How Cells Acquire Energy
light
12 H20 + 6CO2
6O2 + C6H12O6 + 6H2O
The
process of converting
sunlight energy into chemical
energy.
The sun is the primary source of
energy – either directly or
indirectly.
It is used by plants, protists,
algae, and some bacteria.
Photosynthesis
performance
depends on the earth’s
atmosphere and climate.
CO2 buildup could have a
profound impact on PS in the
future.
Joseph
Priestly showed that plants
release air that allows combustion
Jan Ingenhousz showed that sunlight
was necessary for photosynthesis and
that only the green parts release
oxygen.
Jean Senebier showed that CO2 is
required for growth
To
understand photosynthesis,
you must first understand light.
We are only able to perceive
light within the visible
spectrum: Red, Orange, Yellow,
Green, Blue, Indigo, and Violet.
(ROYGBIV)
Above
it (with longer
wavelengths) are infrared (heat),
microwaves, and radio waves
Below
it (with shorter
wavelengths) are UV, Xrays, and
Gamma rays
Light
is seen as a reflection off of
an object.
The object will absorb all colors,
and the one that is not absorbed
is the one that can be seen.
Chlorophyll
and other
pigments are designed to use
the light it absorbs, and reflect
light that cannot be used
effectively
Chlorophyll
a – appears green.
Absorbs blue-violet and red.
Chlorophyll b – appears green.
Absorbs red-orange and blue.
Carotenoids – appear red,
orange, and yellow. Absorbs
blue-violet and blue-green.
 Found
in plant
cells
 Stroma: fluid that
fills inside
 Thylakoids: diskshaped
interconnected
sacs
 Grana: stacks of
thylakoids
2
reactions
• Light Dependent
Photosystem II
Photosystem I
• Light Independent (Calvin
Cycle)
Occur
in the thylakoids of the
chloroplasts during times of light
Purpose is to absorb sunlight
and convert it to ATP that can be
used in the Calvin cycle.
The
pigments in the thylakoid
space organize themselves into
PHOTOSYSTEMS
Photosystems
contain
combinations of chlorophyll a
and b and also other pigments
called phycobilins, and
carotenoids (they help pick up
other wavelengths of light)
Photons
split water molecules
producing O2
When chlorophyll is hit by light,
the electron produced from the
split is elevated to a higher
energy level (it is "excited")
The
excited electron is then
passed to a PRIMARY
ELECTRON ACCEPTOR of the
Electron Transport Chain as
begins to travel down the ETC.
Energy provided in the ETC is
used to make ATP from ADP
Photons
(again) boost electrons
to a higher energy state
electrons travel down another
electron transport chain,
Energy is used to make NADPH
from NADP.


Sunlight enters the chloroplast
in the thylakoids. Pigments
absorb the light energy and
release excited electrons.
Water molecules are split, ATP
and NADPH are formed, and
oxygen is released
The
ATP and the NADPH of the
light dependent reactions are
used for the next main step, the
Calvin cycle (Light independent
reactions)
Calvin
Benson Cycle
The enzymes that catalyze the
reactions of the Calvin Benson
Cycle USE the energy in ATP
and NADPH, produced in the
thylakoids by the light reactions,
to reduce CO2 to sugars.
Occurs
in the stroma in the
chloroplast
The Calvin Cycle is named after
Melvin Calvin the American
scientist who worked out the
details of the pathway.


The function of this pathway is
to produce a single molecule
of glucose (C6H12O6)
To accomplish this, the CB
cycle must repeat 6 times and
use 6 CO2 molecules.
3
phases:
1.Carbon Fixation
2.Reduction
3.Regeneration of RuBP
Carbon
dioxide is fixed or
attached to a 5-carbon sugar
called RuBP, producing a 6carbon compound rubisco.
Each unstable 6 carbon
molecule splits into 2 (3 Carbon
compounds) known as PGA.
 ATP
and NADPH are then used to
convert PGA to PGAL.
 PGAL is VERY energy rich!
2
PGAL can be removed from
the cycle at this point and used
for the formation of larger
carbohydrates such as glucose,
sucrose, and starch.
The other 10 PGAL are kept in
the cycle for the next
step….regeneration
ATP
used to convert PGAL to
RuBP – which is what we need to
start the Calvin Benson Cycle
again.


Enzymes attach CO2 to RuBP (5
carbon compound) to make
rubisco (6 carbon compound)
Rubisco is unstable and splits
into 2 PGA (3 carbon
compound)
PGA
accepts a phosphate from
ATP to make PGAL
2 PGAL combine to make
glucose
10 PGAL recycled to form RuBP
to start cycle over.
Light
quality
Light intensity
Light Period
Carbon dioxide availability
Water availability
 http://www.sciencebuddies.org/mentoring/pr
oject_ideas/HumBeh_img019.gif
 http://www.daviddarling.info/images/chloropl
ast.jpg
 http://www.biologycorner.com/resources/light
-dependent.gif
 http://www.biologycorner.com/bio4/notes/ph
otosynthesis.html
 http://www.biologycorner.com/bio4/notes/ph
otosynthesis.html