INTRODUCTION - Chapter 13 Photosynthesis In Higher Plants class 11 ncert solutions Biology - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 1:

By looking at a plant externally can you tell whether a plant is C₃ or C₄? Why and how?

Answer:

One cannot distinguish whether a plant is C₃ or C₄ by observing its leaves and other morphological features externally. Unlike C₃ plants, the leaves of C₄ plants have a special anatomy called Kranz anatomy and this difference can only be observed at the cellular level. For example, although wheat and maize are grasses, wheat is a C₃ plant, while maize is a C₄ plant.

Question 2:

By looking at which internal structure of a plant can you tell whether a plant is C₃ or C₄? Explain.

Answer:

The leaves of C₄ plants have a special anatomy called Kranz anatomy. This makes them different from C₃ plants. Special cells, known as bundle-sheath cells, surround the vascular bundles. These cells have a large number of chloroplasts. They are thick-walled and have no intercellular spaces. They are also impervious to gaseous exchange. All these anatomical features help prevent photorespiration in C₄ plants, thereby increasing their ability to photosynthesise.

Question 3:

Even though a very few cells in a C₄ plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?

Answer:

The productivity of a plant is measured by the rate at which it photosynthesises. The amount of carbon dioxide present in a plant is directly proportional to the rate of photosynthesis. C₄ plants have a mechanism for increasing the concentration of carbon dioxide. In C₄ plants, the Calvin cycle occurs in the bundle-sheath cells. The C₄ compound (malic acid) from the mesophyll cells is broken down in the bundle-sheath cells. As a result, CO₂ is released. The increase in CO₂ ensures that the enzyme RuBisCo does not act as an oxygenase, but as a carboxylase. This prevents photorespiration and increases the rate of photosynthesis. Thus, C₄ plants are highly productive.