📑 Topics on this page (Jump to Topic):
📌 1. Discovery of Cell & Cell Theory
- The cell is the structural and functional unit of life. Robert Hooke (1665) saw dead cells in cork and coined the word "cell".
- Leeuwenhoek (1674) first saw living cells (bacteria, protozoa). Robert Brown (1831) discovered the nucleus.
- Cell theory — Schleiden (1838, plants) and Schwann (1839, animals); Virchow (1855): "all cells arise from pre-existing cells".
- Largest cell — ostrich egg; longest — nerve cell; smallest — Mycoplasma (PPLO).
| Prokaryotic | Eukaryotic |
|---|---|
| No nuclear membrane (nucleoid) | Well-defined nucleus |
| No membrane-bound organelles | Mitochondria, ER, Golgi etc. |
| 70S ribosomes | 80S ribosomes (in cytoplasm) |
| Bacteria, blue-green algae | Plants, animals, fungi, protists |
📌 2. Cell Organelles & Functions
| Organelle | Main function / fact |
|---|---|
| Plasma membrane | Selectively permeable; lipid-protein (fluid mosaic model) |
| Cell wall | Cellulose in plants, chitin in fungi; absent in animal cells |
| Nucleus | Control centre; DNA/chromosomes |
| Mitochondria | "Powerhouse"; ATP; own DNA and 70S ribosomes |
| Chloroplast | Photosynthesis; plants only; own DNA |
| Ribosome | Protein synthesis; non-membranous |
| Endoplasmic reticulum | RER — proteins; SER — lipids and detoxification |
| Golgi apparatus | Packaging and secretion; dictyosomes in plants |
| Lysosome | "Suicide bag"; digestive enzymes |
| Vacuole | Large central in plants; maintains turgor |
| Centrosome | In animal cells; forms spindle during division |
- Plant cells have a cell wall, chloroplasts and a large vacuole; animal cells have centrosomes and prominent lysosomes.
- Osmosis — movement of water across a semi-permeable membrane from lower to higher solute concentration. Plasmolysis — shrinking of a cell in a hypertonic solution.
📌 3. Cell Division
| Mitosis | Meiosis |
|---|---|
| In somatic cells | In germ cells (gamete formation) |
| 2 daughter cells | 4 daughter cells |
| Chromosome number same (2n → 2n) | Chromosome number halved (2n → n) |
| Growth, repair | Variation through crossing over |
- Stages of mitosis: prophase → metaphase → anaphase → telophase (PMAT). Chromosomes are most clearly visible at metaphase, aligned at the equator.
- Humans have 46 chromosomes (23 pairs) — 22 pairs of autosomes + 1 pair of sex chromosomes; gametes have 23.
⚠️ Exam Traps:
- Robert Hooke saw dead cells; Leeuwenhoek first saw living cells.
- The ribosome has no membrane but is still counted as an organelle.
- Mature human red blood cells have no nucleus.
📌 4. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. Who first coined the term "cell"? Practice
Correct answer: (B)
In 1665 in a thin slice of cork.
In 1665 in a thin slice of cork.
Q2. The nucleus was discovered by: Practice
Correct answer: (D)
In 1831 in orchid cells.
In 1831 in orchid cells.
Q3. Which organelle is called the "powerhouse" of the cell? Practice
Correct answer: (A)
Produces ATP through cellular respiration.
Produces ATP through cellular respiration.
Q4. Which is known as the "suicide bag" of the cell? Practice
Correct answer: (C)
Its digestive enzymes can digest the cell itself.
Its digestive enzymes can digest the cell itself.
Q5. The site of protein synthesis is: Practice
Correct answer: (B)
Joins amino acids according to mRNA.
Joins amino acids according to mRNA.
Q6. The plant cell wall is mainly made of: Practice
Correct answer: (C)
The fungal cell wall is made of chitin.
The fungal cell wall is made of chitin.
Q7. Which of these is absent in an animal cell? Practice
Correct answer: (D)
Animal cells also lack chloroplasts.
Animal cells also lack chloroplasts.
Q8. Which organelles have their own DNA? Practice
Correct answer: (B)
Hence they are called semi-autonomous organelles.
Hence they are called semi-autonomous organelles.
Q9. "All cells arise from pre-existing cells" was stated by: Practice
Correct answer: (C)
1855 — Omnis cellula e cellula.
1855 — Omnis cellula e cellula.
Q10. The largest single cell is: Practice
Correct answer: (B)
The longest cell is the nerve cell.
The longest cell is the nerve cell.
Q11. The smallest known cell is: Practice
Correct answer: (A)
PPLO — lacks a cell wall.
PPLO — lacks a cell wall.
Q12. A prokaryotic cell has: Practice
Correct answer: (D)
No nuclear membrane; DNA in the nucleoid.
No nuclear membrane; DNA in the nucleoid.
Q13. Lipid synthesis and detoxification are functions of: Practice
Correct answer: (C)
RER carries ribosomes — protein synthesis.
RER carries ribosomes — protein synthesis.
Q14. Which organelle packages cell secretions? Practice
Correct answer: (A)
In plants it is called dictyosome.
In plants it is called dictyosome.
Q15. Mitosis produces: Practice
Correct answer: (A)
Chromosome number stays the same.
Chromosome number stays the same.
Q16. In meiosis the chromosome number: Practice
Correct answer: (C)
2n → n; during gamete formation.
2n → n; during gamete formation.
Q17. Crossing over occurs during: Practice
Correct answer: (D)
A source of genetic variation.
A source of genetic variation.
Q18. Chromosomes are most clearly visible during: Practice
Correct answer: (A)
Aligned on the equatorial plate.
Aligned on the equatorial plate.
Q19. Shrinking of a plant cell in a hypertonic solution is called: Practice
Correct answer: (D)
Water moves out of the cell.
Water moves out of the cell.
Q20. The "fluid mosaic model" of the plasma membrane was given by: Practice
Correct answer: (B)
Proposed in 1972.
Proposed in 1972.