Download Ch. 8 Photosynthesis

Photosynthesis and Cellular Respiration!
C-8-1
Remember! – We get our energy from cellular respiration!
Photosynthesis and cellular respiration form a cycle that
links organisms to each other and the environment.
The products of one make the starting materials for the
other:
Photosynthesis:
*C atoms pulled from the CO2 are used to form carbs
and other cds
*H+ atoms are pulled from H2O are used to power the
biochemical pathways to form the carbs etc.
(remember NAD+ - NADH)
*Leftover oxygen atoms form O2 as a byproduct.
So: CO2 +
H2O
+
light --------- CH2O +
O2
Cellular Respiration: (reverse of photosynthesis)
*H+ atoms pulled from carbs and joined with O2 to
form H2O
*Biochemical pathways breakdown the carbs and
organic cds – energy stored in these molecules
*C atoms are split from carbs and are linked with O2
to form CO2 as a by-product
SO: C6H12O6 +
O2 === CO2 + H2O + 36 ATP
Energy is stored in Carbon Compounds
Plants: ~ stored energy in carbs in leaves
~ transport carbs to all parts of plant = xylem
~ use sugar to make other things like proteins,
NA, lipids, and other carbs
~ excess sugar stored as starch for future use
Remember - we can't break down cellulose so we don't get
all of the energy out of plant that we could!
Crops - plants grown for human consumption
~ corn, rice, wheat
We get more than 1/2 of our energy needs from these
crops!
Investigating Photosynthesis
C-8-2
Several scientists contributed to the discovery of
how photosynthesis works...
1600's - Jan van Helmont:
~ wanted to find out if trees grew by taking
material out of the soil
Experiment ~ measured mass of seed and mass
of soil
~ added water periodically - re-measured
after 5 years
Result? ~ mass of tree changed, mass of soil
almost unchanged!
Conclusion ~ most of mass was gained by water
*however, this was not completely correct!
- accounts for "hydrate" part of
carbohydrate but not the "carb" part!
1700's - Joseph Priestley:
~ did another experiment to show another
product of photosynthesis
Experiment -~ placed a candle under a jar and
watched how the flame slowly went out.
~ reasoned that something must be keeping
the candle lit for a while - was O2
~ tried exper. with a live sprig of mint under
the jar for a few days...
Result? ~ the candle could be relit!
Conclusion ~ discovered that plants produce
the substance required for the candle to
burn... oxygen!
A few years later...Jan Ingenhousz:
~ showed the effect observed by Preistley was
happened only when the plant was exposed to light
These 3 scientists contributed to other scientist's
work whom discovered that plants produce carbs
and O2 in the presence of sunlight and CO2
Photosynthesis
8-3
Takes place in 3 stages:
1.) Energy is captured from sunlight
2.) Light energy is converted to chemical energy
(ATP and NADPH)
3.) ATP and NADPH power the synthesis of
organic molecules using C from CO2
This process takes place in the chloroplasts in the
leaves.
Chloroplasts have many internal compartments and
features:
Chlorphyll is embedded in the thylakoid membrane!
Light!
~ form of radiant energy - transmitted
through waves and can travel through a vacuum
~ consist of tiny energy packets called photons
Electromagnetic spectrum:
As wavelength increases, the energy decreases!
Photon are either reflected or absorbed by an
object as they hit it, which causes it's color!
Then why are leaves green?
~ they absorb all other colors and reflect
green!
*Molecules have atoms that absorb light pigments!
*Chlorophyll is a pigment that absorbs mostly red,
blue, and violet light and reflects green
2 types: chlorophyll a and chlorophyll b
Other color producers are the carotenoids absorb mostly blue and green and reflect red,
orange, and yellow!
*These are responsible for the fall leaf colors!
They capture energy of different wavelengths
than chlorophyll!
Photosystems: - contain chlorophylls and
carotenoids an clusters an reside in the thylakoid
and the chloroplasts
Photosystem I:
~ boost e- to a higher energy level by
absorbing light with a wavelength of 700nm
Photosystem II:
~ boost e- by absorbing wavelength at 680nm
(higher energy)
Reaction center - area of a photosystem where the
e- is boosted and leaves the chloprophyll molecule
Light energy to chemical energy: "Light reaction"
Photo II actually happens first!!
~light comes in and hits PII and breaks up
molecules of H2O into H+, O, and e~O2 leaves as a by-product
~ e- gets an energy boost from the photon
at 680nm and then travels down the
ETC
~ along the way the e- gives energy to the
proton pump which pumps in H+ into
the thylakoid
~ e- reaches PI and gets another photon
boost at 700nm
~ e- travels down the second ETC an
leaves through the reducing protein to
meet up with NADP+ to become
NADPH (this goes to the Calvin Cycle
next)
~ The H+ that is built up in the inner space
of the thylakoid diffuses out through
the ATP synthase which is used to
convert ADP into ATP (ATP then goes
to the Calvin Cycle)
The Calvin Cycle
a.k.a. - light independent reaction
Photosynthesis equn is:
CO2
+ H2O

Balance the equation...
C6H12O6
+ O2
CO2
+ H2O

C6H12O6
+ O2
How this works...
*Use 6 CO2 mol. from atmosphere
*these combine w/(6)5C mol.  12 (3)C mol.
*12 mol. get converted to higher energy forms via
ATP and NADPH
*2 of the 3C mol. are removed form the cycle to
make sugars and other macromol.
*the other 10 mol. are converted into 6-5C mols to
be used in the next cycle