Photosynthesis
Energy and Life
• Plants and some other types of organisms are able to use
light energy from the sun to produce food.
• Autotrophs: organisms such as plants, which make their
own food
• Heterotrophs: obtain energy from the foods they consume
• All living organisms must be able to produce energy from
the environment in which they live, store energy for future
use, and use energy in a controlled manner.
Autotrophs
Heterotrophs
Chemical Energy and ATP
• A quick source of energy that is stored in the chemical
bonds of a molecule that can be used quickly and easily by
the cell is called adenosine triphosphate (ATP).
– ATP is an energy molecule
– The energy of ATP becomes available when the
molecule is broken down.
– The addition and release of a phosphate group on
adenosine diphosphate creates a cycle of ATP
formation and breakdown. This means the cell doesn’t
have to store all the ATP it needs.
ATP Continued
• Cells use this energy to make new cells, maintain homeostasis,
and to power functions (like movement).
• The characteristics of ATP make it exceptionally useful as the
basic energy source of all plant cells.
ATP
Adenine
Ribose
3 Phosphate groups
Comparison of ADP and ATP to a
Battery
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Energy
Adenosine triphosphate (ATP)
Fully
charged
battery
Comparison of ADP and ATP to a
Battery
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Energy
Adenosine triphosphate (ATP)
Fully
charged
battery
Photosynthesis
• Photosynthesis: Plants use energy from the sun to convert
water and carbon dioxide into high energy carbohydrates
(sugars and starches) and give off oxygen as a waste
product.
• Photosynthesis happens in 2 phases: light-dependent
reactions and light-independent reactions.
• In addition to water and carbon dioxide, photosynthesis
requires light and chlorophyll, a molecule in chloroplasts.
Photosynthesis Equation
•
Photosynthesis: Reactants and Products
Light Energy
Chloroplast
CO2 + H2O
Sugars + O2
Light and Pigments
• Plants gather the sun’s energy with light absorbing molecules
called pigments. The plants’ principal pigment is chlorophyll.
• 2 types of chlorophyll: Chlorophyll a and Chlorophyll b
• Chlorophyll absorbs light very well in the blue-violet and red
regions of the visible spectrum. However, chlorophyll does
not absorb light very well in the green region of the spectrum.
Green is reflected by leaves, which is why plants look green.
Chlorophyll Light Absorption
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
V
B
G
YO
R
The Reactions of Photosynthesis
• Photosynthesis takes place inside the chloroplasts
• The Chloroplasts contain saclike photosynthetic membranes
called thylakoids, which are arranged in stacks known as
grana. The space outside of the grana is called the stroma.
• Proteins in the thylakoids membrane organize chlorophyll and
other pigments into clusters known as photosystems, which
are the light collecting units of chloroplasts.
Chloroplasts
Light Dependent Reactions
• Light-dependent reaction: uses light energy to produce
oxygen and convert ADP and NADP+ into energy carriers ATP
and NADPH
• The light dependent reactions take place within the thylakoid
membranes (granum) of chloroplasts.
Light-Dependent Reactions
Photosystem II
Hydrogen
Ion Movement
Chloroplast
ATP synthase
Inner
Thylakoid
Space
Thylakoid
Membrane
Stroma
Electron
Transport Chain
Photosystem I
ATP Formation
Calvin Cycle
• Calvin Cycle: uses the energy carriers ATP and NADPH from
the light-dependent reactions to produce high-energy sugars.
(Calvin cycle is also called the light independent reaction)
• Calvin Cycle takes place in the stroma, outside the grana.
Calvin Cycle
CO2 Enters the Cycle
Energy Input
ChloropIast
5-Carbon
Molecules
Regenerated
6-Carbon Sugar
Produced
Sugars and other compounds
Factors Affecting Photosynthesis
• Water, light, and temperature all affect photosynthesis
Photosynthesis Concept Map
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
takes place in
use
NADPH
Stroma
of
O2
Chloroplasts
uses
ATP
NADPH
to produce
High-energy
sugars
Photosynthesis: An Overview
Light and Water
CO2
Chloroplast
Chloroplast
NADP+
ADP + P
LightDependent
Reactions
Calvin
Cycle
ATP
NADPH
O2
Sugars