Tamil Nadu HSE First Year Zoology cheat sheet

Taxonomic hierarchy from broadest to narrowest: Kingdom, Phylum, Class, Order, Family, Genus, Species; binomial names italicised with genus capitalised, species lowercase.

Five-kingdom classification (Whittaker): Monera (prokaryote), Protista (eukaryote unicellular), Fungi (chitin wall, absorptive), Plantae, Animalia; viruses are excluded as non-cellular.

Animalia diagnostic rule: multicellular, heterotrophic, no cell wall, most with nervous tissue and muscular movement at some stage; Porifera lack true tissues.

Symmetry key: Porifera mostly asymmetric, Cnidaria radial, Platyhelminthes bilateral; coelom states are acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), coelomate (Annelida onward).

Chordate four features: notochord, dorsal hollow nerve cord, paired pharyngeal gill slits, post-anal tail; Urochordata and Cephalochordata are invertebrate chordates.

Vertebrate class markers: Chondrichthyes cartilaginous skeleton, Osteichthyes bony with operculum, Amphibia moist skin and three-chambered heart, Aves feathers and four-chambered heart, Mammalia mammary glands and hair.

Arthropod success traits: chitinous exoskeleton, jointed appendages, segmented body, moulting (ecdysis); Insecta is the largest class with three body regions and six legs.

Echinoderm unique features: water vascular system, tube feet, calcareous endoskeleton, radial adult with bilateral larva, and remarkable regeneration.

Earthworm (Pheretima) external markers: clitellum in segments 14-16, one pair of male genital pores at segment 18, female pore on segment 14, and dorsal blood vessel visible as a dark line.

Earthworm digestive tract: mouth to pharynx, oesophagus, gizzard (segments 8-10 for grinding), intestine with typhlosole increasing absorptive surface; calciferous glands neutralise acids.

Cockroach (Periplaneta) anatomy: 13-chambered heart, Malpighian tubules for excretion, tracheal respiration via ten pairs of spiracles, and compound eyes on the head.

Cockroach mouthparts are of the biting-chewing type: labrum, mandibles, maxillae, labium and hypopharynx; sexes differ by anal cerci and the broader abdomen of the female.

Frog (Rana) key structures: three-chambered heart, hepatic portal system, lungs plus skin respiration, and a muscular tongue attached anteriorly for flicking prey.

Tissue level rule: epithelia are classified by cell shape (squamous, cuboidal, columnar) and by layer number (simple versus stratified); squamous lines alveoli and blood vessels.

Connective tissue ranking by matrix: loose areolar is most widespread, dense regular forms tendons and ligaments, cartilage and bone are skeletal, blood is fluid with plasma matrix.

Muscle rule: skeletal is striated, multinucleate and voluntary; smooth is non-striated and involuntary; cardiac is striated, involuntary and intercalated discs allow rapid impulse spread.

Four primary tissue types: epithelial, connective, muscular and nervous; organ systems combine organs that share a function.

Neuron structure: cell body (cyton), dendrites carry impulses toward the cell, axon conducts away, and the myelin sheath speeds conduction; a synapse is the functional junction.

Epithelial functions include protection, absorption, secretion and filtration; tight junctions and desmosomes bind adjacent epithelial cells.

Glandular epithelium: exocrine glands secrete through ducts, endocrine glands are ductless and release hormones into blood.

Blood as connective tissue: plasma with albumins, globulins and fibrinogen; erythrocytes carry haemoglobin, leucocytes defend, thrombocytes or platelets aid clotting.

Organ-system integration: nervous and endocrine systems coordinate, while circulatory and respiratory systems cooperate to deliver oxygen and remove carbon dioxide.

Bone and cartilage comparison: bone is hard, vascularised and has Haversian canals; cartilage is flexible, avascular and lacks canals.

Homeostasis rule: feedback loops maintain internal constancy; negative feedback reverses a change, positive feedback amplifies it, as in oxytocin-driven labour.

Human dental formula for one half of each jaw: incisors 2, canines 1, premolars 2, molars 3, giving 32 permanent teeth; enamel is the hardest substance.

