All Free Biology MCQs with Answers

3431. Final electron acceptor in respiratory chain is:

• A. Cytochrome A
• B. Oxygen
• C. Cytochrome a3
• D. Cytochrome C

Explanation: The final acceptor of electrons in the respiratory chain is oxygen (O2). During oxidative phosphorylation, which is the last stage of cellular respiration, electrons are transferred through a series of protein complexes in the inner mitochondrial membrane (or the plasma membrane in prokaryotes). This process is part of the electron transport chain.

3432. The end product of anaerobic respiration in humans and other mammals is:

• A. Pyruvic acid
• B. Ethanol
• C. Lactic acid
• D. Glucose

Explanation: The end product of anaerobic respiration in humans and other mammals is lactic acid. In the absence of sufficient oxygen, cells resort to anaerobic respiration to generate energy. Anaerobic respiration involves the incomplete breakdown of glucose and results in the production of lactic acid as a byproduct. The specific process is known as lactic acid fermentation. During this process, pyruvate, which is an intermediate product of glycolysis, is converted into lactic acid. This reaction helps to regenerate NAD+ from NADH, allowing glycolysis to continue in the absence of oxygen.

3433. A biochemical process which occurs within a cell to breakdown complex compounds to produce energy is called:

• A. Respiration
• B. Photosynthesis
• C. Oxidation Reduction
• D. Photophosphorylation

Explanation: The biochemical process that occurs within a cell to break down complex compounds to produce energy is called cellular respiration. Cellular respiration is a set of metabolic reactions that take place in cells to extract energy from organic molecules, such as glucose. The energy released during cellular respiration is used to produce adenosine triphosphate (ATP), which serves as the primary energy currency for cellular activities.

3434. Which part of the chlorophyll molecule absorbs light?

• A. Phytol
• B. Porphyrin ring
• C. Pyrrole
• D. Thylakoid membrane

Explanation: The part of the chlorophyll molecule that absorbs light is the porphyrin ring, which is a complex cyclic structure containing a centrally coordinated magnesium ion (Mg²⁺). The porphyrin ring is responsible for the pigment's ability to absorb light energy during the process of photosynthesis. The porphyrin ring consists of alternating single and double bonds, creating a conjugated system. This conjugated system allows chlorophyll to absorb light in the visible spectrum. The absorption of light by chlorophyll is most efficient in the blue and red regions of the electromagnetic spectrum.

3435. Which light is mostly absorbed by chlorophyll-a?

• A. Violet Light
• B. Green Light
• C. Red Light
• D. Yellow Light

Explanation: Chlorophyll-a is the primary form of chlorophyll used in photosynthesis. It is blue-green in color and absorbs light mostly in violet-blue and orange-red light. It absorbs the most energy from the wavelength of violet light.

3436. The term glycolysis refers to the conversion of:

• A. Pyruvate to Glucose
• B. Glucose to Pyruvate
• C. Citric acid to CO2
• D. Both Pyruvate to Glucose and Glucose to Pyruvate

Explanation: The term "glycolysis" refers to the conversion of glucose into pyruvate. Glycolysis is the initial stage of cellular respiration, and it takes place in the cytoplasm of cells. The process involves a series of enzymatic reactions that break down one molecule of glucose, a six-carbon sugar, into two molecules of pyruvate, each containing three carbon atoms.

3437. In Citric Acid Cycle Acetyl CoA combines with:

• A. Glucose
• B. CO2
• C. Rubisco
• D. Oxaloacetate

Explanation: In the citric acid cycle (also known as the Krebs cycle or tricarboxylic acid cycle), acetyl-CoA combines with oxaloacetate to initiate the cycle. This condensation reaction is catalyzed by the enzyme citrate synthase. This reaction marks the beginning of the citric acid cycle. Citrate is a six-carbon compound, and as it undergoes a series of reactions, carbon atoms are released as carbon dioxide, and high-energy electrons are transferred to carrier molecules NADH and FADH2. The cycle ultimately regenerates oxaloacetate, which can combine with another molecule of acetyl-CoA to continue the cycle. The citric acid cycle is a key component of cellular respiration, generating NADH, FADH2, and ATP.

3438. The following statement is true for the absorption spectra of photosynthesis:

• A. Chlorophyll a and b have the same absorption spectra.
• B. Chlorophyll a and b have different absorption spectra.
• C. Chlorophyll a and carotenoids have the same absorption spectra.
• D. Carotenoids and chlorophyll b have the same absorption spectra.

Explanation: Yes, chlorophyll-a and chlorophyll-b, the two main types of chlorophyll found in photosynthetic organisms, have slightly different absorption spectra. Chlorophyll-a and chlorophyll-b absorb light most efficiently in the blue and red regions of the electromagnetic spectrum, but they have different absorption peaks. While chlorophyll-a is directly involved in the conversion of light energy to chemical energy in the photosystems, chlorophyll-b expands the range of light that can be captured and utilized for photosynthesis.

3439. Which of the following is absent in C4 Plants:

• A. Calvin Cycle
• B. Bundle Sheath Cells
• C. PEP Carboxylase
• D. CO2 Fixation in Mesophyll Cells

Explanation: In C4 plants, CO2 fixation occurs in the mesophyll cells, but it follows a unique pathway compared to C3 plants. C4 plants are adapted to minimize photorespiration by initially fixing CO2 in the mesophyll cells using the enzyme PEP Carboxylase, forming a four-carbon compound (oxaloacetate). This compound is then transported to the bundle sheath cells, where the Calvin cycle occurs. Therefore, the statement that CO2 fixation is absent in mesophyll cells is incorrect.The Calvin cycle is indeed present in C4 plants, but it occurs in the bundle sheath cells, not the mesophyll cells. Bundle sheath cells are essential for the Calvin cycle in C4 plants, and PEP Carboxylase is vital for the initial CO2 fixation. Thus, options A, B, and C are incorrect.

3440. Organization of photosynthetic pigment into clusters is:

• A. Photosynthesis
• B. Photosystem
• C. Photosynthetic cluster arrangement
• D. Calvin system

Explanation: The organization of photosynthetic pigments into clusters is referred to as a 'photosystem.' A photosystem is a complex of pigments and proteins that work together to capture light energy and initiate the process of photosynthesis. There are two main types of photosystems in photosynthetic organisms: Photosystem I (PSI) and Photosystem II (PSII). Options A, C, and D are incorrect as they do not accurately describe the organization of photosynthetic pigments into clusters.