All Free Biology MCQs with Answers

3211. The main process that occurs in the dark reaction in photosynthesis is:

• A. That water is split
• B. Light energy is converted into chemical energy
• C. That glucose is oxidized
• D. That carbon-dioxide is fixed
• E. None of the above

Explanation: The main process that occurs in the dark reaction (also known as the Calvin Cycle) in photosynthesis is the synthesis of glucose. The dark reaction takes place in the stroma of chloroplasts and does not directly require light. It follows the light-dependent reactions (such as photosystem I and II) that capture and convert light energy into chemical energy in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). In the Calvin Cycle, the primary goal is to use the ATP and NADPH produced during the light-dependent reactions to convert carbon dioxide (CO2) into glucose. The key steps of the Calvin Cycle include carbon fixation, reduction, and regeneration of the starting molecule (RuBP, ribulose-1,5-bisphosphate). The final product is glucose, which can be used by the plant for energy and other metabolic processes.

3212. In paper chromatography xanthophyll will give _ color:

• A. Orange
• B. Grey
• C. Yellow
• D. Blue-Green

Explanation: In paper chromatography, xanthophylls are pigments that are often responsible for giving a yellow color. Xanthophylls are a type of carotenoid pigment found in plants, and they contribute to the yellow, orange, and red colors in various plant tissues. In paper chromatography, these pigments can be separated based on their different affinities for the paper and the mobile solvent. During paper chromatography, a sample containing xanthophylls is spotted onto a piece of filter paper. As the solvent travels up the paper, it carries the pigments along with it. Xanthophylls, being yellow pigments, will manifest as yellow bands or spots on the paper when the chromatography is complete.

3213. Aerobic respiration results in how much ATP?

• A. 2
• B. 36
• C. 18
• D. 32

Explanation: In eukaryotic cells, aerobic respiration typically results in a net gain of approximately 36 ATP molecules per molecule of glucose. This energy yield is a sum of ATP produced during glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation in the electron transport chain.

3214. Immediate source of energy for cellular respiration is:

• A. Lipids
• B. ATP
• C. Proteins
• D. Carbohydrates

Explanation: The immediate source of energy for cellular respiration is adenosine triphosphate, or ATP. ATP is a molecule that stores and releases energy in cells. During cellular respiration, the complex organic molecules, such as glucose, are gradually broken down in a series of enzymatic reactions. The energy released during these reactions is used to synthesize ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi).

3215. In the Krebs cycle, substrate-level phosphorylation accompanies the formation of:

• A. Citrate
• B. Alpha-ketoglutarate
• C. Succinate
• D. Fumarate

Explanation: Coenzyme A is removed from Succinyl CoA to form succinate. The reaction releases sufficient energy which is used to combine GDP and Pi forming GTP. GTP reacts with ADP to form ATP while GTP is again converted into GDP. In this way a molecule of ATP is generated in this reaction

3216. Which part of the cell does glycolysis occur in?

• A. Mitochondrion
• B. Chloroplast
• C. Cytoplasm
• D. Nucleus
• E. Vacuole

Explanation: Glycolysis, the first stage of cellular respiration, occurs in the cytoplasm of the cell. It is a series of biochemical reactions that break down one molecule of glucose into two molecules of pyruvate. Unlike the subsequent stages of cellular respiration (such as the citric acid cycle and oxidative phosphorylation), glycolysis does not take place in the mitochondria. Instead, it occurs in the cytoplasm, which is the gel-like substance that fills the cell and surrounds the cellular organelles.

3217. The process by which one molecule of Glucose splits up into molecules of Pyruvate is called:

• A. Glycolysis
• B. Oxidative Phospholyration
• C. Electron Transport Chain
• D. Kreb's Cycle
• E. Calvin Cycle

Explanation: The process by which one molecule of glucose splits up into molecules of pyruvate is called glycolysis. Glycolysis is the first stage of cellular respiration, which occurs in the cytoplasm of the cell. During glycolysis, a molecule of glucose, a six-carbon sugar, is broken down into two molecules of pyruvate, each containing three carbon atoms.

3218. Where does the Calvin Cycle occur?

• A. Stroma
• B. Cytosol
• C. Thylakoid Membrane
• D. No specific location

Explanation: The Calvin Cycle, also known as the dark reactions or light-independent reactions of photosynthesis, occurs in the stroma of the chloroplasts. The chloroplast is an organelle found in plant cells and some other eukaryotic cells, and it is the site of photosynthesis.

3219. RuBP + O2 ---Rubisco---> PGA + _ .

• A. Phosphoglycerate
• B. Phosphoglycolate
• C. Glycerate
• D. Glycolate

Explanation: When RuBP reacts with oxygen instead of CO₂ in a process called photorespiration, RuBisCO catalyzes the formation of one molecule of 3-phosphoglycerate (PGA) and one molecule of 2-phosphoglycolate (Phosphoglycolate). This process occurs when plants have less CO2 but high O2.

3220. First stable compound during Calvin cycle is:

• A. 3-phosphoglycerate
• B. Glyceraldehyde 3 - phosphate
• C. 1, 3 bisphosphoglycerate
• D. Ribulose bisphosphate

Explanation: The first stable compound formed during the Calvin Cycle is 3-phosphoglycerate (3-PGA). The Calvin Cycle, also known as the light-independent reactions of photosynthesis, is a series of enzyme-catalyzed reactions that take place in the stroma of chloroplasts. The cycle begins with the process of carbon fixation, where carbon dioxide from the atmosphere is combined with a five-carbon sugar called ribulose-1,5-bisphosphate (RuBP) using the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO).