प्राणीशास्त्र Zoology

थोडक्यात सारांश

Protochordates are simple marine chordates without a vertebral column or a cranium. They show the three basic chordate characters – notochord, dorsal hollow nerve cord and pharyngeal gill slits – at least at some stage. They are divided into Urochordata and Cephalochordata (Hemichordata is studied with them in many syllabi). This topic covers their characters, examples and the significance of retrogressive metamorphosis.

महत्त्वाचे मुद्दे

• Chordate characters: (1) a rod-like notochord on the dorsal side; (2) a dorsal, hollow, tubular nerve cord; (3) pharyngeal gill slits; also a post-anal tail in many.
• Protochordates are also called Acraniata (no skull) and lower chordates.
• All are marine; most are small.
• Hemichordata (Balanoglossus, tongue worm): body has proboscis, collar and trunk. The "stomochord" in the proboscis was once thought to be a notochord, so it was placed in Chordata; now it is usually treated as a separate non-chordate phylum. Larva: tornaria (similar to echinoderm larvae).
• Urochordata (Tunicata) (Herdmania, Ascidia, Doliolum, Salpa): notochord only in the tail of the larva. Adult is sac-like, sessile, covered by a tunic made of tunicin (a cellulose-like substance).
• Cephalochordata (Branchiostoma, formerly Amphioxus, the lancelet): notochord extends from head to tail and persists throughout life. All three chordate characters are present in the adult.
• Branchiostoma is fish-shaped, burrows in sand, and feeds by filter feeding (ciliary feeding).
• Herdmania larva (ascidian tadpole) is free-swimming with all chordate characters; it settles and loses notochord, tail and most of the nerve cord. This is retrogressive metamorphosis.

महत्त्वाच्या संज्ञा

• Notochord – flexible, rod-like supporting structure of vacuolated cells, lying dorsal to the gut.
• Endostyle – ciliated, glandular groove on the pharynx floor that makes mucus to trap food; thought to be homologous to the thyroid gland.
• Atrium – cavity around the pharynx into which water passes through gill slits.
• Tunic (test) – outer covering of tunicates.
• Myotomes – V-shaped (<-shaped) muscle blocks of Branchiostoma.
• Retrogressive metamorphosis – change from an advanced larva to a simpler, degenerate adult.

महत्त्वाची माहिती

• Herdmania pallida is a common solitary ascidian on the Indian coast.

५ महत्त्वाचे प्रश्न

Q1. Name the three fundamental characters of chordates.

A dorsal notochord, a dorsal hollow tubular nerve cord, and paired pharyngeal gill slits. They are present at least at some stage of the life cycle.

Q2. What is an endostyle?

The endostyle is a ciliated, mucus-secreting groove on the ventral side of the pharynx in protochordates. It traps food particles in mucus. It is considered the forerunner of the thyroid gland of vertebrates.

Q3. Explain retrogressive metamorphosis in Herdmania.

• Larva is tadpole-like, free-swimming with notochord, nerve cord, gill slits and tail.
• Larva attaches by adhesive papillae.
• Tail with notochord is absorbed; nerve cord reduces to a ganglion.
• Pharynx enlarges with many gill slits; body rotates; tunic forms.
• Adult is sessile and simpler: an advanced larva becomes a degenerate adult.

Q4. Describe the general characters of Branchiostoma.

• Laterally compressed, fish-like, both ends pointed.
• Notochord and nerve cord along the whole body.
• Many gill slits opening into an atrium; atriopore.
• Oral hood with buccal cirri; wheel organ; filter feeding.
• Myotomes; no paired fins; no heart (contractile vessels).
• Excretion by protonephridia with solenocytes.
• Labels: oral hood, cirri, notochord, nerve cord, pharynx, gill slits, atriopore, myotomes, anus.

Q5. Discuss the systematic position of Balanoglossus.

• Earlier in Chordata because of stomochord, gill slits and dorsal nerve cord (partly hollow).
• Stomochord is now seen as a buccal diverticulum, not a true notochord.
• Tornaria larva resembles echinoderm larvae.
• Hence now treated as a separate phylum Hemichordata, linking non-chordates and chordates.

परीक्षेसाठी टीप

A comparison table of Urochordata and Cephalochordata is a common question. Learn retrogressive metamorphosis in clear steps.

थोडक्यात सारांश

Cyclostomes are the most primitive living vertebrates. They have no jaws and no paired fins, and their round mouth works like a sucker. Lampreys (Petromyzon) and hagfishes (Myxine) are the living examples. This topic covers the general characters of Cyclostomata, the external features and habits of Petromyzon, its ammocoete larva, and the systematic position of the group.

