All Free Biology MCQs with Answers

3301. Why is oxygen important for aerobic cellular respiration?

• A. It provides the hydrogen nuclei needed to create a proton gradient in the intermembrane space
• B. It is important in creating oxaloacetic acid in the Krebs cycle
• C. It is needed for glycolysis, which begins the process of respiration in cells
• D. It is the final electron acceptor in the electron transport chain

Explanation: The final electron acceptor in cellular respiration is atmospheric oxygen. It receives electrons and also picks up H+ ions to form water molecules. The energy released by electrons is used for generation of ATP by oxidative phosphorylation.

3302. What is the number of carbon atoms in pyruvic acid?

• A. 8
• B. 2
• C. 3
• D. 4

Explanation: Pyruvic acid has the molecular formula C3H4O3. It has 3 carbon atoms.you can remember it by keeping in mind the fact that one glucose molecule splits into two pyruvic acid molecules in glycolysis. As glucose has 6 C-atoms, each pyruvate should have 3 C-atoms.

3303. The enzyme responsible for carboxylation in the Calvin Benson cycle is?

• A. Pepsin
• B. Rubisco
• C. Isomerase
• D. Peptide

Explanation: Rubisco is the enzyme that catalyzes the fixation of Carbon dioxide in Ribulose Bisphosphate in the Calvin Benson cycle also known as the Calvin Cycle.

3304. The complete oxidation of glucose takes place in:

• A. Alcoholic fermentation
• B. Aerobic respiration
• C. Lactic fermentation
• D. Anaerobic respiration

Explanation: Aerobic respiration takes place in the presence of oxygen and results in the complete oxidation of glucose. On the other hand, anaerobic respiration takes place in the absence of oxygen, and hence glucose is partially oxidized. Alcoholic and lactic fermentation are the two types of anaerobic respiration.

3305. Glycolysis occurs in which part of the cell?

• A. Mitochondria
• B. Golgi bodies
• C. Chloroplast
• D. Cytoplasm

Explanation: The enzymes for glycolysis are present in the cytoplasm so the process occurs in the cytoplasm.

3306. The site of the dark reaction of photosynthesis within chloroplast is:

• A. Grana
• B. Stroma
• C. Frets
• D. Thylakoid

Explanation: The dark or light-independent reaction of photosynthesis occurs in the stroma of the chloroplasts and utilizes carbon dioxide, adenosine triphosphate (ATP), and NADPH.

3307. The net number of ATPs per molecule of glucose during aerobic respiration is:

• A. 30
• B. 36
• C. 38
• D. 40

Explanation: In aerobic respiration, there are two types of phosphorylation: oxidative and substrate-level phosphorylation. Substrate level phosphorylation occurs during glycolysis and Kreb's cycle and leads to the formation of a net of 4 ATP molecules. Oxidative phosphorylation occurs in the inner mitochondrial membrane via the electron transport system and leads to the formation of 32 ATP molecules. Hence, the net number of ATPs formed is 32 + 4 = 36

3308. Which of the following is the "dollar" for the cell?

• A. Chromosome
• B. ATP
• C. DNA
• D. Enzyme

Explanation: ATP is the energy currency of the cell as it can be used to transfer energy from one reaction to another.

3309. Which of the following statement is true about ATP?

• A. ATP is a co-enzyme
• B. ATP is an enzyme
• C. ATP is a prosthetic part of an enzyme
• D. ATP is an organic ion

Explanation: Coenzymes are organic detachable cofactors that are derived from vitamins.ATP, NAD+, and FAD+ are a few examples of coenzyme.

3310. The correct order of electron transfer in photosynthesis is:

• A. H₂O --> NADPH --> Calvin cycle
• B. None of these
• C. H₂O --> O₂ --> NADPH
• D. H₂O --> PS-I --> PS-II

Explanation: 'H₂O --> NADPH --> Calvin cycle' is the correct option as water is first split to form oxygen, hydrogen ions, and electrons. The electrons and hydrogen ions are used to reduce NADP+ to NADPH. This NADPH, which contains the electrons, is then utilized in the calvin cycle to eventually form carbohydrates.