 2.1 gives four types of nutrients needed for a healthy diet.
State one other type of nutrient needed for a healthy diet.

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

• Topic B7.2 — Digestive system (Part (a))
• Topic B7.3 — Digestion (Part (b))
• Topic B7.1 — Diet (Part (c))

▶️ Answer/Explanation

(a)(i) the anus: E ; the liver: G
The anus is the terminal opening of the alimentary canal, labelled E in the diagram. The liver is a large organ located above the stomach, labelled G.

(a)(ii) absorption: D or F ; digestion: A or B or F
Absorption of nutrients occurs mainly in the small intestine (D) and also in the large intestine (F). Digestion begins in the mouth (A), continues in the stomach and small intestine, and also occurs in the large intestine (F) where bacteria digest some material.

(b) physical / mechanical ; insoluble ; soluble ; chemical
Physical/mechanical digestion breaks food into smaller pieces, increasing surface area. Chemical digestion breaks down large insoluble molecules into small soluble molecules that can be absorbed through the intestinal wall into the blood.

(c)(i) Percentage of protein = (8.5 ÷ 235) × 100 = 3.6%
To calculate percentage, divide the mass of protein by the total mass of the rice and multiply by 100.

(c)(ii) Vitamins / minerals / water
A balanced diet requires vitamins, minerals (such as calcium and iron), and water in addition to carbohydrates, fats, proteins and fibre.

Question

(a) Fig. 1.1 shows the parts of a human tooth.
(i) State the names of the parts labelled A and B in Fig. 1.1.
(ii) State the type of digestion that teeth are responsible for.
(b) Cavities are holes in the teeth caused by poor care of teeth. A survey records the average number of cavities that 12-year-old school students have in one school. Every five years, the survey is repeated with another group of 12-year-olds in the same school. Fig. 1.2 shows a bar chart of the results.
(i) Calculate the percentage decrease in the average number of cavities between 1985 and 2015 in Fig. 1.2.
(ii) Suggest three reasons for the trend seen in Fig. 1.2.
(c) The mouth has a good supply of blood. List two main components of blood.

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

• Topic B7.3 — Digestion (Part (a))
• Topic B7.3 — Digestion / data interpretation skills (Part (b))
• Topic B9.4 — Blood (Part (c))

▶️ Answer/Explanation

(a)(i) A — enamel; B — pulp (cavity)

Label A points to the hard white outer covering of the crown, which is enamel.
Label B points to the soft central region containing nerves and blood vessels, which is the pulp (cavity).

(a)(ii) Mechanical (physical) digestion

Teeth break food into smaller pieces by a physical/mechanical action.
No chemical change to the food molecules occurs, so this is mechanical (physical) digestion.

(b)(i) Average number of cavities in 1985 = 4.6; in 2015 = 0.8; percentage decrease ≈ 83%

Percentage decrease is calculated using \(\text{percentage decrease} = \dfrac{\text{decrease in value}}{\text{original value}} \times 100\).
Decrease in value \(= 4.6 – 0.8 = 3.8\).
Percentage decrease \(= \dfrac{3.8}{4.6} \times 100 \approx 83\%\).

(b)(ii) Any three from: improved dental care/technology; reduced sugar consumption / more calcium in diet; better dental health education; fluoride added to water/toothpaste

Better access to dentists and modern dental treatments reduces cavity formation.
Lower sugar intake and improved diet reduce the substrate available for cavity-causing bacteria.
Increased public health education and fluoride use (in water or toothpaste) strengthen enamel and improve oral hygiene.

(c) Any two from: red blood cells; white blood cells; plasma; platelets

Blood is made up of four main components.
These are red blood cells, white blood cells, platelets, and plasma.
Any two of these components score full marks.

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