All Free Biology MCQs with Answers

3961. How many carbon atoms are present in Ribulose phosphate?

• A. 5
• B. 4
• C. 6
• D. 3

Explanation: Ribulose phosphate specifically refers to ribulose-1,5-bisphosphate (RuBP), a 5-carbon sugar phosphate. It plays a critical role in the Calvin Cycle by acting as a substrate for the enzyme RuBisCO during the carbon fixation stage. This process is essential for converting atmospheric carbon dioxide into organic compounds in plants.Option A is correct because RuBP has 5 carbon atoms. Options B, C, and D are incorrect as they suggest different carbon counts that do not match the structure of ribulose phosphate.

3962. It moves cyclically in cyclic photophosphorylation:

• A. Oxygen
• B. Electrons
• C. ATP
• D. NADPH

Explanation: In cyclic photophosphorylation, electrons move cyclically through the electron transport chain of the thylakoid membrane. They are returned to the chlorophyll molecule, creating a cyclic flow that generates ATP. Oxygen is not involved in cyclic photophosphorylation. It is produced in non-cyclic photophosphorylation . ATP is produced during both cyclic and non-cyclic photophosphorylation. In cyclic photophosphorylation,NADPH is not produced in significant amounts in cyclic photophosphorylation. It is primarily generated in non-cyclic photophosphorylation.

3963. Enzymes for light-dependent reactions are present in:

• A. Outer membrane of the chloroplast
• B. Inner membrane of the chloroplast
• C. Stroma of the chloroplast
• D. Thylakoid membranes of the chloroplast

Explanation: The correct answer is the thylakoid membranes of the chloroplast. Light-dependent reactions take place here, where chlorophyll and other pigments capture light energy. The thylakoid membranes also house the electron transport chain and ATP synthase, which are vital for converting light energy into chemical energy in the form of ATP and NADPH. The outer and inner membranes do not contain the necessary enzymes and structures for these processes, while the stroma is involved in the light-independent Calvin Cycle.

3964. Which one of these occurs in dark reactions of photosynthesis?

• A. Formation of ATP
• B. Release of oxygen
• C. Release of hydrogen
• D. Synthesis of PGAL

Explanation: The dark reactions, also known as the Calvin Cycle or light-independent reactions, involve the synthesis of PGAL from carbon dioxide and other molecules. PGAL is a three-carbon sugar that can be used in the synthesis of glucose and other carbohydrates.

3965. The ATP synthesis in plants during the ETC is called?

• A. Photophosphorylation
• B. Photolysis
• C. Chemiosmosis
• D. All of these

Explanation: During the light-dependent reactions of photosynthesis, ATP is synthesized through a process called chemiosmosis. This involves the movement of protons across the thylakoid membrane, which generates a proton gradient. ATP synthase then uses this gradient to synthesize ATP from ADP and inorganic phosphate. While photophosphorylation is the overall process of ATP formation using light energy, chemiosmosis specifically describes the mechanism within the electron transport chain that produces ATP. Photolysis is unrelated to ATP synthesis as it involves the breakdown of water. Therefore, the correct answer is chemiosmosis.

3966. Photosystem I absorbs maximum wavelength of light?

• A. 700 nm
• B. 600 nm
• C. 750 nm
• D. 770 nm

Explanation: Photosystem I, also known as P700, is optimized to absorb light at a wavelength of 700 nanometers. This specific wavelength is crucial for its function in the electron transport chain during photosynthesis, facilitating efficient energy capture and conversion. Other wavelengths like 600 nm, 750 nm, and 770 nm do not align with the absorption peak of Photosystem I, either falling short or exceeding the range in which Photosystem I operates most effectively.

3967. Chlorophyll are found embedded in the_membranes.

• A. Stroma
• B. Grana
• C. Thylakoid membrane
• D. Intergrana

Explanation: The thylakoid membranes are the sites within chloroplasts where chlorophyll pigments are embedded. These membranes are integral to the light-dependent reactions of photosynthesis, as they house the photosystems that capture and convert light energy into chemical energy. The stroma, while important for the Calvin cycle, does not contain chlorophyll. Grana are stacks of thylakoid membranes, but the chlorophyll is specifically within the membranes themselves. 'Intergrana' is not a recognized term in the context of chloroplast structure.

3968. Bacteriochlorophylls include which of the following?

• A. Chlorophyll a
• B. Chlorophyll c
• C. Chlorophyll b
• D. None of these

Explanation: Chlorophyll a,b,c,d and e are not present in bacteriochlorophyll.

3969. The part of chlorophyll molecule that is embedded in the core of thylakoid membrane is:

• A. Hydrophilic
• B. Hydrophobic
• C. Both of these
• D. None of these

Explanation: The part of the chlorophyll molecule that is embedded in the core of the thylakoid membrane is the hydrophobic tail which consists of a long carbon chain that sticks the chlorophyll molecules within the hydrophobic interior of the membranes. This allows them to capture light efficiently and convert it into chemical energy which can be used by the plant.

3970. Wavelength of light that is mainly absorbed by the plants?

• A. Orange
• B. Red
• C. Green
• D. Both A and B

Explanation: The correct answer is red light, which is highly absorbed by chlorophyll in plants and plays a vital role in photosynthesis, especially in photosystem II. In contrast, orange light is absorbed but contributes less effectively to the photosynthetic process. Green light is primarily reflected, not absorbed, making it less useful for photosynthesis. Therefore, the most effective wavelength of light for photosynthesis is red.