NCERT Rapid Revision — Biology

"The fluid mosaic model of the cell membrane was proposed by Singer and Nicolson (1972)."

"The centromere holds two chromatids together. Based on centromere position: metacentric, sub-metacentric, acrocentric, telocentric."

"During G1 phase, the cell is metabolically active and grows. DNA synthesis occurs in S phase."

"Meiosis ensures production of haploid gametes. The synapsis (pairing of homologous chromosomes) occurs during zygotene."

"Watson and Crick proposed the double helix model of DNA in 1953. Chargaff's rule: A=T, G=C."

"Semi-conservative replication was proved by Meselson and Stahl (1958) using ¹⁵N isotope and CsCl density gradient."

"The genetic code is a triplet codon (64 codons = 61 amino acid + 3 stop codons: UAA, UAG, UGA). AUG = start codon (Met)."

"Human Genome Project (1990–2003): 3164.7 million base pairs, ~30,000 genes. Less than 2% of genome codes for proteins."

"Mendel chose garden pea (Pisum sativum) because it has bisexual flowers, short life cycle, and many contrasting traits."

"Linkage was discovered by Morgan in Drosophila. Morgan also proposed the chromosomal theory of inheritance along with Sutton."

"Down syndrome (Trisomy 21), Klinefelter (47,XXY), Turner (45,XO), Patau (trisomy 13), Edward (trisomy 18)."

"Lindeman's 10% law: Only 10% of energy is transferred from one trophic level to the next. Maximum energy is at producer level."

"India has 2 biodiversity hotspots: Western Ghats + Sri Lanka; Eastern Himalayas. World has 34 hotspots."

"Logistic growth follows S-curve (sigmoid). N = K/2 gives maximum growth rate. K = carrying capacity."

"EcoRI cuts between G↓AATTC. Recognition sequences are palindromes. EcoRI produces 4-base sticky ends (cohesive ends)."

"PCR (Polymerase Chain Reaction) — Kary Mullis (Nobel 1993). 3 steps: Denaturation (94°C) → Annealing (50-65°C) → Extension (72°C)."

"Blotting: Southern = DNA, Northern = RNA, Western = Protein. All named after Edwin Southern (DNA) — others are humorous derivatives."

"Bt toxin: cry genes (crystal proteins) from Bacillus thuringiensis. Activated by alkaline pH of insect gut. Biopesticide."

"Cardiac output = stroke volume (70 mL) × heart rate (72/min) ≈ 5040 mL/min. SA node is the pacemaker of heart."

"GFR = 125 mL/min = 180 L/day. Of this, 99% is reabsorbed. Urine = 1.5 L/day. ADH controls water reabsorption."

"Resting membrane potential = −70 mV (more K+ inside, more Na+ outside). Depolarisation: Na+ rushes in."

"Tidal volume = 500 mL. ERV = 1100 mL. IRV = 3000 mL. RV = 1100 mL. TLC = TV + IRV + ERV + RV = 5700 mL."

"Spermatogenesis: Spermatogonia → Primary spermatocyte (meiosis I) → Secondary spermatocyte (meiosis II) → Spermatids → Spermatozoa."

"Primary oocyte is arrested in prophase I of meiosis until puberty. Released as secondary oocyte at ovulation. Arrested again in metaphase II until fertilisation."

"hCG (human Chorionic Gonadotropin) is secreted by trophoblast at day 8. Maintains corpus luteum. Detected by pregnancy test kits."