Tamil Nadu HSE Second Year Zoology cheat sheet

Asexual modes: binary fission (Amoeba), budding (Hydra, yeast), fragmentation (Spirogyra), gemmule (sponges), conidia (Penicillium), zoospore (Chlamydomonas), bulbils (Dioscorea).

Oestrus cycle occurs in non-primate mammals; menstrual cycle occurs in primates including humans, repeating about every 28 days.

Spermatogenesis: spermatogonium (2n) → primary spermatocyte (2n) → meiosis I → secondary spermatocyte (n) → meiosis II → spermatid (n) → spermiogenesis → sperm; one primary spermatocyte yields 4 sperm.

Oogenesis is unequal: one primary oocyte yields one ovum plus three polar bodies; meiosis II completes only after sperm entry.

Menstrual phases in order: menstrual (days 1-5, progesterone low, corpus luteum regresses), follicular/proliferative (FSH-driven, oestrogen rises), ovulation (~day 14, LH surge), luteal/secretory (progesterone from corpus luteum).

hCG, hPL, oestrogen and progesterone are secreted by the placenta; hCG maintains the corpus luteum in early pregnancy and is the basis of pregnancy tests.

Fertilisation occurs in the ampullary-isthmic junction of the fallopian tube; the zona pellucida blocks polyspermy after the cortical reaction.

Implantation of the blastocyst occurs about 7 days after fertilisation; the trophoblast forms the embryonic part of the placenta.

Oxytocin drives uterine contractions in parturition and milk ejection; prolactin drives milk synthesis; colostrum is rich in IgA antibodies.

Mendel's law of segregation: alleles of a gene separate during gamete formation; law of independent assortment applies only to genes on different chromosomes or far apart on the same chromosome.

Test cross (cross to homozygous recessive) reveals the genotype of a dominant phenotype; a 1:1 ratio indicates heterozygosity.

Incomplete dominance gives an intermediate phenotype (e.g., Antirrhinum pink); codominance expresses both alleles (AB blood group); multiple alleles exist at the ABO locus (I^A, I^B, i).

Sex-linked recessive disorders (haemophilia, colour blindness) appear mostly in males because males are hemizygous (XY); carrier females transmit to 50% of sons.

Human chromosomal disorders: Down syndrome = trisomy 21; Klinefelter = 47,XXY; Turner = 45,X0; Edward = trisomy 18; Patau = trisomy 13.

DNA structure: antiparallel double helix, 10 bp per turn, pitch 3.4 nm, rise per base pair 0.34 nm; A pairs with T (2 H-bonds), G with C (3 H-bonds).

Semiconservative replication: helicase unwinds, primase lays RNA primer, DNA polymerase III extends 5'→3', ligase seals Okazaki fragments on the lagging strand.

Transcription in eukaryotes uses RNA polymerase I (rRNA), II (mRNA), III (tRNA); the lac operon is induced when lactose binds the repressor, freeing the operator.

Genetic code is triplet, degenerate, non-overlapping, comma-less and nearly universal; AUG is the start codon and also codes methionine; UAA, UAG, UGA are stop codons.

Miller-Urey experiment passed electric sparks through CH4, NH3, H2 and water vapour and produced amino acids, supporting chemical evolution of organic monomers.

Oparin-Haldane hypothesis: life arose from abiogenic organic molecules in a reducing primitive atmosphere, followed by coacervates and protobionts.

Lamarckism: use and disuse plus inheritance of acquired characters; disproved by Weismann's germ-plasm experiments.

Darwin's natural selection requires heritable variation, overproduction, differential survival and differential reproduction; fitness means reproductive success, not strength.

Homologous organs share common ancestry but may differ in function (forelimbs of vertebrates); analogous organs (wings of insects and birds) show convergent evolution.

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, large population and no selection; deviation indicates evolution is occurring.

Evidence for evolution: fossil strata, vestigial organs (vermiform appendix, coccyx), embryological similarities, and molecular homology in cytochrome c and rRNA sequences.

Human evolution sequence: Australopithecus → Homo habilis → Homo erectus → Homo neanderthalensis → Homo sapiens; bipedalism preceded large brain size.

