All Free Biology MCQs with Answers

3451. Which of the following releases 7.3 kcal energy when terminal phosphate is lost?

• A. NADP
• B. ADP
• C. ATP
• D. FAD

Explanation: ATP has three phosphate groups. Energy is stored in the bonds joining the phosphate groups. The covalent bond holding the third phosphate group carries about 7,300 calories of energy.

3452. To reduce one molecule of O2 _ _ _ electron(s) must be passed through the electron transport chain and _ _ _ molecule(s) of NADH ls(are) oxidized.

• A. 1:1
• B. 4:4
• C. 1:2
• D. 4:2

Explanation: For every 2 electrons carried by respiratory electron chain, one molecule of NADH is oxidized. This gives a ratio of 2:1. Here, four electrons will pass through the chain. So, 2 molecules of NADH will be oxidized which makes option D correct.

3453. "Photo-phosph-rylation" is:

• A. ATP synthesis by food energy
• B. ATP synthesis by solar energy
• C. ATP synthesis by source of water
• D. ATP synthesis by source of NADH2

Explanation: It is the process of utilizing light energy to convert ADP to ATP.

3454. Which type of mammalian cell does not carry out oxidative phosphorylation?

• A. Cardiac muscle cells
• B. Liver cells
• C. Neurons
• D. RBCs

Explanation: RBCs have a biconcave shape and it lacks nucleus and mitochondria and hence many metabolic pathways such as oxidative phosphorylation. Instead, RBCs depend on the anaerobic conversion of glucose via pyruvate to lactate.

3455. A drug reduces mitochondrial activity in nephrons of the kidney. Which chemical will be present in increased amounts in the urine?

• A. Ammonia
• B. Glucose
• C. Hydrogen bicarbonate
• D. Urea

Explanation: This happens because in mitochondria aerobic respiration occurs(breakdown of food in presence of oxygen)The food is glucose.Aerobic respiration:Glucose+O2=CO2 + ATPSo if the mitochondrial activity is reduced then glucose will not be used and will be excreted out through urine.

3456. During which of the following processes ATP is produced? (I) Photosynthesis(II) Aerobic respiration(III) Anaerobic respiration

• A. I only
• B. II only
• C. I and II only
• D. I, II and III only

Explanation: ATP is produced during photosynthesis as well as aerobic and anaerobic respiration.

3457. Green plants carry on respiration

• A. Only during the day
• B. Only at night
• C. During both day and night
• D. Only when photosynthesis is going on

Explanation: Respiration is the process by which cells generate energy from glucose and oxygen, and it is a continuous metabolic activity necessary for the plant's survival. While photosynthesis primarily occurs during the day when there is light available, respiration occurs 24/7 because plants need energy both for their daytime activities and to support basic functions like growth and maintenance during the night when there is no sunlight for photosynthesis. Therefore, plants respire both during the day and at night to maintain their life processes.

3458. Photophosphorylation during photosynthesis results in the formation of:

• A. ATP
• B. NAD
• C. FAD
• D. ADP

Explanation: Photophosphorylation is the process of utilizing light energy from photosynthesis to convert ADP to ATP.

3459. A process of CO₂ fixation in photosynthesis by which the first product is the four-carbon oxaloacetate molecule is called:

• A. C3 photosynthesis
• B. C4 photosynthesis
• C. Light reaction
• D. Cyclic electron flow

Explanation: The correct answer is C4 photosynthesis. In C4 photosynthesis, carbon dioxide is initially fixed into a four-carbon compound, oxaloacetate, which is an adaptation to minimize photorespiration and increase efficiency under specific environmental conditions. This process occurs in plants like maize and sugarcane, where the fixation happens in mesophyll cells and is then transferred to bundle sheath cells where the Calvin cycle takes place.C3 photosynthesis is incorrect because it involves the direct fixation of CO₂ into a three-carbon compound, not oxaloacetate.The light reaction is incorrect, as it deals with the conversion of light energy into chemical energy without involving carbon fixation.Cyclic electron flow is incorrect because it focuses on electron transport in the light-dependent reactions and does not relate to the carbon fixation process.

3460. The first stable product of the Calvin cycle is

• A. 3-phosphoglycerate
• B. 1,3-biphosphoglycerate
• C. Glyceraldehyde-3-phosphate
• D. Ribulose-5-phosphate

Explanation: The correct option is 3-phosphoglycerate, as it is the first stable product formed during the Calvin cycle after carbon fixation. 1,3-biphosphoglycerate is an unstable intermediate formed later in the reduction phase. Glyceraldehyde-3-phosphate is produced after further reduction steps and is used for glucose synthesis. Ribulose-5-phosphate is an intermediate involved in the regeneration of ribulose-1,5-bisphosphate, not a direct product of carbon fixation.