Chapter 8 Photosynthesis
Every living system except archebacteria is dependent on photosynthesis
First experiment dealing with photosynthesis:
J.B. Van Helmont (1577-1644)
-he had a willow tree that weighed 5 lbs.
-he placed it in a bucket with 200 lbs of earth
-he covered the roots and added water only - that was it!
-5 years later the willow weighed 169 lbs 3 oz.
soil weighed 199 lbs and 14 oz
-the assumption was that the water changed into the
tree
Photosynthesis: process that is responsible for the recycling
of carbon.
CO2 only .03% of the atmosphere
CO2 taken up by plants via photosynthesis which yields food for
growth and energy
-animals eat the plant and use the carbon for growth
When animals and plants die they decay and CO2 is released
Carbon is constantly recycled
DR. BARSTOW READ AN ARTICLE WHICH WILL APPEAR ON THE INTERNET (AT THE
END OF THIS DAY'S NOTES) AND IS AVAILABLE IN THE BLC
ATP very important for photosynthesis
SESEE FIGURE 8.2 PG. 139
Electromagnetic Spectrum
-shorter wavelength contains more energy
-Visible light
-measured in nanometers
-violet light contains more energy than red light
When light strikes an object it:
1) transmitted (goes through it)
2) reflected (bounces off it)
3) absorbed
White light occurs when all wavelengths are transmitted
Black light occurs when all wavelengths are absorbed
Plants are green because they reflect and transmit the wavelengths they are
not using for photosynthesis.
Chlorophyll A and B absorb the red and blue wavelengths and
transmit green
-pigments (chlorophyll A and B) do the absorbing
- when chlorophyll breaks down in the fall, the carotenoids transmit
and reflect orange and yellow
Photosynthesis can be divided into 2 parts:
1) light reactions
-take place in the thylakoids of the chloroplast
3 results
1) ATP produced
2) NADPH2 is produced
3) Oxygen is released from water (photolyssis)
2) Enzymatic Reactions or Light-Independent reactions
-takes place in the stroma
Results in:
A. Fixing of CO2 into forming sugars using ATP and
NADPH2 from light reactions
B. Called the Calvin Cycle
SEE FIGURE 8.6 & 8.7
guard cells control opening of stoma which allows CO2 to enter
-diffuses into chloroplast
-thylakoids stacks known as granum
-lamella connect thylakoids together
-space in between thylakoids is known as the stroma
Light Reactions:
-take place in thylakoid membranes
1) Light excites the chlorophyll which creates a lot of
energy
-energy used to move electrons
-a pair of electrons are removed from chlorophyll
-they are moved through an electron transport
system and generate NADPH2 from NADP
-reduce NADPH to NADPH2
2) Water is split (photolysis) into oxygen and 2 hydrogen
ions plus two electrons
-the electrons replace the electrons removed from
the chlorophyll in step 1
-oxygen is released
3) ATP formation by chemiosmosis
-hydrogen ions are pumped into the thylakoid interiors
-form a chemosmotic pH gradient
-the flow of the hydrogen ions out of the
thylakoid interior produces ATP
SEE FIGURE 8.10
AMERICAN SCIENTIST, 55,3,1967
The Saga of the Argon Atoms past, present, and future is revealed in the excerpt from a book by a former President of Sigma Xi and still the guiding spirit in the Grants-in-Aid of Research Program of The Society. Harlow Shapley, in Beyond the Observatory (222 pages; $5.50; Charles Scribner's Sons, 1966) in the second of the essays with a title "Breathing the Future and the Past" counts the atoms in a single deep breath and draws from his meditation a moral for "ingenious but short-sighted man." The essays reveal wit, wisdom, and charm, range from astronomy to practical sociology, from neutrinos to galaxies.
"Here today, gone tomorrow, are the atoms that we are now breathing. The atomic mixture remains uniform with respect to the three main components, by weight nitrogen 76 per cent, oxygen 23 per cent, argon 1 per cent. Near the earth's surface the nitrogen and oxygen are in molecular form: we symbolize them as N2 and O2. Near the top of the atmosphere these gases are in atomic form, N1 and O1, because the energy of sunlight breaks each molecule into two atoms. The argon of the atmosphere is always in atomic form, and its atomic weight and atomic motions are such that the earth's gravity does not permit its escape from the earth into interplanetary space. In the composition of the sun and most other stars hydrogen and helium together make up more than 99 per cent.
