All Free Biology MCQs with Answers

4031. Type of respiration which involves step by step breakdown of carbon chain molecules in the cell is called:

• A. External respiration
• B. Pulmonary respiration
• C. Cellular respiration
• D. Cutaneous respiration

Explanation: Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), which is used to power various cellular activities. ATP is often referred to as the "energy currency" of the cell. Cellular respiration occurs in three main stages: glycolysis, the citric acid cycle (also known as the Krebs cycle), and oxidative phosphorylation (including the electron transport chain and chemiosmosis).

4032. End products or yeast fermentation, bacterial fermentation, and anaerobic respiration are:

• A. Citric acid, Lactic acid, Carbon dioxide, and Water
• B. Ethyl alcohol, Citric acid, and Carbon dioxide
• C. Ethyl alcohol, Lactic acid, Carbon dioxide, and Water
• D. Methanol, Lactic acid, Citric acid

Explanation: End products or yeast fermentation, bacterial fermentation, and anaerobic respiration are ethyl alcohol, lactic acid, carbon dioxide, and water.

4033. Oxidative phosphoryltion, synthesis of ATP in the presence of oxygen occurs in:

• A. All types of cells
• B. All primitive cells
• C. All anaerobic cells
• D. All aerobic cells

Explanation: Oxidative phosphoryltion, synthesis of ATP in the presence of oxygen occurs in all aerobic cells.

4034. The electrons excited from photo system-II pass directly to:

• A. Ferredoxin
• B. Plastocyanin
• C. Plastoquinone
• D. Carotenoids

Explanation: Plastoquinone is a lipophilic molecule that functions as an electron carrier in the electron transport chain of photosynthesis. It is a quinone derivative and plays a crucial role in transferring electrons from photosystem II (PSII) to the cytochrome b6f complex during the light-dependent reactions of photosynthesis.

4035. All of the following rnembranes are involved in chemiosmosis except:

• A. Plasma Membrane
• B. Thylakoid
• C. Cristae
• D. Mesosome

Explanation: Chemiosmosis is the movement of ions across a semipermeable membrane-bound structure, down their electrochemical gradient. In eukaryotes, it occurs in the mitochondria(cristae) during cellular respiration and in the chloroplasts(thylakoid) during photosynthesis. In prokaryotes, it occurs in mesosomes. Proton gradient is required because the breakdown of this gradient leads to the release of energy. Splitting of water is required which takes place on the inner side of the membrane and the protons that are produced, they accumulate within the lumen of the thylakoids. ATP synthase enzyme is required that allows diffusion of protons back across the membrane, this releases energy to activate the ATPase enzyme which catalyzes the formation of ATP. The closed membrane system is not required. Only a membrane is required for the development of a proton gradient across the membrane of the thylakoid and the proton accumulation is towards the inside of the membrane. So, the correct answer is 'Closed membrane system'.

4036. How many ATP molecules shouId be produced from the complete oxidation of a molecule of active acetate or acetyl CoA?

• A. 38 ATP
• B. 15 ATP
• C. 12 ATP
• D. 19 ATP

Explanation: 12 ATP molecules shouId be produced from the complete oxidation of a molecule of active acetate or acetyl CoA.

4037. The enzyme, which forms glucose -6- phosphate, is:

• A. Phosphorylase
• B. Phosphatase
• C. Hexokinase
• D. Gluco-synthetase

Explanation: Hexokinase is an enzyme that catalyzes the phosphorylation of glucose or other hexoses (six-carbon sugars) to produce hexose phosphate. This phosphorylation is the first step in the process of glycolysis, a central pathway in cellular metabolism that involves the breakdown of glucose to produce energy in the form of ATP.

4038. Inside the stroma of chloroplast, there is a suspended:

• A. Membrane system
• B. Set of enzymes
• C. Membrane system and set of enzymes
• D. Chlorophyll

Explanation: Thylakoid membranes making grana and enzymes associated with photosynthesis, attached to these membranes, are suspended in stroma of chloroplast.

4039. Electron acceptors of photosynthetic electron transport chain are parts of:

• A. Thylakoid membranes
• B. Outer chloroplast membrane
• C. Lamellar membranes
• D. Inner chloroplast membrane

Explanation: Thylakoid membranes sites for cyclic and non-cyclic photophosphorylation.

4040. Chlorophyll and other pigments absorb light energy which is converted into chemical energy of:

• A. NADH and NADPH
• B. ATP and NADPH
• C. ATP and NADH
• D. FADH and NADPH

Explanation: It is assimilatory power (ATP) and reducing power (NADPH) respectively required for dark reaction.