IGCSE Biology Paper-3: Specimen Questions with Answers 332 - 333 of 358

Passage

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

Dicotyledonous Leaf

Question 332 (1 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.

Question 333 (2 of 4 Based on Passage)

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Describe two ways in which tissue A is adapted for maximum photosynthesis.

Explanation

Palisade Cells

  • The palisade cells are the main site of photosynthesis, as they have many more chloroplasts than spongy mesophylls.
  • Large Vacuole: Restricts chloroplasts to a layer near the outside of the cell where they can be reached by light more easily.
  • Cylindrical Arrangement: They are arranged at right angles to the upper epidermis, reducing the number of light-absorbing cross walls preventing light from reaching the chloroplasts. This also allows long-narrow air spaces between them, providing a large surface area for gaseous exchange.
  • Movement of chloroplasts: Proteins can move the chloroplasts within cells to absorb maximum light.
  • Thin cell walls: to allow gases to easily diffuse through them.
Cylindrical Arrangement

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