Section A — Detailed Solutions (Cell
Biology)
Q1. Define cell biology.
Answer:
Cell biology is the branch of biology that studies the structure, function, and behavior of
cells, which are the basic units of life. It includes the study of cell organelles, cell division,
signaling, and interaction with their environment.
Q2. What are prokaryotic and eukaryotic cells? Give examples.
Answer:
• Prokaryotic cells lack a true nucleus and membrane-bound organelles. Example:
Bacteria, Archaea.
• Eukaryotic cells have a well-defined nucleus and organelles. Example: Plant cells,
Animal cells, Fungi.
Q3. Write a function of mitochondria.
Answer:
Mitochondria are known as the "powerhouse of the cell" because they produce energy in the
form of ATP through cellular respiration.
Q4. What is the plasma membrane composed of?
Answer:
The plasma membrane is primarily composed of a phospholipid bilayer embedded with
proteins, cholesterol, and carbohydrates following the Fluid Mosaic Model.
Q5. What is the role of lysosomes in cells?
Answer:
Lysosomes contain hydrolytic enzymes that digest unwanted materials, damaged organelles,
and foreign invaders, acting as the "waste disposal system" of the cell.
Q6. Define apoptosis.
Answer:
Apoptosis is a genetically programmed process of controlled cell death, essential for
maintaining tissue homeostasis and removing damaged or unwanted cells.
Q7. What are stem cells?
Answer:
Stem cells are undifferentiated cells that have the ability to self-renew and differentiate into
various specialized cell types under certain conditions.
Q8. Name two differences between mitosis and meiosis.
Answer:
Mitosis Meiosis
Produces 2 identical daughter cells Produces 4 genetically different cells
Involved in growth and repair Involved in sexual reproduction
Q9. What is endoplasmic reticulum? Name its types.
Answer:
The endoplasmic reticulum (ER) is a network of membranous tubules involved in protein and
lipid synthesis.
Types:
• Rough ER (with ribosomes)
• Smooth ER (without ribosomes)
Q10. Write the importance of ribosomes in a cell.
Answer:
Ribosomes are essential for protein synthesis by translating messenger RNA (mRNA) into
polypeptide chains. They can be free in the cytoplasm or attached to the rough ER.
Section B — Detailed Solutions (Cell
Biology)
Q1. Discuss the structure and function of mitochondria with a diagram.
Answer:
• Structure:
o Mitochondria are double-membrane organelles.
o The outer membrane is smooth and permeable.
o The inner membrane is folded into structures called cristae to increase
surface area.
o The matrix inside contains enzymes, DNA, and ribosomes.
• Functions:
o Produces ATP through oxidative phosphorylation (cellular respiration).
o Involved in apoptosis (cell death signaling).
o Helps in calcium storage and heat production in brown fat.
Diagram:
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[ Outer Membrane ]
[ Inner Membrane with Cristae ]
[ Matrix ]
[ DNA and Ribosomes inside ]
(I can also create a neat diagram if you want for your notes.)
Q2. Explain the structure and functions of plasma membrane.
Answer:
• Structure:
o Made up of a phospholipid bilayer with embedded proteins (integral and
peripheral).
o Carbohydrates are attached to proteins/lipids forming
glycoproteins/glycolipids.
o Cholesterol molecules provide stability.
• Functions:
o Acts as a selective barrier controlling the entry and exit of substances.
o Helps in cell signaling and communication.
o Provides mechanical support and maintains cell shape.
Model: Fluid Mosaic Model (1972, Singer and Nicolson)
Q3. Describe the phases of the cell cycle.
Answer:
The cell cycle consists of:
• Interphase:
o G₁ phase: Cell growth and preparation for DNA replication.
o S phase: DNA replication occurs.
o G₂ phase: Further growth and preparation for mitosis.
• M phase (Mitosis):
o Division of the nucleus and cytoplasm.
• Cytokinesis: Final division into two daughter cells.
Note: Cells can enter G₀ phase (resting phase) from G₁ if they do not divide.
Q4. Differentiate between prokaryotic and eukaryotic cells.
Answer:
Prokaryotic Cell Eukaryotic Cell
No true nucleus (nucleoid region) True nucleus with nuclear membrane
No membrane-bound organelles Membrane-bound organelles present
Smaller size (1–10 µm) Larger size (10–100 µm)
Example: Bacteria Example: Animal cells, Plant cells
Q5. Explain apoptosis and its biological importance.
