Zoology प्राणीशास्त्र

Quick summary

Mammals are warm-blooded vertebrates that have hair on the body and mammary glands that feed the young with milk. They have the most developed brain among animals. Humans, cows, bats, whales and the platypus are mammals. This topic covers general characters, the three subclasses, dentition and adaptations.

Key points

• Mammalia comes from "mamma" (breast). Mammals are सस्तन प्राणी in Marathi.
• Hair on the body; skin has sweat and sebaceous (oil) glands.
• Mammary glands in females secrete milk.
• External ear (pinna) present in most.
• Diaphragm – a muscular sheet that separates the thoracic and abdominal cavities; helps in breathing.
• Heart four-chambered; only the left aortic arch persists.
• RBCs are non-nucleated and usually biconcave (camel and llama have oval RBCs).
• Two occipital condyles; usually seven cervical vertebrae (even in the giraffe).
• Lower jaw made of a single bone (dentary).
• Three ear ossicles in the middle ear: malleus, incus and stapes.
• Teeth are thecodont, heterodont and diphyodont.
• Most are viviparous; the embryo is nourished through a placenta.
• Homeothermic; brain with well-developed cerebrum and corpus callosum (in placentals).

Important terms

• Thecodont – teeth set in sockets of the jaw bone.
• Heterodont – different types of teeth: incisors, canines, premolars, molars.
• Diphyodont – two sets of teeth in life: milk teeth and permanent teeth.
• Dental formula – number of each type of tooth in one half of upper and lower jaw.
• Placenta – structure joining foetus and mother for exchange of food, gases and wastes.
• Echolocation – using echoes of high-pitched sounds to locate objects (bats, dolphins).

Formulas

• Human (adult) dental formula: I 2/2, C 1/1, PM 2/2, M 3/3 = 8/8 per half → total 32 teeth.
• Human milk teeth: I 2/2, C 1/1, M 2/2 = 5/5 per half → total 20.
• How to calculate: total teeth = 2 × (upper + lower in one half). For adult human: 2 × (8 + 8) = 32.

Key facts

• Some Indian eutherian orders: Primates (monkey), Chiroptera (bats – only flying mammals; flying fox Pteropus), Rodentia (rat, squirrel), Proboscidea (elephant), Carnivora (tiger, dog), Artiodactyla (cow, deer).
• Blue whale is the largest living animal; whales and dolphins are aquatic mammals that breathe with lungs.

5 important questions

Q1. Why are monotremes considered primitive mammals?

Monotremes lay eggs like reptiles and have a cloaca, and their mammary glands have no nipples. But they have hair and feed young with milk, so they are mammals with reptile-like features.

Q2. Write the dental formula of an adult human and find the total number of teeth.

Dental formula: I 2/2, C 1/1, PM 2/2, M 3/3. Teeth in one half of both jaws = 8 + 8 = 16. Total = 2 × 16 = 32 teeth.

Q3. Give the general characters of Mammalia.

• Hair; sweat and sebaceous glands; mammary glands.
• Pinna; three ear ossicles.
• Diaphragm; four-chambered heart; left aortic arch.
• Non-nucleated RBCs.
• Thecodont, heterodont, diphyodont teeth.
• Viviparous (except monotremes); placenta in eutherians.

Q4. Compare Prototheria, Metatheria and Eutheria.

• Reproduction: eggs / immature young in pouch / placenta-fed developed young.
• Cloaca: present / absent (or reduced) / absent.
• Nipples: absent / present inside pouch / present.
• Body temperature: relatively low and less constant in monotremes.
• Examples for each.

Q5. Describe adaptations of aquatic mammals.

• Streamlined body; forelimbs into flippers; hind limbs lost (whales).
• Thick blubber for insulation and buoyancy.
• Nostrils (blowhole) on top of head.
• Large lungs; holding breath long; slowing of heart while diving.
• Echolocation in dolphins.
• Hair reduced; tail with horizontal flukes.

Exam tip

Practise dental formula calculations; they are easy marks. Remember "seven neck vertebrae" and "non-nucleated RBCs" as standard one-liners.

Quick summary

The integument is the skin with all the structures that grow from it. It protects the body and also helps in sensation, temperature control, respiration in some animals, and secretion. Each vertebrate class has its own special skin derivatives: scales in fishes and reptiles, glands in amphibians, feathers in birds and hair in mammals. This topic covers the basic structure of skin and a comparative account of integument and its derivatives in vertebrates.

