Presentation on theme: "Cellular Energy Photosynthesis & Respiration Part 1: Photosynthesis."— Presentation transcript:
Cellular Energy Photosynthesis & Respiration Part 1: Photosynthesis
Photosynthesis It is the process that converts sunlight energy into chemical energy stored in the form of organic compounds (like glucose) Equation: The CO 2 is drawn in from the surrounding air through the stomata, while the water is pulled up from the roots and travels through the xylem. Light is absorbed by the chlorophyll. The glucose (carbs) will be transported around the plant by the phloem for a variety of uses (cell respiration, cellulose and starch formation, etc.) and the O 2 will either be eliminated into the air, or some is use in cellular respiration. 6CO 2 + 6H 2 O +light ---> C 6 H 12 O 6 + 6O 2
Photosynthesis Occurs in the chloroplast of plant cells The first half of the reaction occurs in the thylakoid (multiple thylakoids form a granum); the second half happens in the stroma (fluid) Utilized by autotrophs (plants, algae, some bacteria)
Photosynthesis: Major Steps of the Light Dependent Reactions Light-Dependent Reactions (Light Reactions) Sunlight strikes chlorophyll a located in the membrane of the thylakoids in Photosystem II.This excites the electrons in the chlorophyll. Energized electrons from the chlorophyll move through a chain of proteins in the thylakoid membrane called the electron transport chain. Here they go through a series of oxidation reduction reactions, losing energy as the move through the chain. As they lose this energy, they are pumping H+ into the thylakoid from the stroma (fluid surrounding the thylakoids). At the same time, light is hitting a different chlorophyll a location in Photosytem I. The electrons as excited here as well and move from the chlorophyll molecule through a series of proteins also called an electron transport chain. (This ETC is simply in Photosystem I, not Photosystem II.) The electrons from Photosystem I, move through the ETC, moving closer to the top of the membrane which is near the stroma. Eventually, they reach the end, and each joins with an energy carrier called NADP + and a H +. They form a high energy energy carrier called, NADPH.
Photosynthesis: Major Steps of the Light Dependent Reactions At the same time, energy is from the light is being used to split water molecules (located inside the thylakoids) apart into 2 H +, 2 electrons, and O (photolysis), releasing oxygen (More than 1 water is needed to make O 2 ). Those electrons combine with the chlorophyll a in Photosystem II, to replenish the electrons that were lost when the process started. This allows the light to strike the molecule of chlorophyll a PSII again, allowing its new electrons can be become excited and start the process all over again. The electrons that were originally in PSII, reach the end of the ETC and join with the chlorophyll a molecule at the beginning of PSI, which allows the second half to start all over again as well. (Refer back to bullet point 3) The electrons were using their energy to pull H + into the thylakoid, and water was just split releasing H + there as well. This makes the inside of the thylakoid positive when compared to the outside. This gradient represents potential energy. This energy is harnessed by an enzyme called ATP synthase. ATP synthase is located in the thylakoid membrane. It is used to create ATP by attaching a P to ADP. The potential energy is being converted into chemical energy, ATP, when ATP synthase pushed a H + out of the thylakoid into the stroma. ATP is created. 5
6 Photosynthesis: Major Steps of the Light Independent Reactions Light-Independent Reactions (Calvin Cycle, Dark Reactions) The ATP and NADPH produced in the first step are used in this step which occurs in the stroma of the chloroplast. Carbon dioxide is taken in from the air through the stomata. In this step, a series of enzyme assisted reactions occur to create 3-carbon organic compounds. The incorporation of the CO 2 into forming an organic compound is called carbon fixation. The carbon in the CO 2 is “fixed” (converted) into a new molecule. A series of reactions will take 3 CO 2 molecules and arrange them into a variety of 3-carbon molecules along the path of the cycle. The energy stored in the ATP and NADPH are used to create the 3-carbon product, converting them back into ADP and NADP + to be used again in the light dependent reactions. The key thing to note, is that at the end glucose has NOT been made. A 3- carbon organic molecule has left the cycle. Two complete cycles will release 2, 3-carbon molecules (hence the 6 carbon found on glucose.) Some of these will combine to form glucose for cellular respiration, some will form starches, and many can come together to form complex carbs such as cellulose. They can be used to form a variety of organic material.