महत्त्वाचे मुद्दे

• Cyclostomata means "round mouth" (cyclos = circle, stoma = mouth). They belong to the superclass Agnatha (jawless vertebrates).
• Body is long and eel-like, soft and without scales; skin is slimy with mucous glands.
• No jaws; the mouth is a circular suctorial buccal funnel with horny epidermal teeth. A rasping tongue scrapes flesh.
• No paired fins; only median dorsal and caudal fins.
• Notochord persists throughout life; vertebrae are only small cartilaginous rudiments (arcualia).
• Skeleton is entirely cartilaginous; cranium is incomplete.
• Single median nostril (monorhinous) leading to a hypophyseal sac.
• Gills in pouches: Petromyzon has 7 pairs of external gill openings.
• Heart is two-chambered (one auricle, one ventricle) with a sinus venosus.
• Only two semicircular canals (lamprey) or one (hagfish) in each internal ear.
• Lampreys are ectoparasites on fishes: they attach with the buccal funnel, rasp the skin and suck blood. Saliva contains an anticoagulant (lamphredin).
• Sea lampreys are anadromous: they live in the sea and migrate to rivers to breed, then die.

महत्त्वाच्या संज्ञा

• Agnatha – vertebrates without jaws.
• Buccal funnel – cup-shaped sucker around the mouth.
• Ammocoete larva – blind, filter-feeding larva of Petromyzon living in river mud.
• Endostyle – ciliated groove in the pharynx of the ammocoete; it becomes the thyroid gland in the adult.
• Anadromous – migrating from sea to fresh water for breeding.

महत्त्वाची माहिती

• The ammocoete looks like Amphioxus: it has a notochord, endostyle, filter feeding with cilia, and no jaws. After 3–7 years it metamorphoses into the adult lamprey.

५ महत्त्वाचे प्रश्न

Q1. Why are cyclostomes called jawless vertebrates?

They have a cranium and vertebral rudiments, so they are vertebrates. But they have no jaws; instead they have a round sucking mouth with horny teeth. So they are placed in Agnatha, the jawless vertebrates.

Q2. What is the ammocoete larva? Why is it important?

It is the blind, worm-like, filter-feeding larva of Petromyzon that lives burrowed in river mud. It resembles Amphioxus, and its endostyle becomes the thyroid gland, which links protochordates and vertebrates.

Q3. Give the general characters and classification of Cyclostomata.

• Jawless, eel-like, scaleless body.
• Suctorial mouth with horny teeth; no paired fins.
• Persistent notochord; cartilaginous skeleton.
• Single nostril; 1–16 pairs of gill pouches.
• Two-chambered heart; two or one semicircular canals.
• Classes Petromyzontia and Myxini with examples.

Q4. Describe the external features and parasitic habits of Petromyzon.

• Size, shape and divisions of body (head, trunk, tail).
• Buccal funnel, horny teeth, tongue, eyes, median nostril, gill openings, fins, cloacal aperture.
• Mode of attaching to fish, rasping, sucking blood; anticoagulant.
• Migration and breeding; draw a labelled diagram.

Q5. Discuss the systematic position of Cyclostomata.

• Vertebrate features: cranium, brain, paired eyes and ears, vertebral rudiments, kidney.
• Primitive features: no jaws, no paired fins, persistent notochord.
• Specialised features linked to parasitic life.
• Conclusion: most primitive living vertebrates, a side branch of early jawless fishes (ostracoderms).

परीक्षेसाठी टीप

Always mention the ammocoete larva and its endostyle; it is the most frequently asked short note from this topic.

थोडक्यात सारांश

Fishes are cold-blooded aquatic vertebrates that breathe by gills and swim with fins. They are divided into cartilaginous fishes (Chondrichthyes) and bony fishes (Osteichthyes). This topic covers general characters, classification, scales, swim bladder, migration and parental care, with Indian examples.

महत्त्वाचे मुद्दे

• Fishes (मासे) are poikilothermic (cold-blooded) and live in fresh water and the sea.
• Body is usually streamlined and covered by scales.
• Paired (pectoral, pelvic) and unpaired (dorsal, anal, caudal) fins help in swimming and balance.
• Respiration by gills; a few also breathe air (lungfish, Clarias, Anabas).
• Heart is two-chambered (one auricle and one ventricle) and is called a venous heart because it pumps only deoxygenated blood.
• Lateral line system senses water movement and pressure.
• Kidneys are mesonephric.
• Most are oviparous with external fertilisation.

महत्त्वाच्या संज्ञा

• Placoid scales – tooth-like scales of cartilaginous fishes (sharks).
• Cycloid scales – thin, round scales with smooth edge (rohu, catla).
• Ctenoid scales – thin scales with tiny teeth (comb-like) on the hind edge (perch).
• Ganoid scales – thick, shiny, rhomboid scales of primitive bony fishes.
• Operculum – bony flap covering the gills in bony fishes.
• Swim bladder (air bladder) – gas-filled sac in bony fishes that controls buoyancy.
• Claspers – modified pelvic fins of male sharks used for mating.
• Anadromous migration – from sea to fresh water to spawn (e.g. salmon, hilsa).
• Catadromous migration – from fresh water to sea to spawn (e.g. freshwater eel, Anguilla).

महत्त्वाची माहिती

• Lung fishes (Dipnoi): Protopterus, Lepidosiren, Neoceratodus – show links to amphibians.
• Indian major carps: rohu, catla, mrigal – widely cultured.

५ महत्त्वाचे प्रश्न

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

The fish heart receives only deoxygenated (venous) blood from the body and pumps it to the gills for oxygenation. It never carries oxygenated blood, so it is called a venous heart.