Enzyme locations: salivary amylase acts on starch in the mouth; pepsin (with HCl) digests protein in the stomach; trypsin and chymotrypsin act in the small intestine.

Bile from the liver is stored in the gall bladder; it contains no enzymes but emulsifies fats and neutralises acidic chyme.

Pancreatic juice supplies amylase, lipase and the proteinases trypsinogen and chymotrypsinogen, activated by enterokinase in the duodenum.

Absorption sites: glucose and amino acids via villi into blood capillaries; fatty acids and glycerol form chylomicrons that enter lymph vessels (lacteals).

Villi adaptations: finger-like projections, rich capillary network, lacteal, and microvilli on columnar cells increase surface area.

Gastric secretion is stimulated by gastrin from the pyloric region; secretin and cholecystokinin from the duodenum regulate pancreatic and bile release.

Disorder markers: jaundice from bilirubin accumulation, vomiting reflex controlled by the medulla, and marasmus versus kwashiorkor as protein-energy malnutrition forms.

Human respiratory tract path: nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveoli; alveoli are the only site of gas exchange.

Lung volumes: tidal volume about 500 mL, vital capacity about 3500-4500 mL, residual volume about 1100-1200 mL; vital capacity equals inspiratory reserve plus tidal plus expiratory reserve.

Breathing control: medulla respiratory centre responds mainly to rising carbon dioxide and hydrogen ion concentration, not falling oxygen.

Haemoglobin carries about 97 percent of oxygen as oxyhaemoglobin; carbon dioxide travels mostly as bicarbonate (about 70 percent).

Human heart is four-chambered; the right side handles deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body.

Cardiac conduction order: SA node (pacemaker), AV node, bundle of His, Purkinje fibres; the SA node sets the rhythm.

ECG waves: P is atrial depolarisation, QRS is ventricular depolarisation, T is ventricular repolarisation.

Blood pressure rule: normal around 120/80 mm Hg; hypertension is persistent elevation, and the systolic reading corresponds to ventricular contraction.

Nephron parts: Bowman's capsule with glomerulus filters blood; proximal tubule reabsorbs most glucose, amino acids and water; loop of Henle builds a medullary osmotic gradient; distal tubule and collecting duct fine-tune.

Filtration rule: blood pressure in the glomerulus drives ultrafiltration; proteins and blood cells normally stay in blood.

Hormonal control: ADH increases water reabsorption in the collecting duct; aldosterone increases sodium reabsorption; both reduce urine volume.

Counter-current mechanism: the descending loop of Henle is water-permeable, the ascending limb is water-impermeable and transports salts, enabling urine concentration.

Micturition reflex is controlled by the nervous system; the ureters carry urine to the bladder by peristalsis.

Nitrogenous waste types: ammonotelic (ammonia, aquatic fishes), ureotelic (urea, mammals and amphibians), uricotelic (uric acid, birds and insects, water-saving).

Dialysis substitutes for failed kidneys by removing wastes across a semi-permeable membrane; a healthy kidney also regulates pH and salt balance.

Kidney disorder markers: glycosuria indicates high blood glucose, and kidney stones form from crystallised salts such as calcium oxalate.

Human skeleton: about 206 bones divided into axial (skull, vertebral column, ribs, sternum) and appendicular (limbs and girdles).

Muscle contraction sliding filament rule: myosin heads bind actin, the sarcomere shortens, and ATP plus calcium ions are required.

Sliding filament mechanism relies on actin and myosin filaments; the I band and H zone narrow during contraction while the A band stays constant.

Neuromuscular junction: motor neuron releases acetylcholine, depolarising the sarcolemma and triggering calcium release from the sarcoplasmic reticulum.

Bone types: long (femur), short (carpals), flat (skull bones), irregular (vertebrae); red marrow forms blood cells.

Joints: fibrous are immovable, cartilaginous are slightly movable, synovial are freely movable and contain lubricating synovial fluid.

Muscle types in movement: skeletal muscle works in antagonistic pairs such as biceps and triceps at the elbow.

Disorder markers: myasthenia gravis involves neuromuscular junction failure; gout results from uric acid crystal deposition in joints.

