All Free Biology MCQs with Answers

3341. Which of the following statements is a correct distinction between autotrophs and heterotrophs?

• A. Only heterotrophs require chemical compounds from the environment
• B. Cellular respiration is unique to heterotrophs
• C. Only heterotrophs have mitochondria
• D. Autotrophs, but not heterotrophs, can nourish themselves beginning with entirely inorganic nutrients

Explanation: Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other inorganic nutrients. Heterotrophs depend on autotrophs either directly or indirectly. OPTION A: Autotroph needs chemical compounds from the environment. OPTION B: Cellular respiration is present in both heterotrophy and autotrophy, as both of them require energy in the form of ATP, which is formed by cellular respiration. OPTION C: Both have mitochondria in their cells, which generate energy for cells and work as the powerhouses of the cell. OPTION D: Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other inorganic nutrients.

3342. What enzyme is found in the thylakoid membrane that facilitates chemiosmosis?

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

Explanation: ATP synthase is the enzyme that makes ATP by chemiosmosis. It allows protons to pass through the membrane and uses the free energy difference to phosphorylate adenosine diphosphate (ADP), making ATP.OPTION A: The ATP-dependent DNA ligases catalyze the joining of single-stranded breaks (nicks) in the phosphodiester backbone of double-stranded DNA in a three-step mechanism.OPTION B: Protein kinases catalyze the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function.OPTION C: ATP synthase is a protein that catalyzes the formation of the energy storage molecule ATP using ADP and inorganic phosphate.OPTION D: Dehydrogenase is an enzyme belonging to the group of oxidoreductases that oxidizes a substrate by reducing an electron acceptor.

3343. Breaking of the terminal phosphate of ATP releases about _ kcal/mol of energy.

• A. 20 kcal/mol
• B. 12kcal/mol
• C. 3.5kcal/mol
• D. 7.3kcal/mol

Explanation: The release of terminal phosphate in a single ATP molecule occurs using water; the energy released is equivalent to 7.3 kcal/mol.

3344. The breaking of terminal phosphate of ATP yields energy?

• A. 7 kcal
• B. 8 kcal
• C. 7.5 kcal
• D. 7.3 kcal

Explanation: The hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy.(∆G = −7.3 kcal/mol of energy)

3345. The net yield of H2O in photosynthesis is?

• A. 1
• B. 6
• C. 3
• D. 0

Explanation: In the process of photosynthesis, water (H2O) is split during the light-dependent reactions to provide electrons, protons (H+), and oxygen (O2). The oxygen is released as a byproduct into the atmosphere, while the electrons and protons are used in the subsequent steps of photosynthesis to produce energy-rich molecules like ATP and NADPH. While water is utilized in the photosynthetic process, it is ultimately regenerated and not consumed. Therefore, the net yield of water in photosynthesis is 0 since the same amount of water that is initially used is also produced as a byproduct.

3346. The Van Niel hypothesis about the production of oxygen during photosynthesis was based on the study and investigations on _.

• A. Bacteria
• B. Algae
• C. Protonema
• D. Cyanobacteria

Explanation: This option is correct. The answer is bacteria. The Van Niel hypothesis was based on the study and investigations on bacteria. In his experiments, Van Niel used purple sulfur bacteria, which are a type of bacteria that can perform photosynthesis. He found that these bacteria produced oxygen when they were supplied with water, but not when they were supplied with carbon dioxide. This led him to conclude that the oxygen produced during photosynthesis by bacteria comes from water, not from carbon dioxide.

3347. Where does the light dependent reaction takes place, in the plant cell?

• A. Stroma
• B. Cytosol
• C. Mitochondria
• D. Thylakoid/Grana

Explanation: The light-dependent reactions use light energy to make two molecules needed for the next stage of photosynthesis: the energy storage molecule ATP and the reduced electron carrier NADPH. In plants, the light reactions take place in the thylakoid membranes of organelles called chloroplasts.

3348. Photorespiration in C-4 plants starts from:

• A. Phosphoglycerate
• B. Phosphoenol pyruvate
• C. Glycerate
• D. Glycine

Explanation: The C4 pathway initiates with a molecule called phosphoenolpyruvate (PEP) which is a 3-carbon molecule. This is the primary CO2 acceptor and the carboxylation takes place with the help of an enzyme called PEP carboxylase.

3349. Which two reactions occur during photophosphorylation.

• A. ATP is hydrolysed and NADP is reduced
• B. ATP is hydrolysed and NADPH is oxidized
• C. ATP is synthesized and NADP is reduced
• D. ATP is synthesized and NADPH is oxidized

Explanation: During photophosphorylation, which is part of the light-dependent reactions of photosynthesis, ATP is synthesized through a process known as chemiosmosis. Concurrently, NADP is reduced to NADPH by gaining electrons and protons. This process is crucial for converting light energy into chemical energy stored in ATP and NADPH, which are then used in the Calvin cycle. The incorrect options either mention the hydrolysis of ATP, which does not occur in photophosphorylation, or the oxidation of NADPH, which is incorrect as NADPH is the reduced form.

3350. What type of molecule is Chlorophyll?

• A. Inorganic
• B. Cationic
• C. Anionic
• D. Organic

Explanation: Chlorophyll is considered an organic molecule as it contains carbon atoms and is part of larger organic molecules found in plants. Chlorophyll is a pigment that plays a crucial role in photosynthesis by capturing light energy to power the conversion of carbon dioxide and water into glucose and oxygen.