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 a C6H12O6 + O2
Balance the equation...
CO2 + H2O a C6H12O6 + O2
How this works...
*Use 6 CO2 mol. from atmosphere
*these combine w/(6)5C mol. a 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