All Free Biology MCQs with Answers

4141. Dark reaction in photosynthesis is called so because:

• A. It does not require light energy
• B. Cannot occur during daytime
• C. Occurs more rapidly at night
• D. It can also Occur in darkness

Explanation: Dark reaction in photosynthesis is called so because it does not require light energy.

4142. Calvin cycle occurs in:

• A. Chloroplast
• B. Mitochondria
• C. Glyoximes
• D. Cytoplasm

Explanation: Chloroplasts are cellular organelles found in the cells of plants, algae, and some protists. They are responsible for the process of photosynthesis, a crucial biological process that converts light energy into chemical energy in the form of glucose. Photosynthesis occurs in chloroplasts, allowing plants to produce their own food.

4143. Dark reaction of photosynthesis occurs in:

• A. Stoma of the chloroplast
• B. Space between the two membranes of the chloroplast
• C. Membranes of the Stroma lamellae
• D. Thylakoid membrane of the grana

Explanation: Dark reaction of photosynthesis occurs in stoma of the chloroplast.

4144. During dark reaction of photosynthesis:

• A. CO2 is reduced to organic compound
• B. Chlorophyll is activated
• C. 6C sugar is broken down into 3C sugar
• D. Photolysis

Explanation: This statement is correct. During the Calvin cycle, carbon dioxide is reduced and incorporated into organic compounds, ultimately leading to the formation of glucose. Reduction in this context refers to the addition of electrons and hydrogen to CO2 to form more complex organic molecules.

4145. The initial enzyme of Calvin cycle is:

• A. Ribulose 1,5 bisphosphate carboxylase
• B. Triosephosphate dehydrogenase
• C. Cytochrome oxidase
• D. Hexokinase

Explanation: "The explanation for this question will be added soon!".

4146. How many turns of Calvin Cycle yield one molecule of glucose?

• A. Four
• B. Six
• C. Eight
• D. Two

Explanation: Carbon dioxide fixation occurs during Calvin cycle. There are three stages in the process of Clavin cycle as carboxylation, reduction, and regeneration. One turn of Calvin cycle fixes one molecule of carbon dioxide. There are 6 atoms of carbon required for the synthesis of one glucose molecule. Hence, to produce one molecule of hexose sugar, six turns of Calvin cycle are required. Thus, the correct answer is option B. The other options are incorrect. Four turns of the Calvin cycle would not be enough to produce one molecule of glucose, and eight turns would be excessive. Two turns of the Calvin cycle would produce one molecule of glyceraldehyde-3-phosphate (G3P), which is a precursor to glucose.

4147. Which of the following absorb light energy for photosynthesis?

• A. ChlorophyII
• B. Water molecules
• C. O2
• D. RuBP

Explanation: The answer is A) Chlorophyll.Chlorophyll is a green pigment that is found in chloroplasts, the organelles that are responsible for photosynthesis in plants. Chlorophyll absorbs light energy, which is used to split water molecules and release oxygen. The energy from the light is also used to convert carbon dioxide into glucose.Water molecules, O2, and RuBP do not absorb light energy for photosynthesis. Water molecules are split during the light-dependent reactions of photosynthesis, but they do not absorb light energy themselves. O2 is a byproduct of photosynthesis, and it is not involved in the absorption of light energy. RuBP is a molecule that is used in the Calvin cycle, but it does not absorb light energy.So the only option that absorbs light energy for photosynthesis is chlorophyll.

4148. In photosynthesis energy from light reaction to dark reaction Is transferred in the form of:

• A. ADP
• B. AMP
• C. NADPH
• D. Chlorophyll

Explanation: ADP (adenosine diphosphate) is a molecule that is used to store energy in cells. It is the breakdown product of ATP, which is the main energy currency of cells. However, ADP does not contain any electrons, so it cannot carry energy from the light reactions to the dark reactions. AMP (adenosine monophosphate) is a simpler molecule than ATP. It is not as efficient at storing energy as ATP, and it is not used as an energy currency in cells. It also does not contain any electrons, so it cannot carry energy from the light reactions to the dark reactions. NADPH (nicotinamide adenine dinucleotide phosphate) is a molecule that is used to carry electrons in cells. It is produced in the light reactions of photosynthesis, and it is used in the dark reactions to reduce carbon dioxide. NADPH contains two high-energy electrons, which are used to drive the dark reactions. Chlorophyll is a molecule that absorbs light energy and uses it to drive the light reactions of photosynthesis. It is not involved in the transfer of energy from the light reactions to the dark reactions. Therefore, the answer is C) NADPH NADPH is the molecule that carries energy from the light reactions to the dark reactions in photosynthesis.

4149. Water releases protons. Twelve water molecules will release:

• A. 24H+
• B. 12H+
• C. 48H+
• D. 6H+

Explanation: The answer is A) 24H+ Each water molecule releases two protons when it is split during the process of photolysis. Therefore, twelve water molecules will release 24 protons. The other options are incorrect because they do not represent the correct number of protons released by twelve water molecules. Option B: 12H+ is the number of protons released by two water molecules. Option C: 48H+ is twice the number of protons released by twelve water molecules. Option D: 6H+ is half the number of protons released by twelve water molecules.

4150. In anaerobic respiration in plants:

• A. Oxygen is given out
• B. Carbon dioxide is given out
• C. Carbon dioxide is taken in
• D. Oxygen is taken in

Explanation: "The explanation for this question will be added soon!"