Photosynthesis and Respiration
Photosynthesis is a chemical process by which plants manufacture food as glucose using carbon dioxide, water and sunlight, releasing oxygen as an end product. This glucose is utilized as a direct source of energy in plants for reproduction, growth, as well as an energy reserve. This process occurs in chloroplasts of leaves which have a stroma containing thylakoids. The thylakoid membrane has a chlorophyll pigment that absorbs light energy which is converted and stored in a simple sugar molecule. Aerobic respiration is a process by which glucose is converted into energy for use by plants and other organisms. The chemical bonds of glucose are broken down (glycolysis) to pyruvic acid molecules, which are further broken down in the Krebs cycle. The end product is released as carbon dioxide which is a residue of the pyruvic acid. The electrons and hydrogen ions produced are carried to the electron transport system. Water is then released as well as high levels of energy in form of ATP (Adenosine Tri-Phosphate). The process takes place in mitochondria (Cell structure, par. 2-5). Whilst photosynthesis absorbs light energy releasing glucose and oxygen, aerobic respiration releases energy due to oxidation of glucose in the presence of oxygen.
Role of Fermentation in Energy Generation
Fermentation helps organisms to generate ATP energy in the absence of oxygen. Glucose formed during photosynthesis is broken down starting in the cytoplasm of the cell in two ways depending on oxygen. When oxygen is present, aerobic cellular respiration occurs with complete glucose oxidation generating the highest amount of ATP energy. In the absence of oxygen, anaerobic respiration sets in where glycolysis occurs with pyruvic acid and 2 ATP molecules of energy produced at the end which is utilized by the cell. Some organisms lack required enzymes in krebs cycle and electron transport system and only carry out Glycolysis. Even though aerobic respiration is the major process of ATP energy generation, Prokaryotic organisms and certain eukaryotic organisms still need a supply of energy and therefore use anaerobic respiration. They are able to use other molecules as final electron acceptors e.g. pyruvic acid other than oxygen. The oxidation is usually incomplete resulting in smaller hydrogen-containing organic molecules, ATP energy and heat. Anaerobic Organisms get energy from glucose via Glycolysis pathway. In the process, pyruvic acid is produced which then undergoes changes in different organisms influenced by various enzymes. This leads to formation of lactic acid, ethyl alcohol or acetone and carbon dioxide. These molecules are useful in regeneration of NAD (nicotinamide adenine dinucleotide) required in Glycolysis as opposed to aerobic respiration where it’s generated by the electron transport system (Audesirk et al., 2008).
How Enzyme Catalyzes Reaction
Enzymes catalyse reactions by reducing the activation energy essential for that reaction to occur. They escalate rate of chemical reactions without being altered or shifting chemical equilibrium between reactants and products. They have an active site that binds to substrates forming an enzyme-substrate complex and other sites that bind to cofactors needed for catalysis. The bound substrate is transformed into a product that is generated from the enzyme. The interaction is very specific in nature. Some have sites for binding products /substrates of the reaction that is catalyzed which plays a role in feedback regulation of enzyme activity (Reactions and Enzymes, n.d). A Change in the cell environment affects enzyme production hence regulating their activity. Compartmentalization also helps in regulating activity whereby different metabolic pathways are organized to occur in different cellular compartments. Presence of inhibitors and activators helps regulate enzyme activity in a cell leading to a stable cell environment (Reactions and Enzymes, n.d).
Works Cited
Audesirk, T., Audesirk, G., and Byers, B. (2008). Biology: Life on earth with physiology (8th Ed.). San Francisco, CA: Benjamin Cummings.
Cell Structure. (n.d.). Web.
Reactions and Enzymes, (n.d.). Web.