All Free Biology MCQs with Answers

3551. In the journey of electrons from photosystem II to photosystem I plastocyanin is reduced by:

• A. Plastoquinone
• B. Cytochrome complex
• C. P700
• D. Primary electron acceptor of PS1

Explanation: Plastocyanin is reduced when it accepts an electron from the cytochrome b6f complex, and this electron reduces the copper ion in plastocyanin from Cu²⁺ to Cu⁺. This process is essential for transferring electrons between photosystem II and photosystem I in the electron transport chain of photosynthesis.

3552. Enzyme NADP reductase is responsible for:

• A. Reducing NADP+
• B. Oxidizing NADP+
• C. Reducing Ferredoxin
• D. Reducing P700

Explanation: NADP reductase is an enzyme that plays a key role in the light-dependent reactions of photosynthesis. It is responsible for transferring electrons from ferredoxin to NADP+, reducing it to NADPH.

3553. The PS II, during light reaction,s receives electrons from splitting:

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

Explanation: Water is the true source of electrons for PS II, where photolysis (splitting of water) provides the electrons to start the chain.

3554. How much energy is present in the chemical bond of glucose that is converted into ATP by anaerobic respiration?

• A. 2%
• B. 4%
• C. 10%
• D. 36%

Explanation: Option A is the correct option because This is the accurate estimate for energy conserved as ATP in anaerobic respiration. The rest of the energy remains in the end products (like lactate or ethanol) as they are not fully broken down.

3555. Which one of the following is the end product in electron transport chain taking place at inner mitochondrial membrane?

• A. Carbon dioxide
• B. NADPH
• C. Oxygen
• D. Water

Explanation: The end product of the electron transport chain (ETC) in the inner mitochondrial membrane is water (H₂O). In the final step, oxygen acts as the terminal electron acceptor, combining with electrons and protons to form water. This process also contributes to the generation of ATP through oxidative phosphorylation.

3556. At which of the following reactions of glycolysis, ATP is NOT involved directly?

• A. When 1,3-bisphosphoglycerate is converted into 3-phosphoglycerate
• B. When fructose 6-phospate is converted into fructose 1,6-bisphosphate
• C. When glucose is converted into glucose 6- phosphate
• D. When glyceraldehyde 3-phosphate is converted into 1,3-bisphosphoglycerate

Explanation: ATP is not directly involved in the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in glycolysis.

3557. In Cyclic Photophosphorylation, which one of the following processes of light dependent reaction, of photosynthesis is NOT included?

• A. Absorption of light
• B. ATP synthesis
• C. Photoexcitation
• D. Photolysis of water

Explanation: Photolysis of water occurs only in non-cyclic photophosphorylation, where water is split to release electrons, protons, and oxygen.

3558. Which one of the following types of phosphorylation occurs in electron transport chain, when NADH transfer electrons to coenzyme Q in inner mitochondrial membrane?

• A. Cyclic Phosphorylation
• B. Non-cyclic Phosphorylation
• C. Oxidative Phosphorylation
• D. Substrate level Phosphorylation

Explanation: ATP generation in the mitochondria's electron transport chain, where electrons move through complexes, ultimately combining with oxygen to form water is called oxidative phosphorylation.

3559. Which one of the following is the first electron accepter from FADH2 during electron transport chain?

• A. Coenzyme Q
• B. Cytochrome a
• C. Cytochrome b
• D. Cytochrome c

Explanation: Coenzyme Q, also known as ubiquinone, is a lipid-soluble molecule in the electron transport chain located in the inner mitochondrial membrane. It transports electrons from Complex I and Complex II to Complex III, acting as a mobile electron carrier. Coenzyme Q also plays a role in maintaining the proton gradient across the membrane, which drives ATP synthesis. Its antioxidant properties further protect cells from oxidative damage.

3560. What is the range of carbon dioxide in the air?

• A. 0.003-0.004%
• B. 0.03-0.04%
• C. 0.3-0.4%
• D. 3-4%

Explanation: The correct answer is Option B:0.03-0.04%. The range of carbon dioxide in the air is typically around 0.03-0.04%. Options A, C, and D are incorrect because they either have the decimal point in the wrong place or are off by a factor of 10.