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CIE iGCSE Co-Ordinated Science B3.1 Diffusion Exam Style Questions Paper 4

CIE iGCSE Co-Ordinated Science Paper 4 - All Chapters

Question

(a) Fig. 4.1 shows a cross-section of a leaf.
(i) State the letter in Fig. 4.1 that identifies the cells that control loss of water vapour from a leaf.
(ii) State the names of the parts labelled A and B in Fig. 4.1.
(iii) Describe two ways in which the part labelled G in Fig. 4.1 is adapted for photosynthesis.
(b) Carbohydrates produced by photosynthesis are transported to areas of the plant described as sinks.
(i) Describe how the carbohydrates are transported to the sinks.
(ii) State two uses of carbohydrates in sinks.
(c) Carbon dioxide diffuses into a leaf during gas exchange.
State two factors which increase the rate of diffusion during gas exchange.

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

• Topic B6.2 — Leaf structure (Part (a))
• Topic B8.4 — Translocation (Part (b))
• Topic B3.1 — Diffusion (Part (c))

▶️ Answer/Explanation

(a)(i) D

D identifies the guard cells in Fig. 4.1.
Guard cells control the opening and closing of the stomata, regulating water vapour loss.

(a)(ii) A – (upper) epidermis; B – cuticle

A is the upper epidermis, the outer protective layer of cells.
B is the waxy cuticle that covers the epidermis and reduces water loss.

(a)(iii) any two from: contains lots of chloroplasts; located at the top of the leaf; tightly packed/column shaped

The palisade mesophyll (G) contains many chloroplasts to absorb light efficiently.
The cells are positioned near the top of the leaf and are tightly packed and column-shaped, maximising light capture for photosynthesis.

(b)(i) as sucrose, by translocation, in the phloem

Carbohydrates are converted to sucrose for transport.
They are moved through the phloem tissue by the process of translocation, from the source (leaf) to the sinks.

(b)(ii) any two from: storage; respiration; growth

Carbohydrates delivered to sinks may be used for respiration to release energy.
They may also be used for growth or converted to starch for storage.

(c) any two from: increased surface area; increased temperature; steeper concentration gradient; shorter diffusion distance

A larger surface area or a steeper concentration gradient increases the rate of diffusion.
A higher temperature and a shorter diffusion distance also speed up the diffusion of carbon dioxide into the leaf.

Question

(a) A student investigates the effect of temperature on the rate of diffusion of red dye into agar jelly cubes.
The student prepares three cubes of agar jelly A, B and C. 

  • Each cube is equal in size.
  • A is kept at 30 °C, B is kept at 25 °C, C is kept at 20 °C.
  • Three separate containers of red dye are also kept at 30 °C, 25 °C and 20 °C.
  • Each cube is immersed in red dye equal to its temperature for 10 minutes.
  • The cubes are then removed from the dye and cut in half.

Fig. 7.1 shows the cubes cut in half.

Table 7.1 shows the results.

(i) Calculate the rate of diffusion for cube A.

▶️Answer/Explanation

0.10 cm per min

Calculation: Rate = Diffusion distance/Time = 1.0 cm/10 min = 0.10 cm/min
Experimental observation: The higher temperature (30°C) shows fastest diffusion, consistent with kinetic theory.

(ii) Use the results in Table 7.1 to describe the relationship between temperature and the rate of diffusion.

▶️Answer/Explanation

As temperature increases, the rate of diffusion increases (positive correlation).

Scientific explanation: 1. Higher temperature → greater kinetic energy of dye molecules
2. More frequent and energetic collisions
3. Faster net movement from high to low concentration

(iii) State one variable, other than the size of the cubes, that should be kept constant in this investigation.

▶️Answer/Explanation

Possible answers: • Concentration of red dye
• Immersion time (10 minutes)
• Type of agar jelly
• pH of the solution

Control importance: Keeping these constant ensures only temperature affects results (fair test).

(b) Explain why the red dye diffuses into the agar jelly.

▶️Answer/Explanation

1. Concentration gradient exists (high dye concentration outside → low inside jelly)
2. Dye molecules move randomly (Brownian motion)
3. Net movement down concentration gradient until equilibrium

Molecular level: Dye particles collide with agar pores and gradually spread through available spaces.

(c) Materials diffuse in and out of living cells. Name the gas produced by respiration that diffuses out of cells. 

▶️Answer/Explanation

Carbon dioxide (CO2)

Biological context: This waste product of aerobic respiration moves from high concentration in cells to lower concentration in blood/capillaries.

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