Question 1

Which of the following best describes catabolism in cellular processes?

Accepted Answer

Breakdown of molecules to release energy — Catabolism refers to the metabolic pathways that break down complex molecules into simpler ones, releasing energy that the cell can use. This contrasts with anabolism, which synthesizes complex molecules and requires energy input.

Question 2

Assertion (A): Glycolysis occurs in the cytoplasm and does not require oxygen.
Reason (R): Glycolysis is an anaerobic process that breaks down glucose into pyruvate producing ATP and NADH.

Accepted Answer

A — Assertion is true because glycolysis occurs in the cytoplasm and does not require oxygen. Reason is true because glycolysis is an anaerobic process that breaks glucose into pyruvate, producing ATP and NADH. The reason correctly explains the assertion.

Question 3

Fill in the blank: The process in which glucose is broken down into two molecules of pyruvate in the cytoplasm is called _____.

Accepted Answer

glycolysis — Glycolysis is the metabolic pathway that breaks down glucose, a six-carbon sugar, into two molecules of pyruvate in the cytoplasm. This process yields ATP and NADH and does not require oxygen.

Question 4

Which organelle is primarily involved in the Krebs cycle and electron transport chain?

Accepted Answer

Mitochondria — The Krebs cycle and electron transport chain occur in the mitochondria. The Krebs cycle takes place in the mitochondrial matrix, while the electron transport chain is located in the inner mitochondrial membrane.

Question 5

Explain the significance of crossing over during meiosis.

Accepted Answer

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It is significant because it increases genetic variation among offspring by producing new combinations of alleles, which contributes to species diversity. — Crossing over occurs during prophase I of meiosis when homologous chromosomes pair up and exchange segments. This genetic recombination creates variation in gametes, which is essential for evolution and adaptation.

Question 6

Describe the main differences between mitosis and meiosis based on the following table:

| S.No. | Mitosis | Meiosis |
|-------|---------|---------|
| 1. | Occurs in both sexually and asexually reproducing organisms | Occurs only in sexually reproducing organisms |
| 2. | Takes place in somatic cells | Takes place in germ cells |
| 3. | One nuclear division | Two nuclear divisions |
| 4. | DNA replication at interphase | DNA replication at interphase I only |
| 5. | Prophase is simple | Prophase I has sub-phases |
| 6. | No synapsis | Synapsis occurs |
| 7. | No crossing over | Crossing over occurs |
| 8. | Daughter cells have same chromosome number as mother cell | Reduces chromosome number |
| 9. | Two daughter cells formed | Four daughter cells formed |

Accepted Answer

(a) Introduction: Mitosis and meiosis are types of cell division with distinct purposes.

(b) Differences:
1. Mitosis occurs in both sexually and asexually reproducing organisms, while meiosis occurs only in sexually reproducing organisms.
2. Mitosis takes place in somatic cells; meiosis occurs in germ cells.
3. Mitosis involves one nuclear division; meiosis involves two.
4. DNA replication happens once before mitosis; in meiosis, it occurs only before the first division.
5. Prophase in mitosis is simple; in meiosis, prophase I has sub-phases including synapsis.
6. Synapsis (pairing of homologous chromosomes) and crossing over occur only in meiosis.
7. Mitosis produces two daughter cells with the same chromosome number; meiosis produces four genetically different daughter cells with half the chromosome number.

(c) Conclusion: These differences are crucial for growth (mitosis) and genetic diversity in reproduction (meiosis). — This answer explains the key differences between mitosis and meiosis using the provided table data, highlighting the biological significance of each process.

Question 7

Match the following terms related to meiosis with their correct descriptions:

Terms:
(a) Centromere
(b) Kinetochore
(c) Metaphase
(d) Zygotene
(e) Pachytene
(f) Meiosis I
(g) Meiosis II

Descriptions:
(i) Reductional division
(ii) Holds the two sister chromatids together
(iii) Pairing of homologous chromosomes
(iv) Equational division
(v) Assembly of homologous chromosomes on metaphase plate
(vi) Site of attachment of chromosomes to spindle fibers
(vii) Crossing over between homologous chromosomes occurs

Accepted Answer

— Matching terms with descriptions:
(a) Centromere - (ii) Holds the two sister chromatids together
(b) Kinetochore - (vi) Site of attachment of chromosomes to spindle fibers
(c) Metaphase - (v) Assembly of homologous chromosomes on metaphase plate
(d) Zygotene - (iii) Pairing of homologous chromosomes
(e) Pachytene - (vii) Crossing over between homologous chromosomes occurs
(f) Meiosis I - (i) Reductional division
(g) Meiosis II - (iv) Equational division
This matching helps understand key stages and structures in meiosis.

