Group of animals that not have a backbone in their body.

The animal kingdom is divided into two subgroups:

The five classes in which vertebrates are classified are:

Are cold-blooded and live their whole life in the water; they have gills to take the oxygen from the water; fish have find and the body covered by scales, and they lay thousands of eggs at a time.

Live part of their lives in the water and part on land; lay many eggs in the water; they have moist smooth skin, they have four legs.

Have dry and thick skin covered with scales; they have four legs or may have not; usually ley eggs or live young; they have no ears, instead they have wholes; they are cold-blooded.

Group that have wings and feathers covering their body; they have hollow bones; have beaks and two legs; they are warm-blooded; wholes instead of ears.

Have fur covering their body; they are warm blooded and most of them give birth to live young; female mammals produce milk to feed and nurse their babies; four legs and warm-blooded. Human kind belong to mammal’s classification.

Is the internal skeleton that vertebrates have.

Is the hard external covering of some animals such as arthropods.

Are divided into: Sponges, Cnidarians, Flatworms, Roundworms, and Mollusks.

Is any substance that directly or indirectly harms or alters Earth´s environment and the organisms living there.

The three main types of pollution are:

Is the most important air pollutant because of the majority amount of different toxic gas substances released to the atmosphere.

Car exhaust, power plants, soot, carbon monoxide, sulfur dioxide, nitrogen oxide, etc. Releases huge amounts of gases that generate:

Natural substance in our planet that can be in the three different states: solid, gas, and liquid.

The _________________ in the poles contain the solid water, the atmosphere contains the water vapor, and the oceans, rivers, lakes, and ponds, etc. contain the liquid water on Earth.

About 97% of the water in the planet is found in the:

People can have: health, education, food security, help an economic growth, gender equality, less diseases, more animals and crops surviving; if they get:

This water is salty and not suitable for drinking.