NCERT Summary: Summary of Biology - 9

Amphibians

Overview. Amphibians are vertebrates that typically live part of their life in water and part on land. Most species lay eggs in water. The young usually hatch as aquatic larvae that differ markedly from the adult form and undergo metamorphosis to become terrestrial or semi-aquatic adults. Amphibians are ectothermic (commonly called cold-blooded), so their body temperature varies with the environment.

Characteristics

• Reproduction: Most lay jelly-coated eggs in water; embryos develop into free-swimming larvae (for example, a tadpole) that later metamorphose into the adult form.
• Respiration: Depending on the species and life stage, respiration may occur through gills, lungs, the lining of the mouth, the skin, or a combination of these.
• Skin and moisture: Skin is usually moist and permeable, helping in cutaneous respiration but making many amphibians sensitive to pollution and drying.
• Thermoregulation: They cannot maintain a constant internal temperature and often hibernate in cold climates.
• Diversity and distribution: There are over 6,400 known species worldwide; amphibians are absent only from Antarctica and Greenland.

Common groups

Amphibians include frogs and toads, salamanders and newts, and the limbless caecilians. Habitats range from deserts to rainforests, ponds and high mountain meadows. Most have four limbs, but some groups (for example caecilians) are limbless.

African Clawed Frog (Xenopus laevis)

Distribution and habitat. Native to southern and eastern Africa, including South Africa, Namibia and Angola; it occupies warm, stagnant pools and quiet streams.

Key features and behaviour. It has three short claws on each hind foot and spends much of its time underwater, surfacing only to breathe. It lacks a protrusible tongue and uses its forelimbs and unwebbed fingers to push food into the mouth.

Poison dart frogs

Distribution and habitat. Native to tropical Central and South America; they inhabit humid rainforests and may be terrestrial or arboreal.

Adaptations and defence. Many species are brightly coloured (aposematism) to warn predators. They secrete potent skin toxins; some species produce alkaloid poisons that can be lethal. Several species are critically endangered due to habitat loss and collection.

Frogs (general)

There are over 5,000 species of frogs. Typical frogs have a short, stout body, long hind limbs for jumping, and no tail as adults. They produce characteristic calls (croaks, ribbits) used in communication. Species vary greatly in size and ecology; some are tiny (for example the Coquí), some very large, and some carry toxins for defence.

Reptiles

Overview. Reptiles are air-breathing vertebrates with dry, scaly skin. They first appeared hundreds of millions of years ago and were the dominant land vertebrates during the Mesozoic Era (often called the "Age of Reptiles"). Reptiles are ectothermic and generally rely on behavioural means (basking, seeking shade) to regulate body temperature.

General characteristics

• Skin: Covered with scales or scutes made of keratin.
• Respiration: Breathe by lungs; some species can also absorb oxygen through membranes in the mouth when submerged.
• Reproduction: Most lay leathery eggs on land; in many species incubation temperature can influence the sex of the young.
• Evolutionary history: The first reptiles appeared around 340 million years ago during the Carboniferous Period.
• Diversity: There are about 8,000 known reptile species today.

Reptiles: lizards, snakes and others (general)

Common reptile groups include crocodilians (crocodiles and alligators), lizards, snakes, turtles and tortoises. Lizards generally have four limbs and a tail (some can shed and later regenerate the tail). Snakes are limbless and move by lateral undulation or other modes of locomotion. Crocodilians are semi-aquatic and are powerful predators with strong jaws and substantial size in many species.

Alligator

Distribution and size. Native species occur in the United States and in eastern China. Alligators are covered with tough scales and can reach lengths of around 15 feet in large individuals and weights that may exceed one thousand pounds in exceptional cases.

Adaptations. They have powerful jaws for crushing prey and are well adapted to life in freshwater habitats. Fossil evidence shows crocodilians and their relatives have existed for around 200 million years.

Anaconda

Distribution and habitat. Anacondas are large, non-venomous snakes native to tropical South America; they inhabit swampy and waterlogged areas and are excellent swimmers.

Feeding and behaviour. The green anaconda is among the heaviest snakes; the largest recorded specimens may exceed 30 feet in length in some reports, though typical large sizes are smaller. They subdue prey by constriction-coiling around and squeezing to prevent breathing-and swallow it whole.

