METABOLISM AND SOURCES OF
ENERGY
METABOLISM
When we speak about metabolism what do we
mean?
 What kind of chemical reactions do you think
take place in our bodies?
 Growth (making proteins)
 Response (nerve reactions)
 Movement (energy needed from respiration)
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Metabolism describes all the chemical reactions
in our bodies
The way our metabolism functions is extremely
important as our bodies need to have constant
and stable conditions
The maintainance of stable conditions in our
bodies is called homeostasis
WHAT DO YOU THINK WOULD
HAPPEN IF…

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There were no reactions to break down sugar in
our blood
There were no reactions to build new tissues
when we get damaged
There were no reactions to send signals to your
brain that you are touching something hot
LEARNING CHECK
What is meant by metabolism?
 Can you name some example of metabolism in
the human body
 What word describes the maintainance of
reactions in our body?

Reactions that involve breaking big molecules
into smaller molecules release energy and are
called catabolic
Eg. Respiration

Reactions that involve making bigger molecules
out of smaller ones molecules use up energy and
are called Anabolic
Eg. Photosynthesis
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Most reactions take place in a number of steps
which need to be carefully controlled if the cell is
to function properly
Enzymes are the most important controllers of
cellular reactions
LEARNING CHECK
What does the term catabolic reaction mean?
 What does the term Anabolic reaction mean?
 Can you give an example of each type?
 What molecules re responsible for controlling
reactions in our body?
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SOURCES OF ENERGY

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The main source of
energy for all life is
the sun
Certain pigments such
as chlorophyll can
absorb light

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When they absorb light they use it to form the
chemical bonds in bio molecules such as
carbohydrates
Remember photosynthesis is the way plants
make their own food (glucose-which is a
carbohydrate)
CELLULAR ENERGY

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This is the energy released by the reactions in a
cell
When bio molecules such as carbohydrates are
broken down the bonds are broken and energy is
released
Some of this energy is used by the cell and the
rest is lost as heat
IN SUMMARY
Photosynthesis in
Plants builds up
molecules with energy
rich bonds (glucose)
 Respiration breaks
down glucose and
releases this energy
from the bonds
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This is how plants
provide energy from
the sun for everything
else on earth!
LEARNING CHECK
What is the source of all energy on earth?
 In cells where is this energy found?

SYLLABUS

You should be able to do the following for
Ordinary level Cell Metabolism:
Define the term: metabolism.
 State that solar energy is source of energy on
Earth.
 State that cellular energy sourced from chemical
energy in ATP
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