All Free Biology MCQs with Answers

3371. Cellular respiration is essentially what type of process?

• A. Oxidation
• B. Reduction
• C. Redox
• D. None of the above options are correct

Explanation: Cellular respiration is a redox (reduction-oxidation) process. Redox reactions involve the transfer of electrons from one molecule to another.During cellular respiration, there are several redox reactions occurring, as electrons are transferred from glucose (or other organic molecules) to oxygen. The process involves the oxidation of glucose (and other fuel molecules) and the reduction of oxygen.In glycolysis, glucose is partially oxidized, resulting in the formation of two molecules of pyruvate. During this process, NAD+ (nicotinamide adenine dinucleotide) is reduced to NADH by accepting electrons from glucose.In the subsequent stages of the citric acid cycle and the electron transport chain, further oxidation of fuel molecules occurs. NADH and another electron carrier, FADH2 (derived from FAD), donate their electrons to the electron transport chain. The electrons are then passed through a series of protein complexes in the inner mitochondrial membrane, ultimately leading to the reduction of molecular oxygen (O2) to form water (H2O).

3372. What is pyruvate broken down to in yeast?

• A. Acetyl CoA
• B. Alcohol
• C. Lactic acid
• D. All of these options are correct

Explanation: In yeast and other microorganisms during fermentation, pyruvate is typically broken down into ethanol (ethyl alcohol) and carbon dioxide through a process called alcoholic fermentation. This is a way for yeast to generate ATP (energy) in the absence of oxygen. During this process, pyruvate, which is a three-carbon compound, is converted into ethanol, a two-carbon alcohol, and carbon dioxide is released as a byproduct. This fermentation process is utilised in the production of alcoholic beverages and also plays a role in the rising of bread dough when yeast ferments sugars in the absence of oxygen.

3373. The reaction of carbon dioxide and RUBP is catalyzed by?

• A. ATP synthase
• B. Globulin
• C. Rubisco
• D. NADH dehydrogenase

Explanation: The reaction between carbon dioxide (CO2) and ribulose-1,5-bisphosphate (RuBP) is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known as Rubisco. This reaction is a crucial step in the Calvin cycle, which is the light-independent phase of photosynthesis responsible for the fixation of carbon dioxide and the synthesis of carbohydrates. Rubisco adds carbon dioxide to RuBP, leading to the formation of an unstable six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).

3374. The radiations most important to life are called?

• A. UV light
• B. Visible light
• C. Both Options A and B are correct
• D. None of these options is correct

Explanation: The radiations most important to life are typically referred to as "biologically relevant" or "biologically important" radiations. These include the various forms of electromagnetic radiation that play essential roles in biological processes and ecosystems. The most notable among them is visible light, which is crucial for photosynthesis and, therefore, supports the foundation of many life forms on Earth. Visible light is essential for many forms of life on Earth, it's important to recognize that various types of electromagnetic radiation play crucial roles in different biological processes. Visible light, which includes the colors of the rainbow (red, orange, yellow, green, blue, indigo, violet), is a type of electromagnetic radiation that can be detected by the human eye. Plants, algae, and some bacteria use the energy from visible light to drive photosynthesis, the process by which they convert light energy into chemical energy.

3375. How many carbons does citrate have in the Krebs' cycle?

• A. 5
• B. 6
• C. 8
• D. 4

Explanation: Citrate, the first compound formed in the Krebs cycle (also known as the citric acid cycle or tricarboxylic acid cycle), has six carbon atoms. Its chemical formula is often written as C6H8O7, indicating six carbon atoms, eight hydrogen atoms, and seven oxygen atoms. The Krebs cycle is a series of chemical reactions that takes place in the mitochondria of cells, and citrate is a key intermediate in this cycle.

3376. Visible light used in photosynthesis ranges from nm?

• A. 300-700
• B. 350-750
• C. 380-750
• D. 390-790

Explanation: Visible light, which ranges from approximately 380 to 750 nanometers (nm) in wavelength, is indeed crucial to life on Earth. This range of wavelengths includes the different colors of light, from violet at the shorter end to red at the longer end. Visible light is essential for photosynthesis in plants, algae, and some bacteria, as it provides the energy needed to convert carbon dioxide and water into glucose and oxygen.

3377. What reactant is utilized during the sugar production in photosynthesis?

• A. ATP
• B. NADH
• C. Carbon dioxide
• D. All of the above

Explanation: During photosynthesis, carbon dioxide (CO2) is utilized in the process of sugar production. Photosynthesis is the biochemical process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose (a type of sugar) and oxygen. The overall equation for photosynthesis is:6 CO2 + 6 H2O + light energy → C6H12O6 (glucose) + 6 O2In this equation, carbon dioxide (CO2) from the atmosphere is one of the reactants, along with water (H2O) and light energy captured by chlorophyll pigments in the chloroplasts of plant cells.

3378. The electrons from Fd to NADP are transferred by which enzyme?

• A. NADP Oxidase
• B. NADP reductase
• C. ATP synthase
• D. Both A and B

Explanation: The transfer of electrons from ferredoxin (Fd) to NADP+ during the light-dependent reactions of photosynthesis is facilitated by the enzyme ferredoxin-NADP+ reductase (FNR). This enzyme plays a key role in the conversion of NADP+ to NADPH, which is an important molecule for the synthesis of sugars during the photosynthetic process. The transfer of electrons from ferredoxin to NADP+ is part of the final steps in the electron transport chain of the thylakoid membrane.

3379. Acetyl CoA completely oxidizes to Carbon dioxide and liberates _.

• A. NADH and FADH
• B. NADP and FADP
• C. ATP
• D. ATP, NADH and FADH2

Explanation: When acetyl CoA undergoes complete oxidation in the citric acid cycle (also known as the Krebs cycle or tricarboxylic acid cycle), it liberates carbon dioxide and transfers high-energy electrons to carrier molecules. The overall chemical reaction for the complete oxidation of one molecule of acetyl CoA in the citric acid cycle is:Acetyl CoA+3NAD++FAD+GDP+Pi+2H2 O→2CO2 +3NADH+3H++FADH2 +GTP+CoAThe NADH and FADH2 generated in this process carry high-energy electrons to the electron transport chain, where they contribute to the synthesis of ATP through oxidative phosphorylation. The carbon dioxide produced is a byproduct of the decarboxylation reactions that occur during the citric acid cycle.

3380. Which of the following organisms have the greatest problem with photorespiration?

• A. C4 plants
• B. Heterotrophs
• C. C3 plants
• D. CAM plants

Explanation: C3 plants have the disadvantage that in hot dry conditions their photosynthetic efficiency suffers because of a process called photorespiration. When the CO2 concentration in the chloroplasts drops below about 50 ppm, the catalyst rubisco that helps to fix carbon begins to fix oxygen instead. Thus the rate of photosynthesis begins to decrease, posing a problemC4 plants-including maize, sugarcane, and sorghum-avoid photorespiration by using another enzyme called PEP during the first step of carbon fixation. This step takes place in the mesophyll cells that are located close to the stomata where carbon dioxide and oxygen enter the plant.