PROKARYOTE (bacteria, archaea):
  No membrane-bound nucleus (nucleoid region)
  No membrane-bound organelles
  Smaller (1-10 μm)
  Circular DNA, often with plasmids
  70S ribosomes (50S + 30S subunits)
  Cell wall: peptidoglycan (bacteria)
  Binary fission for reproduction

EUKARYOTE (plants, animals, fungi, protists):
  True nucleus with nuclear envelope (pores)
  Membrane-bound organelles: ER, Golgi, mitochondria, etc.
  Larger (10-100 μm)
  Linear chromosomes in nucleus
  80S ribosomes (60S + 40S subunits)
  Cell wall in plants (cellulose), fungi (chitin), absent in animals
  Mitosis/meiosis for reproduction

Similarities: Both have DNA, cell membrane, cytoplasm, ribosomes

INTERPHASE (90% of cycle):
  G₁ (Gap 1): Cell grows, synthesises proteins, RNA
  S (Synthesis): DNA replication (2N → 4N DNA content)
  G₂ (Gap 2): Continues growth, prepares for division

M PHASE (Mitosis + Cytokinesis):
  Prophase:   chromosomes condense, spindle forms, nuclear envelope breaks
  Metaphase:  chromosomes align at metaphase plate (equatorial plate)
  Anaphase:   sister chromatids pulled to poles by spindle fibres
  Telophase:  nuclear envelopes reform, chromosomes decondense
  Cytokinesis: cell divides into 2 identical daughter cells (2N each)

CHECKPOINTS: G₁/S, G₂/M, Spindle assembly — quality control
CDK-Cyclin complexes regulate checkpoint transitions

LAW OF SEGREGATION (First Law):
  Each organism carries 2 alleles for each trait
  Alleles segregate into separate gametes
  Example: Tt plant → 1/2 T gametes + 1/2 t gametes

LAW OF INDEPENDENT ASSORTMENT (Second Law):
  Alleles of different genes assort independently
  Applies to genes on different chromosomes
  Example: Round+Yellow × Wrinkled+Green → 9:3:3:1 ratio

Exception: Linked genes (same chromosome) → do NOT assort independently
           Morgan discovered linkage and crossing over

Dihybrid cross: RrYy × RrYy → 16 combinations → 9:3:3:1 phenotype ratio
Probability RrYy parent: R (3/4) × Y (3/4) = 9/16

RESTING MEMBRANE POTENTIAL: -70 mV (inside negative)
  K⁺ more concentrated inside | Na⁺ more concentrated outside
  Na⁺/K⁺ ATPase maintains gradient (3 Na⁺ out, 2 K⁺ in)

ACTION POTENTIAL (nerve impulse):
  1. Stimulus reaches threshold (-55 mV)
  2. Na⁺ voltage-gated channels open → Na⁺ rushes IN → depolarisation
  3. Membrane potential reaches +30 to +40 mV (peak)
  4. Na⁺ channels inactivate | K⁺ channels open → K⁺ rushes OUT
  5. Repolarisation: membrane potential returns to -70 mV
  6. Hyperpolarisation (briefly more negative) then resting

REFRACTORY PERIOD: brief period after AP where another AP cannot fire
  Absolute: no AP possible | Relative: requires stronger stimulus

SYNAPSE: action potential → neurotransmitter release →
         receptor binding → EPSP or IPSP in next neuron

CELL ORGANELLES:
  Mitochondria: ATP synthesis (powerhouse) | own DNA | double membrane
  Chloroplast: photosynthesis | own DNA | double membrane (plants only)
  Ribosome: protein synthesis | 70S (prokaryote) 80S (eukaryote)
  ER: smooth (lipids) | rough (has ribosomes, protein secretion)
  Golgi: modifies, sorts, packages proteins | secretory pathway
  Lysosome: hydrolytic enzymes, cell digestion | suicidal bag
  Nucleus: stores genetic info | nucleolus: rRNA/ribosome synthesis

GENETICS: Dominant masks recessive | Co-dominance | Incomplete dominance
  Sex-linked: gene on X chromosome (X-linked, more in males)
  Blood groups: ABO (I^A I^B i) | Rh factor (DD/Dd = +, dd = -)

PLANT PHYSIOLOGY:
  Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy)
  C3 plants: 3-carbon first product (wheat, rice, most plants)
  C4 plants: 4-carbon intermediate, efficient in hot/dry (maize, sugarcane)
  Transpiration: water loss through stomata | root pressure | osmosis