Photosynthesis
Chapter 8
Energy and Life
Section 8-1
Energy and Life
• Energy is the ability to do work.
• All living things use energy stored in
chemical compounds to survive. (FOOD)
• Heterotrophs – eat food to get energy
• Autotrophs – make their own food from
sunlight and inorganic molecules to get
energy.
• When are you not using energy?
Chemical Energy and ATP
• Energy from food is changed into another form
cells can use.
• Adenosine Triphosphate (ATP) – energy
molecule of the cell (made by what organelle?)
• Must break down the foods to generate the ATP.
• Breaking the bonds between the phosphate
atoms will release the energy from ATP.
• Used ATP is now ADP. (what is ADP?)
• Energy stored in foods (glucose) will change
ADP back into ATP.
ATP
Section 8-1
The ATP molecule!
(Know this structure)
Adenine
Ribose
3 Phosphate groups
Figure 8-3 Comparison of ADP and
ATP being made from ADP!
ATP to a Battery
Section 8-1
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Energy
Adenosine triphosphate (ATP)
Fully
charged
battery
This energy that will be stored into the
ATP molecule which comes from food!
Photosynthesis: An Overview
Section 8-2
Who Were the Scientists?



Jan Van Helmont – 1643
1. What do plants take from the soil?
2. Trees gain mass from water not soil.
Joseph Priestley – 1771
1. Something in the air kept candle burning.
2. Plants released oxygen.
Jan Ingenhouz – 1779
1. Oxygen was only produced by plants in
the presence of light.
Photosynthesis Equation
• 6CO2 + 6H2O ------- C6 H12O6 + 6O2
Light
Carbon dioxide
Light
+ water ------
sugar +
oxygen
• Photosynthesis uses the sunlight to
convert water and carbon dioxide into
oxygen and high-energy sugars (glucose)!
• What will the plant do with the sugar it has
made?
• Generate ATP for cellular processes!
Light and Pigments
•
Photosynthesis uses pigments in the leaf to
obtain sunlight.
•
Pigments absorb and reflect light.
•
Chlorophyll is the green pigment in
chloroplasts. Why is it green?
Two main types of chlorophyll:
Chlorophyll a and Chlorophyll b
•
Other pigments (red, orange, yellow) are found in
Plastids which will absorb energy and transfer to
chlorophyll.
Figure 8-5 Chlorophyll Light Absorption
Section 8-2
What wavelengths
does chlorophyll
work the best in?
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
What wavelengths
does chlorophyll
not work well in?
Chlorophyll a
Which color light
would a plant grow
best under: Green,
red, yellow?
V
B
G
YO
R
Photosynthesis: Reactants and Products
Section 8-2
The Reactions of
Photosynthesis
Section 8-3
The Chloroplast
Structure of Chloroplast:
1. Thylakoids – saclike photosynthetic
membrane (they look like pancakes!)
a. Contains light absorbing pigments
b. Light Dependent reaction occurs here
2. Grana(um) – stacks of thylakoids
3. Stroma – space surrounding the thylakoids
a. Calvin cycle occurs here.
The Reactions
Two reactions run the photosynthesis process:
1. Light-Dependent reaction
- sunlight required to run; it is a
reactant
2. Calvin Cycle (aka Light-Independent reaction)
- no sunlight required to run
- however, needs products of light
reaction to run.
Light Dependent Reaction
• Takes place in the thylakoids
• Sunlight excites electrons in chlorophyll
• Electron energy passed to carrier
molecule NADP+ to make NADPH.
• H2O is broken down to use H+ ions to
convert ADP to ATP by ATP synthase
protein.
• Oxygen atoms released as waste.
Figure 8-7 Photosynthesis: An Overview
Section 8-3
H2O
CO2
NADP+
ADP + P
LightDependent
Reactions
Calvin
Cycle
ATP
NADPH
O2
Sugars
Light Independent Reaction or
Calvin Cycle
• Takes place in the stroma.
• CO2 combines a 5 carbon sugar to
produce two 3-carbon molecules.
• Catalyzed by the enzyme RUBISCO.
• ATP and NADPH from light phase convert
the 3-carbon molecules into glucose!
Figure 8-7 Photosynthesis: An Overview
Section 8-3
H2O
CO2
NADP+
ADP + P
LightDependent
Reactions
Calvin
Cycle
ATP
NADPH
O2
Sugars
How is the Rate of
Photosynthesis Controlled?
• Availability of water – lack of water slows
process down – plants in warm climates
have waxy coating to reduce water loss
• Temperature – best rate occurs between
0 and 35 degrees Celsius
• Intensity of light – increasing light
intensity increases rate