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on 18 December 2012

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Transcript of Photosynthesis

Photosynthesis By: Angel Tshakatumba Calum Ward Justine Bendico Intro As we all should know, photosynthesis is what a plant uses to create energy. “Photo” is the Greek word for “light” and “synthesis” is to “put together”, so photosynthesis means “putting things together with light”. This presentation will hopefully expand on what you already know, as well as give you some new insight. History of Photsosynthesis 1648 – 1782 1772 Joseph Priestley proved that plants “restored” air that fire took up when he placed a sprig of mint inside a closed container with a candle and found that the candle continued to burn. This discovery later helped Lavoisier isolate and identify oxygen gas. 1779 Jan Ingenhousz discovered that only the green parts of plants release oxygen and only when exposed to sunlight. 1804-1988 Exchanges of gases in plants is discovered scientists build upon each others discoveries, eventually complete uncovering the process of photosynthesis The Chloroplast Diagram As you already know, the chloroplast is an organelle found only in plant cells. Chloroplasts are where photosynthesis takes place, and cells containing chloroplast organelles are found in the ground tissue of plants. Let's take a closer look at the chloroplast. The Process Photosynthesis has two stages; the light dependent stage (or, the light stage), and the light independent stage (or, the dark stage. Light independent is more correct, as it does not necessarily have to be dark). Light Dependent
Stage If that confused you The Light Independent Stage Applied Trivia For the sake of time, this will only cover major breakthroughs. The following discoveries formed the basis for scientists to discover what we know today. 1862-1864 Julius Sachs works out the overall equation of photosynthesis: 6 CO2 + 6 H2O + solar energy C6H12O6 + O2 1905 F.F. Blackman and G.L.C. Matthaei Find a temperature-dependent, but light-independent as well as a light-dependent, but temperature-independent reaction. They theorized a two-step mechanism involving a photochemical (or light reaction) and a non-photochemical with a high temperature coefficient (indicating an enzymatic reaction). 1932 Emerson and Arnold conclude that the products of photosynthesis are not determined by the amount of chlorophyll molecules capturing light, but by the number of enzyme molecules carrying out light independent reactions. 1945-1957 Melvin Calvin and his colleagues determine the pathway by which CO2 becomes carbohydrates, naming it the Calvin cycle. The chloroplasts general purpose is to use photosynthesis to create sugars and starches for the plant. The energy from the sun's light triggers and is used to combine Carbon Dioxide (CO2) with water creating sugar and oxygen. The chloroplast has two membrane to protect its interior. Inside the chloroplast is the stoma where reactions occur and sugar is created. A stack of thylakoid is called a grana. Connecting the granum of the chloroplast are lamallae. These act as a skeleton, keeping the granum held together and at the safest, most efficient distance from each other. The lamallae and the granum are bordered with chlorophyll. Thylakoids are the site of the light dependent stage of photosynthesis, and the stroma the site for the light independent stage. Basically, Carbon Dioxide gas (CO2) is reduced into carbohydrates through a complex set of reactions. The electron that makes these reactions possible comes from
water. The energy to start the process is provided by light, which was absorbed by chlorophyll pigment on the outside of the thylakoid where all this is taking place. Leaves are green because of chlorophyll, but not because chlorophyll is green. Chlorophyll and carotenoids pigments absorb the other colors of light, leaving green to either pass through or be reflected by the light. When these pigments are no longer needed and are discarded, we are able to see the light they normally would absorb.
Banana's turn yellow for this reason as well. A photon from the sun's light is absorbed by a molecule of chlorophyll, the energy of which is passed on to an electron "exciting" it. This is the term used when an electron receives energy but has no where to put it. The excited electron goes through the electron transport chain, where after a long and very, very complex set of reactions involving enzymes and electrion carriers, we end up with ATP and NADPH. The knowledge gained from breaking down the photosynthetic process has been used to create solar panels, harnessing the suns energy and converting it into electricity. Solar panels are used in calculators with or instead of batteries. The light independent stage converts the products of the light dependent stage into energy the cell can use, as well as enzymes to be re-used when the cycle starts over.
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