Chameleon

Distribution and habitat. Native mainly to Africa and Madagascar, with species also in southern Europe and Asia; habitats include rainforest, savanna and semi-desert.

Distinctive features. Known for skin colour changes which relate to mood, social signalling and physiological state rather than perfect background matching; independent eye movement (each eye can rotate nearly 360°) and a long, rapidly projecting sticky tongue for capturing prey.

Cobra

Distribution and habitat. Found in Africa and Asia, cobras occupy diverse habitats from rainforests to savannas and arid areas.

Defence and venom. Many cobras display a characteristic hood-created by expanded ribs in the neck-when threatened. Some species are highly venomous; the King Cobra is the world's longest venomous snake.

Crocodile

Distribution and behaviour. Native to tropical regions of Africa, Asia, the Americas and Australia; crocodiles favour freshwater rivers, lakes and wetlands. They are ancient reptiles with a fossil record extending over 200 million years.

Hunting. Crocodiles are ambush predators that wait near water to seize fish or terrestrial prey that come close to the water's edge.

Coral snake

Distribution and appearance. In the United States coral snakes are found in the southeastern states and parts of the southwest. They are relatively small (average about 3 feet) and are strikingly banded in red, black and yellow/white.

Venom. Coral snakes are highly venomous.

Iguana

Distribution and diet. Iguanas are primarily Neotropical, found in Central and South America and the Caribbean. The green iguana lives near water in tropical rainforests. Most iguanas are largely herbivorous though some species take animal matter.

Thermoregulation. Being ectothermic they bask to warm up and seek shade or water to cool down.

Komodo dragon

Distribution and status. A large monitor lizard native to several Indonesian islands; it is the largest living lizard, growing up to around 10 feet and >200 lb in large individuals.

Diet and behaviour. Carnivorous and occasionally cannibalistic; feeds on deer, pigs and other animals. Komodo dragons are now considered vulnerable or endangered in the wild.

Lizards (general)

There are over 5,000 species of lizards worldwide. Many are small and harmless; some have remarkable abilities-running briefly over water, autotomising (shedding) the tail to escape predators, or ejecting blood as a defensive display. Some species (for example the monitor lizard) can grow very large. A few lizards (for example the Gila monster) are venomous; others such as geckos and iguanas are commonly kept as pets.

Black mamba

Distribution and behaviour. Native to sub-Saharan Africa, the black mamba inhabits open grasslands and woodlands. It is one of Africa's deadliest snakes and can move rapidly across the ground, reaching high speeds for short bursts.

Colour and name. Despite the name, its body is generally grey, grey-brown or olive; the name refers to the black interior of the mouth.

Vipers

Distribution and traits. Vipers are a family of venomous snakes with a near-global distribution (absent from Australia and Madagascar). They range from small species to very large ones, possess long hinged fangs for injecting venom, and include species such as the bushmaster.

Turtle

Shell and distribution. Turtles are reptiles with a bony or leathery shell; they occur in most parts of the world. Some are terrestrial, many are semi-aquatic and others are fully marine.

Anatomy and reproduction. The shell is covered by keratinous scutes (the same material as human fingernails). Turtles have a beak rather than teeth. Females lay eggs on land.

Tortoise

Tortoises are land-dwelling relatives of turtles with sturdy, columnar legs suited to walking. Many tortoise species are long-lived, with documented lifespans sometimes exceeding 100-150 years in certain cases.

Sea turtles

Distribution and status. Sea turtles occur in all oceans except the Arctic. Large species (for example the leatherback) may reach shell lengths up to around 2 metres and weights approaching several hundred kilograms. Many sea turtle species are threatened or endangered and spend most of their life at sea but must surface to breathe.

Sea snakes

Adaptations. Sea snakes inhabit warm tropical coastal waters of the Indian and Pacific Oceans and are highly adapted to aquatic life, with paddle-like tails for swimming. Most sea snakes are venomous and must surface to breathe air.

Pitvipers

Found in parts of Europe, Asia and the Americas, pitvipers have a heat-sensing pit between each eye and nostril that helps detect warm blooded prey. Examples include rattlesnakes and copperheads.

