Question

${{C}_{4}}$ plants are more efficient in photosynthesis than ${{C}_{3}}$ plants due to
(a)Lower rate of photorespiration
(b)Higher leaf area
(c)Presence of a larger number of chloroplast in the leaf cells
(d)Presence of thin cuticles.

Answer 1

Hint: The Kranz anatomy is seen in one type of plant resulting in an increased number of chloroplasts in the bundle sheath cell than that of mesophyll cells. The carbon fixation in bundle sheath occurs twice in one type whereas in the other it occurs only once.

Complete answer:
The efficiency of ${{C}_{3}}$ and ${{C}_{4}}$ plants are based on carbon fixation. In ${{C}_{4}}$ plants have enzyme sites to increase the concentration of carbon dioxide with any reaction. The ${{C}_{4}}$ plants have unique anatomy to accumulate carbon dioxide in the bundle sheath cells surrounded by rubisco enzyme whereas the ${{C}_{3}}$ plants don't have a bundle sheath of carbon dioxide.

Additional Information:

${{C}_{4}}$ plants	${{C}_{3}}$ plants
- ${{C}_{4}}$ plants are those where 4-carbon compound product oxaloacetate is synthesized by the carbon fixation.	-Most plants are ${{C}_{3}}$ plants as 3-carbon compound product 3-phosphoglyceric acid is synthesized by the carbon dioxide fixation.
-These plants show high enzymatic activity which is responsible for the decarboxylation of the 4-carbon compound from the xylem and phloem.	-The ${{C}_{3}}$ cycle involves a one-step process where the enzyme RuBisCO causes an oxidation reaction in which some of the energy used in photosynthesis is lost in a process known as photorespiration.
-The first carbon dioxide acceptor is PEP i.e. phosphoenolpyruvate.	-The first carbon dioxide acceptor is RuBp i.e. Ribulose- 1,5 bisphosphate which is 5 carbon compounds.
-In these plants, carbon fixation occurs in bundle sheath.	- In these plants, carbon fixation occurs in mesophyll cells which are present on the surface of the leaf.
- Due to no photorespiration, carbon dioxide fixation is resistant to heat, drought, and high water use efficiency.	- The ${{C}_{3}}$ plant completes the Calvin cycle six times to form ATP to combine a six-carbon molecule of glucose i.e. ${{C_6}{H_{12}}{O_6}}$.

So, the correct answer is ‘lower rate of photorespiration.’

Note: -Plants that exhibit the Calvin cycle in the dark reaction of photosynthesis are known as ${{C}_{3}}$ plants whereas plants that exhibit Hatch- Slack pathway during the dark reaction are called ${{C}_{3}}$ plants.
-Tobacco being a typical ${{C}_{3}}$ plant shows some characteristics of ${{C}_{4}}$ photosynthesis in the cells of stems and petioles that are surrounded by the xylem and phloem which can supply carbon for photosynthesis from vascular tissue instead of stomata.
-Example of ${{C}_{4}}$ plant – Sugarcane, maize, sorghum, amaranth, etc.
-Example of ${{C}_{3}}$ plant – Barley, oats, peanuts, spinach, soybeans, etc.