BiologyPrinciples of Inheritance & Variation· Class 12
Monohybrid ratio
“3 tall to 1 short — the ratio that cracked genetics open.”
A single-trait cross gives a 3:1 phenotype ratio (1:2:1 genotype) in F2.
Memory trick: 3:1 seen; 1:2:1 underneath.
Fundamentals
1,200 must-knows for NEET & JEE
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
300 fundamentals
BiologyPrinciples of Inheritance & Variation· Class 12
Sex determination in humans
“It's the father's chromosome contribution that tips the coin.”
XX is female, XY is male; the sperm decides the child's sex.
Memory trick: XY = male; sperm decides.
BiologyMolecular Basis of Inheritance· Class 12
DNA structure
“Watson and Crick's twisted ladder is the most famous molecule in biology.”
A double helix with complementary base pairing: A–T and G–C.
Memory trick: A–T, G–C, always.
BiologyMolecular Basis of Inheritance· Class 12
Semi-conservative replication
“DNA copies itself by unzipping and rebuilding each half — proven by Meselson and Stahl.”
Each new DNA molecule keeps one old strand and one new strand.
Memory trick: Half old, half new.
BiologyMolecular Basis of Inheritance· Class 12
Central dogma
“Genes are recipes; proteins are the dishes finally served.”
Genetic information flows DNA → RNA → protein.
Memory trick: Transcribe then translate.
BiologyMolecular Basis of Inheritance· Class 12
Codon
“The genetic code reads three letters at a time, like a molecular Morse.”
A triplet of mRNA bases that codes for one amino acid.
Memory trick: 3 bases → 1 amino acid.
BiologyEvolution· Class 12
Natural selection
“It's survival of the best-fitted, not merely the strongest.”
Individuals best adapted to their environment survive and reproduce more.
Memory trick: Best-adapted, not strongest.
BiologyEvolution· Class 12
Homologous vs analogous organs
“A human arm and a whale flipper share bones; a bird wing and insect wing don't.”
Homologous organs share ancestry but differ in function; analogous organs share function but not ancestry.
Memory trick: Homologous = same origin.
BiologyHuman Health & Disease· Class 12
Innate vs acquired immunity
“Skin is your castle wall; antibodies are trained archers who remember each enemy.”
Innate immunity is general and present from birth; acquired immunity is specific and develops after exposure.
Memory trick: Acquired immunity remembers.
BiologyHuman Health & Disease· Class 12
Active vs passive immunity
“A vaccine trains your army; antivenom lends you someone else's.”
Active immunity is your own antibodies (vaccine/infection); passive is ready-made antibodies (mother's milk, antivenom).
Memory trick: Vaccine = active; antivenom = passive.
BiologyHuman Health & Disease· Class 12
Antibiotics act on bacteria only
“Taking antibiotics for a viral cold does nothing but breed resistance.”
Antibiotics kill or stop bacteria; they don't work on viruses.
Memory trick: Useless against viruses.
BiologyHuman Reproduction & Reproductive Health· Class 12
Fertilisation site
“Sperm and egg meet in the oviduct; the embryo then travels to implant in the uterus.”
In humans, fertilisation occurs in the fallopian tube, not the uterus.
Memory trick: Egg meets sperm in the oviduct.
BiologyHuman Reproduction & Reproductive Health· Class 12
Placenta
“A temporary organ that is baby's lifeline for nine months.”
Connects the embryo to the mother for nutrient, gas and waste exchange, and makes hormones.
Memory trick: Baby's lifeline in the womb.
BiologyBiotechnology & its Applications· Class 12
Recombinant DNA technology
“We reprogrammed bacteria to brew human insulin — a medical revolution.”
Inserting a desired gene into a vector and host cell to mass-produce a product.
Memory trick: Gene + vector + host.
BiologyBiotechnology & its Applications· Class 12
Restriction enzymes
“Biology's precise scissors, cutting DNA only at chosen 'words'.”
Molecular scissors that cut DNA at specific palindromic sequences.
Memory trick: Cut at specific sites.
BiologyBiotechnology & its Applications· Class 12
PCR
“PCR is a DNA photocopier — and the backbone of modern diagnostics.”
A technique that makes millions of copies of a DNA segment using primers and Taq polymerase.
Memory trick: Amplifies DNA copies.
BiologyEcosystem & Ecology· Class 12
Food chain & energy flow
“That 10% rule is why top predators are always rare.”
Energy flows one way through trophic levels, with only ~10% passing to the next.
Memory trick: ~10% up each level.
BiologyEcosystem & Ecology· Class 12
Decomposers
“Nature's clean-up crew, returning nutrients to the soil.”
Bacteria and fungi that break down dead matter and recycle nutrients.
Memory trick: Recyclers of the ecosystem.
BiologyBiodiversity & Conservation· Class 12
Biodiversity
“A diverse ecosystem is a diversified portfolio — more resilient to shocks.”
The variety of life; higher diversity makes ecosystems more stable.
Memory trick: More variety = more stability.
BiologyBiological Classification· Class 11
Five-kingdom classification
“One tidy system to sort every living thing from bacteria to blue whales.”
Whittaker grouped life into Monera, Protista, Fungi, Plantae and Animalia.
Memory trick: Monera, Protista, Fungi, Plantae, Animalia.
BiologyBiological Classification· Class 11
Viruses
“A virus is a hijacker — lifeless until it commandeers a living cell.”
Non-cellular particles of nucleic acid in a protein coat; they replicate only inside a host.
Memory trick: Alive only inside a host.
BiologyBiological Classification· Class 11
Bacteria
“The bacteria in your gut outnumber your own cells.”
Single-celled prokaryotes; some help (gut flora, nitrogen fixers), some cause disease.
Memory trick: Prokaryotic, everywhere.
BiologyThe Living World· Class 11
Binomial nomenclature
“Linnaeus gave every organism a universal two-word ID card.”
Every species gets a two-part Latin name: genus + species (e.g. Homo sapiens).
Memory trick: Genus capitalised, species lowercase.
BiologyPlant Kingdom· Class 11
Gymnosperms vs angiosperms
“An apple's flesh is the angiosperm's clever way of protecting its seeds.”
Gymnosperms bear naked seeds (pines); angiosperms bear seeds enclosed in fruit (flowering plants).
Memory trick: Angiosperm = flowering, fruit-covered seed.