Q2. What is the function of the swim bladder?

The swim bladder is a gas-filled sac in bony fishes. It helps keep the fish at a desired depth by changing the amount of gas (hydrostatic organ). In some fishes it also helps in breathing or making sound.

Q3. Describe the different types of scales in fishes.

• Placoid: dermal, tooth-like with basal plate and spine; sharks.
• Ganoid: rhomboid, covered with ganoin; Lepisosteus.
• Cycloid: thin, circular, smooth edge; rohu.
• Ctenoid: thin, comb-like teeth on hind margin; perch.
• Draw one sketch of each.

Q4. Write a note on migration in fishes.

• Regular movement from one place to another for breeding, feeding or climate.
• Anadromous: sea → river (salmon, hilsa).
• Catadromous: river → sea (Anguilla).
• Others: diadromous, potamodromous (within fresh water), oceanodromous (within sea).
• Factors: breeding, food, temperature, hormones.
• Dams can block migration routes.

Q5. Describe parental care in fishes with examples.

• Nest building: stickleback male builds nest and guards eggs.
• Mouth brooding: Tilapia keeps eggs in mouth.
• Brood pouch: male sea horse (Hippocampus) carries eggs in a pouch.
• Some catfish guard eggs.
• Benefit: higher survival of young.

परीक्षेसाठी टीप

Learn the comparison table of cartilaginous and bony fishes. Migration and parental care are often asked as long notes.

थोडक्यात सारांश

Amphibians are cold-blooded vertebrates that live both in water and on land. They were the first vertebrates to move onto land. Frogs, toads, salamanders and caecilians are amphibians. This topic covers general characters, classification, the frog as a type, metamorphosis and parental care.

महत्त्वाचे मुद्दे

• Amphibia means "double life" (amphi = both, bios = life). Frog is बेडूक in Marathi.
• Poikilothermic; show hibernation (winter sleep) and aestivation (summer sleep).
• Skin is moist, glandular and without scales (except in some caecilians); used in respiration.
• Two pairs of pentadactyl limbs (limbless in caecilians).
• Respiration: gills in larvae; lungs, skin (cutaneous) and buccal lining (buccopharyngeal) in adults.
• Heart is three-chambered – two auricles and one ventricle.
• Cloaca present: common opening for digestive, excretory and reproductive tracts.
• Kidneys mesonephric; adult frog is ureotelic (excretes urea); tadpole is ammonotelic.
• Two occipital condyles on the skull.
• Eggs laid in water; fertilisation mostly external in frogs.
• Development includes a tadpole larva and metamorphosis controlled by thyroxine.

महत्त्वाच्या संज्ञा

• Metamorphosis – change from tadpole to adult: loss of tail and gills, growth of limbs and lungs.
• Nictitating membrane – thin, transparent third eyelid protecting the eye in water.
• Tympanum – eardrum seen as a round area behind the eye.
• Amplexus – mating embrace in frogs; male clasps female so eggs and sperm are released together.
• Nuptial pad – rough pad on the first finger of the male frog in the breeding season.
• Vocal sacs – sacs in male frogs that make loud croaking.
• Neoteny – retention of larval features in a sexually mature animal (e.g. axolotl larva of Ambystoma).

महत्त्वाची माहिती

• The Indian bullfrog is Hoplobatrachus tigerinus (old name Rana tigrina).
• Frog's tongue is bifid (two-lobed) and attached at the front – flicked out to catch insects.
• Frog RBCs are nucleated and oval.

५ महत्त्वाचे प्रश्न

Q1. What is the difference between hibernation and aestivation?

Hibernation is a period of inactivity during winter to avoid cold. Aestivation is a period of inactivity during summer to avoid heat and dryness. Frogs show both, burying themselves in mud.

Q2. What is neoteny?

Neoteny is the condition in which a larva becomes sexually mature and reproduces without completing metamorphosis. Example: axolotl larva of Ambystoma; it is linked with low thyroxine or iodine.

Q3. Describe the metamorphosis of frog.

• Eggs → tadpole with external gills, tail, no limbs; herbivorous.
• Internal gills covered by operculum; then hind limbs, then forelimbs appear.
• Lungs develop; gills disappear.
• Tail is absorbed (by lysosomal enzymes).
• Gut shortens; becomes carnivorous; ureotelic excretion.
• Controlled by thyroxine; iodine needed.

Q4. Give the general characters of Amphibia.

• Dual life; cold-blooded.
• Moist glandular skin; cutaneous respiration.
• Three-chambered heart.
• Two occipital condyles; cloaca.
• Pentadactyl limbs (absent in Apoda).
• Eggs in water; tadpole larva; metamorphosis.

Q5. Explain parental care in amphibians.

• Alytes (midwife toad): male carries egg strings on hind legs.
• Pipa (Surinam toad): eggs develop in pockets on female's back.
• Rhinoderma: male keeps eggs in vocal sac.
• Ichthyophis: female coils around eggs.
• Tree frogs make foam nests.
• Purpose: protect eggs and young from predators and drying.

