Cell Processes

Photosynthesis, Cellular Respiration, and Fermentation

By Brittney Weeks


Photosynthesis is the process in which cells convert water, carbon dioxide, and sunlight into oxygen and glucose. Glucose is food for the cell that provides them with the nutrients they need to stay alive. Photosynthesis converts light energy to chemical change. This process takes place in the chloroplast of the plant cell.

The Stages of Photosynthesis

There are three main stages of photosynthesis. In stage one, energy is captured from the sunlight. In stage two, The light energy is converted into chemical energy and stored in either ADP or NADPH. in stage three, the energy that is stored is used along with carbon dioxide in the formation of organic compounds.
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Cellular respiration

Cellular Respiration is the process in which plant cells convert glucose and oxygen into carbon dioxide and water. This process takes place in the mitochondria of the cell. Cellular respiration is the release of energy that was made during photosynthesis.

Stages of Cellular Respiration- Glycolysis

There are two stages of cellular respiration. Stage one is the breakdown of glucose. In this stage, glycolysis occurs. Glycolysis is an anaerobic process that breaks down glucose by the help of enzymes. Glycolysis happens in many steps. First, two ATP molecules are transported to a glucose molecule in three reactions. After this, the six carbon sugar is broken down into two, three carbon sugars that each have a phosphate. Next, NADPH molecules are made and one more phosphate group is delivered to either three carbon molecule. Lastly, the three carbon molecule is converted to a three carbon pyruvate in four reactions. This also produces four ATP molecules.

Stages of Cellular Respiration- Kreb's cycle and Electron transport chain.

If oxygen is present, the pyruvate that is produced in glycolysis goes to the mitochondria to be converted into a two-carbon compound. One carbon dioxide molecule, one NADH molecule, and one two-carbon acetyl group is produced. This acetyl group will then enter into the Kreb's cycle. A series of enzyme assisted reactions take place in the Kreb's cycle. After the Kreb's cycle, comes the electron transport chain. NADH and FADH2 pass through the electron transport chain which is located in the inner membranes of the mitochondria in eukaryotes. The energy is used to pump the hydrogen ions out of the inner compartment. The ions then gather in the outer compartment. They then diffuse back into the inner compartment through a carrier protein. This carrier protein adds a phosphate group to the ADH resulting in ATP. At the end of this process, water molecules are formed by combining oxygen with the hydrogen.
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Cell Fermentation

If the cell does not have oxygen present, it must undergo the process of fermentation. This process happens after glycolysis in place of the Kreb's cycle. Fermentation allows the recycling of a NAD+ using an organic hydrogen receptor because without oxygen, electrons cannot be transferred from NADH. There are two types of fermentation- lactid and acid. In lactid fermentation, pyruvate is converted to lactid acid. Lactid acid can help in the production of foods such as yogurt and cheese. In alcoholic fermentation, pyruvate is broken down to ethanol. Carbon dioxide is released through this process. One food that alcoholic fermentation aids in is the production of bread.
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Comparing Photosynthesis to Cellular Respiration

The processes of photosynthesis and cellular respiration are basically opposite each other. In photosynthesis, carbon dioxide and water are used to produce glucose and oxygen. In cellular respiration, glucose and oxygen are used to produce carbon dioxide and water. While photosynthesis takes place in the chloroplast of cells, cellular respiration takes place in the mitochondria of cells.
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