All Free Biology MCQs with Answers

3971. Early organisms used_as a source of hydrogen.

• A. Water
• B. Hydrogen sulphide
• C. Hydrogen cyanide
• D. Hydrogen potassium permanganate

Explanation: Under anoxic conditions certain microorganisms utilized the energy of hydrogen sulfide to power their cellular process.

3972. Water insoluble photosynthetic pigment:

• A. Chlorophyll a
• B. Chlorophyll b
• C. Carotenoids
• D. All of these

Explanation: The correct answer is Chlorophyll a because it is a water-insoluble pigment that plays a central role in photosynthesis by capturing light energy. Chlorophyll b is more polar and not classified as water-insoluble, although it assists in capturing light. Carotenoids are water-insoluble but serve different roles in photosynthesis, such as photoprotection and accessory light absorption. Therefore, the statement 'All of these' is incorrect because not all listed options are water-insoluble.

3973. Photosynthesis is absent in:

• A. Seaweeds
• B. Mushrooms
• C. Purple sulphur bacteria
• D. Angiosperms

Explanation: Mushrooms, being fungi, do not have chlorophyll and therefore cannot perform photosynthesis. Seaweeds, purple sulphur bacteria, and angiosperms all contain pigments that allow them to conduct photosynthesis, albeit through different mechanisms. Seaweeds and angiosperms use chlorophyll, while purple sulphur bacteria utilize bacteriochlorophyll, enabling them to harness light energy to create food.

3974. Chlorophyll b is found in which organism?

• A. Green plants
• B. Green algae
• C. Animals
• D. Both A and B

Explanation: Option D is correct because both green plants and green algae contain chlorophyll b, which enables them to carry out photosynthesis. Options A and B are individually incorrect because both groups of organisms have chlorophyll b. Option C is incorrect because animals do not have chlorophyll b and cannot perform photosynthesis.

3975. These all are inorganic compounds except:

• A. NO2
• B. C6H12O6
• C. H2O
• D. H2SO4

Explanation: The correct answer is C6H12O6, which is an organic compound known as glucose. Organic compounds typically contain carbon and are often associated with biological systems. In contrast, the other options-NO2, H2O, and H2SO4-are considered inorganic because they do not contain carbon (except for CO2 and a few other exceptions in inorganic chemistry).

3976. What type of plant cells carry out photosynthesis?

• A. Sclerenchymatous cells
• B. Parenchyma cells
• C. Chlorenchyma cells
• D. Both B and C

Explanation: Chlorenchyma cells are specialized plant cells that contain chloroplasts, making them the primary site for photosynthesis. While parenchyma cells can have various functions, only chlorenchyma cells, a type of parenchyma, are dedicated to photosynthesis due to their chloroplast content. Sclerenchymatous cells are not involved in photosynthesis as they are more focused on providing structural support. The option 'Both B and C' is incorrect because not all parenchyma cells perform photosynthesis, only those that are chlorenchyma do.

3977. Which chemical reactions occur during the process of photosynthesis?

• A. Oxidation only
• B. Reduction only
• C. Both oxidation and reduction
• D. None of these

Explanation: Photosynthesis is a complex redox process encompassing both oxidation and reduction reactions. Water molecules are oxidized, releasing oxygen as a byproduct, while carbon dioxide molecules are reduced, leading to the formation of glucose. This dual process is essential for the conversion of light energy into chemical energy stored in organic compounds. Option A is incorrect because oxidation alone cannot complete the photosynthesis process. Option B is incorrect as reduction alone is insufficient for the entire transformation. Option D is incorrect because it ignores the redox nature of photosynthesis.

3978. Photosynthesis is a process in which_compounds of carbon and hydrogen are reduced to carbohydrates (glucose) using light energy.

• A. Organic
• B. Energy poor
• C. Energy rich
• D. Reduced

Explanation: The reactants (CO2 and H2O) for the reaction do not consist of energy. The photosynthesis reaction takes energy from sunlight, hence this reaction is an energy-poor reaction.

3979. The graph that shows the relative effectiveness of different wavelengths in photosynthesis is?

• A. Actin spectrum
• B. Action spectrum
• C. Absorption spectrum
• D. Emission spectrum

Explanation: The action spectrum is the graph that shows the over all rate of photosynthesis at each wavelength of light. This graph would show that the colored light(s) with the highest peak would show the relative effectiveness of different wavelengths in photosynthesis.

3980. Chlorophyll molecule contains which of the following as a central metal ion?

• A. Fe2+
• B. Zn2+
• C. Cu2+
• D. Mg2+

Explanation: Chlorophyll is a pigment essential for photosynthesis, and its structure includes a magnesium (Mg2+) ion at the center of a porphyrin ring. This central magnesium ion plays a pivotal role in the absorption of light energy. The other metal ions listed, such as iron (Fe2+), zinc (Zn2+), and copper (Cu2+), serve different functions in plant physiology but are not part of the chlorophyll structure. Thus, option D, Mg2+, is the correct answer.