Botany MCQs for NEET — Practice Questions with Answers

(a) : In Krebs cycle, GTP is formed during the conversion of succinyl CoA to succinic acid or succinate. The enzyme required for this reaction is succinyl thiokinase. The phosphorylation in this reaction is substrate level phosphorylation where ATP synthesis is directly linked to the liberation of energy.

(b) In respiraion, from 180gm of glucose 264 gm CO₂+ 108gm H₂O + 686 Kcal energy is formed.

${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6 + 6{\mathrm{O}}_2 \stackrel{ }{\to }6{\mathrm{CO}}_2 + 6{\mathrm{H}}_2\mathrm{O} \mathrm{Kcal}$

Atomic weight of C =12, H = 1, O=16

$$\begin{gathered} {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6 = (12 \times 6 + 12 \times 1 + 16 \times 6) \\ = 180 \mathrm{gm} \\ 6{\mathrm{CO}}_2 = 6(12 + 16 \times 2) \\ = 264 \mathrm{gm} \\ 6{\mathrm{H}}_2\mathrm{O} =6(2 \times 1 + 16) \\ = 108 \mathrm{gm} \\ \therefore \mathrm{From} 1 \mathrm{molecule} \mathrm{or} 180 \mathrm{gm} \mathrm{of} \mathrm{glucose}, \mathrm{through} \\ \mathrm{respiration}, 264 \mathrm{gm} {\mathrm{CO}}_2, 108\mathrm{gm} {\mathrm{H}}_2\mathrm{O} \mathrm{and} 686 \mathrm{Kcal} \mathrm{energy} \mathrm{are} \mathrm{formed}. \end{gathered}$$

(c) : In glycolysis one molecule of hexose sugar (glucose/fructose), a 6C-compound is splitted to form
two molecules of a 3C-compound, pyruvic acid (CH₃COCOOH).

(a) : Glycolysis is the first step of respiration in which glucose is broken down to pyruvate. During glycolysis 1 molecule of glucose is converted to 2 molecule of pyruvic acid in the cytoplasm. These two molecule of pyruvic acid is the converted to acetyl CoA by decarboxylation. This acetyl CoA is the connecting link betwwen glycolysis and Krebs' cycle and functions as substrate entrant for Krebs' cycle. Acetyl CoA thus formed participates in Krebs' cycle and combines with oxaloacetic acid to form citrate.

(c): Oxalosuccinate is decarboxylated to form α-ketoglutarate through the enzyme decarboxylase. It is one of the step involved in Krebs' cycle. It releases one molecule of CO₂.

$\mathrm{Oxalosuccinate} \underset{{\mathrm{Mg}}^{2+}}{\overset{\mathrm{Decarboxylase}}{\to }} \mathrm{\alpha }-\mathrm{ketoglutarate} + {\mathrm{CO}}_2$

Transfer of phosphate group from ATP to a carbohydrate is referred to as phosphorylation and is carried out in presence of phosphorylase enzymes. E.g., glucose (a carbohydrate) is phosphorylated to glucose-6-phosphate by ATP in the presence of enzyme hexokinase or glucokinase and Mg^₂₊ .

(b) The correct sequence of glycolysis is as following

Glucose-6-Phosphate $\to$3-Phosphoglyceraldehyde $\to$3-Phosphoglyceric acid $\to$ Phosphoenol
pyruvate $\to$Pyruvic acid

(C) In glycolysis, water molecule is removed during conversion of 2-phosphoglycerate to phosphoenol pyruvate.

During aerobic respiration, complete oxidation of food takes place. Thus, during it a glucose molecule produces 36 ATP while during fermentation the food oxidises partially and instead of CO₂ + H₂O, formation of ethyl alcohol takes place with production of 2 ATP per glucose molecule.

(c) The ratio of CO₂ formed and O₂ utilised during complete combustion of fuel substances is called respiratory quotient. RQ can be measured by Ganong's respirometer.

           RQ = $\frac{\mathrm{Volume} \mathrm{of} {\mathrm{CO}}_2 \mathrm{evolved}}{\mathrm{Volume} \mathrm{of} {\mathrm{O}}_2 \mathrm{consumed}}$