There are so many different kinds of plants on earth and they are so integrated into the life of humans
and other animals, that they sometimes become invisible. They adapt to any climate and include
flowers,ferns, mosses, conifers as well as green algae. Grains, nuts, vegetables and fruits are part of
mankind's food and many are the origin of medicines and drugs.
We know a plant is alive because it has all the attributes that living people and animals have.
- It is made up of cells
- It needs nutrients, water, air and energy
- It reproduces
- It reacts to its environment
- It grows and dies
What is it that each plant has in common with all the others, even though they are as different as night
and day? Photosynthesis is the main function every plant shares. This is the way they take energy from
the sun and make it into sugar. There are exceptions to this including parasites which take their energy
from the host plant. Another thing each plant has in common is cell walls. All cells have a membrane,
but plant cells have an additional wall made from cellulose.
The light from the sun is electromagnetic energy. When that energy reaches a plant, reactions within the
plant take place for the storage of that energy in the form of sugar molecules. All of the light from the
sun is not used by the plant. Only certain colors are used for photosynthesis. The blue and red
wavelengths are most often used. Green wavelengths are not used, and that is why they appear green.
The color that is seen is the wavelength that is not absorbed by the object. In order to live and grow, a
plant needs enough space, the right temperature, light, air, water, nutrients and time. Given these
conditions they will grow indoors and outdoors. Greenhouses are artificially created climates to allow a
plant that needs one type of climate to grow in another place.
Food is not the only thing the plant gives humans and other animals. They produce all of the food
people and animals eat, including meat. Chickens, pigs and cows as well as other animals that humans
use for meat all eat grass, leaves, hay, corn, oats or other seeds.
They also produce oxygen. Oxygen is the gas that is produced by a plant as a byproduct of making food.
All animals as well as the plant need oxygen to live.
Trees and shrubs, grasslands, rainforests and other forests and woods are the habitat for most animals
as well as thousands of other organisms. They provide shelter for animals and an environment in which
to find food. Trees provide shade to keep the ground cool, and tropical rainforests affect the rainfall
patterns over huge areas of the earth.
Grass, trees and small shrubs hold soil together so that it doesn't erode. Their leaves also drop and
decay which helps make new soil rich with nutrients.
Many useful products are created from the plant including fibers for clothing, drugs and medicines.
Wood fuel for heating or cooking is used around the world and even the other products humans use for
fuel including coal, gasoline and natural gas are made from trees and shrubs that died millions of years