IGCSE Biology Paper-3: Specimen Questions with Answers 333 - 334 of 358

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Passage

Fig. shows a diagram of a cross-section of a dicotyledonous leaf, as seen using a light microscope.

Dicotyledonous Leaf

Question 333 (2 of 4 Based on Passage)

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Plants use carbon dioxide for photosynthesis.

(i) Describe where and how carbon dioxide enters a leaf.

(ii) State the two products of photosynthesis in green plants.

Explanation

  • On the surface of the leaves of the plants there are many tiny pores known as stomata or stoma. For photosynthesis green plants take carbon dioxide from the air. The carbon dioxide enters the leaves of the plant through the stomata present on their surface. Each stomatal pore is surrounded by a pair of guard cells. The opening and closing of the pores of stomata is controlled by the guard cells only. When water flows into the guard cells, they swell, become curved and cause the pore to open. On the other hand, the guard cells lose water; they shrink, become straight and close the stomatal pore.
  • Photosynthesis is the name given to the set of chemical reactions performed by plants to convert energy from the sun into chemical energy in the form of sugar. Specifically, plants use energy from sunlight to react carbon dioxide and water to produce sugar (glucose) and oxygen.

Question 334 (3 of 4 Based on Passage)

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Hydrophytes are plants that grow in water. Fig. B. shows a photograph of Indian lotus, Nelumbo nucifera, which is a hydrophyte.

T. S. Dicot Leaf

Describe and explain two adaptations of hydrophytes to their environment.

adaptation …

explanation …

adaptation …

explanation …

Explanation

Hydrophytes are plants that have adapted to life in very wet places. So much so that they only live on or in water. You can remember hydrophytes for the ‘hydro-’ part of their name, meaning ‘water.’ Hydrophytes like the water lily have little to no root system, unlike land plants, because roots simply aren՚t as necessary since water is so readily available.

Most leaves in hydrophytes are thin, and many can float freely. The part of plants that allow for gas exchange, called the stomata, are located only on the part of the plant surface that՚s exposed to air. Finally, underwater plants will often lack stomata since they no longer need to exchange gases with the atmosphere anymore. They instead exchange gases with the water they live in.

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