परीक्षेसाठी टीप

Remember the three orders with one Indian example each, and that the frog heart is three-chambered. Parental care examples are frequently asked.

थोडक्यात सारांश

Reptiles are cold-blooded, mostly terrestrial vertebrates with dry, scaly skin. They were the first vertebrates fully adapted to life on land, because they lay shelled (cleidoic) eggs with protective membranes. Lizards, snakes, turtles, tortoises and crocodiles are reptiles. This topic covers characters, classification, poisonous and non-poisonous snakes, and the snake bite and venom.

महत्त्वाचे मुद्दे

• Reptilia means "creeping" (repere = to creep). Snake is साप in Marathi.
• Poikilothermic; skin dry, without glands, covered by epidermal scales or scutes.
• Lungs are the only respiratory organs.
• Heart is three-chambered (two auricles, partly divided ventricle); in crocodiles it is four-chambered.
• One occipital condyle.
• Skull classified by temporal openings: anapsid (turtles), diapsid (lizards, snakes, crocodiles).
• Kidneys metanephric; mostly uricotelic (excrete uric acid, saving water).
• Fertilisation internal; most lay cleidoic (shelled) eggs on land; embryo has amnion, chorion, allantois and yolk sac – they are amniotes.
• Development direct (no larva).
• Mesozoic era is called the "Age of Reptiles" (dinosaurs).

महत्त्वाच्या संज्ञा

• Cleidoic egg – egg with a hard or leathery shell that prevents drying; allows development on land.
• Ecdysis – shedding of the outer skin in snakes and lizards.
• Jacobson's organ – smell organ on the roof of the mouth; the forked tongue brings particles to it.
• Autotomy – self-breaking of tail to escape a predator (wall lizard).
• Fangs – long teeth that inject venom.
• Antivenom – serum with antibodies that neutralises snake venom.

महत्त्वाची माहिती

• The "Big Four" venomous snakes of India: Indian cobra (Naja naja), common krait (Bungarus caeruleus), Russell's viper (Daboia russelii) and saw-scaled viper (Echis carinatus).
• Neurotoxic venom (cobra, krait) affects the nervous system – breathing failure. Haemotoxic venom (vipers) affects blood and blood vessels – bleeding, swelling.

५ महत्त्वाचे प्रश्न

Q1. What is a cleidoic egg?

A cleidoic egg is a large-yolked egg covered by a protective shell, with membranes like amnion and allantois. It does not dry out on land, so reptiles and birds can breed away from water.

Q2. Name the Big Four venomous snakes of India.

Indian cobra (Naja naja), common krait (Bungarus caeruleus), Russell's viper (Daboia russelii) and saw-scaled viper (Echis carinatus).

Q3. Distinguish between poisonous and non-poisonous snakes.

• Poisonous: fangs and poison glands present; head often triangular (vipers); ventral scales broad, covering full width.
• Krait: large hexagonal vertebral scales along the back; cobra: hood.
• Non-poisonous: no fangs; ventral scales may be narrow (python); tail gradually tapering.
• Note: these rules have exceptions; treat every bite seriously.

Q4. Give the general characters of Reptilia.

• Dry scaly skin; no glands.
• Lungs only; cold-blooded.
• Three-chambered heart (four in crocodiles).
• One occipital condyle.
• Uricotelic; metanephric kidneys.
• Internal fertilisation; cleidoic eggs; amniotes.

Q5. Write a note on snake venom and first aid for snake bite.

• Venom is modified saliva from modified salivary glands; mixture of proteins and enzymes.
• Types: neurotoxic, haemotoxic (and cardiotoxic, myotoxic).
• First aid: keep patient calm and still; immobilise the bitten limb; remove rings and tight items.
• Do not cut, suck or apply ice; avoid tight tourniquets.
• Take to hospital quickly for antivenom (polyvalent ASV in India).

परीक्षेसाठी टीप

Learn the Big Four with scientific names, and the type of venom of each. Draw a sketch of the head of a poisonous snake showing fangs and poison gland.

थोडक्यात सारांश

Birds (Aves) are warm-blooded vertebrates with feathers, and forelimbs modified into wings. Most can fly, and their whole body is adapted for flight. This topic covers general characters, flight adaptations, types of feathers, migration and the classification of birds, with Archaeopteryx as a connecting link.

महत्त्वाचे मुद्दे

• Birds (पक्षी) are the only animals with feathers.
• Homeothermic (warm-blooded): body temperature stays constant.
• Forelimbs are wings; hind limbs are for walking, perching or swimming; the hind limb has scales.
• Beak without teeth (in modern birds).
• Pneumatic bones – light, hollow bones with air spaces.
• Heart is four-chambered; only the right aortic arch remains.
• Lungs are compact and connected to air sacs; air flows through lungs in one direction, giving very efficient breathing.
• Syrinx is the voice box (at the base of the trachea).
• Digestive tract has a crop (stores food) and a gizzard (grinds food).
• No urinary bladder; uricotelic.
• One occipital condyle; oviparous with large cleidoic eggs; parental care well developed.
• Usually only the left ovary and oviduct are functional in females.

