🧬Biology
Cell Biology
Cell structure, organelles (mitochondria, Golgi, ER), cell membrane, cell division (mitosis, meiosis).
Class 11Class 12
What You Will Learn in Cell Biology
Cell biology studies the structure, function, and behaviour of cells — the basic structural and functional units of all living organisms.
- Prokaryotes (no nucleus, smaller 1-10μm): bacteria, archaea. Eukaryotes (membrane-bound nucleus, larger): plants, animals, fungi.
- Plasma membrane: phospholipid bilayer + proteins (Singer-Nicolson fluid mosaic model).
- Cell organelles: mitochondria (powerhouse, ATP via aerobic respiration), chloroplast (photosynthesis, only in plant cells), ribosome (protein synthesis).
- ER: rough ER (ribosomes, protein synthesis + transport), smooth ER (lipid synthesis, detoxification).
- Golgi apparatus: modifies, packages, and sorts proteins/lipids for secretion or internal use.
- Cell division: mitosis (growth/repair, 2 identical daughter cells), meiosis (sexual reproduction, 4 haploid cells).
Example
Mitochondria convert glucose + O₂ → ATP + CO₂ + H₂O, providing ~36-38 ATP per glucose molecule.
Expected Exam Questions — Cell Biology
Q1.What is the fluid mosaic model of the plasma membrane?
Answer: Proposed by Singer & Nicolson (1972): membrane is a phospholipid bilayer (fluid) with proteins embedded/floating (mosaic). Phospholipids have hydrophilic heads (outside) and hydrophobic tails (inside). Proteins serve as channels, receptors, transporters.
Q2.Distinguish between mitosis and meiosis.
Answer: Mitosis: somatic cells, produces 2 identical diploid daughter cells, 1 division, no genetic recombination — for growth and repair. Meiosis: sex cells, produces 4 haploid gametes, 2 divisions (Meiosis I + II), genetic recombination via crossing over in Prophase I — for sexual reproduction.
Q3.What is the role of ribosomes? Where are they found?
Answer: Ribosomes are sites of protein synthesis (translation) — read mRNA and link amino acids. Found free in cytoplasm (for cytoplasmic proteins) or attached to rough ER (for secretory/membrane proteins). Made of ribosomal RNA (rRNA) + proteins: 80S in eukaryotes (60S+40S), 70S in prokaryotes (50S+30S).
🔘 MCQ Practice — Cell Biology
MCQ 1.Which organelle is called the 'powerhouse of the cell'?
A. Chloroplast
B. Ribosome
C. Mitochondria ✓
D. Golgi apparatus
✓ Correct Answer: Mitochondria
MCQ 2.The fluid mosaic model describes the structure of:
A. Cell wall
B. Plasma membrane ✓
C. Nuclear envelope
D. Ribosome
✓ Correct Answer: Plasma membrane
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