1. Prokaryotic Cell vs Eukaryotic Cell
| Feature | Prokaryotic cell | Eukaryotic cell |
|---|---|---|
| Examples | Bacteria, cyanobacteria, mycoplasma and PPLO | Protists, fungi, plants and animals |
| Size and multiplication | Generally smaller; multiply more rapidly | Generally larger; multiply less rapidly |
| Nucleus and DNA | No nuclear envelope; naked genomic DNA is usually a single circular chromosome. Plasmids may occur. | Organised, membrane-bound nucleus; genetic material arranged into chromosomes |
| Membrane-bound organelles | Absent | Present, including ER, Golgi complex, lysosomes, mitochondria and vacuoles |
| Ribosomes | 70S = 50S + 30S | Cytoplasmic 80S = 60S + 40S |
| Special structures | Cell envelope, mesosome, inclusions; bacterial flagellum may occur | Complex cytoskeletal and locomotory structures; centrosome in animal cells |
NCERT anchor Ribosomes are non-membrane-bound organelles found in both cell types; prokaryotes lack the other membrane-bound organelles.
2. Plant Cell vs Animal Cell
| Feature | Plant cell | Animal cell |
|---|---|---|
| Outer covering | Rigid cell wall outside plasma membrane | Plasma membrane is the outer delimiting structure |
| Plastids | Present | Absent |
| Vacuole | Large central vacuole; may occupy up to 90% of cell volume | Large central vacuole absent |
| Centrioles | Absent in almost all plant cells | Present; assist in cell division |
| Cell connections | Plasmodesmata can traverse wall and middle lamella | No plasmodesmata |
3. Passive Transport vs Active Transport
| Feature | Passive transport | Active transport |
|---|---|---|
| Energy requirement | No energy required | Energy-dependent; ATP is used |
| Direction | Along a concentration gradient, from higher to lower concentration | Against a concentration gradient, from lower to higher concentration |
| Examples | Simple diffusion of neutral solutes; osmosis, the diffusion of water | Na+/K+ pump |
| Polar molecules | Cannot pass directly through non-polar lipid bilayer; require carrier proteins for facilitated transport | Can be moved by energy-dependent membrane carriers |
Exam clue Osmosis is diffusion of water across a selectively permeable membrane; it does not require ATP.
4. Rough ER vs Smooth ER
| Feature | Rough ER (RER) | Smooth ER (SER) |
|---|---|---|
| Surface | Ribosomes attached to outer surface | Ribosomes absent |
| Abundance | Prominent in cells actively involved in protein synthesis and secretion | Prominent where lipids are synthesised |
| Main role | Protein synthesis and secretion | Lipid synthesis |
| Special NCERT fact | Extensive and continuous with the outer nuclear membrane | Synthesises lipid-like steroidal hormones in animal cells |
5. Types of Plastids
| Plastid | Pigment / contents | Main role / examples |
|---|---|---|
| Chloroplast | Chlorophyll and carotenoid pigments; thylakoids arranged into grana | Traps light energy for photosynthesis; common in mesophyll cells |
| Chromoplast | Carotene, xanthophylls and other fat-soluble carotenoids | Produces yellow, orange or red colour in plant parts |
| Leucoplast | Colourless; storage plastid | Amyloplast: starch (potato); elaioplast: oils/fats; aleuroplast: proteins |
Chloroplast layout Stroma contains enzymes for carbohydrate and protein synthesis; thylakoid membranes contain chlorophyll and enclose the lumen.
6. 70S Ribosome vs 80S Ribosome
| Feature | 70S ribosome | 80S ribosome |
|---|---|---|
| Subunits | 50S large + 30S small | 60S large + 40S small |
| Location | Prokaryotic cytoplasm; also mitochondria and chloroplasts | Eukaryotic cytoplasm and rough ER |
| Shared composition | Both are non-membrane-bound and made of RNA and proteins; both are sites of protein synthesis. | |
| Meaning of S | Svedberg unit: sedimentation coefficient, an indirect measure of density and size. | |
7. Cilia vs Flagella
| Feature | Cilia | Flagella |
|---|---|---|
| Length | Short | Comparatively longer |
| Movement role | Work like oars to move the cell or surrounding fluid | Responsible for cell movement |
| Eukaryotic internal structure | Plasma-membrane covered; axoneme normally has nine peripheral microtubule doublets and two central microtubules (9+2 array). | |
| Origin | Both emerge from centriole-like basal bodies. | |
| Prokaryotic counterpart | Bacterial flagella occur, but are structurally different from eukaryotic flagella. | |
8. Chromosome Types by Centromere Position
| Type | Centromere position | Arms formed |
|---|---|---|
| Metacentric | Middle | Two equal arms |
| Sub-metacentric | Slightly away from middle | One shorter and one longer arm |
| Acrocentric | Close to one end | One extremely short and one very long arm |
| Telocentric | Terminal | Centromere at the end |
Remember Centromere holds the two chromatids of a chromosome; kinetochores are disc-shaped structures on its sides.