Most students in plant science at this point in their careers will have a basic idea that light is very important to plants for a number of reasons. One of which is that it is important to plant growth. Plants need light. A little over 300 years ago, in one of the first carefully designed biological experiments ever reported, the Belgian physician Jan Baptista van Helmont (1577-1644) offered the first experimental evidence that soil alone does not nourish the plant. Van Helmont grew a small willow tree in an earthenware pot, adding only water to the pot. At the end of five years, the willow had increased in weight by 74.4 kilograms, whereas the earth had decreased in weight by only 57 grams. He incorrectly concluded that that all the substance of the plant was produced from the water and none from the soil or air! Toward the end of the eighteenth century, the English scientist Joseph Priestly (1733-1804) reported that he had accidentally hit upon a method of restoring air that had been injured by the burning of a candle. A living sprig of mint turned air that would not support a candle into air that would. Later Jan Ingenhouse showed that this process required sunlight. All horticultural plants, except edible mushrooms, require light to complete their life cycles. Through the process of photosynthesis, plants convert light energy into chemical energy, which they use for growth, development, and the maintenance of life. Light is also important to plants for pigment (color) formation, plant growth habit, plant shape, plant size, flowering, fruiting, seed germination, onset of dormancy, onset of plant hardiness, leaf movements, formation of storage organs, autumn coloration, and defoliation of temperate zone trees.
Photosynthesis lecture part 1
Photosynthesis Edgar Lee Masters. 1916. Spoon River Anthology “ Now every gardener knows that plants grown in cellars Or under stones are twisted and yellow and weak.”
What Organisms Photosynthesize? Purple Photosynthetic Bacteria Cyanobacteria Green Plants
Review of Photosynthesis Basics <ul><li>6CO 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O </li></ul><ul><li>Through this process over 150 billion metric tons of sugar are estimated to be produced worldwide </li></ul><ul><li>Energy from the sun processed mostly by chloroplasts in eukaryotic cells drives most life on the planet </li></ul>light
Overview of the next 2 lectures. <ul><li>Conversion of Light Energy to Short-Term Chemical Energy (light-dependent reactions) </li></ul><ul><li>Short-term Chemical Energy + CO 2 used to produce CHOs which can be stored to supply energy for plant function (light-independent reactions) </li></ul><ul><li>Customizing the process, implications of C 3 , C 4 , and CAM carbon fixation </li></ul>
Summary of Light Dependent Reactions <ul><li>Sunlight energy captured by reaction centers </li></ul><ul><li>Energy from excited electrons used to form NADPH 2 . </li></ul><ul><li>Proton gradient that form between the thylakoid lumen and stroma used to drive the formation of ATP </li></ul>