Cell Biology
Subject: General Science — Biology | Topic: Cell Biology Exam: AP Group 2 (APPSC) | Sources: NCERT Class IX, Lucent's GS
Introduction
Cell biology covers cell discovery, structure, organelles, division, and osmosis. APPSC typically asks 1-2 questions — organelle functions ("powerhouse of the cell," "suicide bags") and plant vs animal cell differences are the most tested.
Discovery and Cell Theory
- Robert Hooke (1665): First observed cells in cork; coined the term "cell."
- Anton van Leeuwenhoek: First observed living cells (bacteria, protozoa) using a microscope.
- Cell Theory (Schleiden & Schwann, 1839): All living organisms are made of cells. The cell is the basic structural and functional unit of life.
- Rudolf Virchow (1858): "Omnis cellula e cellula" — all cells arise from pre-existing cells.
Types of Cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | No true nucleus (nucleoid region) | Well-defined nucleus with membrane |
| Organelles | No membrane-bound organelles | Membrane-bound organelles present |
| Size | 1-10 μm | 10-100 μm |
| Examples | Bacteria, Blue-green algae (Cyanobacteria) | Plant cells, Animal cells, Fungi |
Cell Organelles
| Organelle | Function | Nickname |
|---|---|---|
| Cell membrane | Selectively permeable; controls entry/exit | — |
| Cell wall | Rigidity and protection (cellulose in plants) | — |
| Nucleus | Control centre; contains DNA | "Brain of the cell" |
| Rough ER | Protein synthesis and transport (has ribosomes) | — |
| Smooth ER | Lipid synthesis, detoxification | — |
| Ribosomes | Protein factories; made of RNA and protein | — |
| Golgi Apparatus | Packaging, modification, dispatch of proteins; forms lysosomes | "Post office of the cell" |
| Lysosomes | Digestive enzymes; break down worn-out organelles | "Suicide bags of the cell" |
| Mitochondria | Aerobic respiration; produce ATP; have own DNA | "Powerhouses of the cell" |
| Chloroplasts | Photosynthesis; contain chlorophyll; own DNA (plant cells only) | — |
| Vacuoles | Storage; large central vacuole in plants (50-90% volume) | — |
| Centrosomes | Cell division; form spindle fibres (animal cells) | — |
Plant Cell vs Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present (cellulose) | Absent |
| Chloroplasts | Present | Absent |
| Large central vacuole | Present | Small, temporary vacuoles |
| Centrioles | Absent in most | Present |
| Shape | Fixed (rectangular) | Irregular |
Both have: cell membrane, nucleus, mitochondria, ER, Golgi, ribosomes.
Cell Division
| Type | Daughter Cells | Chromosome Number | Purpose | Occurs In |
|---|---|---|---|---|
| Mitosis | 2 identical | Same as parent (diploid) | Growth and repair | Somatic cells |
| Meiosis | 4 different | Half (haploid) | Gamete formation | Reproductive cells |
Stages of mitosis: Prophase → Metaphase → Anaphase → Telophase (PMAT).
Osmosis and Diffusion
| Process | Definition | Example |
|---|---|---|
| Diffusion | Movement from high to low concentration | Perfume smell spreading |
| Osmosis | Water movement through semipermeable membrane from dilute to concentrated | Root absorption of water |
| Solution Type | Effect on Cell |
|---|---|
| Hypertonic (more solute outside) | Cell shrinks (plasmolysis in plants) |
| Hypotonic (less solute outside) | Cell swells (turgid in plants; may burst in animal cells) |
| Isotonic (equal) | No net movement |
Tissues (Overview)
- Plant tissues: Meristematic (dividing, at tips) and Permanent (parenchyma, collenchyma, sclerenchyma, xylem, phloem).
- Animal tissues: Epithelial (covering), Connective (bone, blood, cartilage), Muscular (movement), Nervous (impulse transmission).
Likely Exam Questions
-
Mitochondria are called the: Ans: Powerhouses of the cell
-
Lysosomes are known as: Ans: Suicide bags of the cell
-
The cell wall in plants is made of: Ans: Cellulose
-
Human cells have how many chromosomes? Ans: 46 (23 pairs)
-
Meiosis produces how many daughter cells? Ans: 4 (with half the chromosome number)
-
Who coined the term "cell"? Ans: Robert Hooke (1665)
-
The organelle responsible for packaging and dispatch of proteins is: Ans: Golgi Apparatus
-
In a hypertonic solution, a plant cell: Ans: Shrinks (undergoes plasmolysis)
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Which organelle has its own DNA besides the nucleus? Ans: Mitochondria (and chloroplasts in plant cells)
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The basic unit of life is: Ans: The cell