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02.06 Introduction to Photosynthesis
Transcript of 02.06 Introduction to Photosynthesis
In Module 2 Lesson 6, I have learned about the process of photosynthesis. During photosynthesis, there are two different stages of reactions; light-dependent reactions and light-independent reactions. Sunlight, water, and carbon dioxide are used in photosynthesis, but in this presentation I will focus only on a carbon atom's journey through this process, cellular respiration, and the transition between the two. The carbon atom we will observe is named Connie.
Light-independent reactions occur after light-dependent reactions. They use chemical energy from that previous stage of photosynthesis (ATP and NADPH) and carbon dioxide to build energy storage molecules like glucose. These molecules are more stable and long-term then ATP and NADPH. Then, Connie the carbon atom enters the cycle from the atmosphere. An enzyme from the chloroplast's stroma combines her with other carbon-based molecules, making her part of a three-carbon compound. She and the other parts of the compound are put through different reactions where they are broken down, so some of the atoms around Connie are removed from the carbons. Energy from ATP and NADPH are used here. The molecules at the end of these reactions still have a three-carbon chain, but Connie has changed so she is now different. 12 three-carbon molecules are made, and then 2 (including Connie) out of that are removed to build organic compounds; the rest continue in the cycle. The 2 removed molecules are bonded to make a six-carbon molecule, like glucose. Connie has gone from one singular carbon atom to a six-carbon molecule.
In summary, light-independent reactions use six carbon dioxide molecules to make one six-carbon molecule, which ATP and NADPH provide the energy for.
Photosynthesis begins with the light-dependent reactions. They occur within thylakoids in chloroplasts. Chlorophyll absorbs sunlight, giving off high-energy electrons. Those electrons go through a series of electron transport carriers called electron transport chains that are inside of the thylakoid membranes. Then the proteins use some energy from the electrons to extract hydrogen ions from the stroma (gel-like fluid inside chloroplasts). These hydrogen ions build up in the thylakoid space and then are moved by diffusion back to the stroma through ATP synthase, a protein channel in thylakoids. As this occurs, the ions bond a phosphate group to an ADP molecule to form ATP. This will be important to Connie later, in the light-independent reactions.
At the transport chain's ending, NADP+ molecules pick up the high-energy electrons, originally absorbed from the sun, and hydrogen ions and transform into NADPH molecules, which can carry the important electrons into the light-independent reactions stage of photosynthesis. For this to happen again, the hydrogen ions and high-energy electrons are replaced. A water-splitting enzyme takes electrons from water molecules collected by the plant and gives them to chlorophyll molecules. This process splits the water molecules apart into hydrogen ions and oxygen. Oxygen is released by the plant into the air, and the hydrogen ions and chlorophyll can now be used for new cycles of light-dependent reactions (where Connie comes in).
In summary, the light-dependent reactions trap the sun's energy and form ATP and NADPH molecules, and releases oxygen into the atmosphere.
Glucose and oxygen are the reactants of cellular respiration. During this process, this is where the formula happens and Connie becomes a carbon atom again. She is then released from the organism and can start the entire process over again, being absorbed from the air by a plant and combined with water and solar energy to make photosynthesis happen.
Connie and Light-Dependent Reactions
Connie and Light-Independent Reactions
From photosynthesis to Respiration
Photosynthesis converts sunlight into stored chemical energy. Cellular respiration takes that chemical energy and converts it to ATP, energy that can be used directly by the cell. Since Connie had been turned into a glucose molecule, she can now be transformed by cellular respiration into ATP because the products of photosynthesis are the reactants of cellular respiration. Glucose (Connie) and oxygen are combined to make carbon dioxide, water, and energy (both ATP and heat). In this way, Connie has now returned to her original state as a carbon atom.
This is a representation of Connie during light-dependent reactions.
This is a representation of Connie during light-independent reactions.
Photo credit: http://prezi.com/yd5pics2kdwl/the-carbon-atom-in-photosynthesis/
Photo Credit: http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%2010/chap10.htm
This diagram shows a representation of Connie and how she would go from photosynthesis to cellular respiration.
Photo Credit: http://mrbouyer.com/Mr_B_Place/Mr_B_Science/daily_lessons/bcell1.htm
This image shows the process of cellular respiration and how Connie would fit into the process.
Photo Credit: http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/bio%20101%20lectures/cellular%20respiration/cellular.htm