Cell Biology

Step 1: Match each organelle with its function.
• Nucleolus → site of RNA synthesis (4).
• Sphaerosomes → store lipids in plant cells (1).
• Peroxisomes → involved in fatty acid breakdown via β-oxidation (2).
• Plasmodesmata → facilitate transport of macromolecules between plant cells (3).
Step 2: Match with provided options.
Only option (B) corresponds to the correct mapping: P-4, Q-1, R-2, S-3.
Step 3: Conclusion.
Thus, option (B) correctly matches organelles with their functions.

Step 1: Understanding the reaction.
The given reaction is: The standard electrode potentials are: and Step 2: Calculating the standard emf.
The standard emf for the reaction is: Here, is reduced (cathode) and is oxidized (anode). So: Step 3: Conclusion.
The standard emf of the cell is 0.50 V.

Step 1: Understanding the cell cycle.
The phases of the eukaryotic cell cycle include G1, S, G2, and M. The correct sequence of these phases is essential to understanding how cells divide and replicate. The S phase is where DNA replication occurs, G1 and G2 are growth phases, and M is mitosis.
Step 2: Analyzing the options.
The figure representing the correct sequence follows the order of G1, S, G2, M.
(A) Figure A: Incorrect. The sequence does not follow the typical order.
(B) Figure B: Correct — This shows the correct sequence of phases: G1 → S → G2 → M.
(C) Figure C: Incorrect. The order is reversed in some places.
(D) Figure D: Incorrect. This is not the correct order.
Step 3: Conclusion.
The correct answer is (B) Figure B, as it shows the correct order of phases in the cell cycle.

Step 1: Understanding the drugs.
Taxol and colchicine are both drugs that affect microtubules. Taxol stabilizes microtubules, preventing their disassembly, while colchicine prevents microtubule formation by binding to tubulin.
Step 2: Analyzing the options.
(A) Taxol causes DNA damage and colchicine prevents microtubule formation: Incorrect — Taxol does not primarily cause DNA damage.
(B) Taxol stabilizes microtubules and colchicine inhibits protein synthesis: Incorrect — Colchicine does not affect protein synthesis, but microtubule formation.
(C) Taxol destabilizes microtubules and colchicine promotes microtubule formation: Incorrect — This is the opposite of their actual modes of action.
(D) Taxol stabilizes microtubules and colchicine prevents microtubule formation: Correct — This correctly describes the effects of taxol and colchicine on microtubules.
Step 3: Conclusion.
The correct answer is (D) Taxol stabilizes microtubules and colchicine prevents microtubule formation.

Step 1: Understanding myeloid lineage.
The myeloid lineage includes cells such as erythrocytes, macrophages, and granulocytes. These cells develop from hematopoietic stem cells in the bone marrow. T and B lymphocytes, on the other hand, develop from the lymphoid lineage.
Step 2: Analyzing the options.
(A) Macrophages: Correct — Macrophages develop from the myeloid lineage.
(B) T lymphocytes: Incorrect — T lymphocytes develop from the lymphoid lineage.
(C) B lymphocytes: Incorrect — B lymphocytes also develop from the lymphoid lineage.
(D) Erythrocytes: Incorrect — Erythrocytes develop from the myeloid lineage.
Step 3: Conclusion.
The correct answer is (A) Macrophages, as they develop from the myeloid lineage.

Step 1: Using the Nernst equation for calculating cell potential. The cell potential is calculated using the standard electrode potentials for the half-reactions: For the Daniell cell:
- The reduction half-reaction at the cathode (copper): - The oxidation half-reaction at the anode (zinc): Step 2: Calculating the standard cell potential. Final Answer:

Step 1: Understanding the apoptosome.
The apoptosome is a large protein complex involved in the initiation of apoptosis, which is a programmed cell death process. The apoptosome is formed in response to stress or damage signals, and it plays a crucial role in activating caspases that execute the cell death process.
Step 2: Analyzing the options.
- (A) Cytochrome c is released from mitochondria during apoptosis and is a key molecule that triggers the formation of the apoptosome, but it is not itself a component of the apoptosome.
- (B) Correct: Procaspase 9 is a key component of the apoptosome. When cytochrome c binds to apoptotic protease activating factor-1 (Apaf-1), it activates procaspase 9, which then initiates the caspase cascade leading to cell death.
- (C) Caspase 3 is activated downstream of procaspase 9. It is involved in the execution phase of apoptosis but is not a component of the apoptosome.
- (D) Caspase 8 is involved in the extrinsic apoptotic pathway and does not directly participate in the apoptosome formation.
Step 3: Conclusion.
The apoptosome contains procaspase 9 as a major component.
Final Answer:

Step 1: Identify target of HIV-1.
HIV specifically binds to CD4 receptors, which are highly expressed on T-helper lymphocytes (CD4+ cells).
Step 2: Mechanism.
Entry requires CD4 receptor plus co-receptors (CCR5 or CXCR4). The virus destroys T-helper cells, leading to immunodeficiency.
Step 3: Rule out other options.
- Cytotoxic T cells (CD8+) are not directly infected.
- Plasma cells and B-lymphocytes are not the primary targets.
Final Answer:

Step 1: Recall phases of cell cycle.
- G1 (Gap 1): Cell growth and preparation.
- S (Synthesis): DNA replication occurs.
- G2 (Gap 2): Further growth and preparation for mitosis.
- M (Mitosis): Chromosome segregation and cytokinesis.
Step 2: Compare sequences.
Only option (A) correctly follows the standard cell cycle order.
Final Answer:

Step 1: Define asymmetric cell division.
In asymmetric cell division, daughter cells receive equal genetic material (chromosomes), but they differ in cytoplasmic determinants such as RNA, proteins, and organelles. This leads to functional diversity.
Step 2: Evaluate options.
- (A) Incorrect. Chromosomes are always equally distributed in daughter cells during normal mitosis/meiosis. Unequal distribution would cause aneuploidy, not asymmetry.
- (B) Correct statement. Chromosomes are equally distributed.
- (C) Correct statement. RNA and proteins are unequally distributed.
- (D) Correct statement. Cytoplasmic contents differ between cells.
Final Answer: