All Free Biology MCQs with Answers

3441. Which wave lengths are mainly absorbed by chlorophyll?

• A. Violet blue and red
• B. Green and blue
• C. Violet and orange
• D. Red and indigo

Explanation: Chlorophyll primarily absorbs light in the blue and red regions of the electromagnetic spectrum. The violet-blue and red wavelengths are most efficiently absorbed by chlorophyll, while green wavelengths are less effectively absorbed and are, instead, reflected, which is why chlorophyll-containing plants appear green to our eyes.

3442. Which statement about chlorophyll is not true?

• A. It contains terminal carbonyl group
• B. It contains phyto tail
• C. It contains porphyrin ring
• D. It contains magnesium

Explanation: Chlorophyll is a complex molecule involved in photosynthesis, and it does contain a terminal carbonyl group. The carbonyl group is a functional group consisting of a carbon atom double-bonded to an oxygen atom. In chlorophyll, the carbonyl group is typically present in a phytol side chain. Chlorophyll molecules consist of a porphyrin ring system with a magnesium ion at the center. The phytol side chain, which contains the terminal carbonyl group, is hydrophobic and anchors the chlorophyll molecule in the thylakoid membrane of chloroplasts. The terminal carbonyl group is involved in the overall structure and function of chlorophyll, contributing to its interaction with light and its role in capturing energy during the light-dependent reactions of photosynthesis. Chlorophyll absorbs light energy, and the carbonyl group is part of the chromophore responsible for the absorption of specific wavelengths of light.

3443. Oleic acid is a fatty acid with 18 carbon atoms. It breaks down into 9 acetyl groups. It is estimated that these nine acetyl groups would generate _ ATP molecules.

• A. 81
• B. 98
• C. 101
• D. 108

Explanation: The breakdown of oleic acid into acetyl-CoA units involves beta-oxidation, where each acetyl-CoA enters the citric acid cycle. Each acetyl-CoA contributes approximately 10 ATP through both the citric acid cycle and oxidative phosphorylation. Therefore, 9 acetyl-CoA molecules result in 9 x 12 = 108 ATP. The other options are incorrect due to miscalculations or incorrect assumptions about the ATP yield per acetyl-CoA.

3444. Approximately how much calories of free energy is stored in plant biomass for every mole of CO2 fixed during photosynthesis ?

• A. 110
• B. 112
• C. 114
• D. 116

Explanation: The conversion of carbon dioxide (CO2) and water (H2O) into glucose (C6H12O6) involves the capture of light energy and its conversion into chemical energy. The actual energy stored in the glucose molecule can then be released through cellular respiration to produce ATP. The estimate of 114 kilocalories per mole of CO2 fixed likely considers the overall efficiency of photosynthesis and subsequent energy transfer processes. However, it's crucial to note that this is an approximation, and the actual energy yield can vary. Different sources and studies might provide slightly different estimates based on specific conditions and assumptions.

3445. PGAL is formed during the oxidative phase of _.

• A. Calvin Cycle
• B. Glycolysis
• C. Oxidative Phosphorylation
• D. None of the above options are correct.

Explanation: PGA formed in the Carbon fixation of calvin cycle is reduced into phosphoglyceraldehyde. The products of light reaction i.e. NADPH and ATP used in this process. Each molecule of phosphoglyceric acid (PGA) receives energy from ATP and hydrogen from NADPH of light reaction, forming phosphoglyceraldehyde (PGAL) and water.

3446. Van Neil's hypothesis about the production of oxygen during photosynthesis was based on the study and investigations of:

• A. Bacteria
• B. Algae
• C. Protonema
• D. Cyanobacteria

Explanation: Van Niel's hypothesis was formulated from his work with photosynthetic bacteria that utilized hydrogen sulfide (H₂S) instead of water, releasing sulfur instead of oxygen. This led him to propose that plants split water (H₂O) to release oxygen during photosynthesis. His hypothesis was later confirmed by experiments using heavy isotopes of oxygen (O18). The other options-algae, protonema, and cyanobacteria-were not the focus of Van Niel's original research on this specific hypothesis.

3447. Location of photosynthetic pigments in purple sulfur bacteria:

• A. Thylakoids
• B. Grana
• C. Stroma
• D. Cytoplasm

Explanation: Purple sulfur bacteria are prokaryotic organisms that perform photosynthesis without chloroplasts. Their photosynthetic pigments, including bacteriochlorophylls and carotenoids, are located in the cytoplasm. This differs from eukaryotic photosynthetic organisms, which house their pigments in chloroplasts with structures such as thylakoids, grana, and stroma. Therefore, the cytoplasm is the correct location of photosynthetic pigments in purple sulfur bacteria, while thylakoids, grana, and stroma are incorrect options because they are components of chloroplasts, which are absent in these bacteria.

3448. The quantitative study of energy relationship in a biological system is called?

• A. Bioenergetics
• B. Biochemistry
• C. Biotechnology
• D. Biophysics

Explanation: The quantitative study of energy relationships in a biological system is called bioenergetics. Bioenergetics encompasses the study of how living organisms acquire, transform, and utilize energy. It includes the processes involved in the conversion of energy, such as photosynthesis in plants and cellular respiration in both plant and animal cells. The study of bioenergetics helps scientists understand the flow of energy in biological systems and the mechanisms by which living organisms generate and use energy for various physiological processes.

3449. Which of the following chemical activity is involved in the conversion of pyruvate into acetaldehyde during anaerobic respiration?

• A. Reduction
• B. Decarboxylation
• C. Oxidation
• D. Phosphorylation

Explanation: During anaerobic respiration, specifically in a process called alcoholic fermentation, decarboxylation is involved in the conversion of pyruvate into acetaldehyde. This process occurs in certain microorganisms, such as yeast, under anaerobic conditions.Decarboxylation: Pyruvate loses a carbon dioxide (CO2) molecule, resulting in the formation of acetaldehyde. This step is catalyzed by the enzyme pyruvate decarboxylase. Pyruvate→Acetaldehyde+CO2

3450. In glycolysis, the conversion of Glucose-6-phosphate to fructose-6-phosphate involves:

• A. Phosphorylation
• B. Oxidation
• C. Isomerization
• D. Reduction

Explanation: Isomerization is the formation of an isomer of a molecule such as glucose 6-phosphate is converted to fructose 6-phosphate via isomerization they both have the same molecular formula and different structural formula.