Cell Biology
Key Concepts
| # | Concept | Explanation |
|---|---|---|
| 1 | Prokaryotic vs Eukaryotic | Prokaryotes (bacteria) lack nucleus & membrane-bound organelles; Eukaryotes (plants, animals, fungi) have both. |
| 2 | Cell Organelles & Functions | Mitochondria → ATP powerhouse; Chloroplast → photosynthesis; Ribosome → protein synthesis; Lysosome → digestion & suicide bag. |
| 3 | Cell Theory (3 Tenets) | All living things composed of cells; cell is basic unit of life; all cells arise from pre-existing cells. |
| 4 | DNA Packaging | Prokaryote = circular naked DNA; Eukaryote = DNA + histone proteins → chromatin → chromosomes inside nucleus. |
| 5 | Plasma Membrane | Fluid-mosaic model: phospholipid bilayer + proteins; selectively permeable; helps transport & recognition. |
| 6 | ATP Factory | 90% of cellular ATP made by mitochondria via aerobic respiration; matrix & cristae are key sites. |
| 7 | Cell Division Sequence | Interphase (G₁→S→G₂) → Mitosis (PMAT) → Cytokinesis; meiosis halves chromosome number for gametes. |
| 8 | Difference: Plant vs Animal Cell | Plant: cell wall (cellulose), large vacuole, chloroplast; Animal: centrosome, small/absent vacuole, no wall. |
15 Practice MCQs
1. Which cell organelle is called the “powerhouse of the cell”?
**Options:** A) Golgi body B) Mitochondria C) Lysosome D) Endoplasmic reticulumAnswer: B) Mitochondria
Solution: Site of Krebs cycle & oxidative phosphorylation → ATP.
Shortcut: Remember “M” for Might (power).
Tag: Organelle functions
2. Cell theory does NOT state that:
**Options:** A) Cells arise from pre-existing cells B) Cell is basic unit of life C) All cells have nucleus D) All living things are made of cellsAnswer: C) All cells have nucleus
Solution: Prokaryotic cells lack nucleus; theory never claims universal nucleus.
Shortcut: “No nucleus” in theory → eliminate C straightaway.
Tag: Cell theory
3. The site of photosynthesis in plant cells is:
**Options:** A) Mitochondria B) Peroxisome C) Chloroplast D) GlyoxysomeAnswer: C) Chloroplast
Solution: Contains chlorophyll; thylakoids house light reaction, stroma has Calvin cycle.
Shortcut: “Chloro” ≈ chlorophyll → photo.
Tag: Plant organelles
4. Which of the following is absent in animal cells?
**Options:** A) Centriole B) Ribosome C) Cell wall D) Plasma membraneAnswer: C) Cell wall
Solution: Only plants, fungi & bacteria have cell walls; animals rely on only membrane.
Shortcut: “Wall is for plants—animals walk without walls.”
Tag: Plant vs Animal
5. The suicide bag of the cell is:
**Options:** A) Lysosome B) Ribosome C) Centrosome D) MesosomeAnswer: A) Lysosome
Solution: Contains hydrolytic enzymes; bursts to digest cell debris or self-destruct.
Shortcut: “Lyse” = break → suicide.
Tag: Organelle nickname
6. Nucleolus is the site of synthesis of:
**Options:** A) DNA B) mRNA C) rRNA & ribosome assembly D) tRNAAnswer: C) rRNA & ribosome assembly
Solution: Dark-stained region inside nucleus; produces ribosomal subunits.
Shortcut: “Nucle-O-lus → Rib-O-some” (both “O”).
Tag: Nucleus
7. The stage of mitosis when chromosome pairs align at equatorial plate is:
**Options:** A) Prophase B) Metaphase C) Anaphase D) TelophaseAnswer: B) Metaphase
Solution: Meta = middle; spindle fibres attach to centromeres.
Shortcut: “M” for Middle.
Tag: Mitosis stages
8. In prokaryotes, chromosome is:
**Options:** A) Linear & histone-bound B) Circular & naked C) Linear & naked D) Circular & histone-richAnswer: B) Circular & naked
Solution: Single double-stranded circular DNA without histones.
Shortcut: “Pro = no frills → no histones, no ends (circular).”
