All Free Biology MCQs with Answers

3271. How does each photoexcited electron pass from PS2 to PS1?

• A. ETC
• B. Chemiosmosis
• C. Photolysis
• D. Photosynthesis

Explanation: Light excites electrons in chlorophyll P680 in PSII.These high-energy electrons are transferred to the primary electron acceptor of PSII.The electrons pass through a series of electron carriers in the ETC, including:Plastoquinone (PQ)Cytochrome b6f complex (which pumps protons into the thylakoid lumen, aiding ATP synthesis)Plastocyanin (PC) (which transfers electrons to PSI)Excitation in Photosystem I (PSI)The electrons arrive at chlorophyll P700 in PSI, where they get re-excited by light.The energized electrons are then passed to ferredoxin (Fd) and finally used to reduce NADP+ to NADPH.

3272. The complete breakdown of glucose molecules takes place in which of the following?

• A. Alcoholic fermentation
• B. Lactic acid fermentation
• C. Aerobic respiration
• D. None of these options are correct

Explanation: Aerobic respiration is the process where cells use oxygen to convert glucose into energy (ATP), releasing carbon dioxide and water as byproducts. This highly efficient process occurs in the mitochondria of most living organisms, including plants and animals, to power essential functions like muscle contraction, growth, and body heat.

3273. The enzymes required for the Kreb cycle are found in _.

• A. F¹ particles
• B. Lysosomes
• C. Cytoplasm
• D. Matrix

Explanation: The Krebs cycle enzymes are membrane proteins found within the matrix of the mitochondria, except for succinate dehydrogenase, which is an integral membrane protein locked to the inner mitochondrial membrane.

3274. _ is the site of light-independent reaction.

• A. Thylakoid membrane
• B. Thylakoid space
• C. Stroma
• D. Grana

Explanation: The light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place. Thylakoids are arranged in stacks called grana.The chloroplast matrix is called the stroma and contains enzymes that catalyse the light-independent reactions of photosynthesis. But stroma is not the site for light reactions. Stromal lamellae connect two or more grana to each other. In this way, the lamellae act as a skeleton of the chloroplast, maintaining efficient distances between the grana, thereby maximising the overall efficiency of the chloroplast. Dark reaction does not depend directly on the presence of light but is dependent on the products of light reaction i.e., ATP and NADPH. The dark reaction occurs through the Calvin cycle.

3275. The enzymes required in Glycolysis are present in:

• A. Golgi Apparatus
• B. Cell cytoplasm
• C. Inner Mitochondrial Membrane
• D. Matrix of Mitochondria

Explanation: Glycolysis is the process where glucose breaks partially to form pyruvic acid. Further the pyruvic acid enters as a substrate to continue the respiratory pathway. It takes place in the cytoplasm.It does not depend upon the availability of the oxygen.

3276. In aerobic respiration which of the following is correct?

• A. Pyruvate is completely oxidized to form carbon dioxide and water
• B. Pyruvate is completely oxidized to form oxygen and water
• C. Pyruvate carboxylated to produce citrate
• D. Pyruvate is converted to ethanol and carbon dioxide

Explanation: In aerobic respiration, glucose is oxidised to form pyruvate during glycolysis. This is followed by Link reaction, Krebs cycle and Electron transport chain all of which leads to the formation of ATP, water and CO2. During the citric acid cycle, pyruvate is completely oxidized, converting it into carbon dioxide (CO2) and high-energy electron carriers (NADH and FADH2).

3277. At the last step of Glycolysis, which of the following compound is formed:

• A. Pyruvic acid/ Pyruvate
• B. Lactic acid
• C. Ethyl Alcohol
• D. Fructose Phosphate

Explanation: The last step in glycolysis is catalyzed by the enzyme pyruvate kinase. Conversion of the PEP into pyruvate results in the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate).

3278. NADP, nicotinamide adenine dinucleotide phosphate, is a carrier of:

• A. OH group
• B. O2 group
• C. Hydrogen
• D. Phosphate

Explanation: NADP+ is a coenzyme that functions as a universal electron carrier, accepting electrons and hydrogen atoms to form NADPH, or nicotinamide adenine dinucleotide phosphate.

3279. When we extract Carotenoids from its source we see that it is:

• A. Violet in color
• B. Blue green in color
• C. Yellow green in color
• D. Yellow to orange red in color

Explanation: Carotenoids also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi.

3280. In which of the following does no net gaseous exchange take place between leaves and the atmosphere?

• A. Day
• B. Night
• C. Dawn and Dusk
• D. Midnight

Explanation: At dawn and dusk, the intensity of light is low. At this moment the amount of oxygen released from photosynthesis is equal to the amount of oxygen used in respiration. Similarly, the amount of carbon dioxide released from respiration is equal to the amount of carbon dioxide produced in photosynthesis. It is called "Compensation Point." Hence, option C is correct.