Key points

• Skin (त्वचा) has two layers: the outer epidermis (from ectoderm) and the inner dermis (from mesoderm).
• The epidermis is stratified epithelium; its lowest layer is the dividing stratum germinativum (Malpighian layer). In land vertebrates the outer cells fill with keratin and form a dead stratum corneum.
• The dermis has connective tissue, blood vessels, nerves, muscles and chromatophores (pigment cells).
• Derivatives are of two kinds: epidermal (horny scales, feathers, hair, claws, nails, hoofs, horns, beaks, most glands) and dermal (bony scales of fishes, bony plates, antlers, scutes of crocodiles).
• Fishes: skin is slimy with mucous glands and covered by dermal scales – placoid (sharks; tooth-like, with dentine and a hard enamel-like layer), ganoid (Lepisosteus), cycloid and ctenoid (bony fishes).
• Amphibians: skin is thin, moist and without scales; rich in mucous glands and poison (granular) glands; it is an important respiratory organ.
• Reptiles: dry skin with very few glands; covered by epidermal horny scales and scutes; the old skin is shed by ecdysis (moulting).
• Birds: body covered with feathers; skin is thin and dry; the only skin gland is the uropygial (preen) gland near the tail, whose oil waterproofs feathers. Legs have horny scales; beak and claws are horny.
• Mammals: skin has hair and many glands – sweat, sebaceous (oil), mammary and scent glands; also nails, claws, hoofs and horns.
• Horns and antlers: true horns of cattle and goats have a bony core with a permanent keratin sheath; antlers of deer are branched bone, usually only in males, shed and regrown every year; the rhinoceros horn is made only of compact keratin fibres.

Important terms

• Keratinisation – filling of epidermal cells with the tough protein keratin.
• Chromatophores – pigment-bearing cells responsible for skin colour and colour change.
• Contour (quill) feather – main body and flight feather with shaft and vane.
• Down feather – soft, fluffy feather for insulation.
• Filoplume – hair-like feather with a few barbs at the tip.
• Arrector pili – small muscle that makes hair stand erect.

Key facts

5 important questions

Q1. Distinguish between horns and antlers.

Horns have a bony core with a permanent keratin sheath, are unbranched and are found in both sexes of cattle. Antlers are solid branched bone, covered by "velvet" skin while growing, usually found only in male deer, and shed every year.

Q2. What is the uropygial gland?

It is the oil gland on the upper side of the tail base of birds. It is the only skin gland in birds; its oily secretion is spread over feathers with the beak to keep them waterproof.

Q3. Give the general structure and functions of vertebrate skin.

• Epidermis: layers, keratinisation.
• Dermis: connective tissue, vessels, nerves, chromatophores.
• Functions: protection, sensation, temperature control, excretion, respiration (amphibians), vitamin D synthesis, colour.
• Labelled diagram of mammalian skin.

Q4. Write a comparative account of integument in vertebrates.

• Fish, amphibian, reptile, bird and mammal skin in turn.
• Special features and derivatives of each class.
• Show the evolutionary trend from moist glandular to dry keratinised skin on land.

Q5. Describe the epidermal and dermal derivatives of the integument.

• Epidermal: horny scales, feathers (types), hair (structure), claws, nails, hoofs, beaks, glands.
• Dermal: fish scales (types with diagrams), bony plates, antlers.
• Mixed: teeth and placoid scales (dentine from dermis, enamel from epidermis).

Exam tip

Draw the four types of fish scales and the structure of a contour feather; diagrams carry heavy weightage in comparative anatomy answers.

Quick summary

The heart is a muscular pump that drives blood around the body. In vertebrates it evolved from a simple two-chambered heart in fishes to a four-chambered heart in birds and mammals, gradually separating oxygenated and deoxygenated blood. This topic gives a comparative account of the heart in fishes, amphibians, reptiles, birds and mammals, along with single and double circulation.

Key points

• The vertebrate heart develops from a straight tube on the ventral side; it folds into an S-shape and becomes divided into chambers.
• The primitive heart has four parts in a row: sinus venosus → atrium (auricle) → ventricle → conus arteriosus.
• Fishes: two-chambered (one auricle, one ventricle) plus sinus venosus and conus arteriosus (cartilaginous fishes) or bulbus arteriosus (bony fishes). It carries only deoxygenated blood, so it is called a venous heart. Circulation is single: heart → gills → body → heart.
• In lungfishes the auricle is partly divided – a step towards the land heart.
• Amphibians: three-chambered – two auricles and one ventricle. The right auricle gets deoxygenated blood from the body; the left auricle gets oxygenated blood from the lungs. Mixing in the single ventricle is reduced by a spiral valve in the conus (truncus) arteriosus and by ventricular folds. Circulation is double but incomplete.
• Reptiles: two auricles and a ventricle partly divided by an incomplete septum, so mixing is less. Sinus venosus is reduced; conus is absent, and three separate vessels arise from the ventricle.
• Crocodiles have a four-chambered heart with complete ventricular septum, but the two systemic arches are connected by the foramen of Panizza.
• Birds and mammals: four-chambered heart – two auricles and two ventricles completely separated. There is complete double circulation: pulmonary (heart → lungs → heart) and systemic (heart → body → heart). Sinus venosus is reduced to the SA node (pacemaker), and conus is absent.
• Birds keep the right systemic aortic arch; mammals keep the left.
• Complete separation of blood allows high metabolism and warm-bloodedness (homeothermy).

Important terms

• Sinus venosus – thin-walled chamber collecting venous blood in lower vertebrates.
• Conus arteriosus – muscular, contractile tube in front of the ventricle with valves (sharks, amphibians).
• Bulbus arteriosus – non-contractile elastic base of ventral aorta in bony fishes.
• Single circulation – blood passes through the heart once per round.
• Double circulation – blood passes through the heart twice per round.
• SA node – sino-atrial node, the pacemaker of the heart.

Key facts

5 important questions

Q1. Why is the fish heart called a venous heart?

