HOW DO FISH BREATHE?

Fish are vertebrates (animals with backbone) that live in the sea and in fresh water. Like all animals they have to breathe in oxygen. Lungs would simply fill up with water, so instead fish have feathery gills at the back of the head that extract oxygen from water as it flows over them.

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WHY IS BLOOD RED?

Blood is red because most of its cells are packed with a red-substance called haemoglobin. Using this, the red blood cells pick up vital oxygen and deliver it to the body's cells. To achieve this and other roles, such as removing waste, blood is pumped along blood vessels by the heart.

How dry is a desert?

The dry conditions in the deserts occur due to the lack of rain and snow, which is usually less than 25cm (9.8 in) in a year. The driest desert on Earth is the Atacama, Chile, where in many parts there has not been any rainfall in living memory. Hot desert are found close to the tropics, where the Sun's rays are strongest. Hot desert are freezing at night because there are no clouds to trap the Earth's heat.

HOW DO MOUNTAINS GROW?

Where the plates of Earth's crust crash into each other, land is pushed upward, forming mountains. The Himalayas are the tallest mountains on Earth, and the youngest. They formed over the last 145 millions years, as India crashed into Asia. Mountains are also formed when volcanoes erupt and molten rock builds up into steep mounds.

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