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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WHAT STARTED THE AGE OF DISCOVERY?

The desire of European merchants to control the trade in luxury goods from Asia- silk, cotton, and spices- combined with the technology advances in shipbuilding and navigation led to a wave of long-distance voyages of exploration that redrew the map of the globe between the 15th and 18th centuries.

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.

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