All Free Biology MCQs with Answers

3991. Photosystem II has reaction center of:

• A. P680
• B. P700
• C. P730
• D. P660

Explanation: There are two types of photosystems named as PS-I and PS-II. PS-I has type of chlorophyll that absorbs maximum wavelenght of 700 nm while PS II has type of chlorophyll a that absorbs maximum wavelenght of 680 nm.

3992. Some photosynthetic organisms contain chloroplasts that lack photosystem II yet are able to survive. The best way to detect the "lack of photosystem II" in these organisms would be:

• A. To determine if they have thylakoids in the chloroplasts
• B. To test for liberation of O2 in the light
• C. To test for CO2 fixation in the dark
• D. To do experiments to generate an action spectrum

Explanation: Photosytem II is involved in the photolysis of water (as a result oxygen is evolved) If photosystem II is absent in organism, oxygen will not be liberated.Photosynthesis has two types of reactions: initial light-dependent reactions and late light-independent reactions. The photosystem II (PSII) is the first protein complex responsible for the initial light-dependent reactions. This photosystem captures sunlight to catalyze the generation of an electrochemical transmembrane proton (H+) gradient, which is subsequently used to synthesize ATP. Photosystem II produces molecular oxygen (O2) by oxidizing two molecules of water (H2O) into one molecule of oxygen. In conclusion, the statement 'the best way to detect the lack of photosystem II in these organisms would be to test for the liberation of O2 in the light' is TRUE.

3993. NADP+ reductase transfers electron from:

• A. NADP+ to ferredoxin
• B. Ferredoxin to NADP+
• C. ADP to ATP
• D. Cytochrome complex to NADP+

Explanation: NADP+ reductase transfers electron from ferredoxin to NADP+.

3994. Which is not true for dark reaction?

• A. Does not require light directly
• B. It uses ATP
• C. Also called Z-scheme
• D. G3P is produced

Explanation: Z-scheme is another name use for light dependent reaction of photosynthesis because electrons move in zigzag fashion.

3995. The process in which carbon from CO2 is incorporated into organic molecules:

• A. Glycolysis
• B. Calvin cycle
• C. Krebs cycle
• D. Light dependent reactions

Explanation: The Calvin cycle, also known as the Calvin-Benson cycle, is a series of biochemical reactions that take place in the stroma of chloroplasts during the light-independent reactions of photosynthesis. It is named after Melvin Calvin, who played a key role in elucidating its pathway. The Calvin cycle is crucial for the synthesis of carbohydrates, such as glucose, from carbon dioxide and water, using the chemical energy stored in ATP and NADPH produced during the light-dependent reactions.

3996. If 12 NADPH are used in Calvin cycle, then how many glucose molecule will be formed:

• A. One
• B. Six
• C. Two
• D. Twelve

Explanation: Since 6 molecules of NADPH are used for the synthesis of 1 G3P in Calvin cycle, so for the synthesis of one glucose molecule that requires 2 G3P molecules, 12 molecules of NADPH are required.For the synthesis of one glucose molecule, 6 Calvin cycles are necessary and a total of 18 ATP, 12 NADPH are consumed in 6 Calvin cycles.

3997. Calvin cycle is also known as C3 pathway due to:

• A. Initial incorporation of 3 CO2 molecules
• B. Production of 3 carbon G3P
• C. Production of 3 carbon 3PGA
• D. Cycle has 3 steps

Explanation: Because the product of initial carbon fixation is a three- carbon compound, the Calvin cycle is also known as C3 path

3998. For fixing 3 molecules of CO2 in Calvin cycle, what is needed?

• A. 9ATP + 6NADPH2
• B. 18ATP + 12NADPH2
• C. 6ATP + 9NADPH2
• D. 3ATP + 3NADPH2

Explanation: The chemical equation of dark reaction is: 3CO2 + 6NADPH + 9ATP → (CH2O)3 + 6NAPD +9ADP+ 9Pi + 3H20 (Carbohydrate) For every molecule of CO2 entering the Calvin cycle, 3 molecules of ATP and 2 molecules of NADPH are used.

3999. Which of the following can perform anaerobic repiration?

• A. Bacteria
• B. Yeast
• C. Skeletal muscles
• D. All A,B,C

Explanation: Aerobic organisms use oxygen to produce energy for their metabolism. Almost all types of cells are adapted to do respiration without oxygen.

4000. In cellular respiration, product formed as a result of release of energy:

• A. ATP
• B. Oxygen
• C. NADH
• D. Glucose

Explanation: Cellular respiration is a process in which energy is released in the form of ATP due to catabolism of organic substance.