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Photosynthesis

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Photosynthesis is the process by which plants, some bacteria, and some protistans use the energy from sunlight to produce sugar and oxygen which cellular respiration converts into ATP, the "fuel" used by all living things. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll. Most of the time, the photosynthetic process uses water and releases the oxygen that we absolutely must have to stay alive. Oh yes, we need the food as well!

Photosynthesis doesn't just give oxygen to us, it gives food too. This is call an autotroph, an organism that produces its own food. An animal that eats the plants are called heterotroph, an organism that cannot produce its own food.

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If you wonder how carbon dioxide enters the plant, this is how it enters through the stomata, small openings on the undersides of the leaves.

The formula for photosynthesis is 6H2O + 6CO2 ---------->C6H12O6+ 6O2

Joseph Priestley, who do you think Joseph Priestly is? Joseph was the man who discovered photosynthesis.

JOSEPH PRIESTLEY

The great men of science of today stand on the shoulders of giants. Joseph Priestley was one such intellectual "giant" whose works laid the foundation for that branch of science which we now call Chemistry. Although Priestley is best known for his experiments with gases especially that which we now call oxygen, he was extraordinarily prolific in his writings on other areas of intellectual endeavors. He had important contributions in the fields of education, moral philosophy, theology, metaphysics, political economy, history and physical science.

Joseph Priestley was born at Fieldhead, in the parish of Birstal, not far from Leeds, in the northern English county of Yorkshire, on March 13, 1733 according to the Old Style Calendar, the Gregorian calendar not coming into use until 1751, after which he celebrated on March 24. He was the oldest of the six children - four sons and two daughters - of Jonas Priestley, a dresser and finisher of cloth and Mary Swift, a farmer's daughter. Mary, having children so fast, sent Joseph as an infant to live at his maternal grandfather's farm some miles away, returning to his father's house after his mother's death only to be adopted by his childless Aunt Sarah (Mrs. John Keighly, his father's sister) when he was nine. It was at the Keighly household that he was exposed to discussions of theological questions and to liberal political attitudes for many of the dissenting ministers of the neighborhood were welcome there. He remained with his aunt until her death in 1764.

During his boyhood, Joseph went to the local schools where he learned Greek and Latin at an early age, and during school holidays, Hebrew. In his mid teens he fell seriously ill with tuberculosis of the lungs, was forced to drop out of school, and for a time abandoned his plan of entering the ministry. As he gathered strength after his illness, he taught himself French, Italian, and German and learned Chaldean, Syrian and Arabic. Privately, he also learned the rudiments of geometry, algebra and mathematics.

Soon he was ready to pursue the goal of his boyhood, the ministry. By this time, however, he had started to question some of the orthodox tenets of the Calvinist faith. He decided not to go to the Academy at Mile End, where he would have been required to profess his loyalty every six months to ten printed articles of the faith. He went instead to the more liberal Daventry Academy.

At this time, Dissenting Academies became the center of liberal education since the doors of the great universities were closed to believers of nonconformist doctrines. The academy at Daventry offered Joseph the opportunity of learning the traditional subjects as well as natural and experimental philosophy. It was here that his interest in natural phenomena and experimentation was encouraged. But his dominant inclination was still towards theology. After Daventry, Priestley accepted his first position with a poor congregation at Needham Market in Suffolk where he remained for three years. He was not very successful in his ministry as his preaching was hampered by a serious speech impediment, and his popularity was diminished by his Unitarian tendencies. He was invited to preach at Nantwich, in Cheshire. The congregation there was more accepting of his unorthodox theology so he felt more welcome. His responsibilities expanded to that of schoolmaster and private tutor. The increased income enabled him to buy instruments that he needed for his original researches.

His success as a teacher in Nantwich opened the door to a post as tutor in "polite" and classical languages at a new Dissenting Academy in Warrington where he spent six happy years.

