Transcript Bio392-8-3 - The Reactions of Photosynthesis-11

Section 8-3
A Look Into the Future
It is 100 years in the future and you are a research
scientist. An enormous volcanic eruption has recently
sent huge quantities of dust and ash into
the atmosphere.
Working with a partner, make a list of how this event will
affect each of the following:
1. photosynthesis
2. plant life
3. animal life
4. human societies
Chapter 8.3
The Reaction of Photosynthesis
The Chloroplast
•  Site of photosynthesis
The Chloroplast
• Inner membrane  thylakoid
– Highly folded so there is an increased surface area
for absorption of sunlight
• Stacks of thylakoids  grana
• Clusters of chlorophyll and other pigments 
photosystems
• Liquid filling of chloroplast  stroma
Electron Carriers
• A carrier molecule is a compound that can
accept a pair of high-energy electrons and
transfer them along with most of their
energy to another molecule
• Main electron carrier of photosynthesis
 NADP+
 Turns into NADPH when it is carrying
electrons
Photosystems
• There are two different groupings of
photosystems in photosynthesis
 Light dependent reactions
• Happens on the  thylakoid membrane
• Has 2 photosystems (II and I)
 Light independent reactions
• Happens in the  stroma
• Also known as the  Calvin cycle
Figure 8-7 Photosynthesis: An Overview
Section 8-3
Water
Chloroplast
CO2
Light
NADP+
Chloroplast
ADP + P
Calvin
Cycle
LightDependent
Reactions
ATP
NADPH
Sugars
O2
Light Dependent Reactions
•  Part of photosynthesis that requires
light
• Use light energy to produce ATP and
NADPH, as well as oxygen
Light Dependent Reactions
 Pigments of photosystem II absorb light
• Energy is absorbed by electrons
• High energy electrons are transferred to
the electron transport chain
– These electrons are replaced
by electrons produced by the
breakdown of water
• Water is broken down into  2 electrons,
2 H+ ions, and 1 oxygen atom
– Oxygen is released
– Hydrogen is broken apart and released
inside the thylakoid
Light Dependent Reactions
• The high energy electrons are
passed through the  electron
transport chain between
photosystem II to photosystem I
– The energy from the electrons is used
to transport H+ ions from  the stroma
into the inner thylakoid space
Light Dependent Reactions
 Light
hits the
electrons that
are now in
photosystem I
to excite them
again
Light Dependent Reactions
– These high energy electrons are picked up by NADP+
– The NADP+ also picks up the H+ ions to make NADPH
Light Dependent Reactions
• As the electrons move onto the NADP+,
 more H+ ions are pumped across the
membrane
– Eventually, the outside of the thylakoid
becomes negatively charged and the inside
becomes positively charged
• Difference in charge provides the energy to make
 ATP
Light Dependent Reactions
• Thylakoid membrane
contains an enzyme
called ATP synthase
 H+ ions pass through
it to synthesize ATP
– This energy will be
used to make energycontaining
carbohydrates
Light Dependent Reactions Video
• Part 1
• Part 2
Figure 8-10 Light-Dependent Reactions
Light Dependent Reactions
Section 8-3
Photosystem II
Hydrogen
Ion Movement
Chloroplast
ATP synthase
Inner
Thylakoid
Space
Thylakoid
Membrane
Stroma
Electron
Transport Chain
Photosystem I
ATP Formation
Light Dependent Reactions
Calvin Cycle Video
• Calvin Cycle
Light Independent Reactions
• Also known as the  Calvin cycle
• Plants use the energy that  ATP and
NADPH contain to build high-energy
compounds that can be stored for a long
time
•  Does not require light
Light Independent Reactions
•  Six carbon dioxide molecules enter the
cycle from the atmosphere to produce 1
6-carbon sugar
• As the cycle continues,  12 3-carbon
molecules are created
– These 3-carbon molecules obtain energy from
ATP and NADPH to become high energy 3carbon molecules.
Light Independent Reactions
• Two of the 12 3-carbon molecules are
removed from the cycle
– Used to make  sugars, lipids, amino acids,
and other materials needed for plant
metabolism and growth
– Rest of the 3-carbon molecules combine to
make  6 5-carbon molecules
Factors that Affect Photosynthesis
• Presence of water
 Lack of water slows down photosynthesis
– Plants also have evolved ways to help prevent water loss (waxy
covering on leaves)
• Temperature
 Enzymes function best at 0-35 degrees Celsius
• Intensity of Light
 Increasing light intensity increases the rate of photosynthesis
– There is a certain amount of light intensity where the amount of
photosynthesis within a plant does not change
Figure 8-11 Calvin Cycle
Section 8-3
CO2 Enters the Cycle
Energy Input
ChloropIast
5-Carbon
Molecules
Regenerated
6-Carbon Sugar
Produced
Sugars and other compounds
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
use
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
NADPH
O2
takes place in
Stroma
uses
ATP
NADPH
of
to produce
Chloroplasts
High-energy
sugars
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
use
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
NADPH
O2
takes place in
Stroma
uses
ATP
NADPH
of
to produce
Chloroplasts
High-energy
sugars