All Free Biology MCQs with Answers

3261. What is the least common electron transport chain?

• A. Non-cyclic electron flow
• B. Cyclic electron flow
• C. Circular electron flow
• D. Both Options B and C are correct

Explanation: Circular electron flow is not a well-known or commonly occurring electron transport chain. In photophosphorylation, the electron flow may be acyclic, i.e., starting from Photosystem 2 going to Photosystem 1 and ending in NADPH, or it may be cyclic, i.e., only cycles around Photosystem 1 if the NADPH:ATP ratio is higher than normal. The latter is relatively rare.

3262. What is the final product of the Krebs cycle?

• A. Malate
• B. Succinate
• C. Oxaloacetate
• D. Fumarate

Explanation: The Krebs cycle, also known as the citric acid cycle, begins when acetyl-CoA combines with oxaloacetate to form citrate. Through a series of reactions, citrate is converted back to oxaloacetate. At the end of the cycle, oxaloacetate is regenerated, making it the final product. This regeneration is crucial as it allows the cycle to continue by accepting another acetyl-CoA. Malate, succinate, and fumarate are intermediates in the cycle and are not the final product. Malate is further oxidized to oxaloacetate, succinate is converted to fumarate, and fumarate is hydrated to malate. Thus, only oxaloacetate completes the cycle, ready to initiate the next round.

3263. Chlorophyll molecule contains which ion as a central metal ion?

• A. Fe²⁺
• B. Zn²⁺
• C. Cu²⁺
• D. Mg²⁺

Explanation: Magnesium is the central atom in a chlorophyll molecule, essential for its function in photosynthesis. It is crucial for chlorophyll's function in photosynthesis, as it helps the pigment absorb light energy and is essential for energy transfer and electron donation within the photosystem

3264. What are the end products of the electron transport chain in animals?

• A. ATP
• B. Carbon dioxide
• C. Water
• D. Both Options A and C are correct

Explanation: The end products of the electron transport chain are water and ATP. A number of intermediate compounds of the citric acid cycle can be diverted into the anabolism of other biochemical molecules, such as nonessential amino acids, sugars, and lipids.

3265. This is a reduced compound:

• A. CO2
• B. O2
• C. NADH
• D. NAD+

Explanation: NAD+ is the oxidized form of the molecule; NADH is the reduced form of the molecule after it has accepted two electrons and a proton (which together are the equivalent of a hydrogen atom with an extra electron). When electrons are added to a compound, they are reduced.

3266. Photosystems are located in the _.

• A. Stroma
• B. Chloroplast envelope
• C. Thylakoid membranes
• D. Intergrana

Explanation: Photosystems I and II are integral parts of the thylakoid membranes within chloroplasts, where they play a critical role in the light-dependent reactions of photosynthesis by capturing light energy and converting it into chemical energy. The stroma, chloroplast envelope, and intergrana do not house photosystems; the stroma is involved in the Calvin cycle, the envelope regulates transport, and the intergrana are spaces between granal stacks.

3267. Cytochromes are electron transport intermediates containing?

• A. Myoglobin
• B. Haem
• C. Globulin
• D. Fibrin

Explanation: Cytochromes are proteins that contain "haem" as a prosthetic group. They function as electron carriers in redox reactions, playing a vital role in cellular respiration and energy production, ATP.

3268. Enzymes for light-dependent reactions of photosynthesis would most likely be associated with:

• A. Outer membrane of the chloroplast
• B. Inner membrane of the chloroplast
• C. Stroma of the chloroplast
• D. Thylakoid membranes of the chloroplast

Explanation: Enzymes for light-dependent reactions are associated with the thylakoid membranes of the chloroplasts since Light dependent reaction occurs here.

3269. The electron transport chain in plants consists of an electron carrier called?

• A. Pq
• B. Pc
• C. Pt
• D. Po
• E. Both A and B

Explanation: Pq (plastoquinone) is the electron carrier in the electron transport chain of plants.Pc (plastocyanin) is another electron carrier protein, but it is not involved in the electron transport chain between PSII and PSI.The associated electron transport chain is NADH → Complex I → Q → Complex III → cytochrome c → Complex IV → O2, where Complexes I, III, and IV are proton pumps, while Q and cytochrome c are mobile electron carriers.

3270. The path of electrons through the two photosystems is called:

• A. S scheme
• B. X scheme
• C. Z scheme
• D. Y scheme

Explanation: The Z scheme describes the electron transport pathway through Photosystem II (PSII) and Photosystem I (PSI) in the light-dependent reactions of photosynthesis. It is characterized by a 'Z' shape in the energy diagram of electrons as they are excited by light energy and transferred through various components of the electron transport chain, ultimately resulting in the production of ATP and NADPH, which are utilized in the Calvin cycle.The other options, such as S scheme', 'X scheme', and 'Y scheme', are incorrect because they are not established terminologies or models in the context of photosynthesis electron transport.