Pythons

Distribution and behaviour. Pythons occur in Africa, Asia and Australasia. Some species (for example the reticulated python) reach exceptional lengths, sometimes reported over 30 feet. Pythons kill by constriction and consume large prey whole. Introductions of Burmese pythons in the Florida Everglades in the 1990s have become an important conservation and management concern.

Rattlesnake

Distribution and characteristic features. Rattlesnakes are venomous pitvipers native to the Americas. They possess a distinctive rattle at the tip of the tail formed of interlocking keratin segments; the rattle is vibrated as a warning when the snake feels threatened. They prey on small mammals, birds and reptiles.

Facts about reptiles

• Approximately 8,000 species of reptiles are known today.
• The first reptiles appeared around 340 million years ago (Carboniferous Period).
• Reptiles are ectothermic and have scales.
• The Mesozoic Era is commonly described as the Age of Reptiles.
• In several reptile species, sex determination of embryos can depend on incubation temperature.
• Some of the largest reptiles today include the leatherback turtle, Komodo dragon and saltwater crocodile.

Birds

Overview. Birds are warm-blooded vertebrates (endotherms) distinguished by the presence of feathers, forelimbs modified as wings, and a beak instead of teeth. There are over 8,000 bird species worldwide. Birds show a wide range of adaptations for flight, feeding and habitat use.

Adaptations for flight and life in air

• Skeleton: Many birds have lightweight, often hollow bones and a fused skeleton that provides strength with reduced weight.
• Feathers: Provide lift, insulation and, in many species, display; feathers are a key avian innovation.
• Respiratory system: Efficient lungs and air-sacs facilitate high oxygen uptake, enabling flight and breathing at high elevations.
• Feet and perching: Many species have foot anatomy and tendons that allow them to lock on a perch while sleeping.

Albatross

Large seabirds of the Southern Ocean and North Pacific, the albatrosses have the greatest wingspans among living birds. Their long, narrow wings are superb for dynamic soaring over the ocean but complicate take-off and landing.

Swan

Swans are the largest waterfowl, found across many continents. The trumpeter swan has a wingspan that can reach about 10 feet. Swans feed by reaching and sweeping with their long necks, allowing them to graze underwater without full diving.

Vulture

Vultures are scavengers found on several continents. They feed primarily on carrion and in many species have an acute sense of smell and excellent vision. Many vultures have a bare or partly featherless head, which helps keep them clean when feeding on carcasses.

Ruby-throated hummingbird

Found across parts of North America and into Central America, this tiny hummingbird frequents gardens and forest edges. It can hover and manoeuvre in all directions due to powerful flight muscles and unique wing mechanics, feeding on nectar and small insects.

Parrot

Parrots occur in tropical and warm regions worldwide including India and Australasia. There are roughly 372 species. Many parrots are highly intelligent, capable of vocal learning and some degree of associative understanding of words and contexts.

Ostrich and penguins

The ostrich is a large, flightless bird native to Africa, adapted for running at high speeds (up to about 45 miles per hour). Penguins are flightless aquatic birds predominantly of the Southern Hemisphere and are specialised for swimming; their wings have evolved as flippers.

Peacock (Peafowl)

Peafowl include three species: the blue peafowl of India and Sri Lanka, the green peafowl of Java and Myanmar, and the Congo peafowl of Africa. The male peacock is famous for its iridescent tail "train" with eye-like markings, used in courtship display.

Kiwi

The kiwi is a small, flightless, nocturnal bird endemic to New Zealand and is an endangered species. It has a rounded body, long bill and is a national symbol of New Zealand.

Hornbill

Hornbills are tropical birds of Africa and Asia with a heavy, often brightly coloured downward-curved bill. Many are omnivorous and handle food by tossing it to the back of the throat because their tongues are short.

Great blue heron

A large wading bird of the Americas, it feeds in shallow water using long legs to wade and a sharp bill to spear fish, frogs and other small prey. Nests are built near water in trees or bushes.

Golden eagle

One of the best known large birds of prey in the Northern Hemisphere; it has a wingspan over 7 feet, excellent eyesight (many times better than a human's) and powerful talons and beak for capturing and tearing prey.

Conservation and human relevance. Many birds are important in ecosystems as pollinators, seed dispersers, predators and scavengers. Several species are threatened by habitat loss, hunting, pollution and introduced predators; conservation measures include protected areas, captive breeding and legal protection.