Atmosphere, Water and Pollution

Section: Earth and Space | Syllabus: Cambridge Primary Stage 5 Science (0097)

Earth's Atmosphere

The atmosphere is the layer of air surrounding Earth.
Air is a mixture of gases, not a single substance.
Nitrogen makes up the largest part of air; oxygen is the next largest part.
Air also contains small amounts of carbon dioxide, water vapour and other gases.

Air is mostly nitrogen and oxygen, with small amounts of other gases

Pure water contains only water particles and nothing else.
Most natural water - including seawater, river water and rainwater - contains dissolved salts, minerals and other substances.
Clear water is not necessarily pure, because dissolved substances can be completely invisible.
Safe drinking water is not the same as pure water - clean drinking water usually still contains small amounts of dissolved minerals that are safe, and even healthy, to drink.

Pollution is the introduction by humans of substances that harm the environment.
Examples include exhaust gases, factory smoke, sewage, oil spills, pesticides and plastic litter.
Pollution can harm living organisms, damage habitats and reduce water and air quality.
Evidence about the amount, source and effect of a pollutant helps people decide how best to reduce it.

Type of pollution	Common source	Possible effect
Air pollution	Vehicle exhaust, factory smoke	Harms breathing in humans and animals
Water pollution	Sewage, oil spills, chemical run-off	Harms aquatic plants and animals
Land pollution	Plastic litter, pesticides	Harms soil, plants and wildlife

Worked Example: Explaining Impure Water

Question: A clear sample of seawater contains no visible pieces of solid. Explain why it is not pure. [1]

A dissolved substance can be present even when it cannot be seen. Answer

Seawater contains dissolved salts and other substances, so it is not pure even though it looks clear.

MistakeClear water must be pure.

FixDissolved substances may be invisible; pure water contains only water particles.

Interactive revision notes, videos and practice questions load below.