"Since about 1 per cent of your breath is argon we can determine approximately the number of atoms in your next argonic intake. The calculations are really rather simple and straightforward, but to some readers this dizzy arithmetic is repulsive and I shall simply state the results. In your next determined effort to get oxygen to your lungs and tissuesyou are taking in, besides the nitrogen and oxygen, 30,000,000,000,000,000,000 atoms of argon; in briefer statement 3 X 1019. (Count the zeros!) A few seconds later you exhale those argon atoms along with quintillions of molecules of carbon dioxide. The plants will appreciate your carbon dioxide molecules and make vital use of them when sunlight and chlorophyll do their magic of putting the carbon into the plant tissues and releasing the oxygen into the air where we breathing animals can use it for our living.
"A wonderfully effective cooperation is going on in this atomic exchangethe animals, such as you, breathe out carbon dioxide for the plants; the plants release oxygen for the animals, which again serve the plants with carbon dioxide, which then serve oxygen to the animals . . . A biological barter economics is in operation, with carbon and oxygen atoms serving as units of exchange, along with sunlight.
"If the plants were completely removed from the surface of the earth, the atmospheric oxygen would soon disappear because it would all be absorbed into the soil and rocks. With the oxygen decreasing, all the animals would gradually smother. On the other hand, if animal life were entirely removed from the earth, the plants would have to depend skimpily on the carbon dioxide of volcanoes and of organic decay. Animals and plants need each other vitally.
"Now let us follow the career of one argon-rich breathyour next exhalation, let us suppose. We shall call it Breath X. It quickly spreads. Its argon, exhaled this morning, by nightfall is all over the neighborhood. In a week it is distributed all over the country; in a month, it is in all places where winds blow and gases diffuse. By the end of the year, the 3 X 1019 argon atoms of Breath X will be smoothly distributed throughout all the free air of the earth. You will then be breathing some of those same atoms again. A day's breathing a year from now, wherever you are on the earth surface, will include at least 15 of the argon atoms of today's Breath X.
"This rebreathing of the argon atoms of past breaths, your own and others', has some picturesque implications. The argon atoms associate us, by an airy bond, with the past and the future. For instance, if you are more than twenty years old you have inhaled more than 100 million breaths, each with its appalling number of argon atoms. You contribute so many argon atoms to the atmospheric bank on which we all draw, that the first little gasp of every baby born on earth a year ago contained argon atoms that you have since breathed. And it is a grim fact that you have also contributed a bit to the last gasp of the perishing.
"Every saint and every sinner of earlier days, and every common man and common beast, have put argon atoms into the general atmospheric treasury. Your next breath will contain more than 400,000 of the argon atoms that Gandhi breathed in his long life. Argon atoms are here from the conversations at the Last Supper, from the arguments of diplomats at Yalta, and from the recitations of the classic poets. We have argon from the sighs and pledges of ancient lovers, from the battle cries at Waterloo, even from last year's argonic output by the writer of these lines, who personally has had already more than 300 million breathing experiences. Our next breaths, yours and mine, will sample the snorts, sighs, bellows, shrieks, cheers, and spoken prayers of the prehistoric and historic past.
"There was a time when very little argon existed in the earth's atmosphere, and practically no free oxygen at all. That was some billions of years ago. The oxygen has been built up to its present abundance on the earth by the breathing of green plants, and the argon, over the millennia, has grown to its present percentage as the result of the radioactivity of one of the isotopes of the potassium of the rocks. That radioactive decay steadily goes on. In 5 billion years our atmosphere will contain about twice as much argon as it does now.
"There ought to be a morale to this story of argon. It tells us of the dramatic smallness of the units of matter. It reminds us of the turbulence in that healthful gaseous envelope which we call our atmosphere. It associates us intimately with the past and the future. It argues that to live long and naturally we want to have in our atmosphere only salutary atomsoxygen, nitrogen, and argon. We do not want to have anywhere in our atmosphere the man-made atoms of strontium-90, iodine-131, and similar artifacts produced by ingenious but short-sighted man.
The moral could be: Respect your breath! Keep it decent!"