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Photosynthesis
Plants – An Overview
• Have existed on this planet for nearly 400 million years.
• Without plants, life on Earth would not exist as we
know it.
• Plants provide many great resources to planet Earth,
including sources of food, oxygen, and habitat for other
organisms.
• Plants are known as producers, because they make or
produce their own food through the process of
photosynthesis .
Photosynthesis
• Photosynthesis is shown in the picture and equation
given below.
The Photosynthesis Equation
What is it?
• Plants use energy from the sun to convert
carbon dioxide and water into oxygen and
sugars.
• Plants use some of the sugar for food. The
cells break down the sugar molecules to
release the energy they contain.
The Photosynthesis Equation
Where does it happen?
• In chloroplasts: Some sugar molecules are
converted into other compounds like cellulose.
Other sugar molecules may be stored for later
use.
• When you eat food made by plants, like carrots or
potatoes, you are eating the plant’s stored energy
The Photosynthesis Equation
Which organisms use it?
• Plants (land or water) and phytoplankton
What do we call organisms that make their
own food?
• Producers or “autotrophs”
Photosynthesis continued
• Plants are autotrophic or autotrophs, which literally
means “self-feeders.”
• Photosynthesis is a process that is unique to plants and
some protists; without photosynthesis there is no
recycling of the oxygen and carbon dioxide in the
atmosphere.
The Two Stages of Photosynthesis
Stage 1: Capturing the Sun’s Energy
What happens in stage 1?
• Chloroplasts are green organelles inside plant
cells.
• The main photosynthetic pigment in chloroplasts
is chlorophyll.
• Chlorophyll captures light energy
The Two Stages of Photosynthesis
Stage 2: Using Energy to Make Food
What happens in stage 2?
• Roots absorb the water and stomata absorbs the
carbon dioxide.
• Stomata are small openings in the underside of
leaves.
• Chloroplasts use the water and carbon dioxide
and with energy from the sun, undergo a series of
chemical reactions.
The Two Stages of Photosynthesis
(Cont.)
Stage 2: Using Energy to Make Food
• The reactions produce products:
-- sugar that has 6 carbon 12 hydrogen and 6
oxygen atoms. Cells can use the energy in sugar to
carry out important cell functions.
-- oxygen, which leaves the leaf through the
stomata.
• Almost all the oxygen in the Earth’s atmosphere is
produced through photosynthesis.