Natural - Unit 2: Animals

There are many different animals and we can divide them into two groups:
- vertebrates (Definition: Animals with spine. They have skeleton)
- invertebrates (Definition: Animals that don´t have spine neither skeleton)


VERTEBRATES

Animals with spine. They have skeleton inside them. Most of the have head, torso, limbs and tail.
We can classify them into five groups:

• Mammals - They hace hair or fur. They breath with lungs and they usually have four legs. They are viviparous (Definition: They are born from their mother´s womb)
• Amphibians - They have moist skin. When they are young they breath with gills, but later they have lungs. Adult amphibians have four legs. They are oviparous (Definition: They are born from eggs)
• Fish - They live in water. They have scales and use fins to swim. They breath with gills. They are oviparous.
• Birds - They are covered with feathers and they have two wings. They breath with lungs. They have two legs. They are oviparous.
• Reptiles - They have dry, scaly skin. They breath with lungs. They are oviparous.

INVERTEBRATES

Animals without spine. They don´t have skeleton inside them. 

Invertebrate animals protect their bodies in different ways:

- some have a shell, such as snails and oysters.

- some have a exoskeleton: a thick exoskeleton, such as crabs and a thin exoskeleton, such as cockroaches

Let´s study three groups of invertebrates:

• Molluscs - They have a soft, muscular body. Ex.: oysters, mussels, snails, octopuses.
• Arthropods - Their body has three parts : head, thorax and abdomen. Many of them have antennae and some wings too. Arthropods with six legs are insects and with eight legs are spiders.
• Worms - They have a long, soft body. Some worms are parasites (Definition: They live inside or on the skin of another animals and feed on them) Ex.: leeches and flatworms.

Animal Nutrition

Not all animals eat the same food. Depending on what they eat, animals can be:

1. Herbivores - They only eat plants. Ex.: rabbits, pandas.
2. Carnivores - They only eat other animals. Ex.: lynxes and spiders
3. Omnivores - They eat plants and other animals. Ex.: bears and mussels

Animal Reproduction

Not all animals reproduce in the same way.

1. Viviparous - They are born directly from their mother (from their mother´s womb). Ex.: sheep, kangaroos and seals.
2. Oviparous - They are born from eggs. Ex.: birds, crocodiles and frogs.

You can study doing these exercises...