Fundamentals
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
“A plant cell is like a green house with thick walls, solar panels (chloroplasts) and a big water tank (vacuole).”
Plant cells have a rigid cellulose cell wall, chloroplasts for photosynthesis, and a large central vacuole; animal cells lack these but contain centrioles and more lysosomes. Trap: never mark centrioles as present in plant cells.
Memory trick: Plant = wall + chloroplast + vacuole; Animal = centrioles
“Rough ER is a factory line with workers (ribosomes) assembling proteins, while smooth ER is a blank conveyor making lipids.”
Rough ER bears ribosomes on its cytoplasmic surface and synthesizes secretory and membrane proteins. Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and Ca²⁺ storage. Trap: don’t assume smooth ER makes proteins.
Memory trick: Rough = ribosomes → protein; Smooth = no ribosomes → lipid
“Seeing the DNA coil in a bacterial cell is like spotting tangled wires inside a laptop’s chassis – the code sits in a region, not in a sealed box.”
Prokaryotes possess DNA that resides in a nucleoid, a non-membrane-bound region of the cytoplasm. The chromosome may be circular or linear and some species have more than one chromosome. In exams, avoid the trap of stating “single circular DNA” for all prokaryotes; remember the nucleoid, not a nucleus.
Memory trick: Nucleoid = No Nucleus; DNA can be C or L, sometimes >1.
“When you chew gum, the same salivary amylase repeatedly breaks starch each time you chew more.”
Enzymes act as catalysts: they lower activation energy and are not consumed in the reaction. After releasing product they are free to bind new substrate. Exam mistake: writing that enzyme amount decreases or that it is used up.
Memory trick: Catalyst = never-gone
“A screwdriver fits only screws with matching head shape, just as an enzyme fits only its substrate.”
The active site’s geometry permits binding of only one (or very few) substrates, giving each enzyme high specificity. This prevents random reactions in the cell. Trap: never assume one enzyme catalyses many unrelated substrates.
Memory trick: One lock = one key
“Your muscles contract because actin and myosin proteins slide past each other like tiny ropes.”
Proteins are polymers of amino acids that form the body’s structural framework, enzymes and transport carriers. The sequence of amino acids folds into a specific 3D shape that determines function. A common exam slip is to label every protein as an enzyme – only a subset act as catalysts.
Memory trick: ENZ ≠ all PRO
“Your hair’s keratin is a protein that never catalyzes reactions.”
Not all proteins are enzymes; many serve structural roles (keratin, collagen) or transport (hemoglobin). Enzymatic activity requires a specific active-site geometry, which most proteins lack. Exams often deduct marks for assuming every protein speeds up reactions.
Memory trick: KERATIN ≠ ENZYME
“A bicycle’s chain is like glucose—quick energy that powers motion.”
Carbohydrates are sugars and their polymers that provide rapid energy (glucose) and structural support (cellulose). Polymerisation into starch or glycogen stores energy for later use. A frequent trap is mixing up energy-release with structural function.
Memory trick: Starch-plant pantry, Glycogen-animal pantry
“Your liver stores glycogen like a pantry, while a potato stores starch in its tuber.”
Starch is the plant’s storage polysaccharide, glycogen is the animal counterpart, and cellulose forms rigid plant cell walls. Confusing starch with glycogen leads to wrong answers on storage-site questions in NEET.
Memory trick: Starch in Starch-y plants, Glycogen in Guts
“Your eye’s iris color is set by DNA, the master blueprint, while messenger RNA delivers the instructions to build pigment.”
DNA holds the complete genetic code; RNA copies (mRNA) and transports the code for protein synthesis, while other RNAs have catalytic or regulatory roles. Exams test the distinction – DNA is the permanent archive, RNA is the working copy.
Memory trick: DNA=Library, RNA=Librarian
“The flu virus’s genome is RNA, showing RNA can also store genetic code.”
Both DNA and RNA can store genetic information; some viruses (e.g., influenza, HIV) use RNA as their genome, disproving the myth that only DNA does. Questions may ask which nucleic acid can act as a genome in viruses – answer: RNA.
Memory trick: RNA stores info in some viruses
“A wrong key in a lock (competitive) can be out-matched by adding many keys, but a broken gear inside (non-competitive) stops the lock no matter how many keys you try.”
Competitive inhibition: inhibitor binds the active site → apparent Km increases, Vmax unchanged; high substrate concentration overcomes it. Pure non-competitive inhibition: inhibitor binds an allosteric site on both E and ES → Vmax decreases, Km unchanged; extra substrate cannot restore activity. Trap: mixed inhibition changes both Km and Vmax; uncompetitive inhibition lowers both Km and Vmax.
Memory trick: Compete → Km↑, Vmax=; Pure non-compete → Vmax↓, Km=
“Butter stays solid in the fridge, while olive oil flows, because butter’s straight chains pack tight, oil’s kinked chains keep it liquid.”
