Photosynthesis in ${\mathrm{C}}_4$ plants is relatively less limited by atmospheric ${\mathrm{CO}}_2$ levels because
1. The primary fixation of ${\mathrm{CO}}_2$ is mediated via PEP carboxylase.
2. Effective pumping of ${\mathrm{CO}}_2$ into bundle sheath cells.
3. Four carbon acids are the primary initial ${\mathrm{CO}}_2$ fixation products.
4. RuBisCO in ${\mathrm{C}}_4$ plants has higher affinity for ${\mathrm{CO}}_{2.}$

Which of the following statements is incorrect?
1. RuBisCO is a bifunctional enzyme
2. In C₄ plants, the site of RuBisCO activity is mesophyll cell
3. The substrate molecule for RuBisCO activity is a 5-carbon compound
4. RuBisCO action requires ATP and NADPH 

The first stable product of CO₂ fixation in sorghum is:

In sugarcane plant,${}^{14}\mathrm{CO}_2$ is fixed in malic acid in which the enzyme that fixes ${\mathrm{CO}}_2$ is
1. Ribulose biphosphate carboxylase
2. Phosphoenol pyruvic acid carboxylase
3. Ribulose phosphate kinase
4. Fructose phosphatase

Identify the incorrect statement regarding the enzyme PEP carboxylase:
1. PEP carboxylase has a lower Km for bicarbonate ions, hence, higher affinity — than RuBisCO.
2. ${\mathrm{O}}_2$ is a very poor substrate for this enzyme.
3. It plays an important role in ${\mathrm{C}}_4$ cycle but not in CAM plants.
4. PEP carboxylase is also significant in non-photosynthetic metabolic pathways.

Radioactive carbon [${}^{14}\mathrm{C}$] was fed to a plant during the day and after a short time was traced to oxaloacetate. The plant used in the experiment will be:

${\mathrm{C}}_4$ plants are able to photosynthesize with no apparent photorespiration because of:
1. absence of Calvin cycle.
2. use of PEP carboxylase for primary carbon dioxide fixation.
3. absence of RuBisCO.
4. presence of tissues that do not require oxygen.

Identify the incorrect comparison between C₃ and C₄ photosynthetic plants:

Consider the two statements:

I. The C₄ photosynthesis pathway uses more energy than the C₃ photosynthesis pathway.
II. C₄ plants are able to more efficiently fix carbon in drought, high temperatures, and in limitations of nitrogen or CO₂.

1. Both I and II are correct and II explains I
2. Both I and II are correct but II does not explain I
3. Only I is correct
4. Both I and II are incorrect