Because it receives and pumps only deoxygenated (venous) blood. This blood goes to the gills for oxygenation and then directly to the body without returning to the heart.

Q2. What is the foramen of Panizza?

It is an opening that connects the left and right systemic aortic arches at their base in crocodiles. Through it a little mixing of blood can occur even though the ventricles are fully separated.

Q3. Describe the heart of a fish and an amphibian.

• Fish: external and internal structure, valves, blood flow, single circulation. Diagram.
• Frog: two auricles, ventricle, sinus venosus, truncus with spiral valve, blood flow, double incomplete circulation. Diagram.

Q4. Give a comparative account of the heart in vertebrates.

• Basic plan and embryonic origin.
• Class-by-class description with chambers and changes in sinus venosus and conus.
• Evolutionary trend: separation of oxygenated and deoxygenated blood.
• Table and diagrams.

Q5. Distinguish between single and double circulation with suitable examples.

• Definitions with flow-charts.
• Fish (single), amphibians and reptiles (double incomplete), birds and mammals (double complete).
• Advantages of complete double circulation.

Exam tip

Use one neat comparative diagram showing all five hearts side by side; label chambers and arrows of blood flow.

Quick summary

Aortic arches are paired blood vessels that run from the ventral aorta through the pharyngeal (gill) region to the dorsal aorta. All vertebrate embryos start with six pairs, but different classes keep or lose different arches as gills are replaced by lungs. This topic covers the basic plan of six arches and their fate in fishes, amphibians, reptiles, birds and mammals.

Key points

• In the embryo, six pairs of aortic arches (numbered I to VI from front to back) connect the ventral aorta to the paired dorsal aortae, one arch through each visceral arch.
• Arch I is the mandibular arch, II the hyoid arch, and III–VI are branchial arches.
• In all jawed vertebrates arches I and II disappear early (only small remnants remain in the head).
• Fishes: arches pass through gills, where each splits into afferent (to gills) and efferent (from gills) branchial arteries. Sharks usually keep five pairs (II–VI); bony fishes keep four pairs (III–VI).
• Lungfishes: a branch of arch VI goes to the air bladder (lung) – the first pulmonary artery.
• Rule for land vertebrates: arch III becomes the carotid arch (to head), arch IV the systemic arch (to body) and arch VI the pulmonary arch (to lungs). Arch V is lost (except in tailed amphibians).
• Frog (anurans): III carotid, IV systemic, VI pulmocutaneous (to lungs and skin); V lost. Tailed amphibians (urodeles) keep a small arch V.
• Reptiles: both right and left systemic arches (IV) remain and cross each other; III carotid; VI pulmonary.
• Birds: only the right systemic arch (IV) remains.
• Mammals: only the left systemic arch (IV) remains; the right IV forms the base of the right subclavian artery.
• The dorsal part of the left VI arch forms the ductus arteriosus in the foetus, which lets blood bypass the lungs; after birth it closes to form the ligamentum arteriosum.
• The ductus caroticus (link between III and IV in the dorsal aorta) persists in some reptiles and urodeles but is lost in mammals.

Important terms

• Ventral aorta – vessel carrying blood forward from the heart in fishes and embryos.
• Afferent branchial artery – carries blood to the gills.
• Efferent branchial artery – carries oxygenated blood from the gills to the dorsal aorta.
• Pulmocutaneous arch – arch VI of frog supplying lungs and skin.
• Ductus arteriosus – foetal connection between pulmonary trunk and aorta.

Key facts

5 important questions

Q1. Which aortic arch forms the systemic arch in birds and mammals?

The fourth arch forms the systemic arch in both. Birds keep only the right fourth arch, while mammals keep only the left one.

Q2. What is the ductus arteriosus?

It is a short vessel in the foetus formed from the dorsal part of the left sixth arch. It connects the pulmonary artery with the aorta so that blood bypasses the non-working lungs. After birth it closes and becomes the ligamentum arteriosum.

Q3. Describe the basic plan of aortic arches in a vertebrate embryo.

• Ventral aorta, six pairs of arches, dorsal aortae.
• Relation with visceral arches and gill slits.
• Early loss of I and II.
• Diagram of the generalised pattern.

Q4. Give a comparative account of aortic arches in vertebrates.

• Fishes (shark, bony fish, lungfish).
• Amphibians (frog and urodele).
• Reptiles, birds and mammals.
• Fate of each arch with diagrams and the table above.

Q5. Explain the evolutionary changes in aortic arches from aquatic to land vertebrates.

• Reduction in number of arches as gills are lost.
• Development of pulmonary arch from VI.
• Specialisation into carotid, systemic and pulmonary arches.
• Loss of one systemic arch in birds and mammals; link with complete double circulation.

Exam tip

Learn the "III–IV–VI" rule (carotid, systemic, pulmonary) and draw a simple comparative diagram; most of the answer follows from it.

Quick summary

Digestion is the breakdown of complex, insoluble food into simple, soluble forms that the body can absorb. In humans it happens in the alimentary canal with the help of digestive glands and enzymes. This topic covers the human digestive system, digestion in each region, hormones controlling digestion, absorption and assimilation, and common disorders.