महत्त्वाच्या संज्ञा

• Contour feathers (quill feathers) – large feathers giving shape; flight feathers are remiges (wings) and rectrices (tail).
• Down feathers (plumules) – soft feathers that trap air for warmth.
• Filoplumes – hair-like feathers.
• Keel (carina) – ridge on the breast bone (sternum) for attachment of large flight muscles.
• Synsacrum – fused bones of the lower back and pelvis giving rigid support.
• Pygostyle – fused last tail vertebrae.
• Furcula (wishbone) – fused clavicles.

महत्त्वाची माहिती

• Ratitae (flightless running birds): no keel – ostrich, emu, kiwi, rhea.
• Carinatae (flying birds): keeled sternum – pigeon (Columba livia), crow (Corvus), parrot (Psittacula), peacock (Pavo cristatus, India's national bird), sparrow, kingfisher.
• Archaeopteryx (Jurassic fossil, found in Germany): has feathers and wings like birds, and teeth, a long bony tail and clawed fingers like reptiles. It is a connecting link between reptiles and birds.
• Birds evolved from reptilian (theropod dinosaur) ancestors; they have scales on their legs as a reptilian feature.
• Migration – seasonal, two-way, long-distance movement for breeding and food. India receives winter migrants such as the Siberian crane (historically at Bharatpur), flamingos and many ducks. Birds navigate using the sun, stars, Earth's magnetic field and landmarks.

५ महत्त्वाचे प्रश्न

Q1. What are pneumatic bones?

Pneumatic bones are hollow bones filled with air spaces connected to air sacs. They make the skeleton light, which helps birds in flight.

Q2. Why is Archaeopteryx called a connecting link?

Archaeopteryx shows both reptile features (teeth, long bony tail, clawed fingers) and bird features (feathers, wings, beak-like jaws). Hence it links reptiles and birds.

Q3. Describe flight adaptations in birds.

• Streamlined, spindle-shaped body; feathers.
• Forelimbs modified into wings.
• Light, pneumatic bones; keel for flight muscles; synsacrum, pygostyle.
• Air sacs and efficient lungs; four-chambered heart; high metabolism.
• Toothless beak; no urinary bladder; one ovary – reduce weight.
• Good eyesight; large cerebellum for balance.

Q4. Describe the structure of a contour (quill) feather.

• Central shaft: lower hollow calamus (quill) and upper solid rachis.
• Vane on both sides made of barbs.
• Each barb bears barbules with hooklets that interlock.
• Superior and inferior umbilicus on the calamus; after-feather near the superior umbilicus.
• Labels: calamus, rachis, vane, barbs, barbules, inferior umbilicus, superior umbilicus, after-feather.

Q5. Write a note on bird migration.

• Definition and purpose: breeding, food, escape winter.
• Types: latitudinal, longitudinal, altitudinal.
• Preparation: fat storage (hormonal control).
• Navigation: sun, stars, magnetism, landmarks.
• Indian examples and importance of wetlands; threats like habitat loss.

परीक्षेसाठी टीप

List at least eight flight adaptations under headings (external, skeletal, internal). Draw a labelled quill feather.

थोडक्यात सारांश

Chromosomes are thread-like bodies in the nucleus that carry genes. Each species has a fixed number and shape of chromosomes. This topic covers the parts of a chromosome, types based on centromere position, karyotype and idiogram, and two special giant chromosomes – polytene and lampbrush chromosomes.

महत्त्वाचे मुद्दे

• The word chromosome ("coloured body") was coined by Waldeyer (1888).
• A metaphase chromosome has two identical sister chromatids joined at the centromere (primary constriction).
• The kinetochore on the centromere is where spindle fibres attach.
• Some chromosomes have a secondary constriction; the part beyond it is the satellite (SAT chromosome). The secondary constriction may carry the nucleolar organiser region (NOR).
• Telomeres are the protective ends of the chromosome; they stop ends from sticking together.
• Chromosomes are made of DNA, histone and non-histone proteins and a little RNA.
• Autosomes control body characters; sex chromosomes (X, Y) decide sex. Humans have 22 pairs of autosomes and 1 pair of sex chromosomes (2n = 46).
• Types by centromere position: metacentric (centre, V-shaped at anaphase), submetacentric (slightly off-centre, L-shaped), acrocentric (near one end, J-shaped) and telocentric (at the tip, rod-shaped; not found in humans).
• Karyotype is the set of chromosomes of a species arranged by size and shape; its diagram is an idiogram.
• Polytene chromosomes are found in the salivary glands of dipteran larvae (Drosophila, Chironomus). They were discovered by E. G. Balbiani (1881).
• They form by repeated DNA replication without cell division (endoreduplication), giving many parallel strands (about 1,000 in Drosophila). Homologues stay paired (somatic pairing).
• They show dark bands and light interbands. Swollen active regions called puffs or Balbiani rings are sites of active RNA synthesis.
• Lampbrush chromosomes are seen in the diplotene stage of meiosis in oocytes of amphibians, fishes, reptiles and birds. They were first seen by Flemming (1882) and named by Rückert (1892).
• They are very long; paired loops extend sideways from a central axis, giving a "lamp-brush" look. The loops are sites of active transcription, making RNA for the growing egg.