Saturated fats have only single C–C bonds, giving straight chains that pack tightly → high melting point, solid at room temperature. Unsaturated fats contain one or more C=C double bonds that introduce kinks, preventing tight packing → lower melting point, liquid oils. Trap: don’t assume liquid means unsaturated without checking double bonds.
Memory trick: Saturated = Straight → Solid; Unsaturated = Kinky → Liquid.
“A kitchen knife cuts many vegetables without wearing out; similarly an enzyme cuts many substrate molecules and emerges unchanged.”
Enzymes are biological catalysts; they lower activation energy and are released unchanged after each reaction, so they can be reused many times. The myth that they are consumed ignores that the enzyme’s structure is not altered in the catalytic cycle. Trap: assuming enzyme amount limits rate only when substrate saturates the enzyme.
Memory trick: Enzyme = catalyst, not consumable → reuse.
“A growing plant leaf’s cells pause in G1, copy DNA in S, then bulk up in G2 before dividing to expand the leaf.”
Cell-cycle phases are G1 (cell growth), S (DNA replication), G2 (pre-division growth) and M (mitosis). The sequence ensures the genome is copied before chromosomes are separated. Trap: forgetting that M follows G2; no DNA synthesis after G2.
Memory trick: G1 → S → G2 → M, like a relay race
“Students often think DNA copies during mitosis, but the real copy shop is the S phase before the cell even lines up chromosomes.”
A frequent mistake is placing DNA replication in mitosis. In reality, DNA synthesis is confined to the S stage of interphase; M phase only segregates already duplicated chromatids. Trap: answer options that link DNA copying to M are wrong.
Memory trick: DNA = S phase, not M
“When you trim a bonsai, the new shoots grow identical to the parent branch.”
Mitosis is a somatic cell division that produces two genetically identical diploid daughter cells. The sister chromatids separate at anaphase, preserving the original DNA sequence. Exam trap: students sometimes write that crossing over occurs in mitosis – it does not.
Memory trick: Mitosis = 'M'aintain identity (2 identical diploids).
“Like shuffling a deck and dealing four hands, each hand has half the cards and a unique mix.”
Meiosis is a reductional division that halves the chromosome number. One diploid cell undergoes two successive divisions to give four haploid gametes, each genetically different because of crossing-over and independent assortment. The common trap is to assume the products are identical like mitosis.
Memory trick: Meiosis = Mix + Half = 4 unique halves
“During meiosis I, two homologous chromosomes intertwine like ropes and swap strands, creating new genetic patterns.”
Crossing over takes place in prophase I of meiosis between non-sister chromatids of homologous chromosomes, exchanging DNA segments. This recombination creates new allele combinations, the main source of genetic diversity. Trap: many write it occurs in mitosis or after metaphase – it is confined to early prophase I.
Memory trick: Crossing over = C in Prophase I only.
“A copy machine prints two exact sheets (mitosis) while a cutter slices the original into four different drafts (meiosis).”
Mitosis yields two identical diploid cells for growth or repair; meiosis yields four non-identical haploid cells for reproduction. Key differences: one division vs two, chromosome number 2n vs n, and presence of recombination only in meiosis. Trap: mixing up the number of metaphase plates – meiosis has two.
Memory trick: Mitosis 2 same; Meiosis 4 different.
“Your body’s cells are like a double-sided sheet of paper (diploid), whereas sperm and egg are single-sided sheets (haploid).”
Diploid (2n) cells contain two homologous sets of chromosomes, one from each parent, while haploid (n) cells have a single set and are found in gametes. Fertilization fuses two haploid sets to restore the diploid number. Trap: confusing n (distinct chromosomes) with total chromosome count; remember n = number of different chromosomes.
Memory trick: Diploid = double (2), Haploid = half (1).
“A single shoelace is a chromatid; after you tie a knot (replication) you get two identical laces joined at the knot – the chromosome.”
A chromatid is one DNA molecule with its protein coat. In G1 (before replication) a chromosome has a single chromatid. After S-phase each chromosome contains two identical sister chromatids attached at the centromere. A common trap is assuming every chromosome always has two chromatids.
Memory trick: Unreplicated=1, Replicated=2 (U=1, R=2)
“Like baking a cake before the party, cells copy DNA in S phase before the mitotic ‘party’ starts.”
DNA replication occurs only in the S (synthesis) stage of interphase, before mitosis. During M phase chromosomes are condensed and the replication machinery is inactive, so no new DNA is made. Exam trap: any statement that places DNA synthesis in mitosis is incorrect.
Memory trick: S before M – Synthesis before Mitosis
“When sunlight hits a solar panel, electrons flow; similarly thylakoid membranes capture light to split water and make ATP.”
Light reactions occur in the thylakoid membranes of chloroplasts. Photons excite chlorophyll, driving water photolysis → O₂, electrons, and H⁺, which generate ATP via chemiosmosis and NADPH via the electron transport chain. A common trap: forgetting that O₂ comes from water, not CO₂.
Memory trick: O₂ from H₂O, not CO₂ – remember "Water splits, oxygen lifts".