Key points

• Digestion (पचन) has two parts: mechanical (chewing, churning) and chemical (by enzymes).
• Alimentary canal: mouth → buccal cavity → pharynx → oesophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine (caecum, colon, rectum) → anus.
• Wall of the gut has four layers: serosa, muscularis, submucosa and mucosa.
• Mouth: saliva contains salivary amylase (ptyalin) that changes starch into maltose; pH about 6.8. About 30% of starch is digested here.
• Stomach: gastric glands have chief (peptic) cells (pepsinogen, prorennin), oxyntic (parietal) cells (HCl, intrinsic factor) and mucous cells. HCl converts pepsinogen into active pepsin, which breaks proteins into peptones and proteoses. Rennin curdles milk (mainly in infants).
• Small intestine: receives bile (from liver) and pancreatic juice. Bile has no enzymes; its salts emulsify fats.
• Pancreatic juice: trypsinogen (activated to trypsin by enterokinase), chymotrypsinogen, pancreatic amylase, lipase, nucleases.
• Intestinal juice (succus entericus): maltase, sucrase, lactase, dipeptidases, lipases, nucleotidases, nucleosidases.
• Final products: carbohydrates → monosaccharides (glucose, fructose, galactose); proteins → amino acids; fats → fatty acids and glycerol (monoglycerides).
• Absorption mainly in the small intestine through villi and microvilli, which give a huge surface area.
• Large intestine absorbs water, minerals and some drugs; bacteria there make some vitamins (e.g. vitamin K).

Important terms

• Bolus – rounded mass of chewed food mixed with saliva.
• Peristalsis – wave-like muscular contraction moving food along the gut.
• Chyme – acidic, semi-liquid food leaving the stomach.
• Emulsification – breaking fat into tiny droplets by bile salts.
• Lacteal – lymph vessel inside each villus that absorbs fat.
• Chylomicrons – fat-protein droplets made in intestinal cells, carried by lymph.
• Assimilation – use of absorbed nutrients by body cells.

Key facts

• Secretin was the first hormone discovered (Bayliss and Starling, 1902).
• Absorption methods: simple diffusion, facilitated diffusion (fructose), active transport (glucose, amino acids, Na⁺), and fat absorption through lacteals.
• Disorders: jaundice (liver; bile pigments in blood), vomiting, diarrhoea, constipation, indigestion, peptic ulcer.

5 important questions

Q1. What is the role of bile in digestion?

Bile contains bile salts and pigments but no enzymes. Bile salts emulsify fats into small droplets so lipase can act on them. Bile also makes the medium alkaline and helps absorb fats and fat-soluble vitamins.

Q2. What is enterokinase?

Enterokinase (enteropeptidase) is an enzyme from the intestinal mucosa. It changes inactive trypsinogen into active trypsin, which then activates other pancreatic protein-digesting enzymes.

Q3. Describe digestion of proteins in the human gut.

• Stomach: pepsin (activated by HCl) → proteoses and peptones.
• Infants: rennin converts caseinogen to casein (curdling).
• Duodenum: trypsin, chymotrypsin and carboxypeptidase → smaller peptides.
• Intestine: aminopeptidases and dipeptidases → amino acids.
• Absorption of amino acids by active transport into blood.

Q4. Describe the structure of a villus and absorption of food.

• Finger-like projection of intestinal mucosa; covered by columnar cells with microvilli (brush border).
• Inside: network of blood capillaries and a central lacteal.
• Monosaccharides and amino acids enter blood capillaries.
• Fatty acids and monoglycerides form micelles → enter cells → chylomicrons → lacteal → lymph.
• Labels: microvilli, epithelium, capillaries, lacteal, crypts of Lieberkühn.

Q5. Explain the hormonal control of digestion.

• Sight, smell and taste of food start saliva and gastric secretion (nervous control).
• Gastrin increases gastric juice.
• Secretin and CCK act on pancreas and gall bladder.
• GIP slows stomach activity.
• Table of hormone, source and action.

Exam tip

Make a single table of enzymes: source, substrate, product. Most short questions come from it.

Quick summary

Respiration in animals includes breathing (exchange of gases with the environment), transport of gases by blood and the use of oxygen in cells. Different animals use body surface, gills, trachea or lungs. This topic covers respiratory organs, the human respiratory system, mechanism of breathing, lung volumes, transport of gases, regulation and disorders.

Key points

• Respiratory organs: body surface (earthworm), trachea (insects), gills (fish, prawn), book lungs (scorpion), lungs (land vertebrates).
• Human respiratory tract: nostrils → nasal cavity → pharynx → larynx (voice box) → trachea → bronchi → bronchioles → alveoli.
• Trachea is held open by C-shaped cartilage rings.
• Lungs are covered by a double pleural membrane with pleural fluid.
• Gas exchange occurs in the alveoli by diffusion across a very thin respiratory membrane.
• Inspiration (breathing in): diaphragm contracts and flattens; external intercostal muscles lift ribs; chest volume increases; pressure falls; air enters. It is an active process.
• Expiration (breathing out): diaphragm and intercostal muscles relax; volume decreases; air is pushed out. Normal expiration is passive.
• Breathing rate of a normal adult: about 12–16 times per minute.
• Oxygen transport: about 97% carried by haemoglobin as oxyhaemoglobin; about 3% dissolved in plasma.
• CO₂ transport: about 70% as bicarbonate ions, about 20–25% as carbaminohaemoglobin, about 7% dissolved in plasma.
• Regulation: the respiratory rhythm centre is in the medulla oblongata; the pneumotaxic centre is in the pons; chemoreceptors sense CO₂ and H⁺.

