All Free Biology MCQs with Answers

3311. The link between Kreb's cycle and glycolysis in carbohydrate metabolism is:

• A. Citric acid
• B. Oxaloacetate
• C. Succinate
• D. Acetyl CoA

Explanation: Acetyl CoA is the link between glycolysis and Kreb's cycle. Acetyl CoA is formed after decarboxylation of pyruvate. This acetyl CoA then enters Kreb's cycle.

3312. Electron transport chain takes place in which part of the cell?

• A. Cell membrane
• B. Nucleus
• C. Cytoplasm
• D. Mitochondria

Explanation: The electron transport chain (ETC) takes place in the mitochondria. More specifically, it occurs in the inner membrane of the mitochondria

3313. How many ATPs does one NADH ideally give?

• A. 1
• B. 2
• C. 4
• D. 3

Explanation: In the electron transport chain, electron carriers take electrons from NADH and FADH2 and pass them through a chain of complexes. The ETC takes the energy from these electrons and pumps protons (H+) into the intermembrane space. This creates a gradient of a high proton concentration in the intermembrane space and a low concentration in the matrix of mitochondria. ATP synthase uses this energy to make ATP. One NADH makes 3 ATPs and one FADH2 makes 2 ATPs.

3314. Cancer cells require large amounts of ATP. Which of the following produces a high number of ATP?

• A. Glycolysis
• B. Krebs cycle
• C. Oxidative Phosphorylation
• D. Electron transport chain

Explanation: Oxidative phosphorylation is the final stage of cellular respiration and takes place in the inner mitochondrial membrane. It involves the electron transport chain (ETC) and ATP synthase to produce a large number of ATP molecules. Oxidative phosphorylation is highly efficient and can produce up to 34 ATP molecules per glucose molecule, making it the primary process for generating large amounts of ATP in the presence of oxygen.

3315. Glycolysis takes place in:

• A. Nucleus
• B. Cytosol
• C. Mitochondria
• D. Ribosomes

Explanation: Glycolysis is the first step in the process of cellular respiration and occurs in the cytosol of the cell. During glycolysis, one glucose molecule is broken down into two molecules of pyruvate, producing a small amount of ATP and NADH in the process. The cytosol provides the necessary environment for these enzymatic reactions to occur. The nucleus, mitochondria, and ribosomes have different functions in the cell. The nucleus is involved in genetic information storage and processing, the mitochondria are responsible for the later stages of cellular respiration, and ribosomes are the sites of protein synthesis. Thus, glycolysis specifically takes place in the cytosol.

3316. In Anaerobic respiration, how much % of the energy, present within the chemical bond of glucose, is converted into ATP?

• A. 2
• B. 4.5
• C. 5.6
• D. 7.7

Explanation: In Anaerobic respiration only 2% of the energy present within the chemical bond of glucose is converted into ATP.

3317. How does the electron transport system generate ATP ?

• A. Symbiosis
• B. Chemiosmosis
• C. Both of these
• D. None of these

Explanation: Chemiosmosis is the movement of protons down an electrochemical gradient created by a partially permeable membrane via ATP synthase (stalked particles) embedded in the membrane to produce ATP.

3318. Chlorophylls mainly absorb light of which wavelength?

• A. Red blue
• B. Yellow orange
• C. Violet red
• D. Orange red
• E. Both C and D

Explanation: Chlorophyll mainly absorbs light in the violet-blue and orange-red wavelengths, which are crucial for the process of photosynthesis. While options A, B, C, and D each contain elements of light that chlorophyll can absorb, they do not accurately reflect the comprehensive absorption spectrum of chlorophyll. Therefore, the correct answer is option E, which indicates a group of options that may include misleading elements. It's essential to remember that chlorophyll reflects green light, which is why plants appear green, as it is not effectively absorbed.

3319. A metal cofactor which is used in synthesis of glycolysis is?

• A. Fe3+
• B. Mn2+
• C. Co2+
• D. Mg2+

Explanation: "Mg2+" is an inorganic cofactor used in glycolysis to convert glucose into glucose 6-phosphate.

3320. Which molecule passes the mitochondrial membrane to begin the Krebs cycle?

• A. ATP
• B. ADP
• C. NADH
• D. Acetyl CoA

Explanation: The correct answer is Acetyl CoA. Acetyl CoA is generated from pyruvate during glycolysis and enters the mitochondrial matrix, where it combines with oxaloacetate to start the Krebs cycle. This entry is facilitated by specific transport mechanisms across the mitochondrial membrane. Other options such as ATP, ADP, and NADH are involved in the Krebs cycle or related processes but do not serve as the initial molecule entering the cycle:ATP is a product of the cycle, not a participant in its initiation.ADP is converted to ATP during the cycle but does not enter the cycle itself.NADH is generated during the cycle and used in the electron transport chain but is not the starting molecule for the Krebs cycle.