For the first time since his academic days, he found himself in sympathetic surroundings. His colleagues held the same opinions and shared the same ideals with him. If disagreement arose on any point, they looked on controversy as a means of discovering the truth, and not as a sign of moral reprobation. (3)

> It was there in 1762 that Priestley married Mary Wilkinson, daughter of John Wilkinson, one of the leading figures of the emerging Industrial Revolution in England. He described his marriage as

a very suitable and happy connexion, my wife being a woman of an excellent understanding, much improved by reading, of great fortitude and strength of mind, and of a temper in the highest degree affectionate and generous; feeling strongly for others, and little for herself. (6)

A month before his wedding, in anticipation of impending financial obligations, he applied for and was conferred ordination to the Dissenting ministry. His lectures on History and General Policy were his most important work while at Warrington. Through his lectures he attempted to introduce his students to wider realms. He expected his students to become familiar with political theory, laws, grammar, oratory and criticism. He acquainted them with Shakespeare, Milton, and other writers and poets of that time.

During his annual month-long visits to London, he joined the company of men who were known for their liberal politics and their rational dissent. Foremost among these were Richard Price, whose pamphlet, Civil Liberty, is said to have influenced the Declaration of Independence of the American Colonies, and Benjamin Franklin, whose friendship was crucial to his emerging scientific career. He was introduced to scientific society and encouraged to write The History and Present State of Electricity, which included original experiments and illustrations in copperplate. This led to his election as a Fellow of the Royal Society in 1766. Priestley's History was found to be too difficult for ordinary readers so he prepared a version that was more popular. This necessitated the inclusion of some drawings, but he could not find anyone who could do the work. Consequently he forced himself to learn the rules of perspective drawing, and since there was no book to help him with these, he published one himself. In the course of this work, he stumbled on the use of India rubber as an eraser of lead-pencil marks. The preface to his book contains the first printed reference to India rubber erasers.

Soon after, confronted with the obligations of a growing family, he decided to accept the invitation to minister to the concregation at Mill Hill. In 1767, he moved his family to Mill Chapel in Leeds, close to his birthplace.

Joseph Priestley is best known as the discoverer of oxygen. Perhaps a more appropriate description of this accomplishment would be to credit Priestley with the isolation of dephlogisticated air. Our thorough understanding today of the chemical reactivity of oxygen comes from Antoine Lavoisier's systematic theory of combustion. Priestley was an industrious and clever investigator, not a sweeping theoretician with a guiding program of research. In the realm of theory, Priestley's expertise lay in his disputatious and prodigious command of theology, rather than in his chemical prowess. His adherence to the phlogiston theory was persistent.

Priestley's work on electricity is eclipsed by his memorable experiments on air, which began in 1767 and peaked in 1774. The proximity of his house to a public brewery set the stage for many experiments on fixed air (carbon dioxide). Access to an abundant source of fixed air eventually led to an understanding of the nature of the effervescence found in mineral waters such as those of Spa, a resort in Belgium. Restorative sparkling beverages and baths were simply water containing fixed air. His first scientific publication was on the impregnation of water with fixed air. This achievement won for him the prestigious Copley Medal of the Royal sociecty. The carbonated beverages of today trace their origin to Priestley's initial experiments.

Experiments on air in the eighteenth century posed challenges to the natural philosopher. Today we unhesitatingly regard air as a solution of gases and confidently understand the chemical and physical properties that distinguish one colorless gas from another. However, centuries ago there was considerable confusion. In Priestley's time air was subjected to only simple tests of appearance, odor, and solubility. Any differences could have been real or, depending on the purity of the samples, caused by contamination. Modern gaseous elements and compounds were known as types of air: nitrous air (NO), phlogisticated air (N2O), acid air (HCl), and reduced fixed air (CO). The "goodness" of air, a measure of its respirability, interested Priestley. In 1771 he noted the restoration of "injured" or depleted air by green plants. He wrote,

The injury which is continually done to the atmosphere by the respiration of such a large number of animals...is, in part at least, repaired by the vegetable creation. (5)

This balance between animal and plant kingdoms is particularly relevant to our present environmental concerns over global warming and rainforest destruction.