Important terms

• Tidal volume (TV) – air breathed in or out in normal breathing (about 500 mL).
• Inspiratory reserve volume (IRV) – extra air that can be breathed in by force (about 2500–3000 mL).
• Expiratory reserve volume (ERV) – extra air that can be breathed out by force (about 1000–1100 mL).
• Residual volume (RV) – air left in lungs even after forced expiration (about 1100–1200 mL).
• Vital capacity (VC) – maximum air breathed out after a maximum breath in.
• Oxygen dissociation curve – sigmoid (S-shaped) graph of percent saturation of haemoglobin against partial pressure of O₂.
• Chloride shift (Hamburger shift) – movement of Cl⁻ into RBCs as HCO₃⁻ moves out, to keep ionic balance.
• Bohr effect – rise in CO₂ (fall in pH) shifts the O₂ dissociation curve to the right, releasing more O₂ to tissues.

Formulas

• Vital capacity: VC = TV + IRV + ERV
• Total lung capacity: TLC = VC + RV
• Functional residual capacity: FRC = ERV + RV
• Inspiratory capacity: IC = TV + IRV
• Minute ventilation = tidal volume × breathing rate. Example: 500 mL × 12 = 6000 mL (6 L) per minute.
• In tissues: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ (enzyme carbonic anhydrase in RBCs).

5 important questions

Q1. Define vital capacity.

Vital capacity is the maximum volume of air a person can breathe out after taking the deepest possible breath. VC = TV + IRV + ERV, usually about 3.5–4.5 litres in a healthy adult (higher in athletes).

Q2. If TV = 500 mL, IRV = 3000 mL, ERV = 1100 mL and RV = 1200 mL, find VC and TLC.

VC = 500 + 3000 + 1100 = 4600 mL. TLC = VC + RV = 4600 + 1200 = 5800 mL.

Q3. Explain the mechanism of breathing in humans.

• Inspiration: diaphragm contracts (flattens), external intercostals contract, ribs and sternum move up and out.
• Thoracic and lung volume increase; pressure falls below atmospheric; air flows in.
• Expiration: muscles relax; volume decreases; pressure rises; air flows out.
• Forced breathing uses internal intercostals and abdominal muscles.

Q4. Describe transport of oxygen and carbon dioxide.

• O₂: binds Hb in lungs (high pO₂) → oxyhaemoglobin; released in tissues (low pO₂, high pCO₂, high temperature, low pH).
• Sigmoid O₂ dissociation curve; Bohr effect.
• CO₂: bicarbonate (carbonic anhydrase), carbamino compounds, dissolved.
• Chloride shift in RBCs; reversal in lungs.

Q5. Write about disorders of the respiratory system.

• Asthma: spasm and inflammation of bronchi; wheezing.
• Emphysema: damaged alveolar walls; smoking a major cause.
• Bronchitis: inflammation of bronchi; cough with mucus.
• Occupational lung diseases (silicosis, asbestosis) in mines and factories.
• Pneumonia and tuberculosis are infections.

Exam tip

Remember the lung-volume formulas and practise one numerical. The O₂ dissociation curve should be drawn as an S-shaped curve with axes labelled.

Quick summary

Blood is a fluid connective tissue that carries oxygen, food, hormones and wastes around the body. It is pumped by the heart through blood vessels. This topic covers the composition of blood, blood groups, coagulation, the structure and working of the human heart, cardiac cycle, ECG, double circulation, lymph and common disorders.

Key points

• Blood (रक्त) has plasma (about 55%) and formed elements (about 45%): RBCs, WBCs and platelets.
• Plasma is about 90–92% water; proteins: albumin (osmotic balance), globulins (defence) and fibrinogen (clotting).
• RBCs (erythrocytes): biconcave, non-nucleated in mammals; contain haemoglobin; life span about 120 days; formed in red bone marrow.
• WBCs (leucocytes): granulocytes (neutrophils – most common WBCs, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
• Platelets (thrombocytes): cell fragments from megakaryocytes; help in clotting.
• ABO blood groups were discovered by Karl Landsteiner (1900). Group O is the universal donor; group AB is the universal recipient.
• Rh factor – an antigen first found in Rhesus monkeys. Rh mismatch between an Rh⁻ mother and an Rh⁺ foetus can cause erythroblastosis foetalis in later pregnancies.
• Human heart: four-chambered, myogenic (beat starts in heart muscle itself), enclosed in a pericardium.
• Conducting system: SA node (pacemaker, in right atrium) → AV node → bundle of His → Purkinje fibres.
• Double circulation: pulmonary (heart → lungs → heart) and systemic (heart → body → heart). Oxygenated and deoxygenated blood never mix in birds and mammals.
• Normal blood pressure about 120/80 mm Hg (systolic/diastolic).