Neuron types by function: sensory (afferent) neurons carry impulses to the CNS, motor (efferent) neurons carry impulses away, and interneurons connect them.

Resting potential rule: inside the axon is negative (about -70 mV) because of potassium leak and the sodium-potassium pump; an action potential reverses this briefly.

Impulse conduction: depolarisation opens sodium channels, repolarisation restores the resting state; myelinated axons conduct saltatory impulses faster.

Synapse transmission is chemical: neurotransmitter released into the synaptic cleft binds receptors on the next membrane; transmission is one-way.

Human brain regions: cerebrum controls voluntary activity and intelligence, cerebellum coordinates balance and posture, medulla controls respiration and heartbeat.

Reflex arc path: receptor, sensory neuron, spinal cord integration, motor neuron, effector; reflexes are involuntary and fast.

Autonomic division: sympathetic prepares the body for stress (fight or flight), parasympathetic restores resting functions.

Eye and ear: rods handle dim light and cones colour vision; the cochlea in the inner ear converts sound into nerve impulses.

Endocrine glands are ductless and secrete hormones into blood; target cells respond because they carry specific receptors.

Pituitary control: anterior pituitary secretes growth hormone, TSH, ACTH, FSH and LH; posterior pituitary stores and releases oxytocin and ADH.

Thyroid hormones thyroxine (T4) and triiodothyronine (T3) need iodine and regulate basal metabolic rate; deficiency causes goitre.

Insulin from beta cells lowers blood glucose; glucagon from alpha cells raises it; both come from pancreatic islets.

Adrenal gland: cortex secretes cortisol and aldosterone, medulla secretes adrenaline and noradrenaline for emergency responses.

Parathyroid hormone raises blood calcium by acting on bone, kidney and intestine; calcitonin from the thyroid lowers it.

Hormone feedback: rising thyroxine inhibits TSH release from the pituitary, a negative feedback loop.

Disorder markers: diabetes mellitus from insulin deficiency, diabetes insipidus from ADH deficiency, and cretinism from childhood thyroid deficiency.

Male reproductive tract: testes produce sperm and testosterone; sperm matures in the epididymis and travels via vas deferens, seminal vesicles and prostate add secretions.

Female cycle: FSH stimulates follicle growth, a mid-cycle LH surge triggers ovulation, and the corpus luteum secretes progesterone.

Menstrual cycle timing: menstrual phase, follicular phase, ovulation near day 14, and luteal phase; progesterone maintains the endometrium.

Fertilisation normally occurs in the fallopian tube; the zygote undergoes cleavage and implants in the uterus as a blastocyst.

Extraembryonic membranes: amnion protects with fluid, chorion contributes to the placenta, allantois handles waste, and the yolk sac is reduced in humans.

Placenta is the exchange organ for nutrients, oxygen and wastes between mother and fetus, and it secretes hormones including hCG.

Contraception categories: barrier methods block gamete meeting, hormonal pills suppress ovulation, and IUDs prevent implantation.

Developmental stages: zygote, morula, blastula, gastrula with three germ layers; ectoderm forms skin and nerves, mesoderm forms muscle and bone, endoderm forms gut lining.

Mendel's laws: dominance, segregation of alleles, and independent assortment of two or more gene pairs on different chromosomes.

Monohybrid cross of heterozygotes gives a 3:1 phenotype ratio; a dihybrid cross gives 9:3:3:1 with independent assortment.

Genotype shorthand: homozygous dominant AA, heterozygous Aa, homozygous recessive aa; a test cross with aa reveals an unknown dominant genotype.

Sex determination: human males are XY and females XX; the father's sperm determines the child's sex.

Human genetic disorders: sickle-cell anaemia and thalassaemia are autosomal recessive; haemophilia is X-linked recessive; Down syndrome is trisomy 21.

Evolution evidence: fossils, homologous organs (same origin, different function), analogous organs (different origin, same function), and molecular similarities.

Darwin's natural selection: heritable variation plus differential survival and reproduction changes allele frequencies over generations.

Hardy-Weinberg rule: allele frequencies stay constant in an ideal population; p + q = 1 and p squared plus 2pq plus q squared = 1.