iGCSE Biology (0610)-8.4 Translocation - iGCSE Style Questions Paper 4

Question

(a) Fig. 4.1 is a photograph of a tree that has been girdled.

Girdling involves removing a complete circle of bark and phloem from around the tree.

(i) Explain why the area above the girdle in Fig. 4.1 will become swollen.
Use the terms source and sink in your answer.

(ii) Explain why the leaves in girdled trees are still able to receive mineral ions from the roots.

(b) Explain why glucose made during photosynthesis is required for the absorption of mineral ions by the roots.

▶️ Answer/Explanation

Solution

(a)(i) The area above the girdle swells because:

Translocation is interrupted when the phloem is removed.
Leaves (source) produce glucose via photosynthesis, which is converted to sucrose.
Sucrose and amino acids are transported via the phloem to the roots (sink).
Since the phloem is cut, sucrose accumulates above the girdle, causing swelling.

Explanation: The swelling occurs due to the buildup of organic compounds that can no longer be transported downward to the roots.

(a)(ii) The leaves still receive mineral ions because:

The xylem remains intact (located deeper in the trunk).
Xylem transports water and dissolved mineral ions upward from roots to leaves.

Explanation: Girdling only removes the phloem (outer layer), leaving the xylem functional for upward transport.

(b) Glucose is required because:

It fuels aerobic respiration in root cells, producing ATP.
ATP provides energy for active transport of mineral ions.
Active transport moves ions against their concentration gradient (from low to high concentration).

Explanation: Without glucose, roots lack energy to absorb essential minerals efficiently.

(c) The balanced equation for photosynthesis is:

\[ 6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2 \]

Explanation: Carbon dioxide and water (in the presence of light and chlorophyll) produce glucose and oxygen.

Question

Aphids are arthropods.

Aphids insert their mouthpieces into the phloem in the stem of a plant to feed.
An aphid is shown in Fig. 2.1.

(a) (i) Identify two features visible in Fig. 2.1 that can be used to classify an aphid as an insect.

Fig. 2.2 is a diagram of a cross-section of a dicotyledonous stem.

(ii) State the letter in Fig. 2.2 that identifies the structure from which aphids feed.

(iii) State the names of two nutrients transported in the phloem.

(b) Scientists investigated the effect of temperature on the rate of translocation.
The data are shown in Table 2.1.

Calculate the percentage change in rate of translocation between 15 °C and 30 °C.
Give your answer to three significant figures.

(c) Fig. 2.3 shows a potato plant growing in the spring and then in the summer.

(i) Explain how translocation changes between spring and summer in the potato plant shown in Fig. 2.3.
Use the terms source and sink in your answer.

(ii) New tubers form on the potato plant in the summer. These tubers are genetically identical.
Identify the type of reproduction that the potato plant is using to form the tubers.

▶️ Answer/Explanation

Solution

(a)(i)
1: Three pairs of legs (insects have six legs).
2: One pair of antennae (used for sensing the environment).

(a)(ii)
M (phloem is labeled as M in Fig. 2.2, where aphids feed).

(a)(iii)
1: Sucrose (main carbohydrate transported in phloem).
2: Amino acids (organic nitrogen compounds for growth).

(b)
Percentage change = \(\left(\frac{4.7 – 2.0}{2.0}\right) \times 100 = 134\%\) (to 3 s.f.).
Calculation: Rate increases from 2.0 to 4.7, yielding a 134% rise.

(c)(i)
Spring: Tubers (sink) release stored sucrose to shoots (source) for growth.
Summer: Leaves (source) photosynthesize, sending sucrose to new tubers (sink) for storage.

(c)(ii)
Asexual reproduction (tubers are clones via vegetative propagation).

iGCSE Biology (0610)-8.4 Translocation – iGCSE Style Questions Paper 4

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