All Free Biology MCQs with Answers

3881. Where are the enzymes located that are involved in the chemical reactions that occur during glycolysis?

• A. Cytoplasm
• B. Mitochondria
• C. Nucleus
• D. Cell membrane

Explanation: The enzymes involved in the chemical reactions of glycolysis are located in the cytoplasm. This is where all ten steps of glycolysis take place, converting glucose into pyruvate and producing ATP and NADH as energy sources for the cell. The cytoplasmic location allows the enzymes to interact efficiently with substrates and intermediates in a fluid environment, making glycolysis a quick and effective process for generating energy without requiring oxygen.Mitochondria: Contain enzymes for aerobic respiration, not glycolysis.Nucleus: Holds enzymes for genetic processes, not energy metabolism.Cell membrane: Involved in transport and signalling, not in glycolytic reactions.

3882. Both glucose and the appropriate enzymes are necessary for glycolysis to begin. Which additional compound must also be present?

• A. Acetyl coenzyme A
• B. ATP
• C. Pyruvate
• D. Reduced NAD

Explanation: The correct answer is ATP. During glycolysis, ATP is initially consumed to provide the energy needed to start the breakdown of glucose. This is crucial for the phosphorylation steps that convert glucose into pyruvate. Acetyl-CoA is involved later in the metabolic pathway, specifically in the citric acid cycle. Pyruvate is the end product of glycolysis, not a starting compound. Reduced NAD (NADH) is generated during glycolysis but is not needed to initiate the process.

3883. During photosynthesis, the oxygen in glucose comes from:

• A. Water
• B. Carbon dioxide
• C. Oxygen in air
• D. Both from water and carbon dioxide

Explanation: Carbon dioxide (CO2) is one of the reactants in photosynthesis. It is taken in by the plant from the atmosphere through tiny pores called stomata on the surface of leaves. Carbon dioxide is reduced in the light-independent reactions (Calvin cycle) using the energy and electrons generated in the light-dependent reactions. The carbon atoms from carbon dioxide are used to build glucose (C6H12O6).

3884. Photosynthesis consists of essentially two biological reaction systems, one following the other. The second of these systems does which of the following?

• A. Fixes carbon dioxide
• B. Works only in the presence of light
• C. Traps light energy
• D. Synthesis of ATP

Explanation: The second set of reactions in photosynthesis is known as the light-independent reactions, or the Calvin Cycle. This process occurs in the stroma of chloroplasts and does not require direct light to proceed. Instead, it uses ATP and NADPH generated from the light-dependent reactions to fix carbon dioxide into glucose. Option A is correct as it accurately describes the main function of the Calvin Cycle. Option B is incorrect as the Calvin Cycle can proceed without light. Option C is incorrect-it describes the role of the light-dependent reactions. Option D is incorrect because the Calvin Cycle does not synthesize ATP; it uses ATP produced from the light-dependent reactions.

3885. The process in which water is split during photosynthesis and essential for photosynthesis:

• A. Hydrolysis
• B. Hemolysis
• C. Plasmolysis
• D. Photolysis

Explanation: Photolysis, also known as photodissociation or photodecomposition, refers to the process by which a chemical compound is broken down or decomposed into smaller parts through the absorption of light energy. This phenomenon is particularly important in the context of photosynthesis and atmospheric chemistry.

3886. The first step in photosynthesis is:

• A. Joining of 3 carbon atoms to from glucose
• B. lonization of water
• C. Excitement of an electron of chlorophyll by a photon of light
• D. Formation of ATP

Explanation: Light Absorption: Chlorophyll molecules, organised into photosystems in the thylakoid membranes, capture photons of light. Electron Excitation: The absorbed light energy excites an electron to a higher energy level. Electron Transfer: The high-energy electron is passed from the chlorophyll molecule to a primary electron acceptor, initiating the flow of electrons through an electron transport chain. Water Splitting (Photolysis): To replace the lost electron, a water molecule is split. This process releases oxygen as a byproduct, along with protons and electrons that replenish the chlorophyll.

3887. Which of the following wavelength is least effective in photosynthesis?

• A. Red light
• B. Green light
• C. Blue light
• D. Violet light

Explanation: The correct answer is green light because it is mostly reflected, not absorbed, by plants, making it the least effective in photosynthesis. Red and blue light are absorbed well by chlorophyll, making them more effective in the photosynthetic process. Violet light, like blue light, is also absorbed efficiently and contributes significantly to photosynthesis.

3888. The assimilatory power in photosynthesis is

• A. ATP
• B. ATP and NADPH2
• C. NADP+
• D. ATP, NADP and CO2

Explanation: Adenosine Triphosphate, commonly known as ATP, is a molecule that plays a crucial role in the transfer of energy within cells. It is often referred to as the "energy currency" of the cell because it provides the energy needed for various cellular processes.

3889. The percentages of light energy fixed in photosynthesis is generally around:

• A. 50%
• B. 1%
• C. 10%
• D. 75%

Explanation: The percentage of light energy fixed in photosynthesis is generally around 1%, which implies that the overall productivity of the biosphere is limited by this low rate of energy conversion. The low efficiency is due to several factors, including that most solar energy is at wavelengths unsuitable for photosynthesis (plants primarily use the red and blue light spectrum), and not all incoming light is absorbed by the leaves.

3890. Photo-oxidation of water in photosynthesis is in association of:

• A. Pigment System I
• B. Pigment System II
• C. Plastocyanin
• D. Cytochrome B6

Explanation: Photo-oxidation of water in photosynthesis is in association of pigment System II. "The explanation for this question will be added soon!".