General Science Questions

The air around us is a mixture of gases, mainly nitrogen and oxygen, but containing much smaller amounts of water and other gases.

Earth's atmosphere is composed of many gases. Their percentages by volume is given by::

 
78% Nitrogen,

21% Oxygen,

0.9% Argon, and

0.03% Carbon dioxide 

And very small percentages of other elements.

Haemoglobin is a protein what carries oxygen in the blood and contains iron metal in it.

The ozone gas present in the atmosphere absorb ultraviolet radiation. It is spread as a ozone layer throughout the stratosphere.

To reduce the risk of bacterial contamination, many foods must be stored in the refrigerator and thus kept below 5 degrees Celsius. These foods are often classified as ‘high-risk foods’ and include – meat, poultry, dairy, seafood, eggs, smallgoods and cooked rice and pasta. This also refers to ready-to-eat foods that have high-risk foods as ingredients and include – casseroles, quiche, pasta salad, pizza, sandwiches and many cakes.

By keeping these high-risk foods under 5 degrees Celsius it stops them from entering the ‘danger-zone’ – temperatures between 5 degrees Celsius and 60 degrees Celsius. The danger-zone is the temperature zone which provides bacteria with the perfect environment to rapidly grow and multiply to numbers that cause food poisoning.

When water is cooled from 4°C to 0°C, its density decreases.

When water cools from 4°C to 0°C, ice crystals begin to form because the water is approaching its freezing point. When water freezes, the water molecules form a lattice that increases the volume. As a result, the density decreases. This is why ice will float on top of water; ice has a lower density than the water.