Ask the children to tell you what they know already about what a tree needs to survive.
Do they know that trees drink and breathe?
Plants needs water, nutrients and energy if they are to survive and grow.
They obtain the water and nutrients from the soil through the root system.
They make their energy by combining the water with carbon dioxide from the air, using solar energy in the form of sunlight. What makes this possible is a green substance in plants, called chlorophyll, and a process called photosynthesis.
Photosynthesis is the process that green plants use to make food and grow. The leaves absorb energy from the sun’s rays (solar radiation) and use it, with the help of chlorophyll in the leaves, to convert carbon dioxide, from the air, and water, from the soil, to make a sugar, called glucose, and oxygen. The glucose is converted into cellulose to make plant cells and the oxygen is released into the air for us to breathe.
During the process of photosynthesis the tree is breathing in carbon dioxide and breathing out oxygen. This breathing, which is the exchange of gases between the plant and the atmosphere, is through small holes in the leaves, called stomata.
The amount of photosynthesis that takes place depends upon:
- the total leaf area of a tree,
- the amount of solar radiation and
- the CO2 concentration of the atmosphere.
Low air humidity, low air temperature and low soil moisture reduce photosynthesis. Below is the chemical reaction for Photosynthesis: