All Free Biology MCQs with Answers

3331. The main purpose of cellular respiration is to _.

• A. Convert potential energy to kinetic energy
• B. Convert kinetic energy to potential energy
• C. Convert stored chemical energy into kinetic energy
• D. Convert energy stored in the chemical bonds of glucose to energy that the cell can use

Explanation: Option D:This option accurately describes the primary purpose of cellular respiration. Glucose is broken down through a series of chemical reactions to release energy stored in its chemical bonds. This energy is then converted into a usable form, such as ATP (adenosine triphosphate), which provides energy for various cellular processes.

3332. The total number of ATP produced when a molecule of glucose undergoes fermentation is?

• A. 4
• B. 36
• C. 2
• D. 38

Explanation: Anaerobic respiration is a type of respiration that produces energy without using oxygen as the final electron acceptor.In microorganisms, the term anaerobic respiration is replaced by fermentation.Fermentation of glucose occurs in two stages.During the first stage, glucose is converted into pyruvate through the multi-step process of glycolysis and 2 ATP and 2 NADH are generated.In the next stage, the pyruvate that is formed during glycolysis is broken down into lactic acid or ethanol and carbon dioxide. ATP is not produced during this stage, instead the 2 NADH generated during the previous stage are consumed.Thus a total of 2 ATPs are generated from the fermentation of a glucose molecule.

3333. Rate of photosynthesis does not depend upon:

• A. Quality of Light
• B. Intensity of Light
• C. Duration of Light
• D. Temperature

Explanation: The correct answer is Duration of Light. The rate of photosynthesis is primarily affected by the quality and intensity of light, as they directly influence the efficiency of the light-dependent reactions. Duration of light affects the total photosynthetic output over time but not the immediate rate once a certain threshold is achieved. The other factors, such as the quality of light, intensity of light, and temperature, have direct and immediate effects on the photosynthetic rate. Quality and intensity determine the energy available for photosynthesis, while temperature influences enzyme activity essential for the reactions involved.

3334. The molecular formula of Chlorophyll a is?

• A. C55H10O4N6 Mg
• B. C55H70 O6 N4 Mg
• C. C55H71 O6 N4 Mg
• D. C55 H72 O5 N4 Mg

Explanation: Chlorophyll is a green pigment found in plants and other photosynthetic organisms that is responsible for absorbing light energy from the sun and converting it into chemical energy. The molecular formula of chlorophyll a, which is the most common form of chlorophyll, is C55H72O5N4Mg.

3335. From one pyruvate passing through Krebs cycle, how many NADH are formed?

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: In the Krebs cycle, also known as the citric acid cycle, one molecule of acetyl-CoA enters the cycle, which is derived from one molecule of pyruvate. During the cycle, a series of enzymatic reactions occur, resulting in the complete oxidation of the acetyl group to carbon dioxide. This process simultaneously produces high-energy molecules: three NADH, one FADH2, and one ATP (or GTP). Therefore, starting with one pyruvate molecule, the Krebs cycle specifically yields three NADH molecules per cycle.Options suggesting one, two, or four NADH molecules are incorrect because they do not accurately reflect the output of the Krebs cycle from one pyruvate-derived acetyl-CoA.

3336. Ribose is an example of which of the following?

• A. Trioses
• B. Pentoses
• C. Tetroses
• D. Hexoses

Explanation: Ribose is a 5-carbon sugar and is a type of pentose sugar. Pentose sugars are important components of nucleic acids such as RNA and DNA. They are also involved in the synthesis of coenzymes like NAD+ and NADP+.

3337. Which of the light is mainly absorbed by the plants?

• A. Orange
• B. Red
• C. Blue
• D. Both B and C

Explanation: Plants mainly absorb red and blue light for photosynthesis, with chlorophyll a and b being the primary pigments responsible for this absorption. However, they also absorb other wavelengths of light, including orange and yellow, although to a lesser extent. The green light is reflected by chlorophyll, which is why plants appear green to the human eye.

3338. PS I have a chlorophyll a molecule that absorbs maximum light of _ nm.

• A. 600
• B. 650
• C. 680
• D. 700

Explanation: Photosystem I (PS I) is one of the two photosystems involved in the light-dependent reactions of photosynthesis. The reaction center of PS I contains a chlorophyll-a molecule that absorbs light most efficiently at a wavelength of 700 nm, hence it is often referred to as P700. This absorption peak distinguishes it from Photosystem II, which absorbs light best at 680 nm, known as P680.Options A (600 nm) and B (650 nm) do not match the peak absorption characteristics of PS I. Option C (680 nm) is specifically characteristic of Photosystem II, not Photosystem I. Therefore, the correct answer is Option D (700 nm).

3339. In bacterias, name the colour of light which is responsible for photosynthesis?

• A. Ultra-Violet
• B. Blue
• C. Red
• D. None of the above options is correct

Explanation: Option A: Ultraviolet light is a different type of light and can not be seen by the naked eye hence it does not have a colour therefore this is not the correct option.Option B: The pigment in bacteria that is responsible for photosynthesis is light-green to blue-green. This is the colour they show hence this cannot be the colour they absorb.Option C: The pigment itself is blueish green therefore it absorbs red light. This option is correct.Option D: Option C is correct.

3340. The Calvin cycle begins when carbon dioxide reacts with?

• A. NADP
• B. ADP
• C. FADH
• D. RuBP

Explanation: The Calvin cycle reactions fix CO2 from the environment into carbohydrate molecules. Enzyme, Rubisco catalyzes this fixation reaction by reacting CO2 with Rubisco.OPTION A: NADP is the reducing agent produced by the light reaction during photosynthesis and is consumed in the Calvin cycle of photosynthesis.OPTION B: Calvin cycle is fueled by ATP; hence, ADP has no role in the Calvin cycle.OPTION C: FADH has no role in the Calvin cycle.OPTION D: Enzyme, Rubisco, catalyzes this fixation reaction by reacting CO2 with Rubisco.