Joseph Priestley simplified experimental techniques for the preparation and collection of gases. His pneumatic trough of 1772 was an admirable apparatus. Gases soluble in water, previously difficult to collect, were collected successfully over mercury. In Wiltshire, England, on August 1, 1774 Priestley focused sunlight through a lens in order to heat a sample of mercuric oxide (red calx). The resulting gas supported the burning of a candle with a vigorous flame, was essentially insoluble in water, and accommodated a mouse under glass for some time. In Priestley's own words,

I have discovered an air five or six times as good as common air. (5)

This "good" air, which accounted for about twenty per cent of atmospheric air, he named dephlogisticated air. In addition, he concluded that calcination imparted to a metal the ability to take this "good" air from the atmosphere. In 1874, one hundred years after this prominent experimental contribution to chemistry, Joseph Priestley was honored by a meeting which led to the founding of the American Chemical Society in 1876.

From Leeds, he had wanted to accompany Captain Cook, as a naturalist, on his second voyage. He was refused because of objections to his religious opinions. He subsequently accepted a position with William Petty, Earl of Shelburne as librarian and tutor to his sons. He was offered a generous compensation which provided for protection in case of his patron's death or of a separation, the use of a house at Calne, the Shelburne residence at Wiltshire during the summers, and as intellectual-in-residence, freedom and resources to engage in his many interests. He published his two major philosophical works, Disquisitions Relating to Matter and Spirit, a materialistic view of man and Experiments and Observations, which contained his major chemical achievements. The period from 1773 to 1780 were the most fruitful years of Priesley's career as a chemist.

Priestley accompanied Lord Shelburne on a tour of the continent. In Paris he met other members of the scientific world. With Lavoisier he spoke of his recent isolation of the gas from the red oxide of mercury, unaware of the importance of his discovery. This was the missing clue from which Lavoisier developed the grand conceptual scheme of the role of oxygen in burning, leading to the overthrow of the phlogiston theory and the revolutionizing of the whole science of chemistry.

Priestley withdrew from his position with Lord Shelburne amicably, with an annuity secure for the rest of his life. Wishing to resume his active ministry he settled at Fairhill, on the outskirts of Birmingham with his family, which now included three sons and a daughter. Among his benefactors were his brother-in-law John Wilkinson, who provided a house for his family, and Josiah Wedgwood, master potter, who supplied him with the funds he needed for his experiments. Also in Birmingham were Matthew Boulton (manufacturer of buckles and buttons) and James Watt, who together were preparing to manufacture the steam engine, Erasmus Darwin, grandfather of Charles Darwin, who is responsible for the theory of evolution, and William Small, a tutor of Thomas Jefferson at the College of William and Mary.

When Priestley arrived in Birmingham in the autumn of 1780, he joined the Lunar society which met at the home of James Keir. The Lunar Society was an informal group of a dozen or so men, sometimes referred to as the "Lunatics", who were interested in natural science and literature. Benjamin Franklin was a frequent guest. The society met once a month in one another's houses on the Monday nearest the full moon. This time was chosen so that the members could return to their homes by moonlight. These meetings were described in a note Darwin wrote to Boulton.

. . . what inventions, what wit, what rhetoric, metaphysical, mechanical, and pyrotechnical, will be on the wing, bandied like a shuttlecock from one to another of your troop of philosophers! (1)

Among his accomplishments during his years in Birmingham were the publication of the first part of Letters to a Philosophical Unbeliever, an attempt to defend natural religion against the skepticism of David Hume; a History of the Corruptions of Christianity, a direct attack on the central tenets of orthodox religion, particularly the doctrine of the Trinity; and a History of the Early Opinions Concerning Jesus Christ, where he set out to prove that the doctrine of the Trinity was not according to Scripture. These three works catalyzed storms of controversy. Priestley was attacked in pamphlets and periodicals, denounced in pulpits and in the House of Commons, and considered as an agent of the Devil because of his unorthodox views.

