All Free Biology MCQs with Answers

3761. Chlorophyll b is found along with chlorophyll a in:

• A. All photosynthetic plants, green algae, and cyanobacteria
• B. Green plants and green algae only
• C. Red algae and brown algae
• D. Photosynthetic bacteria such as purple and green sulfur bacteria

Explanation: Chlorophyll b is found only in green plants and green algae, where it works alongside chlorophyll a to absorb a wider range of light wavelengths for photosynthesis. It is absent in cyanobacteria, which have chlorophyll a and phycobilin pigments instead; in red and brown algae, which contain chlorophylls a, c, or d with other accessory pigments; and in photosynthetic bacteria, which use bacteriochlorophylls instead of chlorophylls a or b. Therefore, the correct answer is Option B: Green plants and green algae only.

3762. Chlorophylls are soluble in:

• A. Water
• B. Alcohol and organic solvents
• C. Dilute acids
• D. Alkalies

Explanation: Chlorophylls are fat-soluble pigments that dissolve in organic solvents (like alcohol, acetone, and ether) but not in water, acids, or alkalis, which instead cause them to break down chemically.

3763. Pick up the one called accessory pigments:

• A. Carotenes
• B. Chlorophyll b
• C. Xanthophylls
• D. All of these

Explanation: Accessory pigments are integral to photosynthesis, as they allow plants to capture a broader spectrum of light wavelengths than chlorophyll a alone can absorb. Carotenes and xanthophylls are types of carotenoids that absorb light in regions that chlorophyll a does not, while chlorophyll b helps extend the light absorption spectrum. Thus, the correct answer is 'All of these' because all listed options are accessory pigments. Options A, B, and C are incorrect individually because each represents only a part of the full range of accessory pigments.

3764. Which chlorophyll transfers energy to chlorophyll a?

• A. Chlorophylls - a
• B. Chlorophylls - b
• C. Carotenoids
• D. Both B and C

Explanation: Both chlorophyll b and carotenoids transfer energy to chlorophyll a during photosynthesis. These pigments are known as accessory pigments because they assist in capturing additional light energy that chlorophyll a cannot absorb efficiently. Chlorophyll b absorbs light mainly in the blue and red-orange regions of the spectrum, while carotenoids absorb primarily blue and violet light. The energy they capture is then transferred to chlorophyll a, which uses it to drive the light-dependent reactions of photosynthesis. In this way, chlorophyll b and carotenoids broaden the range of light wavelengths utilized and enhance the overall efficiency of photosynthesis in plants and algae.

3765. The order of transfer of energy is

• A. Carotenoids → Chlorophyll a → Chlorophyll b
• B. Chlorophyll b → Chlorophyll a → Carotenoids
• C. Carotenoids → Chlorophyll b → Chlorophyll a
• D. Chlorophyll a → Chlorophyll b → Carotenoids

Explanation: Option C is correct.The order of energy transfer is carotenoids → chlorophyll b → chlorophyll a.Chlorophyll b absorbs light energy in the blue-green and far-red regions of the spectrum. This energy is then transferred to chlorophyll a, which is the primary pigment involved in photosynthesis.Chlorophyll a then uses this energy to produce ATP and NADPH, two molecules that are essential for photosynthesis.The energy is then transferred to the reaction centre, where the actual chemical reactions of photosynthesis take place.Carotenoids are accessory pigments that help to absorb light energy and transfer it to chlorophyll a. However, they do not directly transfer energy to chlorophyll a. About 50% of energy is initially transferred to chlorophyll b.So, the order of energy transfer is carotenoids → chlorophyll b → chlorophyll a.

3766. Some carotenoids protect chlorophyll from intense light by:

• A. Absorbing excessive light energy
• B. Dissipating excessive light energy
• C. Transferring excessive light energy to chlorophyll a
• D. Both absorbing and dissipating excessive light energy

Explanation: Option D is correct because carotenoids protect chlorophyll by both absorbing and dissipating excessive light energy as heat. This dual function helps prevent the formation of harmful free radicals that can damage cellular components, including DNA. Options A and B are partially correct because they individually describe parts of the carotenoids' protective mechanism, but only together do they encompass the full protective role. Option C is incorrect because carotenoids do not transfer excessive light energy to chlorophyll a; rather, they manage it to prevent damage.

3767. Protection against intense light is provided by carotenoids to:

• A. Chlorophyll - a
• B. Human eyes
• C. Chlorophyll - b
• D. All of these

Explanation: Option D is correct because carotenoids are versatile pigments that provide protection against intense light across different systems. In plants, they absorb excess light energy to stabilize chlorophyll a and b, preventing free radical formation and ensuring optimal photosynthesis. In humans, carotenoids like lutein and zeaxanthin filter out harmful UV light, protecting the eyes. While options A, B, and C are individually correct, only option D reflects the full range of carotenoid protection.

3768. The absorption spectrum for chlorophyll indicates that absorption is maximum in:

• A. Blue part of the spectrum
• B. Red part of the spectrum
• C. Blue and Red parts of spectrum
• D. White and red part of the spectrum

Explanation: Option C is correct.The absorption spectrum for chlorophyll indicates that absorption is maximum in the blue and red parts of the spectrum. Chlorophyll is a green pigment that is found in plants and algae. It is responsible for absorbing light energy and using it to produce food. The absorption spectrum of chlorophyll shows that it absorbs light most strongly in the blue and red regions of the spectrum. This is because the chlorophyll molecule has a structure that allows it to absorb light in these wavelengths. The blue region of the spectrum corresponds to wavelengths of light that are about 400-500 nanometers (nm). The red region of the spectrum corresponds to wavelengths of light that are about 600-700 nm. The absorption of light in the blue and red regions of the spectrum is important for photosynthesis. This is because these wavelengths of light provide the energy that is needed to split water molecules into hydrogen and oxygen. The hydrogen is then used to produce ATP, a molecule that stores energy. The oxygen is released as a byproduct. So, the absorption spectrum for chlorophyll shows that it is most effective at absorbing light in the blue and red regions of the spectrum. This is important for photosynthesis, as it is the energy from these wavelengths of light that is used to split water molecules and produce ATP.

3769. An absorption spectrum of chlorophylls has:

• A. Two peaks and one valley
• B. One peak and one valley
• C. Two peaks and two valleys
• D. One peak and two valleys

Explanation: The most accurate representation of the absorption spectrum of chlorophylls is two peaks and one valley. The two peaks indicate strong absorption in the blue and red regions of the visible spectrum, while the single valley in the green region explains the green color of plants. This pattern reflects the efficiency of chlorophyll pigments in capturing light energy for photosynthesis while reflecting green light.

3770. Pick up the one having the broadest valley:

• A. Absorption spectrum of chlorophyll a
• B. Absorption spectrum of carotenoids
• C. Absorption spectrum of chlorophyll b
• D. All have broadest valleys

Explanation: Option A is correct: The absorption spectrum of chlorophyll a features the broadest valley around 520-530 nm, indicating the least effective absorption in this green region. This contributes to the green appearance of plants because green light is not absorbed effectively and is reflected. Option B is incorrect: Carotenoids have absorption valleys, but these are narrower than those of chlorophyll a. They absorb light in different regions, such as the blue and violet, helping to capture a broader spectrum of light for photosynthesis. Option C is incorrect: Chlorophyll b's valley in the green region is not as broad as chlorophyll a's, making it less effective in absorbing green light. It primarily absorbs light in the blue and red regions. Option D is incorrect: Not all pigments have equally broad valleys; chlorophyll a is distinct in having the broadest valley among the options provided.