Section 4: How a Plant Grows

Glossary

Lesson 1: Photosynthesis




In Section 3 of this course, we studied the functions of the various parts of a plant. In particular, we learned that it is in the plant's leaves that carbohydrates are produced by the plant. Since this is the product that a plant needs as food and energy for growth, the leaves can be considered the food factory of the plant.


The ability of a plant to manufacture its own food is a primary difference between plants and animals. The process by which a plant does this is called photosynthesis. It uses the sun's energy to combine water and nutrients from the soil with carbon dioxide from the air. Glucose (plant food) is the result of this reaction, which the plant can use to sustain itself, to grow and to reproduce.


The plant uses water and nutrients from the soil, and carbon dioxide from the air to produce glucose to feed itself. The energy required for the process is derived from sunlight. The oxygen given off through the leaf's stomata is used by animals and humans.

This diagram depicts the process of photosynthesis.

©iStock

Photosynthesis happens only in green plants.  It supplies food for the plant and oxygen for other forms of life.  A green plant helped make the oxygen you are breathing today!

Photosynthesis literally means to put together using light. Plants put together the water and nutrients from the soil with the carbon dioxide from the air. Light provides the energy required to do so.
Photosynthesis occurs only in the chloroplasts (tiny sub-cellular structures contained in the cells of leaves and green stems) because that's where the chlorophyll is.

Here is a concise statement of what is actually happening in this process:

The first line of the above statement simply repeats what we have been learning. The second line is the actual chemical equation of the reaction.

Photosynthesis requires water, carbon dioxide, and light. Limiting any one of these (on the left side of the equation) can limit photosynthesis regardless of the availability of the other two substances. For example

  • Without light, the plant will not grow, no matter how much water and/or fertilizer you give it - because there is no photosynthesis.

  • A tightly closed greenhouse can have very little fresh air infiltration, which will limit the amount of carbon dioxide available, thereby limiting plant growth. During winters, many commercial greenhouses provide supplemental carbon dioxide to stimulate plant growth.


A Green Leaf

You are looking at an incredibly clean and efficient factory that produces food for all parts of a plant. But there's more!

Not only does it not produce any pollution at all, its by-products- namely oxygen and water vapour -actually help remove pollutants from the air around it, and also have other beneficial effects on all life forms on our entire planet.