The Overview:
Cell must complete all the chemical reactions required to keep you alive. Even when you are sleeping your body is busy. Your body has to break down food to obtain energy rich carbohydrates which are further broken down so cells can obtain their energy. Twenty-four hours a day, your body works to keep you alive by carrying out a series of chemical changes. The combination of all these chemical changes that take place in an organism is called metabolism. Metabolism is the total chemical activity of a living organism that ultimately produces and consumes energy. Energy continually flows between the anabolic pathway of photosynthesis to the catabolic pathway of cellular respiration.
The Summary:
Photosynthesis is not a single chemical reaction, but rather a set of chemical reactions. In plants, photosynthesis is used to convert light energy from sunlight into chemical energy (glucose). Carbon dioxide, water, and light are used to make glucose, oxygen, and water.
The Setting:
Photosynthesis usually occurs in the leaves. This is where plants can get the raw materials for photosynthesis all in one convenient location – because leaves contain the chloroplasts inside their cells. Chloroplasts are complex organelles that capture light energy from the sun. There are two main parts to chloroplasts: thylakoids and stroma. The thylakoids themselves are made up of stacks that are called grana. The grana contains light-absorbing pigments such as chlorophyll. A group of chlorophyll molecules make up a photosystem that along with ferrodoxintransfer electrons and energy. The stroma is the dense liquid that makes up the rest of the chloroplast.
The Players:
Photosynthesis makes glucose from water and carbon dioxide. Glucose (C6H12O6) is a carbohydrate because it only contains carbon, hydrogen and oxygen. Glucose can join other simple sugars to form larger molecules or it can be broken down to make ATP, the most important biological molecule. You need to use 6 molecules of carbon dioxide to make one molecule of glucose because there are six atoms of carbon in glucose. On the way to making glucose, the cell makes a molecule containing 3 carbons called Glyceraldehyde 3-phosphateor G3P. The breakdown of ATP to ADP (which has one less phosphate group) releases energy for powering all cellular activities in organelles. Another fuel for the cell is NADPH which also stores energy in bonds.
The Overview:
The process of photosynthesis is divided into two main parts: light dependent reactions and light independent or dark reactions. The light dependent reaction happens when solar energy is captured to make a molecule called ATP (adenosine triphosphate). The dark reaction happens when the ATP is used to make glucose (the Calvin Cycle). The light-dependent reactions produce the reactants that the light-independent reactions need. This is just like the relationship between photosynthesis and cellular respiration.
Act One:
Different pigments in the chloroplast absorb different wavelengths or colors of light which starts the light-dependent reactions. The light energy excites and splits water into a proton (H+ ion), an electron and oxygen gas. The excited electrons move to an electron acceptor molecule in the thylakoid membrane which keeps on moving with the aid of photosystemI until it reaches a ferrodoxin. Ferrodoxin transfers the electrons to charge the electron carrier NADP+ forming NADPH. Then when protons move across the channels in the thylakoid membrane,ADP is converted to ATP. Although NADPH and ATP provide cells with large amounts of energy, these molecules are not stable enough to store chemical energy for long periods of time and are quickly passed to the Calvin Cycle to support the reduction reactions required to convert CO2 into carbohydrate.
Act Two:
In the stroma of the chloroplasta series of reactions, called the Calvin Cycle, turn carbon dioxide into a carbohydrate - glucose. This is accomplished in a complicated series of reactions, some of which require energy (ATP) and some of which require “reducing power” (hydrogens). These are, of course, supplied by the light-dependent reaction. Each Calvin Cycle used6 CO2which attach to a compound containing 5 carbons to form 12 compounds each containing 3 carbons. The 3carbon containing compounds use energy (12 ATP) and 12 hydrogen ions from NADPH to form 12 G3P molecules. Some of the G3P molecules leave the cycle and the rest use more ATP to become a molecule with 5 carbons and the cycle can continue. The joining of carbon dioxide with other organic molecules is called fixation so the Calvin Cylce is often referred to as carbon fixation.