Chapter 8:
Photosynthesis
Section 3: Process of Photosynthesis
A. General Formula:
Reactants: Carbon Dioxide and Water
Products: Glucose (Food) and Oxygen
During Photosynthesis, the Suns energy will be converted through a series of
chemical reactions to glucose. This requires an input of CO2 and
produces O2 as a waste product!
1. Two Sets of Chemical Reactions
A. The Light Dependents Reactions (Light Reactions):
Require Light (hence the name)
These reactions take place in chlorophyll
Utilize water and sunlight
Produce ATP (Energy) and NADPH (Energy Storing
Electron Carrier) to be used later on!!
B. The Light Independent Reactions (Dark Reactions or
Calvin Cycle)
Do not require light (Hence the Dark Part)
Take place in the Stroma
Utilize ATP, NADPH, and CO2 from the atmosphere
Produce Glucose and O2 by using the energy gained
from light reactions
2. Light Reactions:
A. Steps in the Process:
1. Photosystem II: collection of chloroplast molecules
Absorbs light energy (photons)
Breaks down water into 3 things
- an Oxygen atom (Which is ½ of O2)
- 2 Hydrogen ions (Important Later)
- 2 Electrons that have absorbed suns
energy (Crazy, Mad Important!)
2. Electron Transport Chain: A collection of molecules on
the thylakoid membrane
As electrons travel down this chain they lose
energy
That energy is used to make ATP!
3. Photosystem I: Captures energy from the sun to reenergize those two electrons
So they don’t lose energy they need to be stored
in a molecules called NADP+
When NADP+ stores those electrons it is
called NADPH- This is another form of
energy!
Inputs: Water, Sunlight
Outputs: ATP, and NADPH (Both forms of energy for the next step)
2.
Dark Reactions/Calvin Cycle:
Take Place in the stroma
Use energy from light reactions to turn
CO2 from the atmosphere into
Glucose!
This an enzyme catalyzed reaction:
Rubisco is the most abundant protein
on the planet!!!
Input: ATP, NADPH (both from Light Reactions)
CO2 from the atmosphere
Output: Glucose- Food for plants (this was the purpose)
ADP, NADP+ Left over after their energy was used
Return to Light Reactions to get more energy
Oxygen
Review:
General Formula
What are the inputs of
the Light reactions?
1. H2O (Water)
2. Sunlight
What are the outputs of
the Light reactions?
1. ATP
2. NADPH
What are the inputs of the Calvin
cycle?
1. Energy (ATP and
NADPH)
2. CO2 (from
Atmosphere)
What are the outputs?
1. Glucose (Food)
2. ADP and NADP+ (To go get more
energy from light reactions
Factors Effecting
Photosynthesis
 Temperature:
Enzymes for Photosynthesis work
best between 0 and 95 degrees
Fahrenheit
Above this we get DENATURATION
of Enzymes
 Light Intensity:
The brighter the light, the greater the
rate of photosynthesis.
(Unless it is too hot!)
 Water Availability:
No water…No photosynthesis
How do Plants in Extreme
Conditions Survive!
 C4 Plants such as corn and sugar cane
Open stomata at night to let CO2 in
when temps are low- prevents
evaporation of water!
 CAM Plants such as cacti and pineapples
also only open their stomata at night and
store CO2 as something else. When light
is available to produce ATP and NADPHPS continues
Sugar Cane: C4 Plant
Grows in Tropical
climates- Very hot,
lots of sunlight
(Dominican Republic, Costa
Rica, Hawaii)
Organ Pipe Cactus: CAM
Plant
Grows in deserts
(Southwestern US, Mexico)