Answer:
• Apoptosis is a programmed process of cell death involving a series of biochemical
events.
• Cells shrink, DNA fragments, and apoptotic bodies are formed, later engulfed by
phagocytes.
• Importance:
o Removes damaged or abnormal cells.
o Helps during embryonic development (e.g., separation of fingers).
o Maintains tissue homeostasis.
o Prevents cancer by eliminating mutated cells.
Q6. Write a short note on cell signaling.
Answer:
• Cell signaling is the mechanism by which cells communicate with each other and
respond to external stimuli.
• Types:
o Autocrine (self-signaling)
o Paracrine (nearby signaling)
o Endocrine (hormonal signaling)
o Juxtacrine (direct contact)
• Key stages:
1. Signal reception by receptors.
2. Signal transduction inside the cell.
3. Cellular response.
Q7. Draw and label a typical eukaryotic animal cell.
Answer:
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[ Cell membrane ]
[ Nucleus ]
[ Cytoplasm ]
[ Mitochondria ]
[ Endoplasmic Reticulum (Rough and Smooth) ]
[ Golgi Apparatus ]
[ Ribosomes ]
[ Lysosomes ]
(Would you like a properly labeled full diagram image? I can create one for your notes.)
Q8. Describe transport mechanisms across cell membranes.
Answer:
Transport mechanisms are:
• Passive Transport (No energy required):
o Simple diffusion: Movement of small molecules like O₂.
o Facilitated diffusion: Movement via carrier proteins (e.g., glucose transport).
o Osmosis: Movement of water.
• Active Transport (Energy required - ATP):
o Movement against concentration gradient (e.g., Na⁺/K⁺ pump).
• Bulk Transport:
o Endocytosis: Intake of materials.
o Exocytosis: Expelling materials.
Q9. Explain the functions of the Golgi apparatus.
Answer:
• Modifies, sorts, and packages proteins and lipids for secretion or delivery to other
organelles.
• Forms lysosomes.
• Involved in the synthesis of cell wall components in plants.
• Participates in the processing of glycoproteins and lipoproteins.
Q10. Describe the role of stem cells in regeneration and therapy.
Answer:
• Regeneration: Stem cells replace damaged tissues (e.g., skin, blood).
• Therapy: Stem cells are used to treat diseases like leukemia (bone marrow
transplants), Parkinson's disease, and spinal cord injuries.
• Potential: Future applications in organ regeneration and personalized medicine.
Section C — Detailed Long Answers (Cell
Biology)
Q1. Describe the structure and function of all major cell organelles.
Answer:
Organelle Structure Function
Double membrane; nuclear
Controls cell activities; DNA storage;
Nucleus pores; contains DNA and
RNA synthesis
nucleolus
Double membrane; cristae;
ATP production via cellular
Mitochondria matrix contains enzymes and
respiration
DNA
Endoplasmic Network of membranous Rough ER: Protein synthesis; Smooth
Reticulum (ER) tubules ER: Lipid synthesis and detoxification
Stack of flattened membranous Modification, packaging, and
Golgi Apparatus
sacs transport of proteins and lipids
Membrane-bound vesicles with Digestion of waste materials and
Lysosomes
enzymes worn-out organelles
RNA and protein molecules,
Ribosomes Protein synthesis
free or attached
Phospholipid bilayer with Selective permeability;
Plasma Membrane
proteins communication
Single membrane with Breakdown of fatty acids and
Peroxisomes
oxidative enzymes detoxification
Network of microtubules, actin Maintains cell shape, enables
Cytoskeleton
filaments movement
Cylindrical structures near Cell division (spindle fiber formation)
Centrioles
nucleus in animals
Q2. Explain mitosis and meiosis with neat diagrams. Compare them.
Answer:
Mitosis:
• Division of somatic cells to produce 2 identical daughter cells.
• Stages:
o Prophase
o Metaphase
o Anaphase
o Telophase
o Cytokinesis
Meiosis:
• Occurs in germ cells to produce 4 non-identical gametes (sperm/egg).
• Two divisions: Meiosis I and Meiosis II.
• Leads to genetic variation.