महत्त्वाच्या संज्ञा

• Chromomere – bead-like thickening along a chromosome.
• Endoreduplication (endomitosis) – DNA copies itself repeatedly without cell division.
• Chromocentre – point where centromeres of all polytene chromosomes join in Drosophila.
• Arm ratio – length of long arm ÷ length of short arm.
• Heteropycnosis – darker or lighter staining of some chromosome regions.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What are telomeres?

Telomeres are the specialised ends of chromosomes made of short repeated DNA sequences. They protect the ends from damage and stop chromosomes from joining each other. They shorten with every cell division.

Q2. What are Balbiani rings?

They are very large puffs on polytene chromosomes of Chironomus salivary glands. At these sites the chromosome loosens and actively makes mRNA for salivary proteins.

Q3. Describe the structure of a chromosome and its types.

• Chromatids, centromere, kinetochore, secondary constriction, satellite, telomere, chromomeres.
• Chemical composition.
• Types by centromere position with diagrams.
• Karyotype and idiogram.

Q4. Describe polytene chromosomes.

• Discovery and occurrence.
• Formation by endoreduplication and somatic pairing.
• Bands, interbands, chromocentre.
• Puffs and Balbiani rings; role in gene expression; effect of ecdysone on puffing.
• Use in gene mapping. Draw a diagram.

Q5. Describe lampbrush chromosomes.

• Discovery and occurrence in oocytes.
• Size; bivalent structure held at chiasmata.
• Axis with chromomeres; paired lateral loops.
• Function: active transcription to store RNA and yolk proteins for the egg.
• Diagram.

परीक्षेसाठी टीप

A comparison table of polytene and lampbrush chromosomes is a ready answer for "distinguish" questions; draw both diagrams if time allows.

थोडक्यात सारांश

Sex determination is the mechanism that decides whether an individual develops as male or female. In most animals it is controlled by sex chromosomes, but in some it depends on chromosome sets or the environment. Genes on the sex chromosomes show a special pattern of inheritance called sex-linked inheritance. This topic covers the chromosomal, genic balance, haplodiploid and environmental methods, and sex-linked, sex-limited and sex-influenced traits.

महत्त्वाचे मुद्दे

• Henking (1891) first saw the "X body" in insects; McClung (1902) linked it with sex.
• XX–XY type: female homogametic (XX), male heterogametic (XY). Found in humans, other mammals and Drosophila.
• XX–XO type: female XX, male has only one X (XO). Found in grasshoppers, cockroaches and bugs.
• ZW–ZZ type: female heterogametic (ZW), male homogametic (ZZ). Found in birds, some reptiles and butterflies.
• ZO–ZZ type: female ZO, male ZZ; found in some moths.
• In humans, the SRY gene on the Y chromosome triggers testis formation, so the Y decides maleness.
• Genic balance theory (C. B. Bridges) for Drosophila: sex depends on the ratio of X chromosomes to autosome sets (X/A). X/A = 1 or more → female; 0.5 or less → male; between 0.5 and 1 → intersex. The Y is needed for male fertility, not for maleness.
• Haplodiploidy: in honeybees, ants and wasps, fertilised eggs (diploid) become females (queen or workers) and unfertilised eggs (haploid) become males (drones) by parthenogenesis.
• Environmental sex determination: in many turtles and crocodiles the incubation temperature of eggs decides sex; in the marine worm Bonellia, larvae that settle on a female's proboscis become tiny males.
• Sex-linked genes lie on the X chromosome. T. H. Morgan (1910) discovered sex-linkage with white-eye in Drosophila.
• X-linked recessive traits (haemophilia, red-green colour blindness) are far more common in males, because one recessive allele is enough in a male (hemizygous).
• They show criss-cross inheritance: a father passes the X-linked trait to his grandson through his daughter (a carrier).
• Y-linked (holandric) genes pass only from father to son, e.g. hypertrichosis of the ear (hairy ear rims).

महत्त्वाच्या संज्ञा

• Homogametic sex – produces one kind of gamete with respect to sex chromosomes.
• Heterogametic sex – produces two kinds of gametes.
• Hemizygous – having only one copy of a gene (X-linked genes in males).
• Carrier – heterozygous female carrying a recessive X-linked allele without showing it.
• Sex-limited trait – expressed in only one sex (beard in men, milk production in cows).
• Sex-influenced trait – autosomal, but dominant in one sex and recessive in the other (pattern baldness).

महत्त्वाची माहिती

Cross: carrier woman (XᴴXʰ) × normal man (XᴴY), where h = haemophilia.

• Result: 50% of daughters are carriers; 50% of sons are haemophilic.
• Haemophilia is called the "royal disease" because Queen Victoria was a carrier.

५ महत्त्वाचे प्रश्न

Q1. What is criss-cross inheritance?

It is the passing of an X-linked trait from a father to his grandson through his daughter, or from a mother to her son. It happens because a son gets his only X from his mother.

Q2. Distinguish between sex-limited and sex-influenced traits.

