Photosynthesis is a chemical reaction used by plants and other organisms to store light energy as chemical energy (cells can use chemical energy to carry out life processes). Plants are a common example of organisms that perform photosynthesis but it is also used by certain species of bacteria, and protist. Students often think about plants when they think about photosynthesis but the are far more bacteria than plants are conducting photosynthesis. Oxygen is a byproduct of photosynthesis, at least half the oxygen of Earth is produced by marine photosynthetic organisms of the ocean!

Photoautotrophs do photosynthesis to make their own food.

• Photo = light
• Auto = self
• Troph = nutrients
• Synthesis = to make something

Photosynthesis takes place of chloroplasts of eukaryotic organisms or within the cell membrane of some prokaryotes.

Carbon dioxide and water act as reactants (starting materials) for photosynthesis while light energy acts as the catalysts . The reaction will produce glucose (sugar) and oxygen gas (O2).

Cellular Respiration

Cellular respiration is a chemical process cells use to breakdown glucose (sugar) to get cellular energy (ATP). This processes uses some of the products of photosynthesis to release the energy stored within glucose. Before cellular respiration can take place the glucose must be prepared using the process “Glycolysis”. Enzymes present in the cell will break down a single glucose molecule (a 6 carbon molecule) into two molecules of pyruvate (a 3 carbon atom containing molecule). A small amount of ATP is also generated as a result of glycolysis.

Glycolysis

Glycolysis is the process of breaking sugar down to form a chemical called “pyruvate”. Glycolysis is required for cellular respiration to occur.

Depending on whether there is enough oxygen present the cell will perform aerobic respiration, if the oxygen levels are not sufficient the cell will be forced to perform anaerobic respiration.

Cellular respiration consists of two pathways;

• Aerobic Cellular Respiration
• Anaerobic Cellular Respiration

Aerobic cellular respiration

Aerobic cellular respiration is the chemical process of using oxygen to transform pyruvate into; carbon dioxide, water, and ATP (adenosine triphosphate). Aerobic cellular respiration is the most efficient method of energy generation available to the cell, it will generate a whopping 36 ATP compared to only 2 ATP being made from glycolysis. In a eukaryotic cell aerobic respiration happens in the mitochondria, while in a prokaryotic cell it occurs in the cellular membrane.

Anaerobic cellular respiration

Anaerobic cell respiration is what occurs when the cell must make ATP to stay alive but there just isn’t enough oxygen present to meet the energy demands. Cells will break down the glucose and produce just 2 ATP (2 is better than 0). Unfortunately such a small amount of ATP is usually not enough to meet the energy demands of the cell and this process is usually just used as a temporary substitute until proper oxygen levels can be reached.

When anaerobic cell respiration happens in an animal cell a third product called lactic acid is created. The muscle cells of your body do anaerobic respiration for short periods of time during intense exercise, this can create fatigue and a sore sensation. Too much lactic acid product can be toxic!

When yeast (fungal) cells perform anaerobic cell respiration they create a waste product known as ethanol. Ethanol is the type of alcohol present in alcoholic beverages such as; wine, beer, vodka and rum. The various colors, flavors, and scents of the alcohol produced depends on the sugar source the yeast were given.

Relationship between photosynthesis and cellular respiration

Photosynthesis and cellular respiration are very closely related chemical reactions. The products of each reactions act as the reactants or starting materials for each respective reaction. The oxygen gas and sugar that is produced from photosynthesis are used as reactants for aerobic cellular respiration. Conversely the water, and carbon dioxide gas made from aerobic cellular respiration act as the reactants for the photosynthesis.