Comparison Table:
Feature Mitosis Meiosis
No. of divisions 1 2
Daughter cells 2 identical 4 non-identical
Chromosome number Same (diploid) Halved (haploid)
Purpose Growth, repair Sexual reproduction
(I can create proper diagrams of mitosis and meiosis stages for you if you want.)
Q3. Discuss the mechanisms of cell communication and signal transduction.
Answer:
• Cell Communication: Cells use signaling molecules (ligands) to communicate.
• Types of Signaling:
o Autocrine
o Paracrine
o Endocrine
o Direct contact (juxtacrine)
• Signal Transduction Pathway:
1. Reception — Ligand binds to receptor.
2. Transduction — Signal is amplified inside the cell (via second messengers
like cAMP).
3. Response — Activation of cellular activities like gene expression.
Important:
• Signal molecules: Hormones, neurotransmitters.
• Receptors: GPCRs, Tyrosine Kinase Receptors.
Q4. Describe the structure of the plasma membrane according to the Fluid Mosaic
Model.
Answer:
• Fluid Mosaic Model (Singer and Nicolson, 1972):
o Plasma membrane is a dynamic, fluid structure with a bilayer of
phospholipids.
o Proteins are embedded (integral) or attached (peripheral) and can move
laterally.
o Carbohydrates attached to proteins/lipids form glycoproteins and glycolipids.
o Cholesterol molecules maintain fluidity.
Key Features:
• Selective permeability.
• Flexibility and self-healing nature.
Diagram: (can be made neatly if you want)
Q5. Explain the role of different organelles in protein synthesis and transport.
Answer:
1. Nucleus: DNA transcribed to mRNA.
2. Ribosomes (on Rough ER): Translate mRNA into polypeptide chains (proteins).
3. Rough ER: Initial folding and modification of proteins.
4. Golgi Apparatus: Further processing, sorting, and packaging of proteins.
5. Vesicles: Transport proteins to various destinations or for secretion.
Q6. Write an essay on programmed cell death (apoptosis) and its significance in health
and disease.
Answer:
• Definition: Controlled process of cell death without causing inflammation.
• Mechanism:
o Activation of caspases (proteases).
o DNA fragmentation, membrane blebbing.
o Formation of apoptotic bodies.
• Significance:
o Normal Development: Removal of unneeded cells during development.
o Immune System: Elimination of infected or harmful cells.
o Cancer Prevention: Kills cells with DNA damage.
• Diseases:
o Too much apoptosis: Neurodegenerative diseases (e.g., Alzheimer’s).
o Too little apoptosis: Cancer.
Q7. What is cancer? How do cancer cells differ from normal cells at the molecular
level?
Answer:
• Cancer: Uncontrolled growth and division of abnormal cells.
• Molecular Differences:
o Mutations in oncogenes and tumor suppressor genes.
o Loss of apoptosis.
o Sustained angiogenesis (blood vessel formation).
o Ability to invade other tissues (metastasis).
o Altered metabolism and evasion of immune detection.
Q8. Explain the importance of stem cells in modern biotechnology.
Answer:
• Types: Embryonic stem cells (pluripotent) and adult stem cells (multipotent).
• Uses:
o Regenerative medicine (e.g., skin grafts, spinal cord injuries).
o Treatment of blood cancers (bone marrow transplants).
o Personalized medicine and organ cloning possibilities.
• Research Areas: Disease modeling, drug testing.
Q9. Discuss active and passive transport mechanisms across membranes.
Answer:
Feature Passive Transport Active Transport
Energy Required? No Yes (ATP)
Direction Down concentration gradient Against concentration gradient
Examples Diffusion, Osmosis Sodium-potassium pump, Proton pumps
• Passive Transport: Diffusion, facilitated diffusion, osmosis.
• Active Transport: Endocytosis, exocytosis, ion pumps.
Q10. Elaborate the events during each phase of the cell cycle.
Answer:
• G₁ Phase: Cell grows; proteins and organelles synthesized.
• S Phase: DNA replication (each chromosome duplicated).
• G₂ Phase: Further growth; preparation for division.
• M Phase:
o Mitosis (Prophase, Metaphase, Anaphase, Telophase)
o Cytokinesis (splitting of cytoplasm).
Checkpoint control ensures damaged DNA is not passed on.
