Question 1

Q1: By looking at a plant externally, can you tell whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$? Why and how?

Accepted Answer

No, it is generally not possible to definitively tell whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$ just by looking at its external features. The key differences between these plants are anatomical and physiological, not morphological. Reasoning: 1.  Anatomical Differences: The primary dis...

Question 2

Q2: By looking at which internal structure of a plant you can tell whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$? Explain.

Accepted Answer

One can tell whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$ by observing the internal structure of its leaf, specifically the arrangement of cells around the vascular bundles. This is known as leaf anatomy. The key internal structure is the 'Kranz' anatomy, which is present in $\mathrm{C}_{...

Question 3

Q3: Even though a very few cells in a $\mathrm{C}_{4}$ plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss...

Accepted Answer

Yes, $\mathrm{C}_{4}$ plants are highly productive despite the Calvin pathway being restricted to the bundle sheath cells. The high productivity is due to their highly efficient mechanism for $\mathrm{CO}_{2}$ fixation which minimizes a wasteful process called photorespiration. Reasons for High Prod...

Question 4

Q4: RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in $\mathrm{C}_{4}$ plants...

Accepted Answer

RuBisCO (Ribulose-1,5-bisphosphate carboxylase-oxygenase) carries out more carboxylation in $\mathrm{C}_{4}$ plants because they have a mechanism that increases the concentration of carbon dioxide at the enzyme's active site. Explanation: 1.  Competitive Binding: The active site of RuBisCO can bind...

Question 5

Q5: Suppose there were plants that had a high concentration of Chlorophyll b, but lacked chlorophyll a, would it carry out photosynthesis? Then why do pla...

Accepted Answer

Part 1: Photosynthesis without Chlorophyll a No, a plant that lacked chlorophyll a would not be able to carry out photosynthesis. Chlorophyll a is the essential, primary photosynthetic pigment. It functions as the reaction centre in both Photosystem I (P700) and Photosystem II (P680). It is the only...

Question 6

Q6: Why is the colour of a leaf kept in the dark frequently becomes yellow, or pale green? Which pigment do you think is more stable?

Accepted Answer

When a leaf is kept in the dark, it becomes yellow or pale green because the chlorophyll pigments degrade, and the more stable yellow and orange accessory pigments become visible. Explanation:    Chlorophyll Synthesis and Degradation: Chlorophyll molecules are not permanent. They are continuously be...

Question 7

Q7: Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunligh...

Accepted Answer

Observation: The leaves on the shady side (or plants kept in the shade) are darker green compared to the leaves on the sunny side. Reason: Leaves adapt to the amount of light they receive to maximize photosynthesis. The darker green color is due to a higher concentration of chlorophyll. 1.  Low Ligh...

Question 8

Q8: Figure 11.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions: (a) At which point/s (A, B o...

Accepted Answer

(a) Light is a limiting factor in the region of the curve where the rate of photosynthesis increases with an increase in light intensity. This is represented by region A. At point A, the rate is directly proportional to the light intensity. (b) In region A, the rate of photosynthesis is directly lim...

Question 9

Q9: Give comparison between the following: (a) $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ pathways (b) Cyclic and non-cyclic photophosphorylation (c) Anatomy o...

Accepted Answer

(a) Comparison between $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ pathways | Feature | $\mathrm{C}_{3}$ Pathway | $\mathrm{C}_{4}$ Pathway | | :--- | :--- | :--- | | Primary $\mathrm{CO}_{2}$ Acceptor | RuBP (Ribulose-1,5-bisphosphate), a 5-carbon compound. | PEP (Phosphoenolpyruvate), a 3-carbon compoun...

NCERT Solutions