All Free Biology MCQs with Answers

3911. Water releases protons, and twelve water molecules will release:

• A. 24H+
• B. 12H+
• C. 6H+
• D. 1H+

Explanation: Each water molecule can release only one proton when it ionises. Therefore, twelve water molecules will release a total of 12 protons. Options suggesting fewer or more protons, such as 1, 6, or 24, are incorrect because they either underestimate or overestimate the number of protons released.

3912. Respiration in plants:

• A. Aerobic respiration
• B. Photosynthesis
• C. Nitrogen fixation
• D. Transpiration

Explanation: The main form of respiration in plants is aerobic respiration. This process breaks down glucose in the presence of oxygen to release energy, carbon dioxide, and water. The energy produced is used for essential functions such as growth, repair, nutrient absorption, and other cellular activities. Other processes like photosynthesis, nitrogen fixation, and transpiration are not forms of respiration because they do not release energy from glucose.

3913. What is the importance of respiration in plants?

• A. It provides oxygen to plants
• B. It liberates energy
• C. It liberates carbon dioxide
• D. All the above

Explanation: The correct answer is B) It liberates energy. Respiration is crucial for breaking down glucose molecules to release energy, which plants need for vital functions like growth and reproduction. Option A is incorrect because respiration consumes rather than provides oxygen. Option C, while acknowledging the release of carbon dioxide, misses the primary goal of energy release. Option D is incorrect, as it implies all statements are equally important, whereas energy liberation is the primary function of respiration.

3914. The energy yield as a result of the total oxidation of one glucose molecule during cellular respiration is to convert:

• A. 38 molecules of ATP
• B. 2 molecules of ATP
• C. 4 molecules of ATP
• D. 18 molecules of ATP

Explanation: The total oxidation of one glucose molecule during cellular respiration produces about 38 molecules of ATP. This occurs through a series of stages, including glycolysis, the Krebs cycle, and the electron transport chain. The energy released in this process is used by cells for essential activities such as growth, repair, and maintenance.

3915. The end products of respiration in plants are

• A. Carbon dioxide, water, and energy
• B. Oxygen and glucose
• C. Carbon dioxide and alcohol
• D. Carbon dioxide and energy only

Explanation: The end products of respiration in plants are carbon dioxide, water, and energy. During this process, glucose is broken down using oxygen to release energy in the form of ATP. The carbon dioxide produced is released into the air, the water may be reused by the plant, and the energy is used for various life processes, such as growth and repair.

3916. What process occurs in plants during anaerobic respiration?

• A. Alcoholic fermentation
• B. Lactic acid fermentation
• C. Photosynthesis
• D. Aerobic respiration

Explanation: During anaerobic respiration in plants, the correct process is alcoholic fermentation. In this process, glucose is broken down without oxygen to produce ethanol, carbon dioxide, and a small amount of energy. The other options-lactic acid fermentation, photosynthesis, and aerobic respiration-are incorrect because they either occur in animals, require oxygen, or involve light energy rather than releasing energy without oxygen.

3917. How many molecules of ATP are gained during anaerobic respiration of one molecule of glucose?

• A. 36
• B. 2
• C. 38
• D. 4

Explanation: During anaerobic respiration, the process of glycolysis breaks down one molecule of glucose into two molecules of pyruvate, yielding four ATP molecules. However, two ATP molecules are used up in the initial steps of glycolysis, resulting in a net gain of two ATP molecules. Option B is correct because it accurately reflects this net gain. Options A and C refer to the ATP yield from aerobic respiration, which involves additional processes such as the citric acid cycle and electron transport chain, resulting in a higher ATP production. Option D incorrectly states the net gain, as it doesn't consider the ATP used during glycolysis.

3918. When yeast ferments glucose, the products are

• A. Carbon dioxide and ethanol
• B. Lactic acid and water
• C. Oxygen and glucose
• D. Hydrogen and methane

Explanation: When yeast ferments glucose without oxygen, it produces ethanol and carbon dioxide through alcoholic fermentation. Other suggested products, such as lactic acid and water, oxygen and glucose, or hydrogen and methane, are incorrect because they occur in different organisms or processes. Therefore, the correct products of yeast fermentation are ethanol and carbon dioxide.

3919. Which of the following statements is true of fermentation?

• A. Fermentation occurs in the absence of oxygen
• B. Fermentation produces large amounts of ATP
• C. Fermentation results in the complete oxidation of glucose
• D. Fermentation produces byproducts such as lactic acid or ethanol

Explanation: Fermentation is an anaerobic process that occurs without oxygen and allows organisms to produce energy when oxygen is unavailable. It generates only a small amount of ATP and does not completely oxidise glucose. Instead, it converts glucose into simpler compounds such as lactic acid or ethanol, depending on the organism. Among the given statements, the correct one is that fermentation produces byproducts like lactic acid or ethanol.

3920. Glycolysis is a process found in:

• A. Animal cells
• B. Red blood cells
• C. Neurons
• D. Epidermal cells

Explanation: Glycolysis is a process that breaks down glucose into pyruvate in the cytoplasm of cells, producing a small amount of ATP and NADH. It occurs in animal cells, providing energy even when oxygen is low. Other cell types, such as red blood cells, neurons, and epidermal cells, do not rely on glycolysis as their primary energy source.