All Free Biology MCQs with Answers

3221. What is the function of Ribulose?

• A. Intermediates in photosynthesis
• B. Respiratory fuel
• C. Intermediates in cellular respiration
• D. Component of DNA and RNA

Explanation: Ribulose is a type of sugar and is involved in several biological processes, particularly in the context of photosynthesis. The most notable role of ribulose is in the Calvin Cycle, which is the light-independent phase of photosynthesis that takes place in the stroma of chloroplasts. In the Calvin Cycle, ribulose plays a key role in the carbon fixation process. Ribulose-1,5-bisphosphate (RuBP), a five-carbon sugar, is crucial in the initial step of the Calvin Cycle. It combines with carbon dioxide (CO2) from the atmosphere with the help of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). This reaction leads to the formation of an unstable six-carbon compound that immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA), which are then used in the synthesis of carbohydrates.

3222. During photosynthesis, in the electron transport chain, 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. It occurs when electrons move from Cyt b6-f complex to Pc.

3223. Photophosphorylation takes place in the _ of the chloroplasts:

• A. Stroma
• B. Granum
• C. Inner membrane
• D. Outer membrane

Explanation: Photophosphorylation takes place in the thylakoid membrane of the chloroplasts. This process, part of the light-dependent reactions of photosynthesis, uses light energy to create a proton gradient across the thylakoid membrane, which then drives the synthesis of ATP from ADP and inorganic phosphate.

3224. During the first three steps of glycolysis, glucose is converted to Fructose 1, 6-diphosphate by the rearrangement of the molecule and addition of two phosphate groups. The phosphate comes from?

• A. Phospholipids of the membrane
• B. ADP
• C. Inorganic phosphates
• D. ATP

Explanation: During the initial steps of glycolysis, ATP molecules are crucial for facilitating the phosphorylation of glucose. In the first step, glucose is phosphorylated by ATP to form glucose-6-phosphate, catalyzed by the enzyme hexokinase. In the third step, another ATP molecule donates a phosphate group to fructose 6-phosphate, forming fructose 1,6-diphosphate through the action of the enzyme phosphofructokinase. These phosphorylation steps are essential for the continuation of glycolysis and subsequent energy production. The other options, like phospholipids and ADP, do not contribute phosphate groups in this metabolic pathway, while inorganic phosphates are not the direct source of phosphorylation in these steps.

3225. Pyruvic acid is the end product of:

• A. Glycolysis
• B. Krebs cycle
• C. Oxidation
• D. Electron transport system

Explanation: Pyruvic acid is the end product of glycolysis, the first stage of cellular respiration. During glycolysis, one glucose molecule is enzymatically converted into two molecules of pyruvic acid in the cytoplasm, with a net gain of ATP and NADH. Glycolysis does not involve oxygen and precedes the Krebs cycle and electron transport chain, which occur in the mitochondria. The Krebs cycle processes acetyl-CoA, not pyruvic acid, and the electron transport system produces ATP and water. Oxidation is a broader term referring to electron loss and is not specific to producing pyruvic acid.

3226. Stroma of chloroplast carries the fixation of:

• A. Nitrogen
• B. Oxygen
• C. Carbon monoxide
• D. Carbon dioxide

Explanation: Carbon dioxide (CO2) is fixed in the stroma of chloroplasts during the light-independent reactions, also known as the Calvin cycle or the dark reactions. In this process, carbon dioxide molecules are captured and converted into organic molecules, such as glucose, through a series of enzymatic reactions. This fixation of carbon dioxide is crucial for the synthesis of organic compounds,

3227. Which type of chlorophyll is found in all types of algae?

• A. Chlorophyll a
• B. Chlorophyll b
• C. Chlorophyll c
• D. Chlorophyll d

Explanation: Chlorophyll a is found in all types of algae. Chlorophyll a is a primary photosynthetic pigment that plays a central role in capturing light energy during the process of photosynthesis. Algae, which are a diverse group of photosynthetic organisms, utilize chlorophyll a along with other pigments for harvesting light energy and converting it into chemical energy.

3228. Carotenoids are related to:

• A. Vitamin A
• B. Vitamin B
• C. Vitamin C
• D. Vitamin D

Explanation: Carotenoids are related to Vitamin A. They are a group of pigments that are responsible for the yellow, orange, and red colors of many fruits and vegetables. In the human body, carotenoids can be converted into Vitamin A, which is important for vision, immune function, and skin health.

3229. Dark reaction of photosynthesis takes place in _ of the chloroplast.

• A. Thylakoids
• B. Grana
• C. Intergrana
• D. Stroma

Explanation: The dark reactions of photosynthesis, also known as the Calvin Cycle or light-independent reactions, take place in the stroma of the chloroplast. The stroma is the fluid-filled region surrounding the thylakoid membranes in the chloroplast. While the light-dependent reactions occur in the thylakoid membrane, the Calvin Cycle, where carbon dioxide is fixed and converted into carbohydrates, occurs in the stroma.

3230. Oxygen, released into the atmosphere, comes from:

• A. CO2
• B. H2O
• C. C6H12O6
• D. CO2 and H2O

Explanation: Oxygen released into the atmosphere during photosynthesis comes from the splitting of water molecules. The oxygen-evolving complex in the thylakoid membrane of chloroplasts is responsible for catalyzing the light-dependent reactions of photosynthesis, where water molecules are split into oxygen, protons (H⁺ ions), and electrons.