IGCSE Biology Paper-4: Specimen Questions with Answers 129 - 131 of 279

Passage

Plants produce glucose in leaves and convert some of it to sucrose.

Question 129 (4 of 7 Based on Passage)

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Roots can be an example of a sink.

Explain why sometimes roots act as a source rather than a sink.

Explanation

Belowground organs of plants (e. g. roots and rhizomes) are sinks during plant growth since they cannot perform photosynthesis. Some organs are both a source and sink. Leaves are sinks when growing and sources when photosynthesizing. Rhizomes are sinks when growing but become sources in the spring when they provide energy for new growth.

Question 130 (5 of 7 Based on Passage)

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Explain how glucose is produced in leaves.

Explanation

Photosynthesis in plants occurs when a plant gets its energy from light, typically sunlight. Using water and carbon dioxide taken in from the surrounding air, a plant can convert these molecules into glucose and oxygen. The plant then releases oxygen into the air. Glucose, which is a sugar, feeds the plant. There are many uses of glucose in plants. Glucose helps plants grow, form flowers, and develop fruit. It also helps plants develop seeds.

Question 131 (6 of 7 Based on Passage)

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In plants the movement of sucrose is usually continuous. However, after 2 hours the movement of sucrose in tube X in Fig. 30.2 stopped.

Suggest why the movement of sucrose in tube X stopped.

Explanation

This movement of water and sugar molecules will continue until the concentration of entire system becomes uniform and will stop once a state of equilibrium is achieved. But if sugar molecules are either removed or converted into starch, the movement will continue endlessly.

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