A sex-limited trait appears only in one sex, though genes are present in both (e.g. beard). A sex-influenced trait appears in both sexes but is dominant in one sex and recessive in the other (e.g. baldness, more common in men).

Q3. Describe the chromosomal mechanisms of sex determination.

• XX–XY with human example and cross.
• XX–XO in grasshopper.
• ZW–ZZ in birds; ZO–ZZ in moths.
• Role of SRY gene.
• Diagrams of each cross.

Q4. Explain the genic balance theory of sex determination in Drosophila.

• Bridges' experiments with triploid females.
• X/A ratio table: normal female, normal male, metafemale, metamale, intersex, triploid female.
• Role of autosomes (male-determining) and X (female-determining).
• Y only for fertility.

Q5. Explain sex-linked inheritance with suitable examples.

• Morgan's white-eye experiment in Drosophila (reciprocal crosses).
• Haemophilia and colour blindness in humans with crosses.
• Characteristics: more males affected, criss-cross pattern, no father-to-son transmission of X-linked traits.
• Y-linked inheritance.

परीक्षेसाठी टीप

Always show crosses in a checkerboard with clear X and Y symbols; a cross without a result statement loses marks.

थोडक्यात सारांश

A mutation is a sudden, heritable change in the genetic material. It may affect a single gene (gene or point mutation) or the structure or number of chromosomes (chromosomal aberration). Mutations are the raw material of evolution but can also cause disease. This topic covers the types and causes of mutations, mutagens, structural changes in chromosomes and changes in chromosome number.

महत्त्वाचे मुद्दे

• The term mutation was given by Hugo de Vries (1901) from his work on the evening primrose (Oenothera lamarckiana). Mutation is उत्परिवर्तन in Marathi.
• H. J. Muller (1927) first produced mutations artificially using X-rays in Drosophila (Nobel Prize 1946).
• Spontaneous mutations occur naturally (errors in DNA replication); induced mutations are caused by mutagens.
• Physical mutagens: X-rays, gamma rays, UV rays (UV forms thymine dimers), high temperature.
• Chemical mutagens: nitrous acid, base analogues (5-bromouracil), alkylating agents (mustard gas, EMS), acridine dyes.
• Gene (point) mutations: substitution – transition (purine replaced by purine, or pyrimidine by pyrimidine) and transversion (purine ↔ pyrimidine); frameshift – insertion or deletion of bases, which shifts the reading frame.
• Effects of substitution: silent (same amino acid), missense (different amino acid, e.g. sickle-cell anaemia) or nonsense (stop codon).
• Structural chromosomal aberrations: deletion (loss of a segment), duplication (a segment repeated), inversion (a segment turned 180°) and translocation (a segment moves to a non-homologous chromosome).
• Inversions are paracentric (centromere outside the inverted part) or pericentric (centromere inside).
• Numerical changes: euploidy – change in whole sets (monoploid n, triploid 3n, tetraploid 4n); aneuploidy – gain or loss of one or a few chromosomes.
• Aneuploidy usually arises by non-disjunction (chromosomes fail to separate at meiosis).
• Polyploidy is common and useful in plants but rare in animals, since it upsets sex determination.

महत्त्वाच्या संज्ञा

• Mutagen – agent that causes mutation.
• Monosomy (2n − 1) – one chromosome missing (Turner syndrome, 45,X).
• Trisomy (2n + 1) – one extra chromosome (Down syndrome, trisomy 21).
• Nullisomy (2n − 2) – one pair missing.
• Reciprocal translocation – exchange of segments between two non-homologous chromosomes.
• Bar eye – duplication of a band region of the X chromosome in Drosophila.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. Distinguish between transition and transversion.

In transition, a purine is replaced by another purine (A ↔ G) or a pyrimidine by another pyrimidine (C ↔ T). In transversion, a purine is replaced by a pyrimidine or vice versa.

Q2. What is non-disjunction?

Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate during cell division. It produces gametes with an extra or a missing chromosome, leading to aneuploidy such as Down syndrome.

Q3. Classify mutations and describe gene mutations.

• Classification: spontaneous/induced; somatic/germinal; gene/chromosomal; dominant/recessive.
• Substitution: transition, transversion; silent, missense, nonsense.
• Frameshift: insertion and deletion with an example sequence.
• Mutagens: physical and chemical.
• Significance in evolution and disease.

Q4. Describe structural chromosomal aberrations.

• Deletion: terminal and intercalary; loop in pairing; cri-du-chat.
• Duplication: tandem, reverse; Bar eye.
• Inversion: paracentric and pericentric; inversion loop at pachytene.
• Translocation: simple and reciprocal; cross-shaped pairing; Philadelphia chromosome.
• Diagrams.

Q5. Explain numerical changes in chromosomes.

• Euploidy: monoploidy, polyploidy (autopolyploidy, allopolyploidy) with examples.
• Aneuploidy: monosomy, trisomy, nullisomy, tetrasomy.
• Cause: non-disjunction with a diagram.
• Human examples: Down, Turner, Klinefelter syndromes.

परीक्षेसाठी टीप

Draw the pairing loops for deletion and inversion and the cross-shaped figure for translocation; they show the examiner you understand the concept.