Important terms

• Coagulation – clotting of blood to stop bleeding.
• Tricuspid valve – between right atrium and right ventricle; bicuspid (mitral) valve – between left atrium and left ventricle.
• Semilunar valves – at the openings of pulmonary artery and aorta.
• Cardiac cycle – events of one heartbeat: atrial systole, ventricular systole and joint diastole (about 0.8 s at 72 beats per minute).
• ECG – electrocardiogram, a graph of the heart's electrical activity: P wave (atrial depolarisation), QRS complex (ventricular depolarisation), T wave (ventricular repolarisation).
• Lymph – colourless fluid from tissue fluid, carried by lymph vessels; has lymphocytes; returns fluid to blood.

Formulas

• Cardiac output = stroke volume × heart rate. Example: 70 mL × 72 beats/min = 5040 mL ≈ 5 L per minute.
• Duration of one cardiac cycle = 60 ÷ heart rate. At 72 beats/min: 60 ÷ 72 ≈ 0.8 s.
• Clotting cascade (simplified): injured tissue/platelets → thromboplastin → prothrombin activator; Prothrombin → Thrombin (needs Ca²⁺); Fibrinogen → Fibrin (by thrombin); fibrin threads trap blood cells → clot.

5 important questions

Q1. Why is the human heart called myogenic?

Because each heartbeat starts in a special group of heart muscle cells, the SA node, and not from a nerve impulse. Nerves only change the rate.

Q2. A person's stroke volume is 75 mL and heart rate is 80 per minute. Find the cardiac output.

Cardiac output = stroke volume × heart rate = 75 × 80 = 6000 mL per minute = 6 litres per minute.

Q3. Describe the structure of the human heart.

• Size of a fist; between lungs, tilted to the left; covered by pericardium.
• Four chambers: two thin-walled atria and two thick-walled ventricles (left ventricle thickest).
• Interatrial and interventricular septa.
• Valves: tricuspid, bicuspid, semilunar; chordae tendineae and papillary muscles.
• Vessels: venae cavae into right atrium; pulmonary veins into left atrium; pulmonary artery and aorta leave ventricles.
• Labels: all chambers, valves, vessels, SA node, AV node.

Q4. Explain the cardiac cycle.

• Atrial systole (about 0.1 s): blood pushed into ventricles.
• Ventricular systole (about 0.3 s): AV valves close ("lub"), semilunar valves open, blood into arteries.
• Joint diastole (about 0.4 s): semilunar valves close ("dub"); chambers fill.
• Total about 0.8 s.
• Relate to ECG waves.

Q5. Describe the ABO blood group system.

• Based on antigens A and B on RBCs and antibodies in plasma.
• A: antigen A, anti-B; B: antigen B, anti-A; AB: both antigens, no antibodies; O: no antigens, both antibodies.
• Importance in transfusion; cross-matching.
• O universal donor; AB universal recipient.
• Inherited by multiple alleles (Iᴬ, Iᴮ, i).

Exam tip

Draw a neat L.S. of the heart with arrows for blood flow. Learn the timings of the cardiac cycle and the ECG waves.

Quick summary

Excretion is the removal of nitrogenous and other wastes from the body. Osmoregulation is the control of water and salt balance. Animals excrete ammonia, urea or uric acid depending on their habitat. This topic covers the types of excretion, excretory organs, the human kidney and nephron, urine formation, hormonal control and osmoregulation in different animals.

Key points

• Ammonotelic animals excrete mainly ammonia (highly toxic, needs a lot of water): most aquatic invertebrates, bony fishes, tadpoles.
• Ureotelic animals excrete urea (less toxic): mammals, adult frogs, marine cartilaginous fishes.
• Uricotelic animals excrete uric acid (least toxic, needs very little water): birds, reptiles, insects, land snails.
• Excretory organs: contractile vacuoles (Amoeba), flame cells (flatworms), nephridia (earthworm), Malpighian tubules (insects), green glands (prawn), kidneys (vertebrates).
• Urea is formed in the liver by the ornithine (urea) cycle (Krebs and Henseleit, 1932).
• Human excretory system: a pair of kidneys, two ureters, a urinary bladder and the urethra.
• Kidney has outer cortex and inner medulla (with renal pyramids); the nephron is the functional unit. Each kidney has about one million nephrons.
• Nephron parts: Bowman's capsule with glomerulus (together the Malpighian body), proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), collecting duct.
• Urine formation: (1) ultrafiltration in the glomerulus; (2) selective reabsorption (mainly in PCT – all glucose and amino acids, most water and salts); (3) tubular secretion (H⁺, K⁺, NH₃, creatinine).
• Counter-current mechanism in the loop of Henle and vasa recta makes the medulla very salty, so concentrated urine can be made.
• Normal adult urine output is about 1–1.5 litres per day.

Important terms

• Glomerular filtration rate (GFR) – volume of filtrate formed per minute by both kidneys (about 125 mL/min, about 180 L/day).
• ADH (vasopressin) – hormone from the posterior pituitary that increases water reabsorption in DCT and collecting duct.
• Aldosterone – hormone from the adrenal cortex that increases Na⁺ reabsorption.
• Renin–angiotensin system – raises blood pressure and GFR; renin comes from the juxtaglomerular apparatus (JGA).
• ANF (atrial natriuretic factor) – from the heart; causes loss of Na⁺ and water, lowering blood pressure.
• Micturition – act of passing urine.
• Dialysis – artificial removal of wastes from blood in kidney failure.

