Energy
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All chemical processes in the cell require
energy.
Both plant and animal cells obtain energy
from “ energy-rich” compounds, such as
glucose (sugar)
The difference is how plants and animals
obtain these compounds.
How do plant and animal cells obtain energy
rich compounds?
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Plants?
Use light to make their
own sugars
(Photosynthesis)
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Animals?
Need to get energy
compounds from their
diet.
Photosynthesis
 Plants
make their own food. This
process is called photosynthesis.
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Photo = Light
Synthesis = To make
Photosynthesis = Make sugar
Where does photosynthesis
occur?

Photosynthesis
occurs in the
leaves of a plant.

Can we be more
specific?
Chloroplasts
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Photosynthesis occurs in chloroplasts
Chloroplasts contain a special substance
called chlorophyll, which makes leaves
green
Chlorophyll captures light  chemical
energy.
The Reaction
light energy

carbon dioxide + water  glucose + oxygen
chlorophyll

Balanced Equation:
light energy

6C02 + 6H2O  C6H12O6 + 6O2
chlorophyll
Photosynthesis
Why do plants need glucose?

Glucose is the food for the plant. It
gives the plant energy to grow.
Glucose

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Some is used right away for the cell’s life
functions.
Other glucose molecules are stored together
to form starch.
Starch and sugar taste different.
Think about fresh corn vs. corn that has been
picked and let to sit for a few days.
So you have sugar now what?

Recall: Plants get their glucose from
photosynthesis, animals get glucose from
their diets.

How do plants and animals then extract the
energy from these glucose molecules?

Both types of cells use: Cellular Respiration
Cellular Respiration

Recall: plant and animals both have
mitochondria.

Most reactions of cellular respiration occur in
the mitochondria.
Mitochondria

The “power-house” of the cell.

glucose (sugar) + oxygen  carbon dioxide
+ water + energy

C6H12O6 + 6O2  6 CO2 + 6H20 + energy
Mitochondria
The Connection

Look at the equations for photosynthesis and
cellular respiration.
Any relationships between the two?

energy + 6C02 + 6H2O  C6H12O6 + 6O2

C6H12O6 + 6O2  6 CO2 + 6H20 + energy

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The products of photosynthesis (C6H12O6 +
6O2) are the reactants for cellular respiration

The products of cellular respiration (6 CO2 +
6H20 ) are the reactants for photosynthesis
Thus we are all connected.

The Connection
Common Misconception
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Trees Need Carbon Dioxide Yes!!
Humans need Oxygen
Yes!!
We give one to the other
Yes!!
Cutting trees would mean less oxygen for us
No!!
There is a surplus of oxygen for us to breathe, however if we
cut down all the trees then what happens?
Increase in the amount of carbon dioxide.
This is why we need trees; they are the lungs of the planet.