Adaptive radiation: Darwin's finches on the Galapagos and marsupials of Australia illustrate divergent evolution from a common ancestor.

Pathogen-disease pairs: Plasmodium → malaria, Wuchereria → filariasis, Ascaris → ascariasis, Entamoeba → amoebiasis, Salmonella typhi → typhoid, Mycobacterium tuberculosis → TB, HIV → AIDS.

Malaria transmission is by the female Anopheles mosquito; the parasite's sexual phase occurs in the mosquito, asexual phase in humans.

Typhoid is confirmed by the Widal test; pneumonia by sputum and chest signs; filariasis causes elephantiasis of the lower limbs and scrotum.

HIV is a retrovirus with reverse transcriptase; it infects helper T cells (CD4+), and AIDS is diagnosed when CD4 count falls below about 200 per microlitre plus opportunistic infection.

Cancer: oncogenes and inactivated tumour-suppressor genes (p53, Rb) drive uncontrolled proliferation; metastasis is spread of malignant cells via blood or lymph.

Drugs: morphine and heroin are opioids; cocaine and amphetamines are stimulants; cannabinoids come from Cannabis sativa; barbiturates are depressants.

Tobacco smoke contains nicotine, CO and carcinogens; it is linked to lung, oral and laryngeal cancer and to emphysema.

Adolescence risk behaviours include substance abuse and unprotected sex; awareness and counselling are the main preventive strategies.

Innate immunity is non-specific and present at birth (barriers, phagocytes, inflammation); acquired immunity is specific and has memory.

Active immunity develops after infection or vaccination and is slow but long-lasting; passive immunity from maternal antibodies or antiserum is immediate but short-lived.

Antibody (immunoglobulin) classes: IgG crosses the placenta, IgM is the first antibody in primary response, IgA is in secretions and colostrum, IgE mediates allergy, IgD is on B-cell surfaces.

Primary immune response is slow and dominated by IgM; secondary response is faster, larger and dominated by IgG because of memory cells.

B cells mature in bone marrow and mediate humoral immunity; T cells mature in the thymus, with helper T cells (CD4) activating B cells and cytotoxic T cells (CD8) killing infected cells.

Vaccines may be live attenuated (BCG, oral polio, MMR), killed (Salk polio, whole-cell pertussis), toxoid (tetanus, diphtheria) or subunit/conjugate; live vaccines are avoided in immunocompromised patients.

Herd immunity protects unvaccinated individuals when a high proportion of the population is immune; the threshold depends on R0 of the pathogen.

Allergy is a hypersensitive IgE-mediated response to allergens such as pollen or dust; anaphylaxis is treated with adrenaline.

Fermented foods: curd from Lactobacillus, idli and dosa batter from Leuconostoc plus yeasts, tempeh from Rhizopus, swiss cheese from Propionibacterium sharmanii, roquefort from Penicillium roqueforti.

Saccharomyces cerevisiae produces ethanol and CO2 in brewing and baking; wine and beer depend on anaerobic fermentation.

Antibiotics: penicillin from Penicillium notatum, streptomycin from Streptomyces griseus, erythromycin from Saccharomyces erythreus; Fleming discovered penicillin, Florey and Chain developed it.

Citric acid from Aspergillus niger, butyric acid from Clostridium butylicum, lactic acid from Lactobacillus, cyclosporin A (immunosuppressant) from Trichoderma polysporum, statins from Monascus purpureus.

Sewage treatment: primary treatment is physical sedimentation; secondary treatment uses aerobic flocs of bacteria and fungi with aeration to reduce BOD.

Biogas from methanogens such as Methanobacterium in anaerobic sludge; the gas is mainly methane with CO2 and H2S traces.

Biofertilisers: Rhizobium in legume root nodules, Azotobacter free-living, Anabaena and Nostoc (blue-green algae) in paddy fields, Glomus as mycorrhiza aiding phosphorus uptake.

Biocontrol: Bacillus thuringiensis (Bt) toxin kills lepidopteran larvae; Trichoderma controls fungal pathogens; Baculovirus is a species-specific insecticide; ladybird and dragonfly control aphids and mosquitoes.

