Published on July 24, 2014
Chemistry of Photosynthesis: To understand guide to photosynthesis, including chemical equations of what goes on and an explanation for each of these chemical reactions Chemistry of Photosynthesis PowerPoint Presentation: Photosynthesis is a process that many plants use to produce energy for themselves. It also takes place in some other living organisms such as algae but it takes place in plants the most. Photosynthesis takes place in the chloroplasts (an organelle in the plant cell) of the plant, usually the ones in the leaves. The chloroplasts contain chlorophyll. Chlorophyll is what absorbs the light energy into the plant so it plays an essential role in the process of photosynthesis. PowerPoint Presentation: The process of photosynthesis involves many different chemical reactions, each triggering the next reaction along the line. Photosynthesis in plants involves the conversion of light energy, water and carbon dioxide into glucose and oxygen. The glucose is used by the plant as energy so it can survive. The water is usually absorbed by the plant through its roots while the light energy (photons) and carbon dioxide are absorbed by the plant through its leaves. A popular simplified equation of how photosynthesis works is: 6 CO 2 (g) + 12 H 2 O (l) + photons -> C 6 H 12 O 6 (aq) + 6 O 2 (g) + 6 H 2 O (l) PowerPoint Presentation: In total, there are two main steps in photosynthesis. The first step is where the light energy is used to high energy molecules such as ATP (Adenosine Triphosphate) and NADPH (Nicotinamide Adenine Dinucleotide Phosphate). ATP is a substance which is part of the animal and plant cells and helps provide the cell with energy. The above step is usually called Light Reactions. The second step, the Calvin-Benson Cycle, involves the ATP and NADPH produced in step 1 being used to turn the carbon dioxide absorbed by the plant into G3P (glyceraldehyde 3-phosphate). When two molecules of 3GP join together, it forms glucose. PowerPoint Presentation: Step 1: - the chlorophyll absorbs the photons (light). In doing so, the chlorophyll loses one electron. This causes a chain reaction and starts a flow of electrons through various substances until NADP + is reduced to NADPH (NADP gains one electron which was lost by the chlorophyll – NADPH is reduced form of NADP + while NADP + is the oxidized form of NADPH – OILRIG ). This process also helps create ATP. The water then turns into oxygen gas. The hydrogen in NADPH comes from the water molecule as well. ADP (adenosine diphosphate) and Pi (inorganic phosphate) are chemicals involved in the formation of ATP. The formula for this is: 2 H 2 O + 2 NADP + + 2 ADP + 2 Pi + light → 2 NADPH + 2 H + + 2 ATP + O 2 PowerPoint Presentation: Step 2: - of photosynthesis, the Calvin-Benson Cycle, is where the NADPH and ATP molecules undergo a process called carbon fixation on the carbon dioxide gas absorbed by the plant. The carbon dioxide is chemically reduced into the precursors of carbohydrates. In this reaction, the enzyme RuBisCo captures carbon dioxide from the air. Then ATP and NADPH turn it into G3P [glyceraldehydes 3-phosphate or C 3 H 5 O 3 -(PO 4 )]. Water is also involved in the reaction, helping form G3P (hydrogen in G3P is from water). The other molecules produced in this reaction like H + , NADP + , ADP and Pi are recycled and used again in step 1 of photosynthesis while the G3P combines with another one so that it has a full outer shell of electrons. This product is sugar. The equation for this is: 3 CO2 + 6 NADPH + 5 H2O + 9 ATP → C3H5O3-PO3 2- + 2 H + + 6 NADP+ + 9 ADP + 8 Pi Mechanism of light phase reaction: -: When the sun light falls on the leaves, the chlorophyll present in the leaves absorbs light photons and becomes excited. This photo excitation results in the displacement of an electron from the normal orbit (of chlorophyll) into a new orbit. If the same electron is returning, the process is termed as cyclic transfer of electrons. However, if the different electron is returning, it is termed as non-cyclic transfer. Mechanism of light phase reaction: - PowerPoint Presentation: The above electrons are captured by Plastoquinone Energy from ATP helps to move the electron from NADPH 2 to phosphoglyceric acid and into the carbon cycle. Cyclic electron transfer: - The expelled electron from the chlorophyll molecule is first accepted by ferredoxin or by another electron acceptor of chloroplast. The electron then traverses via cytochrome b 6 and cytochrome f, the two native cytochromes of chloroplasts and ultimately reaches the original chlorophyll molecule from which it has been expelled. PowerPoint Presentation: This scheme of electron transport is called cyclic photophosphorylation. In the cyclic photophosphorylation the electron that is returned to the chlorophyll, is the same as the one that was expelled. In cyclic photophosphorylation energy is released during the transfer of electrons to cytochromes and the released energy is utilized to synthesize ATP.