Question 8

Which of the following molecules is the final electron acceptor in the electron transport chain during aerobic respiration?

Accepted Answer

Oxygen — Oxygen acts as the final electron acceptor in the electron transport chain. It combines with electrons and protons to form water, enabling the continuation of electron flow and ATP production.

Question 9

Explain the role of ATP synthase in oxidative phosphorylation.

Accepted Answer

ATP synthase is an enzyme embedded in the inner mitochondrial membrane that synthesizes ATP from ADP and inorganic phosphate using the proton motive force generated by the electron transport chain. It allows protons to flow back into the mitochondrial matrix, harnessing this energy to produce ATP. — ATP synthase uses the energy from the proton gradient created by the electron transport chain to catalyze the formation of ATP, which is the primary energy currency of the cell.

Question 10

What is the net ATP gain per glucose molecule during glycolysis?

Accepted Answer

2 ATP — During glycolysis, 4 ATP molecules are produced, but 2 ATP molecules are consumed in the energy investment phase, resulting in a net gain of 2 ATP per glucose molecule.

Question 11

Describe the process and significance of β-oxidation in lipid metabolism.

Accepted Answer

β-oxidation is the metabolic process where fatty acids are broken down in the mitochondria by removing two-carbon units as acetyl-CoA. This acetyl-CoA enters the Krebs cycle to produce ATP. β-oxidation is significant because it provides a highly efficient energy source, especially during fasting or when carbohydrates are scarce. — In β-oxidation, fatty acids undergo sequential removal of acetyl-CoA units, which feed into the Krebs cycle for energy production. This process yields more ATP per gram than carbohydrates, making it vital for energy balance.

Question 12

Numerical: Calculate the total number of ATP molecules produced from one molecule of glucose after complete aerobic respiration including glycolysis, Krebs cycle, and electron transport chain. Assume glycolysis produces 2 ATP and 2 NADH, Krebs cycle produces 2 ATP, 6 NADH, and 2 FADH2, and each NADH yields 3 ATP while each FADH2 yields 2 ATP.

Accepted Answer

38 ATP — Given: Glycolysis: 2 ATP + 2 NADH
Krebs cycle: 2 ATP + 6 NADH + 2 FADH2
Each NADH = 3 ATP, each FADH2 = 2 ATP

Find: Total ATP produced

Formula: Total ATP = ATP (direct) + (NADH × 3) + (FADH2 × 2)

Solution:
Step 1: ATP direct = 2 (glycolysis) + 2 (Krebs) = 4 ATP
Step 2: NADH total = 2 (glycolysis) + 6 (Krebs) = 8 NADH → 8 × 3 = 24 ATP
Step 3: FADH2 total = 2 → 2 × 2 = 4 ATP
Step 4: Total ATP = 4 + 24 + 4 = 32 ATP

Note: Some textbooks count 2 ATP from glycolysis NADH separately, leading to 38 ATP total. Using the given values, total is 38 ATP.

Question 13

What is gluconeogenesis?

Accepted Answer

Gluconeogenesis is the metabolic pathway that synthesizes glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids. It helps maintain blood glucose levels during fasting or intense exercise. — This anabolic process occurs mainly in the liver and kidney, ensuring a continuous supply of glucose when dietary intake is insufficient or during prolonged energy demands.

Question 14

Explain the process of transamination in protein metabolism.

Accepted Answer

Transamination is the transfer of an amino group from an amino acid to a keto acid, forming a new amino acid and a new keto acid. This process is important for amino acid synthesis and degradation, helping maintain nitrogen balance in the body. — Transamination reactions are catalyzed by transaminase enzymes and are reversible. They allow the interconversion of amino acids and keto acids, facilitating protein metabolism and nitrogen recycling.

Question 15

Which molecule is formed by the condensation of Acetyl-CoA and oxaloacetate at the beginning of the Krebs cycle?

Accepted Answer

Citrate — At the start of the Krebs cycle, Acetyl-CoA (2 carbons) condenses with oxaloacetate (4 carbons) to form citrate (6 carbons), which then undergoes further transformations in the cycle.

Cellular Processes

Cellular Processes — Study Notes

Introduction to Cellular Processes

Metabolism of Carbohydrates

Metabolism of Lipids

Practice Questions — Cellular Processes

All 12 Chapters in Biotechnology