ANIMALS

Unit 4: Animals

1.The life processes of animals

• Nutrition
• Sensitivity
• Reproduction

2. Kinds of animals

    Vertebrates
          Characteristics

          Main Groups

             Mammals

                 Birds

                 Reptiles

                 Amphibians

                 Fish.

             

    Invertebrates

          Characteristics

          Main Groups

                 Sponges

                 Cnidarians

                 Worms

                 Molluscs

                 Arthropods

                 Insects

THE LIFE PROCESSES OF ANIMALS

Animals are living things. All living things carry out life processes. We classify animals into different groups according to how they carry out these life processes.

Nutrition in animals

All animals eat food. This food comes from other living things. Through the process of nutrition, animals obtain from food the energy and substances their bodies need.

Depending on the food they eat, animals are classified into carnivores, herbivores, omnivores, scavengers and decomposers.

Sensitivity in animals

Animals receive information about their environment through their sense organs. The sense organs send this information to the brain. The brain decides what to do. This process is called sensitivity.

Senses in animals are different to senses in people. For example, dogs have a highly developed sense of smell. Fish receive information through their skin receptors. Insects have got compound eyes which are very sensitive to movement.

Reproduction in animals

Reproduction enables animals to have offspring similar to themselves. Most animals have sexual reproduction.

This means that a male and a female must come together in order to reproduce.

Depending on the type of reproduction, animals can be oviparous or viviparous:

Oviparous. The offspring grows inside an egg. Birds, insects and fish are oviparous.

Viviparous. The offspring grows inside the mother’s womb. Mammals are viviparous.

KINDS OF ANIMALS

Vertebrate animals

Characteristics of vertebrates

All vertebrate animals have these characteristics:

They have an inner skeleton made up of bones. They have a spinal column.

Their body is divided into head, trunk, limbs and tail. The limbs can be legs, fins or wings, depending on how the vertebrate moves.

There are five groups of vertebrates:

1.    Mammals

2.    Birds

3.    Reptiles

4.    Amphibians

5.    Fish.

Main groups

Mammals

Mammals breathe air through their lungs.

Most of them are covered with hair or fur to keep them warm.

They are viviparous. Young mammals drink their mother’s milk.

There are different types of mammals; some are aquatic, like dolphins and whales. Others can fly, like bats.

Birds

Birds breathe air through their lungs.

Their bodies are covered with feathersand their feet are covered with scales.

Birds have a beak for eating, legs for walking and wings for flying.

Birds are oviparous. Most birds look after their young.

Some birds, such as ducks and penguins live in water.

Reptiles

Reptiles breathe air through their lungs.

Their skin is covered with scales.

Most live on land. Most of them have got four legs to move. Snakes haven’t got legs. They slither.

Reptiles are oviparous. Normally, reptiles do not look after their young.

Some reptiles are aquatic, for example, marine turtles.

Amphibians

Amphibian adults breathe through their lungs and their skin. Amphibians have bare skin.

They move using their four legs.

Amphibians are oviparous. They lay their eggs in water. The babies are called tadpoles. The babies are born in water and breathe through gills.

Fish

All fish are aquatic animals. They breathe through their gills. Their skin is covered with scales. They move using their fins.

Fish are oviparous. Normally, they do not look after their eggs.

Invertebrate animals

Characteristics of invertebrates

Invertebrates include many different types of animals such as ants, snails and jellyfish. Invertebrates do not have a spinal column. Most of them are oviparous.

Some invertebrates live on land and others live in water.

Some invertebrates, such as snails or mussels, have got a shell.

Invertebrates have different types of limbs: crabs have only legs, butterflies have legs and wings, and worms haven’t got legs or wings.

Invertebrates are classified into many different groups:

Main groups

Sponges

Sponges are very simple invertebrates.

They are aquatic and live attached to rocks. They cannot move about.

Their sac-like bodies are covered with pores that filter the nutritive substances in seawater for food.

Cnidarians

Jellyfish are cnidarians. Most jellyfish live in the sea. They move about with the sea currents.

They have jelly-like bodies that look like umbrellas. They have poisonous tentacles that can sting you.

Worms

Worms have got long, soft bodies.

They haven’t got legs.

This group includes very different animals.

Earthworms live in soil, but other worms, for example, fireworms, live in water.

Roundworms and tapeworms can live inside our bodies and cause illnesses.

Molluscs

Molluscs have got soft bodies. Most molluscs have got a shell to protect their bodies, for example, the snail.

Some molluscs have two shells, for example, the scallop.

Arthropods

Arthropods form the most numerous group of invertebrates. They include insects, spiders, crabs and centipedes. All arthropods have a hard exoskeleton. Their bodies are divided into segments.

Insects

Insects are the most abundant arthropods.

Their bodies are divided into three main parts: the head, the thorax and the abdomen.

All insects have two antennae and six legs. Some insects have got two, or four wings.