Key facts

• Osmoregulation in fishes: freshwater fishes live in a hypotonic medium – they gain water, so they produce a lot of dilute urine and absorb salts through gills. Marine bony fishes lose water – they drink sea water, produce little urine and excrete salts through gills. Marine sharks keep high urea in blood to stay nearly isotonic with sea water.
• Disorders: kidney stones (renal calculi), uraemia (high urea in blood), glomerulonephritis, diabetes insipidus (low ADH; large volume of dilute urine).

5 important questions

Q1. Why are birds uricotelic?

Birds excrete uric acid, which is almost insoluble and non-toxic. It can be removed as a paste with very little water. This saves water and is suitable for development inside a shelled egg.

Q2. What is the role of ADH?

ADH (antidiuretic hormone) makes the DCT and collecting duct more permeable to water. More water is reabsorbed, so urine becomes concentrated. Its deficiency causes diabetes insipidus.

Q3. Describe the structure of a nephron with a labelled diagram.

• Malpighian body: Bowman's capsule cup with glomerulus (afferent arteriole in, efferent arteriole out).
• PCT: coiled, brush-bordered cells.
• Loop of Henle: descending and ascending limbs in medulla.
• DCT: coiled; opens into collecting duct.
• Peritubular capillaries and vasa recta.
• Labels: afferent and efferent arterioles, glomerulus, Bowman's capsule, PCT, loop of Henle, DCT, collecting duct, vasa recta.

Q4. Explain the process of urine formation.

• Ultrafiltration: high pressure in glomerulus forces water and small solutes into Bowman's capsule.
• Reabsorption: PCT reabsorbs glucose, amino acids, Na⁺, water; loop concentrates medulla; DCT and collecting duct adjust water (ADH) and Na⁺ (aldosterone).
• Secretion: H⁺, K⁺, NH₃ secreted, maintaining pH.
• Final urine collected in pelvis → ureter → bladder.

Q5. Describe osmoregulation in freshwater and marine fishes.

• Freshwater: body hypertonic; water enters by osmosis; dilute urine; active uptake of salts by gills; little drinking.
• Marine bony: body hypotonic; water lost; drink sea water; little urine; salt-excreting chloride cells in gills.
• Sharks: urea retention (and TMAO); rectal gland excretes salt.

Exam tip

Draw a labelled nephron and write the three steps of urine formation under headings. Remember which animals are ammonotelic, ureotelic and uricotelic.

Quick summary

The placenta is the organ that joins the developing foetus to the mother's uterus. Through it the foetus gets food and oxygen and gives out wastes, and it also makes hormones. This topic covers the formation of the placenta, its classification by foetal membranes, by the distribution of villi and by the closeness of maternal and foetal tissues, and its functions.

Key points

• Placenta (वार / अपरा) is formed from both foetal tissue (chorion with allantois or yolk sac) and maternal tissue (uterine wall, endometrium).
• The foetus is joined to the placenta by the umbilical cord, which has two umbilical arteries and one umbilical vein in humans.
• By foetal membrane: yolk-sac (choriovitelline) placenta – in most marsupials such as kangaroo; chorioallantoic placenta – in eutherian (placental) mammals.
• By distribution of villi: diffuse (villi all over the chorion – pig, horse), cotyledonary (villi in patches called cotyledons – cow, sheep, goat), zonary (villi in a band around the middle – dog, cat), discoidal (villi in a disc – rodents, bats, insectivores, and in man and monkeys, where it is sometimes called metadiscoidal).
• By intimacy (Grosser's classification) – how many maternal layers remain between foetal and maternal blood:
• Epitheliochorial: all three maternal layers stay; chorion touches uterine epithelium (pig, horse).
• Syndesmochorial: uterine epithelium eroded; chorion touches maternal connective tissue (cow, sheep).
• Endotheliochorial: chorion touches the walls of maternal capillaries (dog, cat).
• Haemochorial: chorion bathed directly in maternal blood (man, monkeys, rodents, bats).
• Haemoendothelial: only the foetal capillary wall remains (rabbit, rat at late stage).
• Non-deciduate placentae separate without tearing maternal tissue (pig, cow). Deciduate placentae carry away part of the uterine wall at birth with bleeding (dog, man).

Important terms

• Chorionic villi – finger-like foetal projections that increase the exchange area.
• Decidua – the part of the uterine lining shed at birth.
• Cotyledon – a patch of villi in the cow placenta.
• hCG – human chorionic gonadotropin, made by the placenta; basis of the pregnancy test.
• Placental barrier – the layers between foetal and maternal blood.

Key facts

• Hormones of the placenta: hCG, progesterone, oestrogen, human placental lactogen (hPL) and relaxin.
• Some antibodies (IgG) cross the placenta and protect the newborn; some drugs, alcohol and viruses (e.g. rubella, HIV) can also cross.

5 important questions

Q1. What is a deciduate placenta?

A placenta in which the foetal and maternal tissues are so closely joined that part of the uterine wall (decidua) is torn away at birth, with bleeding. Example: human and dog placenta.