थोडक्यात सारांश

Human genetic disorders are diseases caused by defects in genes or chromosomes. Some follow simple Mendelian inheritance (autosomal or X-linked), while others come from abnormal chromosome number or structure. This topic covers pedigree analysis, important Mendelian disorders, chromosomal syndromes, and prenatal diagnosis and genetic counselling.

महत्त्वाचे मुद्दे

• Pedigree analysis is the study of a trait over several generations of a family using a chart. Squares = males, circles = females, shaded = affected, half-shaded or dotted = carriers.
• Autosomal recessive disorders appear only in homozygous recessive persons; parents are usually normal carriers; more common in marriages between relatives (consanguinity).
• Examples: albinism (no melanin; defect in the enzyme tyrosinase), phenylketonuria (PKU) (lack of phenylalanine hydroxylase; phenylalanine builds up and harms the brain), sickle-cell anaemia, thalassaemia, cystic fibrosis.
• Sickle-cell anaemia: a point mutation in the β-globin gene (chromosome 11) replaces glutamic acid with valine at the 6th position. Red cells become sickle-shaped at low oxygen. HbˢHbˢ persons are ill; HbᴬHbˢ carriers have sickle-cell trait and some resistance to malaria. It is common in parts of Vidarbha and among some tribal communities in India.
• Thalassaemia: reduced synthesis of α or β globin chains, causing severe anaemia; major cases need regular blood transfusion.
• Autosomal dominant disorders need only one defective allele and appear in every generation: Huntington's disease (chromosome 4; nerve degeneration in middle age), achondroplasia (dwarfism), polydactyly.
• X-linked recessive disorders: haemophilia (blood fails to clot), red-green colour blindness, Duchenne muscular dystrophy. Mostly males are affected.
• Chromosomal disorders usually result from non-disjunction during gamete formation.
• Down syndrome (trisomy 21, 47 chromosomes): described by Langdon Down (1866); cause found by Lejeune (1959). Features: short stature, round face, slanting eyes, open mouth with furrowed tongue, broad palm with a single simian crease, mental retardation. Risk rises with mother's age.
• Klinefelter syndrome (47, XXY): tall male, small testes, sterile, may show breast development (gynaecomastia).
• Turner syndrome (45, X): short female, webbed neck, underdeveloped ovaries, sterile.

महत्त्वाच्या संज्ञा

• Proband – the first affected person through whom a family is studied.
• Consanguineous marriage – marriage between close relatives.
• Barr body – inactive X seen as a dark spot in female cells; XXY males have one, XO females have none.
• Amniocentesis – taking amniotic fluid to study foetal cells (around 15–18 weeks).
• Chorionic villus sampling (CVS) – sampling placental tissue (around 10–12 weeks).

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

Q1. What is phenylketonuria?

It is an autosomal recessive disorder in which the enzyme phenylalanine hydroxylase is missing. Phenylalanine is not converted to tyrosine; it accumulates and is changed to phenylpyruvic acid, which damages the brain. A low-phenylalanine diet from birth prevents damage.

Q2. Why are carriers of sickle-cell trait resistant to malaria?

In heterozygous carriers some red cells sickle when infected, and they are destroyed quickly along with the malaria parasite. So Plasmodium falciparum cannot multiply well in them.

Q3. Describe Down syndrome.

• Cause: trisomy 21 by non-disjunction; link with maternal age.
• Karyotype 47, XX or XY, +21.
• Physical and mental features.
• Diagnosis by karyotyping, amniocentesis.
• Draw a simple karyotype sketch or list features.

Q4. Explain sex chromosomal disorders in man.

• Non-disjunction of sex chromosomes.
• Klinefelter syndrome: karyotype, features, Barr body.
• Turner syndrome: karyotype, features, no Barr body.
• Brief note on XYY and XXX.

Q5. Write on pedigree analysis and genetic counselling.

• Pedigree symbols with a sample chart.
• Patterns: autosomal dominant, autosomal recessive, X-linked recessive.
• Genetic counselling: risk calculation, carrier testing, prenatal diagnosis (amniocentesis, CVS), avoiding consanguineous marriages.

परीक्षेसाठी टीप

Learn the karyotype formula for each syndrome; one-mark questions like "47, XXY is seen in ____" are very common.

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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).

महत्त्वाच्या संज्ञा

• 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).

सूत्रे

• 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.

महत्त्वाची माहिती

• 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.

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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.

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

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).

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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).

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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.

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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).

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

• 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.

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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⁺.

महत्त्वाच्या संज्ञा

• 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.

सूत्रे

• 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).

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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).

महत्त्वाच्या संज्ञा

• 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.

सूत्रे

• 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.

५ महत्त्वाचे प्रश्न

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).

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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.

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

• 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).

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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).

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

• 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.

५ महत्त्वाचे प्रश्न

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.

परीक्षेसाठी टीप

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

थोडक्यात सारांश

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.

महत्त्वाचे मुद्दे

• 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.

महत्त्वाच्या संज्ञा

• 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.

महत्त्वाची माहिती

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

५ महत्त्वाचे प्रश्न

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).

परीक्षेसाठी टीप

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