Restriction endonucleases cut DNA at palindromic recognition sites; EcoRI cuts G^AATTC giving sticky ends that allow ligation with vector DNA.

A cloning vector needs an origin of replication, selectable marker (e.g., ampicillin resistance), restriction sites and, for expression vectors, a promoter.

pBR322 carries ampR and tetR markers; insertional inactivation of tetracycline resistance identifies recombinant transformants by replica plating.

Ti plasmid of Agrobacterium tumefaciens is the natural vector for dicot transformation; the bacterium is disarmed by removing tumour genes.

PCR uses Taq polymerase (thermostable), primers, dNTPs and three steps: denaturation (~94 °C), annealing (~55 °C), extension (~72 °C), repeated in cycles.

Gel electrophoresis separates DNA by size; DNA is negatively charged and migrates toward the anode through agarose, then is visualised with ethidium bromide under UV.

Bt cotton carries cryIAc and cryIIAb genes from Bacillus thuringiensis; Bt toxin is inactive in the bacterium and activated by alkaline gut pH in the insect.

RNA interference (RNAi) used in tobacco against Meloidogyne incognita and in Flavr Savr tomato to delay ripening.

Insulin: the A and B chains were separately produced in E. coli, then joined by disulfide bonds; gene therapy's first case was ADA deficiency; ELISA and PCR are used for early disease detection.

Population growth: exponential (J-shaped) dN/dt = rN; logistic (S-shaped) dN/dt = rN(K−N)/K where K is carrying capacity.

Population attributes: birth rate, death rate, sex ratio, age pyramid; a bell-shaped age pyramid indicates a stable population, broad base indicates growth.

Species interactions: mutualism (+,+), commensalism (+,0), parasitism and predation (+,−), competition (−,−), amensalism (−,0).

Gause's competitive exclusion principle: two species competing for identical resources cannot coexist indefinitely; resource partitioning allows coexistence.

Ecological pyramids may be upright (grassland), inverted (tree biomass) or spindle-shaped; pyramids of energy are always upright.

Primary succession begins on bare rock with lichens and mosses (pioneer species); secondary succession follows a disturbance such as fire.

Nutrient cycles: gaseous (carbon, nitrogen) and sedimentary (phosphorus, sulphur); nitrogen fixation, nitrification, denitrification and ammonification are microbial steps.

Ecosystem services include pollination, oxygen release, water purification and nutrient cycling; biodiversity loss reduces their stability.

Ecosystem components: abiotic factors, producers, consumers and decomposers; energy flow is unidirectional and non-cyclic.

Gross primary productivity minus respiration equals net primary productivity; only about 10% of energy passes to the next trophic level (Lindeman's 10% law).

Detritus food chain: dead organic matter → detritivores → predators; it dominates in forest and mangrove ecosystems.

Ecological efficiency is energy transferred to the next trophic level divided by energy received; energy pyramids are always upright because of loss as heat.

Standing state, or biomass, is the mass of living material at a trophic level; standing crop is measured per unit area.

Hydrarch succession proceeds from hydric to mesic conditions; xerarch succession proceeds from xeric to mesic.

Carbon cycle: photosynthesis fixes CO2, respiration and combustion release it; oceans are the largest carbon reservoir after rocks.

Phosphorus cycle has no gaseous phase; phosphorus is released by rock weathering and is often the limiting nutrient in freshwater.

Species-area relationship: log S = log C + Z log A; the slope Z is about 0.1-0.2 for small areas and 0.6-1.2 for very large regions such as continents.

Biodiversity hotspots in India: Western Ghats, Eastern Himalaya and Indo-Burma; the Western Ghats and Sri Lanka hotspot is one of the world's richest.

Levels of biodiversity: genetic, species and ecological; India has about 8% of global species diversity on 2.4% of land area.

Causes of biodiversity loss (the 'evil quartet'): habitat loss and fragmentation, over-exploitation, alien species invasion and co-extinction.

In-situ conservation includes biosphere reserves, national parks and sacred groves; ex-situ includes zoos, seed banks and botanical gardens.

Ramsar sites are wetlands of international importance; the Montreal Protocol phases out ozone-depleting substances such as CFCs.

