CELL ORGANELLES:
Nucleus: stores DNA, controls cell activities, bounded by nuclear envelope
Mitochondria: ATP production (powerhouse), has own DNA and ribosomes, double membrane
Chloroplast: photosynthesis, has own DNA, thylakoid (grana) + stroma
Ribosome: protein synthesis (70S prokaryote, 80S eukaryote)
ER (rough): has ribosomes, protein synthesis and packaging
ER (smooth): lipid synthesis, detoxification
Golgi: modifies, packages, secretes proteins (trans face = secretory side)
Lysosome: digestive enzymes (hydrolases), cell digestion, only in animal cells
Vacuole: water storage in plants (central vacuole, tonoplast membrane)
Centrosome: cell division, forms aster fibers, only in animal cells
CELL DIVISION:
Mitosis phases: Prophase → Metaphase → Anaphase → Telophase → Cytokinesis
P: chromatin condenses | M: chromosomes align at plate | A: centromeres split
T: two nuclei form | C: cytoplasm divides
Result: 2 identical diploid cells (2n → 2n)
Meiosis: 2 divisions producing 4 haploid cells (2n → n)
Meiosis I: homologs separate (reductional division)
Meiosis II: sister chromatids separate (like mitosis)
Crossing over: during prophase I (chiasmata formation)
MENDEL'S LAWS:
Law of Dominance: in heterozygous, dominant allele expresses
Law of Segregation: alleles separate during gamete formation
Law of Independent Assortment: genes on different chromosomes assort independently
RATIOS:
Monohybrid F2: 3:1 (phenotype) | 1:2:1 (genotype)
Dihybrid F2: 9:3:3:1 | Test cross: 1:1:1:1
IMPORTANT GENETICS:
Codominance: ABO blood groups (IA and IB both express in IAIB = AB)
Incomplete dominance: RR (red) × WW (white) → Rr (pink) in snapdragon
Sex-linked: colour blindness (X-linked recessive) | haemophilia (X-linked)
Chromosomal disorders:
Down syndrome: trisomy 21 (47 chromosomes)
Turner syndrome: 45,X (monosomy X, female)
Klinefelter: 47,XXY (male)
DNA REPLICATION:
Semi-conservative: each new DNA has one old + one new strand (Meselson-Stahl)
Enzymes: Helicase (unwind) → Primase (primer) → DNA Pol III (elongate)
DNA Pol I (replace primer) → Ligase (seal gaps)
Direction: always 5' to 3'
ENERGY FLOW:
1% light used in photosynthesis | 10% energy transferred per trophic level
GPP = NPP + R (gross primary productivity minus respiration)
ECOLOGICAL PYRAMIDS:
Pyramid of energy: always upright
Pyramid of biomass: may be inverted (aquatic ecosystems)
Pyramid of numbers: may be inverted (tree ecosystem)
BIOGEOCHEMICAL CYCLES:
Carbon: photosynthesis (CO₂ → organic) | respiration (organic → CO₂)
Nitrogen: fixation (N₂ → NH₃) → nitrification → assimilation → denitrification
Nitrogen fixation: Rhizobium (root nodules), Azotobacter (free-living)
BIODIVERSITY:
Alpha: within habitat | Beta: between habitats | Gamma: landscape
India hotspots: Western Ghats + Sri Lanka | Indo-Burma | Himalayas
IUCN categories: EX (extinct) | EW | CR | EN | VU | NT | LC
In situ conservation: national parks, wildlife sanctuaries, biosphere reserves
Ex situ: botanical gardens, zoos, seed banks, cryopreservation