Tag: Prokaryotic DNA
9. The plasma membrane is primarily composed of:
**Options:** A) Cellulose B) Phospholipids & proteins C) Chitin D) PeptidoglycanAnswer: B) Phospholipids & proteins
Solution: Fluid-mosaic model: bilayer + embedded proteins.
Shortcut: “PP” → Plasma membrane = Phospholipids + Proteins.
Tag: Membrane structure
10. Which organelle detoxifies drugs & alcohol in liver cells?
**Options:** A) Smooth ER B) Rough ER C) Golgi apparatus D) NucleoplasmAnswer: A) Smooth ER
Solution: Lacks ribosomes; houses enzymes for detoxification & lipid synthesis.
Shortcut: “Smooth = Sobriety (detox).”
Tag: ER functions
11. The energy currency of the cell is:
**Options:** A) ADP B) Glucose C) ATP D) NADHAnswer: C) ATP
Solution: Adenosine triphosphate; high-energy phosphate bonds.
Shortcut: “ATP” = A-T-Pay (energy to pay).
Tag: Energy molecules
12. Chromatin is:
**Options:** A) RNA + histones B) DNA + histones C) Lipid + DNA D) Protein + carbohydrateAnswer: B) DNA + histones
Solution: Uncoiled form of chromosome inside nucleus.
Shortcut: “Chromatin” contains “DNAtin”.
Tag: DNA packaging
13. Which process halves the chromosome number?
**Options:** A) Mitosis B) Amitosis C) Meiosis D) CytokinesisAnswer: C) Meiosis
Solution: Two divisions, produces 4 haploid gametes.
Shortcut: “Meio” = less; reduces to half.
Tag: Cell division
14. Peptidoglycan is characteristic cell-wall material of:
**Options:** A) Fungi B) Plants C) Bacteria D) AlgaeAnswer: C) Bacteria
Solution: Provides rigidity; target of penicillin.
Shortcut: “Peptido-” sounds like “pathogen” (bacteria).
Tag: Prokaryotic wall
15. The longest phase of the cell cycle is:
**Options:** A) Prophase B) Metaphase C) Interphase D) CytokinesisAnswer: C) Interphase
Solution: Cell grows, DNA replicates; occupies ~90% of cycle time.
Shortcut: “Inter-” = everyday life → longest.
Tag: Cell cycle
Speed Tricks
| Situation | Shortcut | Example |
|---|---|---|
| Remembering 3 tenets of cell theory | “All-Unit-Pre” | All living → cells; Unit of life; Pre-existing cells |
| Plant vs Animal organelles | “PAC-man” | Plant has Plastids, big Apu-style Vacuole, Cell wall; Animals have Centrosome |
| Mitosis sequence | “PMAT” | Prophase → Metaphase → Anaphase → Telophase (like morning routine: Prepare-Make-Arrange-Tidy) |
| Organelle nicknames | “MRLG” | Mitochondria = Powerhouse; Ribosome = Protein factory; Lysosome = Suicide bag; Golgi = Packaging site |
| DNA forms in cell | “CNH” order | Chromatin (loose) → Nucleosome (beads) → Histones (protein spools) → Chromosome (condensed) |
Quick Revision
| Point | Detail |
|---|---|
| 1 | Prokaryotes: no true nucleus, 70S ribosomes, circular DNA, cell wall = peptidoglycan (bacteria) |
| 2 | Eukaryotes: true nucleus, 80S ribosomes, linear DNA with histones, membrane-bound organelles |
| 3 | Mitochondria have their own 70S ribosomes & circular DNA → supports endosymbiotic theory |
| 4 | Chloroplasts also contain circular DNA; triple membrane system (outer, inner, thylakoid) |
| 5 | SER: detox & lipid synthesis; RER: protein synthesis (has ribosomes) |
| 6 | Vacuoles: plants = large central (tonoplast membrane); animals = small, sometimes contractile |
| 7 | Centrioles: 9+0 microtubule arrangement; form spindle in animal mitosis |
| 8 | Lysosomal enzymes active at acidic pH ~5; rupture causes autolysis |
| 9 | Chromosome number human somatic = 46 (23 pairs); gametes = 23 (haploid) |
| 10 | ATP synthase (F₀-F₁ complex) located in mitochondrial inner membrane & thylakoid membrane |
BETA