Greenhouse gases: CO2, CH4, N2O and CFCs; global warming raises sea level and shifts species ranges.

Eutrophication causes algal blooms and oxygen depletion; biomagnification concentrates persistent pesticides such as DDT up the food chain.

Porifera: cellular level, spongocoel, ostia and osculum, choanocytes, hermaphrodite; Cnidaria: tissue level, radial symmetry, nematocysts, polyp and medusa.

Platyhelminthes are acoelomate and bilaterally symmetrical; Aschelminthes (roundworms) are pseudocoelomate; Annelida onwards are true coelomates.

Arthropoda is the largest phylum: chitinous exoskeleton, jointed appendages, open circulatory system, Malpighian tubules for excretion.

Mollusca: soft body with mantle, visceral hump, radula, and often a calcareous shell; open circulation except cephalopods.

Echinodermata: spiny skin, water vascular system, tube feet, radial symmetry in adults but bilateral larvae; exclusively marine.

Chordate features: notochord, dorsal hollow nerve cord, paired pharyngeal gill slits; Urochordata and Cephalochordata are protochordates.

Vertebrate classes: Pisces (scales, gills, two-chambered heart), Amphibia (three-chambered), Reptilia (three-chambered, except crocodile with four), Aves and Mammalia (four-chambered).

Aves: feathers, hollow bones, air sacs, warm-blooded, oviparous; Mammalia: mammary glands, hair, diaphragm, viviparous (except monotremes).

Epithelial tissues: squamous (exchange), cuboidal (secretion), columnar (absorption), ciliated (movement of mucus); tight, adhering and gap junctions link cells.

Connective tissues: loose (areolar, adipose), dense (tendon, ligament), cartilage, bone, blood; tendon joins muscle to bone, ligament joins bone to bone.

Muscle types: skeletal is striated and voluntary with multinucleate fibres; smooth is non-striated and involuntary; cardiac is striated, involuntary and branched.

Neuron parts: dendrites carry impulses toward the cell body, axon away; a synapse transmits via neurotransmitters; myelin sheath speeds conduction.

Digestive tract order: mouth, oesophagus, stomach, duodenum, jejunum, ileum, caecum, colon, rectum; the villi of the ileum absorb nutrients.

Heart: right side carries deoxygenated blood to the lungs, left side oxygenated to the body; valves prevent backflow (tricuspid right, bicuspid left, semilunar in arteries).

Respiratory tract: nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveoli; alveoli provide a thin, moist surface for gas exchange.

Excretory system: nephron is the functional unit; glomerular filtration, tubular reabsorption and secretion produce urine; kidney, ureter, bladder, urethra.

Digestion: salivary amylase digests starch to maltose; pepsin (with HCl) digests protein in the stomach; trypsin and chymotrypsin act in the duodenum; lipase splits fats.

Bile from the liver emulsifies fats but contains no enzyme; the pancreas secretes amylase, lipase and proteases; absorption is mainly in the small intestine.

Cardiac output = heart rate × stroke volume; normal resting values about 72 beats per minute and 70 mL per beat, giving about 5 L per minute.

Sinoatrial node is the pacemaker; ECG waves: P = atrial depolarisation, QRS = ventricular depolarisation, T = ventricular repolarisation.

Breathing: inspiration is active (diaphragm and external intercostals), expiration passive; tidal volume ~500 mL, vital capacity ~3,500-4,500 mL.

Nephron: ultrafiltration in the glomerulus, reabsorption of glucose and amino acids in the proximal tubule, water in the loop and collecting duct under ADH.

Muscle contraction by the sliding filament model: myosin heads bind actin, the power stroke needs ATP and Ca2+, and acetylcholine triggers depolarisation at the neuromuscular junction.

Nerve impulse: resting potential about −70 mV (Na+/K+ pump), depolarisation by Na+ influx, repolarisation by K+ efflux; conduction is saltatory in myelinated axons.

Hormones: insulin lowers blood glucose, glucagon raises it, thyroxine controls basal metabolic rate, cortisol is a stress hormone, ADH conserves water, aldosterone retains sodium.