Under the Test and Corporation Acts in England, the Dissenter was deprived of the rights of citizenship, and , by law, the Unitarian was not even tolerated. When the French Revolution broke out, the sympathies of the Dissenters lay with those who were strugggling under the yoke of corruption, tyranny and opression. Two years later, festivities were planned to celebrate the auspicious event. On the 11th of July, 1791 a local newspaper printed an advertisement for a dinner to be held at a leading hotel on July 14,

to commemorate the auspicious day (Bastille Day) which witnessed the Emancipation of Twenty-six Millions of People from the yoke of Despotism . . .(1)

The dinner was attended by eighty one men and ended without incident. Dr. Priestley had declined to attend, to the disappointment of the crowd that had gathered to demonstrate their contrary views to Priestley's revolutionary and heretical writings. By evening, the crowd reconvened and, fueled by liquor, sacked and burned the New Meetinghouse where Priestley preached. The Old Meetinghouse was sacked and burned, too. Warned of the murderous multitude, Priestley and his wife left Fairhill, with nothing more than the clothes we happened to have on. They did not realize the magnitude of the danger they were in and stopped at a friend's house a mile away. There they received information that the mob was now at their house looking for them. They moved again a little farther away but not far enough for Priestley to be spared the sight of the holocaust that engulfed his home, his laboratory and especially his library which contained precious manuscripts of works, some of which were as yet unpublished.

Priestley fled to London and was never to return to Birmingham. He moved to Tottenham and then to Hackney. During the following months, Priestley was verbally attacked in the House of Commons, burned in effigy, portrayed in caricatures, denounced in pulpits and subjected to threatening letters. Priestley had by now become an honorary citizen of France which was at war with England. He was snubbed by the Royal Society and was forced to resign his membership when several of his colleagues turned against him. His sons were unable to find work in the area and decided to emigrate to America. He and his wife decided to join them. They sailed from Gravesend on the Samson on April 7, 1794, two weeks after Priestley's 61st birthday.

While the Priestleys were on their journey to America, Laviosier met his death at the guillotine in the Place de la Revolution. The Priestleys landed in New York and proceeded to the capital, Philadelphia. He refused the offer of a chair in chemistry at the University of Pennsylvania, choosing instead to join his son, Joseph, and friend, Thomas Cooper, who were establishing a colony for English Dissenters in central Pennsylvania. He moved 130 miles to the north and settled in the small town of Northumberland on the banks of the Susquehanna River. Within the year, the youngest Priestley son, Harry, died, as did Joseph's wife. Priestley remained active, writing, preaching and experimenting in his newly established laboratory, but the old fire and cheerfulness were gone.

Joseph Priestley missed his circle of friends and decided to spend the winter months in Philadelphia. As the founder of the first Unitarian church in America, his sermons were attended by then Vice President John Adams and other luminaries. When Adams became president, Priestley sided with the Jeffersonian opposition. Jefferson greatly admired Priestley and even consulted him for advice on the curriculum for the University of Virginia which he was planning to found. It was in Philadelphia, during Jeffereson's term, in 1801, that he suffered his first serious illness and nearly died.

During his last journey to Philadelphia he was honored by the Americal Philosophical Society in a testimonial dinner. He offered a benediction to his scientific colleagues in a manner that turned prophetic.

Having been obliged to leave a country which has been long distinguished by discoveries in science, I think myself happy by my reception in another which is following its example, and which already affords a prospect of its arriving at equal eminence. (7)

Although he never fully recovered his health, he continued work on his latest manuscript even when he could no longer rise to dress and shave himself. On February 5, 1804, he had all the children brought to his bedside, and after prayers spoke to each of them separately. He exhorted them all to continue to love each other .

. . . I am going to sleep as well as you: for death is only a good long sleep in the grave, and we shall meet again. (6)

The next morning, he asked his son and Mr. Cooper to bring him the pamphlets they had been working on and dictated clearly and distinctly the additions and alterations he wished to have made. He objected to Mr. Cooper's putting the corrections in his own language. He then repeated over again what he had said before and when done he said

That is right; I have now done. (6)

Half an hour later he was dead. He had put his hand to his face to prevent his son and his wife from observing his quiet departure. The date was February 6, 1804.

Bibliography
 
-Textbook and library books.
 
-Serach Engines like google and ask jeeves.
 
-Memory