Cellular Energy
Chapter 8
8.1 How Organisms Obtain
Energy
All living organisms use energy to carry out all biological
processes.
Energy
• Nearly all the energy on this planet comes from the
sun
• Winds (hurricanes and tornadoes) are powered by
the sun.
• Rivers (and waterfalls) are powered by the sun
(getting the water to higher ground as rain).
• Plants (and indirectly animals) are powered by the
sun.
• Fossil fuels (coal, oil & natural gas) are remains of
dead plants and animals
How do we get energy?
• EATING!
o OUR BODIES BREAK DOWN THE
FOOD WE EAT SO WE CAN GET
ENERGY
Transformation of Energy
• Energy: The ability to do work
• In our cells, energy is stored in the form of ATP…
ATP
• ATP = Adenosine Triphosphate
• 1 large molecule that is made of 5 smaller
molecules bonded together
• Adenine, ribose, and 3 phosphate groups
ATP
• ATP breaks
apart and
releases its
energy to
cells
ENERGY!!!
ATP
• When is
breaks apart,
it releases
energy and
loses a
phosphate
group, now it
is called ADP
Then what?
• ATP breaks apart and creates energy and
ADP…then what happens?
• It is recharged! It uses energy and gains and extra P
is becomes ATP again
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Energy
Adenosine triphosphate (ATP)
Fully
charged
battery
ADP  ATP
How do the things we eat
get energy?
Autotrophs &
Heterotrophs
• Autotrophs – organisms that make their own energy
for food
• Heterotrophs – organisms that need to ingest food
to obtain energy
Energy
• Plants use energy from the sun to grow and make
their own energy
• HOW DO THEY DO THIS?
8.2 Photosynthesis
Light energy is trapped and converted into chemical energy
during photosynthesis
Photosynthesis
• “Photo”– light
• “Synthesis” – putting together
• Process of plants making their own food by
combining carbon dioxide and water to form sugar
and oxygen in the chloroplasts
• Requires energy form the sun to happen
• The process is cyclical, the products from one
reaction are the reactants for the next reaction
• The food produced is
glucose (a simple
sugar) and oxygen
(which we like!)
carbon
dioxide
+ water

glucose
+ oxygen
Which part of the plant do
you think photosynthesis
happens in?
Chloroplast
• Chloroplasts!
• Inside each chloroplast
is where the
photosynthesis reaction
takes place.
Chlorophyll
• Chlorophyll - the main
pigment found in the
chloroplasts responsible for
photosynthesis, they have
the ability to absorb energy
from sunlight
• A pigment is a colored
chemical (like a dye),
chlorophyll gives most leaves
their green color
• Different chlorophylls absorb
different wavelengths of light
Photosynthesis
• There are two parts, light independent, and light
dependent
• Light dependent takes place in the light
• Light independent takes place in the dark
Phase 1: Light Reactions
• The “photo” part
• The light is captured by chloroplasts and turned into
chemical energy (ATP)
Phase 2: The Calvin Cycle
CARBON
DIOXIDE
ATP
CALVIN CYCLE
• In the second
phase, called the
Calvin cycle,
carbon dioxide is
used to make
sugar (glucose)
• The “synthesis” part
• Light independent
GLUCOSE
H2O
Light
Light
Reactions
O2
Chloroplast
ATP
CO2
Calvin
Cycle
Sugar
(Glucose)
8.2 Cellular Respiration
Living organisms obtain energy by breaking down organic
molecules during cellular respiration.
So…
• How do our bodies take food and make it into
energy?
Cellular Respiration!
• Cellular respiration: is a chemical process in which
glucose molecules are broken down to release energy
(ATP) for cellular functions
• Occurs in all living cells
• Cellular respiration is the opposite of photosynthesis
• Completed in the mitochondria
• The products of photosynthesis – oxygen & glucose – are
the reactants needed for cellular respiration, and the
products of cellular respiration – carbon dioxide & water
– are the reactants for photosynthesis
What happens to the food we eat?
1. We break our food down into
small molecules
2. We use the energy
stored in the bonds
in our food to make
ATP
3. A small amount of the food
becomes waste
Like photosynthesis, cellular respiration has a
specific chemical reaction that happens every time.

+
We breathe out
carbon dioxide
We breathe in oxygen and
get glucose from our food
C6H12O6
glucose
+
6O2
oxygen

6H2O
water
+
6 CO2 +
carbon dioxide
Energy
(ATP)
Cellular Respiration
• This process is the reverse of photosynthesis.
Cellular Respiration
Anaerobic
• Does NOT need oxygen
• Happens in cytoplasm
of cell
• Fermentation
Aerobic
• Requires oxygen
• Happens in
mitochondria
• Cellular Respiration
Fermentation
Lactic Acid
• This is done by your
muscles when the
demand for ATP is high,
but you are low in
oxygen. (while working
out) This can cause
soreness in the muscles
Alcohol
• sugar breaks down into
carbon dioxide and
ethanol
• The carbon dioxide
produced in this
manner can be used to
allow bread to rise