Nitrogen makes up 78% of air and is not used by most living things except some bacteria and plant roots. Oxygen makes up 21% of air and is essential for respiration in plants and animals. Carbon dioxide is used by plants in photosynthesis and is essential for making food and sugars while oxygen is produced.

1. Nitrogen Composition of Air
78%
Carbon
Dioxide,
Water
Oxygen
Vapour and
21%
other Gases
1%

2. Oxygen
• makes up 21% of the air.
• it is essential to for most living
things.
• plants and animals take in oxygen
during the process of respiration.
• not only can it be found in air, it is
also found in water and soil.
• is needed for burning.

3. Respiration
The process when living things
take in oxygen in order to break
down digested food to produce
energy.
Oxygen
Digested Energy +
Food Carbon dioxide

4. Nitrogen
• makes up 78% of the air.
• is not used by most living things
except for –
• nitrogen-fixing bacteria in the soil
• the roots of some plants to use it
to form nitrates, e.g. peanuts
• absorbed by plant as nitrates to
make plant protein.

5. Carbon dioxide
• is essential to green plants for
the process of photosynthesis.
• is combined together with
water and the energy from the
sunlight, to make food or simple
sugars. Oxygen is produced in
the process.

6. Water Vapour
• plays an important part in the
water cycle.
• helps to form the clouds in the
sky.
• returns to the Earth in the form
of rain, snow, hale or sleet.

7. Rare Gases
• includes argon, helium,
neon, krypton and xenon.
• are inert, meaning they do
not take part in reactions
under normal circumstances.

8. A Healthy Balance
Carbon
Oxygen
dioxide
produced
used by
from plants
the plants