All Free Biology MCQs with Answers

3591. Coenzyme Q is oxidized by which coenzyme in the ETC?

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

Explanation: Coenzyme Q is oxidized by Cytochrome b in the electron transport chain (ETC). Coenzyme Q is a mobile electron carrier in the ETC and it transfers electrons between complexes lll and lV, facilitating the transfer of electrons from Complex lll to Complex lV.

3592. ATP is used:

• A. To synthesize the macromolecules
• B. To transport of molecules and ions
• C. To perform mechanical work
• D. All of above

Explanation: ATP is the energy currency of the cell, meaning it can be broken down to release energy when needed by the body. All the functions mentioned require energy and thus ATP.

3593. A 25 years old female with chronic fatigue was diagnosed with iron deficiency anemia and low blood count. What is the cause of her fatigue?

• A. Reduction in amount of Fe-S centers
• B. Lowered production of water from the electron transport chain that cause dehydration
• C. iron is important for electron transport chain
• D. Iron is important for NADH production

Explanation: Iron and copper are essential nutrients for all living organisms as cofactors of many enzymes and play important roles in electron transport system (ETS) enzymes which have heme and iron-sulfur centers.

3594. The dark reaction in photosynthesis where sugars are synthesized are called?

• A. Krebs cycle
• B. Calvin Cycle
• C. Galvin cycle
• D. Glycolysis

Explanation: The dark reaction in photosynthesis, where sugars are synthesized, is known as the Calvin Cycle or the light-independent reactions. Despite the name "dark reaction," the Calvin Cycle does not require direct light; however, it relies on the products of the light-dependent reactions. During the Calvin Cycle, carbon dioxide is fixed and reduced to produce carbohydrates, particularly glucose. The key steps of the Calvin Cycle include carbon fixation, reduction, regeneration of the starting molecule, and the eventual synthesis of sugars. This process takes place in the stroma of chloroplasts, and it utilizes the ATP and NADPH produced during the light-dependent reactions to drive the chemical reactions leading to the formation of glucose and other organic molecules.

3595. What percentage of the leaf surface does stomata cover?

• A. 10 %
• B. 50 %
• C. 1-2 %
• D. 0.3 to 0.4 %

Explanation: Option C is correct since stomata are the microscopic pores on leaf surfaces that facilitate gas exchange with the atmosphere, namely, CO2, O2, and H2O, and cover 1-2 % of the leaf surface.

3596. Out of the six molecules of G3P, how many molecules are used to make glucose?

• A. 1
• B. 2
• C. 3
• D. 6

Explanation: Option A is correct since out of every 6 molecules of G3P formed only one molecule leaves the cycle to be used by plants for making glucose. The other molecules are used to regenerate 3 molecules of 5-C RuBP.

3597. How does pyruvate enter the Kreb's cycle after glycolysis?

• A. Pyruvic acid
• B. Acetyl CoA
• C. Carbon dioxide
• D. Both Options A and B are correct

Explanation: Pyruvate enters the Krebs cycle after glycolysis in the form of Acetyl CoA.

3598. Which enzyme is found in the thylakoid membrane that facilitates chemiosmosis?

• A. ATP ligase
• B. ATP kinase
• C. ATP synthase
• D. ATP dehydrogenase

Explanation: "The explanation for this question will be added soon!".

3599. The G3P is end product of which process?

• A. Kreb's cycle
• B. Calvin cycle
• C. Chemiosmosis
• D. Electron transport chain (ETC)

Explanation: The Calvin cycle forms glyceraldehyde - 3 - phosphate (G3P) from inorganic carbon dioxide.

3600. Of the following, which one is a light gathering structure?

• A. Antenna complex
• B. Reaction center
• C. Photosystem
• D. None of these options are correct

Explanation: Antenna complexes are light-harvesting systems (LHC) which are protein-pigment complexes in photosynthetic membranes.