All Free Biology MCQs with Answers

3631. PS I has chlorophyll a molecule that absorbs maximum light of _ nm.

• A. 600
• B. 650
• C. 680
• D. 700

Explanation: Photosystems are the protein complexes involved in photosynthesis. Each photosystem is characterized by the wavelength of light to which its reaction centre is most reactive. Photosystem I, reaction centre pigment chlorophyll-a has an absorption peak at 700nm. Thus photosystem I is also known as P 700 So, the correct answer is '700 nm' A.This is factually incorrect value. B.This is not the maximum wavelength absorption of photosystem I. C.This is the peak absorption of photosystem II

3632. What would happen if green plants disappear from the earth?

• A. Only herbivores die
• B. Only carnivores die
• C. No one will die
• D. Both will die

Explanation: The correct option is D Green plants are the sources of food, energy and oxygen for all organisms. If all green plants disappear from the earth, all the herbivores will die due to the absence of food and oxygen and so will the carnivores. A.Herbivores and carnivores as well. B.Carnivores and herbivores as well . C.Both will die.

3633. The most abundant protein in chloroplast is:

• A. Rubisco
• B. Ribulose
• C. Ribulose bisphosphate
• D. Cytochrome

Explanation: Carbon dioxide fixation in dark reaction is carried out by the enzyme Ribulose bisphosphate carboxylase, also known as Rubisco. It is the most abundant protein in chloroplasts, and probably the most abundant protein on earth. B.It is a 5 carbon( ketoses) carbohydrate and not protein. C.It is a 5 carbon sugar (carbohydrate) used in dark reaction of photosynthesis. D.It is a complex in thylakoid membrane acting as electron carrier.

3634. Incorrect statement for photosynthesis is:

• A. It occurs during daytime
• B. It uses water with CO2
• C. It requires chlorophyll
• D. It uses oxygen

Explanation: Photosynthesis is the biochemical process that occurs during day time and requires chlorophyll for sugar synthesis and uses CO2 as reactant. O2, however, is produced as by- product during light dependent phase of photosynthesis and consumed during cellular respiration.

3635. Conversion of light energy into chemical energy is function of:

• A. Mitochondria
• B. Cytoplasm
• C. Stroma of chloroplast
• D. Grana

Explanation: Light dependent phase of photosynthesis takes place in grana of chloroplast in which light energy is converted into chemical energy. Grana or stacks of disc shaped structures called the thylakoids found inside the chloroplast. The main function of grana is to enhance the efficiency of photosynthesis. The thylakoids contain chlorophyll and other pigments that capture light energy. This energy is then used to drive the synthesis of ATP and the production of energy rich molecules like NADPH which are vital for the subsequent stages of photosynthesis.Grana or stacks of disc shaped structures called the thylakoids found inside the chloroplast. The main function of grana is to enhance the efficiency of photosynthesis. The thylakoids contain chlorophyll and other pigments that capture light energy. This energy is then used to drive the synthesis of ATP and the production of energy rich molecules like NADPH which are vital for the subsequent stages of photosynthesis. Therefore it is grana where Conversion of light energy into chemical energy take place. Therefore it is grana where Conversion of light energy into chemical energy take place.Therefore it is grana where Conversion of light energy into chemical energy take place.

3636. The complete aerobic oxidation of glucose results in the synthesis of as many as _ molecules of ATP.

• A. 16
• B. 26
• C. 36
• D. 46

Explanation: The complete aerobic oxidation of glucose results in the synthesis of as many as 36 molecules of ATP. During aerobic oxidation, glucose undergoes glycolysis, the Krebs cycle, and oxidative phosphorylation. Through these processes, high-energy electrons are transferred, leading to the synthesis of ATP. Glycolysis produces 2 ATP, the Krebs cycle yields 2 ATP, and oxidative phosphorylation generates about 32 ATP. In total, up to 36 ATP molecules are synthesized.

3637. Which of the following process does not need Pyruvic Acid as a substrate?

• A. Alcoholic fermentation
• B. Calvin cycle
• C. Aerobic respiration
• D. Lactic Acid fermentation

Explanation: Calvin cycle does not require pyruvate rather just requires RuBP and CO2 for carbon dioxide fixation, as shown by the diagram below. All other reactions mentioned in other options do require pyruvate.

3638. During photosynthesis, ATP synthesis takes place when electrons move from:

• A. Primary Electron Acceptor (PEA) to Plastoquinone (Pq)
• B. Plastoquinone (Pq) to cytochromes
• C. Cytochrome to Plastocyanin (Pc)
• D. Plastocyanin (Pc) to Photosystem I (PS I)

Explanation: When an electron leaves PSII, it is transferred first to a small organic molecule (plastoquinone, Pq), then to a cytochrome complex (Cyt), and finally to a copper-containing protein called plastocyanin (Pc). As the electron moves through this electron transport chain, it goes from a higher to a lower energy level, releasing energy. Some of the energy is used to pump protons H+ from the stroma (outside of the thylakoid) into the thylakoid interior.This transfer of H+, along with the release of H+ from the splitting of water, forms a proton gradient that will be used to make ATP.

3639. The second ATP is consumed in _ step of glycolysis.

• A. First
• B. Second
• C. Third
• D. Fourth

Explanation: It is formation of fructose 1, 6 bisphosphate from fructose 6 phosphate.

3640. A graph showing the relative effectiveness of different wavelengths of light in driving photosynthesis is called a/an

• A. Photon
• B. Spirogyra
• C. Action spectrum
• D. Accessory pigment

Explanation: The correct answer is Option C: Action spectrum. An action spectrum provides a visual representation of the relative effectiveness of different wavelengths of light in driving photosynthesis, making it essential for understanding how various light wavelengths contribute to photosynthesis. Option A, photons, refers to a basic unit of light energy and does not relate to a graph. Option B, Spirogyra, is a type of algae and is unrelated to the graphical representation in question. Accessory pigment, pertains to pigments that capture additional light energy for photosynthesis, not a type of graph.