Download Photosynthesis and Light - Ms. Mudd`s Science Spot

Photosynthesis and Light
Ms. Mudd 7th Grade Biology
The Nature of Light
• The sun is a source of energy.
• You can feel the sun’s energy as it warms your skin.
• You see the energy in the form of light on objects
around you.
• The light you see is white light.
• When white light passes through a prism you can see it
is made up of the colors of the rainbow.
• Scientists refer to the colors-red, orange, yellow, green,
blue, indigo, and violet-as the visible light spectrum.
When Light Strikes An Object
• White light strikes many objects.
• Some objects like glass allow light to pass through
them.
• This process is called transmission.
• When light hits a shiny surface such as a mirror,
the light bounces back.
• This process is called reflection.
• When dark objects, such as street pavements,
take in light, it is called absorption.
Light Strikes Objects
• Most objects reflect some colors while they
absorb others.
• When white light strikes a lemon, the lemon
absorbs most of the light’s colors.
• However, the lemon reflects the yellow light.
• The lemon looks yellow because your eyes see
the reflected color.
Plants and Light
• Like yellow lemons and most other objects
plants absorb some colors of the visible
spectrum and reflect others.
• When light strikes the green leaves of a plant,
most of the green part of the spectrum is
reflected.
• Most of the other colors of light are absorbed.
Plant Pigments
• When light strikes a leaf, it is absorbed by
pigments found in the leaf’s cells.
• Chlorophyll, the most abundant pigment in
leaves, absorbs most of the blue and red light.
• Most of the green light is reflected rather than
absorbed.
• This explains why chlorophyll appears green in
color, and why leaves usually appear green.
Accessory Pigments
• Other pigments called accessory pigments are
also found in leaves.
• These pigments include orange and yellow
pigments, and they absorb different colors of
light than chlorophyll.
• Most accessory pigments are not visible in
plants because they are masked by
chlorophyll.
Photo means light and synthesis means put together.
Photosynthesis is how plants use light
and water to make sugar. Sugar is
created in the green parts of a plant
and every animal on earth depends on
it. Without plants we would have no
food to eat or oxygen to breath. Here
is a picture to show how it happens.
Plants absorb a common gas called carbon
dioxide, pull water up through their roots and
use light to make sugar. Plants use the sugar
to grow. Plants give off oxygen as a byproduct. The green parts of the plant makes
the sugar and oxygen.
Why Do Leaves Change Color In Fall?
Leaves are nature's food factories. Plants take water
from the ground through their roots. They take a gas
called carbon dioxide from the air. Plants use sunlight to
turn water and carbon dioxide into glucose. Glucose is a
kind of sugar. Plants use glucose as food for energy and
as a building block for growing. The way plants turn
water and carbon dioxide into sugar is called
photosynthesis. That means "putting together with
light." A chemical called chlorophyll helps make
photosynthesis happen. Chlorophyll is what gives plants
their green color.
As summer ends and autumn comes, the days get shorter and shorter. This is how
the trees "know" to begin getting ready for winter.
During winter, there is not enough light or water for photosynthesis. The trees will
rest, and live off the food they stored during the summer. They begin to shut down
their food-making factories. The green chlorophyll disappears from the leaves. As
the bright green fades away, we begin to see yellow and orange colors. Small
amounts of these colors have been in the leaves all along. We just can't see them in
the summer, because they are covered up by the green chlorophyll.
The bright reds and purples we see in leaves are made mostly in the
fall. In some trees, like maples, glucose is trapped in the leaves after
photosynthesis stops. Sunlight and the cool nights of autumn cause
the leaves to turn this glucose, into a red color. The brown color of
trees, like oaks, are made from wastes left in the leaves.