Water needed to make food is taken in from the soil by the roots. It goes up the stem to the leaves. In a leaf we see lines all over the leaf. These are the tubes that take water to all parts of the leaf. They are called veins.
There are very small openings called stomata on the upper-side of the leaves. Air enters the leaves through these openings. These openings are very small that we cannot see them. Leaves take in carbon dioxide from the air to make food.
Green leaves contain chlorophyll and the part of the sunlight falling on a leaf is trapped by the chlorophyll. In leaves water and carbon-dioxide are changed into sugar (i.e. carbohydrates) due to energy from the sunlight.
The food is taken by the veins and the stem to all parts of the plant.
A part of the food is used up by the plant for growth; making flowers, fruits and seeds; repairing damage.
The extra food is changed to a substance called starch and stored in fruits, seeds, leaves, roots or stem. This process of making food is known as photosynthesis. Photo means light and synthesis means putting together. During photosynthesis leaves take the carbon dioxide from the air and add oxygen to it.
Oxygen of the air is used by all living things to breathe and carbon dioxide is given off during breathing.