Photosynthesis &
Respiration
What is Photosynthesis?
The process of photosynthesis is a
chemical reaction.
It is the most important
chemical reaction on our planet.
What is the equation for the
chemical reaction of
photosynthesis?
What is the equation for the
chemical reaction of
photosynthesis?
Six molecules of carbon dioxide react with six
molecules of water
to form 1 molecule of glucose and six molecules of
oxygen.
Describe Photosynthesis
• The process of changing light energy to
chemical energy
• Energy stored as sugar
• Occurs in plants and some algae
• Plants need light energy, CO2, and H2O
• Takes place in the chloroplasts, using
chlorophyll, the green pigment in plants
What are the two parts of
photosynthesis?
• the light reaction
requires light and must be first
• the light-independent reaction
does not require light
but must follow the light reaction
TRIVIA: This used to be called the dark
reaction. Why is not used today?
What happens during
photosynthesis?
• Plants capture light energy and use that
energy to make glucose
• Sunlight provides the energy needed by
chlorophyll to change molecules of carbon
dioxide and water into glucose
• Oxygen is also released in this reaction
The Light Reaction
1. Chlorophyll is energized by sunlight
2. The energy splits a water molecule
3. A. The oxygen is released
B. Energy is stored by hydrogen(NADPH)
and ATP
The Light-Independent Reaction
1. Carbon dioxide combines with RuBP to
form PGA
2. PGA is converted to PGAL (G3P)
3. PGAL (G3P) can be:
a. used as a nutrient for the plant
b. converted back to RuBP (recycled)
c. converted to GLUCOSE
Who first figured out this
process?
Melvin Calvin
Because of his work, the light
independent reaction is known more
commonly as the “CALVIN CYCLE”
It is also known as “carbon fixation”
because carbon is converted to a
usable and organic molecule.
Melvin Calvin
1911 – 1997
Nobel Laureate
Calvin worked with Benson
so
the cycle is also called
the Calvin – Benson cycle
What happens during
photosynthesis?
• Carbon dioxide enters the leaf through holes
called stomata
• CO2 combines with the stored energy in the
chloroplasts through a chemical reaction to
make glucose
• The sugar is moved through tubes in the leaf to
the roots, stems and fruits of the plants
• Some of the sugar is used right away by the
plant for energy; some is stored as starch; and
some is built into plant tissue (example:
cellulose)
Why is this important to us?
1. Because we cannot make our own food
(glucose, energy),
we must get our food from plants.
Plants are the first step in the food chain.
Why is this important to us?
2. The oxygen released during
photosynthesis is necessary for all
living things.
Why do we need oxygen?
For energy . . .
We “burn up” our food.
(OXIDATION REACTION)
Summary
• Location: chloroplasts of green plant cells
•
•
•
•
Reactants: CO2 and H2O
Catalysts: light energy and chloroplasts
Main Product: glucose
By-product: oxygen
• Includes: light reaction and
light-independent reaction (Calvin cycle)
Chemosynthesis
• Bacterial process
• Uses chemicals as energy source instead
of light to make food (carbohydrates)
• Occurs in such places as bottom of the
ocean around vents
What is Cellular Respiration?
Once the energy that was in sunlight is
changed into chemical energy by
photosynthesis, an organism has to
transform the chemical energy into a form
that can be used by the organism.
This process is cellular respiration.
What is Cellular Respiration?
The release of chemical energy for use
by cells.
In what cell part does this occur in eukaryotic
cells?
The mitochondria
Describe Cellular Respiration
• The breakdown of glucose molecules to
release energy
• Takes place in all living things
• Is a step by step process
What is the chemical equation
for cellular respiration?
What two processes make up
cellular respiration?
• The anaerobic phase
takes place first in the cytoplasm
• The aerobic phase
follows the anaerobic phase and
takes place in the mitochondria
The Anaerobic Phase
• First step occurs in the cytoplasm
• Glucose breaks down into pyruvate
(two 3 carbon sugars)
• This is called “GLYCOLYSIS”
• 2 ATPs produced (net gain)
The Aerobic Phase
• Pyruvate enters the mitochondria
• Includes a series of reactions called the
Krebs cycle
• Another part of this process is the
“electron transport chain” - a series of
reactions that end with oxygen
• 34 ATPs produced
Summary
• Location: mitochondria of all eukaryotic
cells
•
•
•
•
Reactants: glucose and oxygen
Catalysts: enzymes
Main Product: energy (ATPs)
By-products: CO2 and H2O
• Includes: anaerobic and aerobic phases
Together, what do
photosynthesis and respiration
form???
THE CARBON CYCLE
So what happens in bacteria
and yeast?
What is FERMENTATION?
Fermentation
• Two types:
– Alcoholic fermentation:
• Yeast - 2 ATPs
• C6H12O6 -> CO2 + ethyl alcohol + energy(2ATPs)
• Lactic Acid fermentation
bacteria and muscle cells (without O2) - 2 ATPs
C6H12O6 -> lactic acid + energy (2 ATPs)
Photosynthesis
&
Respiration
THE END