Download Chapter 6: Photosynthesis

Chapter 6:
Photosynthesis
6-1: Capturing
the Energy in
Light
Energy for Life
Processes
Photosynthesis –
Series of chemical
reactions in which
the product of one
reaction is consumed
in the next reaction.
Energy for Life
Processes
Photosynthesis is
then labeled a
biochemical
pathway.
Photosynthesis
Organic Compounds
+ Oxygen
Autotrophs and
Heterotrophs
Autotrophs
Carbon Dioxide
+ water
Cellular
Respiration
Energy for Life
Processes
Plants use
photosynthesis to
manufacture organic
compounds from CO2
and water.
Energy for Life
Processes
Another product of
photosynthesis is O2.
Energy for Life
Processes
Both Autotrophs and
Heterotrophs
perform cellular
respiration.
Energy for Life
Processes
During cellular
respiration, organic
compounds are
combined with O2 to
produce ATP.
Energy for Life
Processes
CO2 and water are
also released.
Light Absorption in
Chloroplasts
Light Reactions –
The initial reactions
in photosynthesis
that begin with light
absorption.
Light Absorption in
Chloroplasts
Chloroplasts –
Light gathering
organelle contained
in autotrpohs.
Light Absorption in
Chloroplasts
White light from the
sun contains an array
of colors ranging
from red to violet.
Infrared
Ultraviolet
Light Absorption in
Chloroplasts
When white light
strikes an object, its
component colors
can be reflected,
transmitted, or
absorbed.
Light Absorption in
Chloroplasts
If the object contains
a pigment, the
various colors will
react differently.
Light Absorption in
Chloroplasts
Pigment –
A compound that
absorbs light.
Chloroplast
Pigments
Chlorophyll –
Light absorbing
pigment found in the
membrane of
thylakoids.
Chloroplast
Pigments
Chlorophyll a
absorbs red light
Chlorophyll b
absorbs blue light
Chloroplast
Pigments
Chlorophyll b is not
directly involved in
the light reactions
therefore is
considered an
accessory pigment.
Electron Transport
Photosystem I and
Photosystem II play
different roles in the
light reactions.
Electron Transport
The light reactions
begin with accessory
pigments absorbing
light.
Electron Transport
The acquired energy
is passed until it
reaches chlorophyll a
molecules.
Electron Transport
The events that
follow can be divided
into 5 steps:
Electron Transport
Step 1:
Light energy excites
electrons in
chlorophyll a
molecules of
photosystem II.
Electron Transport
Step 2:
The electrons move
to a primary electron
acceptor.
Electron Transport
Step 3:
The electrons are
transferred along the
electron transport
chain.
Electron Transport
Step 4:
Light excites
electrons in
photosystem I.
Electron Transport
Step 4:
As these electrons
move to an acceptor,
they are replaced by
electrons from
photosystem II.
Electron Transport
Step 5:
The electrons from
photosystem I go
through a second chain
+
to combine with NADP
to make NADPH.
Electron Transport
The electrons in
photosystem II are
replaced by the
splitting of water
molecules.
Chemiosmosis
The synthesis of ATP
through the use of
energy from the
excited electrons in
photosystem II.
Chemiosmosis
This ATP is then used
with NADPH to
provide energy for
the second set of
reactions in
photosynthesis.
6-2: The Calvin
Cycle
Carbon Fixation
In the Calvin cycle,
carbon atoms from
CO2 are bonded or
“fixed” into organic
compounds.
Carbon Fixation
There are 3 steps that
occur in the stroma
of the chloroplasts.
Calvin Cycle
Step1:
CO2 diffuses into the
stroma and
combines with a 5
carbon molecule
called RuBP.
Calvin Cycle
Step 1:
This makes a 6
carbon molecule that
immediately splits
into 2 3-carbon PGA
molecules.
Calvin Cycle
Step 2:
2 ATP and 2 NADPH
molecules combine
with PGA to form 2
PGAL molecules.
Calvin Cycle
Step 3:
Most of the PGAL is
converted back into
RuBP.
Calvin Cycle
Step 3:
To do this, more ATP
is needed.
Calvin Cycle
Step 3:
Some of the PGAL
leaves the cycle and
is used to make other
organic compounds
ADP
Organic
Compounds
ATP
Step 3
2 Molecules
of PGAL
P- C C C
RuBP
P- C C C C C -P
C C C -P
CO2
2 Phosphate
2
Step 1
NADP+
Step 2
2 NADPH
2 Molecules
of PGA
2 ADP
2 ATP
P- C C C
C C C -P
C
Balance Sheet for
Photosynthesis
CO2 + H2O + light energy 
(CH2O) + O2
6CO2 + 6H2O + light energy 
C6H12O6 + 6O2
Alternate Pathways
C4 Pathway –
Plants like corn,
sugar cane, and crab
grass use a 4 carbon
molecule to save
water.
Alternate Pathways
CAM pathway –
Cactuses, pineapples,
and others open
stomatas at night to
conserve water.