Q2. Give two hormones produced by the placenta and their roles.

hCG keeps the corpus luteum active in early pregnancy. Progesterone maintains the uterine lining and prevents contractions; oestrogen helps growth of the uterus and mammary glands.

Q3. Classify the placenta on the basis of distribution of villi.

• Diffuse, cotyledonary, zonary and discoidal types.
• Features and examples of each.
• Diagram of each type.

Q4. Classify the placenta on the basis of histological relationship.

• Grosser's classification with the layers separating the two bloods.
• Five types with examples.
• Diagrams showing the layers.
• Trend: fewer layers means more efficient exchange.

Q5. Describe the functions of the placenta.

• Nutrition, respiration and excretion of the foetus.
• Endocrine function: list of hormones.
• Barrier and protective function; passage of antibodies.
• Storage of glycogen and iron.

Exam tip

Make one combined table of type, intimacy and example animal; it can answer three different short questions.

Quick summary

Metamorphosis is the change of a larva into an adult with a very different body form, as in frogs and many insects. Regeneration is the ability to regrow lost or damaged body parts. Both are controlled by hormones and by the reactivation of growth and differentiation in cells. This topic covers metamorphosis in amphibians and insects with its hormonal control, and the types and process of regeneration.

Key points

• Metamorphosis (रूपांतरण) is a post-embryonic change in form, structure and physiology from larva to adult.
• Amphibian metamorphosis: the aquatic, herbivorous, gill-breathing tadpole becomes a land-living, carnivorous, lung-breathing frog.
• Changes in the tadpole: tail and gills are absorbed; limbs develop (hind limbs first); lungs form; mouth widens and horny jaws are lost; gut becomes shorter (herbivore → carnivore); eyelids form; skin thickens; lateral line disappears; excretion changes from ammonia (ammonotelic) to urea (ureotelic).
• Hormonal control: thyroxine (T₄) and T₃ from the thyroid drive metamorphosis. Gudernatsch (1912) showed that tadpoles fed on thyroid tissue metamorphosed early into tiny frogs. The hypothalamus–pituitary (TSH) controls thyroid release. Prolactin acts like a juvenile hormone and slows metamorphosis.
• Neoteny: the larva becomes sexually mature without metamorphosis, as in the axolotl (Ambystoma), usually because of low thyroid activity or iodine shortage.
• Insect metamorphosis: ametabolous (no metamorphosis – silverfish), hemimetabolous/incomplete (egg → nymph → adult – cockroach, grasshopper) and holometabolous/complete (egg → larva → pupa → adult – butterfly, housefly, silkworm, honeybee).
• Insect hormones: brain hormone (PTTH) stimulates the prothoracic gland to release ecdysone (moulting hormone). Juvenile hormone (JH) from the corpora allata keeps the larva in the larval state. High JH + ecdysone → larval moult; low JH → pupal moult; no JH → adult moult.
• Regeneration was first studied scientifically in Hydra by Abraham Trembley (1740).
• Types: morphallaxis – reorganisation of existing tissue without much cell division (Hydra); epimorphosis – new growth from a blastema of dedifferentiated cells (salamander limb, lizard tail); compensatory regeneration – remaining cells divide to restore size (mammalian liver).
• High regeneration power: sponges, Hydra, Planaria, starfish; limited in mammals.

Important terms

• Blastema – mass of undifferentiated cells formed at a wound that regrows the lost part.
• Dedifferentiation – specialised cells lose their special features and become embryonic-like.
• Autotomy – self-breaking of a body part, such as a lizard's tail, to escape predators.
• Instar – larval stage of an insect between two moults.
• Neoteny – retention of larval features in a sexually mature animal.

Key facts

• Steps of epimorphic regeneration: wound healing → dedifferentiation → blastema formation → cell division → redifferentiation and growth.

5 important questions

Q1. What is neoteny? Give an example.

Neoteny is the condition in which a larva becomes sexually mature and breeds without changing into an adult form. The axolotl larva of Ambystoma is the classic example.

Q2. Distinguish between morphallaxis and epimorphosis.

In morphallaxis the lost part is formed by reorganising existing tissue with little cell division, as in Hydra. In epimorphosis a blastema forms at the cut surface and new cells divide to rebuild the part, as in the salamander limb.

Q3. Describe metamorphosis in frog and its hormonal control.

• Larval and adult features.
• Morphological, anatomical and biochemical changes.
• Role of thyroxine, TSH, hypothalamus; Gudernatsch experiment.
• Role of prolactin; neoteny.

Q4. Explain the hormonal control of insect metamorphosis.

• Types of metamorphosis with examples.
• Brain hormone, ecdysone, juvenile hormone and their glands.
• Interaction of ecdysone and JH in larval, pupal and adult moults.
• Diagram of endocrine glands of an insect.

Q5. Write an account of regeneration.

• Definition and history (Trembley).
• Types: morphallaxis, epimorphosis, compensatory.
• Process of limb regeneration in salamander.
• Examples in different animals and its importance in medicine (stem cell research).

Exam tip

For insect metamorphosis, a small table of JH and ecdysone levels at each moult makes the answer clear and quick.