Introduction
Photosynthesis and cellular respiration are very important processes. This paper highlights these two processes by giving an in-depth explanation of how these processes occur, where they occur, their importance, and the equations. The paper starts with the photosynthesis process as it answers the guiding questions, and ends with the cellular respiration process.
Photosynthesis is the process of conversion of light energy into chemical energy and then storing it in sugar bonds. It occurs in plants and algae of the kingdom Protista.
Photosynthesis is a process whereby the green plants utilize energy from the sun to convert water, carbon dioxide and minerals into organic compounds and oxygen. Photosynthesis takes place when water is taken in by the green plant’s roots and is transported by the xylem to the leaves, carbon dioxide is absorbed from the atmospheric air which through the stomata enters the leaves of the green plants after which it diffuses to the cells having chlorophyll (a green pigment capable of transforming light energy into latent form which can be stored and can be utilized when need arises. This process occurs in the chloroplasts of plants and also in some algae. Photosynthesis offers us with oxygen that we require for breathing. In return we exhale carbon dioxide which is useful for plants. Plants are also important to human beings since we depend on them as source of food and also source of food for the animals that we feed on.
The process of photosynthesis
Photosynthesis , a process in which light energy is converted in to chemical energy takes place in the chloroplast by using chlorophyl. It’s a process that takes place in green plants and some species of algae, that is, kingdom Protista. Plants require energy from the sun(light energy), water and carbon dioxide to make sugar. Photosynthesis takes place majorly in the leaves of the plants and almost none or very little takes place in the stem.
Photosynthesis involves two reactions: the light reaction and the dark reaction.
Light reaction- this reaction takes place in thylakoid membrane where light energy is converted to chemical energy. The chemical reaction has to take place in the presence of light.chlorophyl and other more pigments like beta-carotene are arranged in clusters inside thylakoid membrane anddd theeey are take part in light reaction. Each of the pigments that have different colors can absorb slight light of different color and passes its energy for photosynthesis in the molecule of central chlorophyll.the energy that is harvested through light reaction is stored as adenosine triphosphate (ATP), a chemical compound that cells use to store energy.this chemical comprises of nucleotide adenine that has a bond to ribose sugar, and which is bonded three other phosphate groups. The overall equation for the reaction is given below:
6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2
The dark reaction stage – this takes place in the stroma of the chloroplast and converts carbon dioxide to sugar. Light is not needed here; however, the products of the light stage are used. The CO2 and energy from ATP are converted to sugar.
Photosynthesis is a very important process in regulating the earth’s life cycle. The plants, water and sunlight supply the raw sources of energy and helps in air purification and breathing. Without photosynthesis, life is impossible.
Cellular Respiration
This is a set of metabolic processes and reactions, which occur in the cells of living organisms, convert the biochemical energy obtained from the nutrients into ATP (Adenosine Triphosphate), and then release the waste products. Respiration reactions are catabolic and involve the oxidation of one molecule as the other molecule is reduced. Cellular respiration helps cells to gain useful energy that is necessary for the cellular changes.
Plant and animal cells commonly use nutrients such as amino acids, sugar, and fatty acids in respiration. Molecular oxygen called electron acceptor is commonly used as an oxidizing agent. Aerobic organisms are those whose final electron acceptor in respiration is oxygen, otherwise, the organism is anaerobic. The energy from respiration is normally used to synthesize the ATP in order to store it. This energy is used to drive various processes such as locomotion, biosynthesis, and molecules transportation across the cell membranes.
Cellular Respiration Process
The process requires oxygen so that energy can be generated in form of ATP. The reactants include carbohydrates, proteins, and fats; however, the preferred method is the breakdown of pyruvate in glycolisis which requires that pyruvate enters the mitochondrion for its full oxidation by the Krebs cycle.
For aerobic respiration, the general equation is given below:
Organic compounds + Oxygen → Carbon dioxide + Water + Energy
Generally, glucose is the organic compound; however, other nutrients are used as well. The cellular respiration of glucose takes place in three stages: glycolysis, oxidation of pyruvate, and the citric acid cycle (Krebs cycle).
The first stage is the glycolysis. This process is a metabolic pathway and is found in cell cytosol in every living organism. The process does not require oxygen. One molecule of glucose is converted into two molecules of pyruvic acid (pyruvate), producing four molecules of ATP. The respiratory phase however consumes two molecules of ATP. During the pay-off-phase, four phosphate groups are transferred to ADP and four ATP are made. The overall equation is
Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O
NAD+ is a coenzyme and acts as an electron carrier in the cell.
The second stage is the oxidation of pyruvate. The pyruvate from stage one is then oxidized by Pyruvate dehydrogenase complex (PDC) into acetyl-CoA and CO2. PDC is located in the mitochondria of eukaryotic cells and in the cytosol of prokaryotes. The conversion results into the formation of one molecule of CO2 and one molecule of NADH. This stage links glycolysis and the Krebs cycle.
The third stage is the Krebs cycle. In the presence of oxygen, pyruvate molecules from glycolysis produce acetyl-CoA and aerobic respiration process results in the mitochondria, which leads to Krebs cycle inside mitochondrial matrix, and the molecule is oxidized to CO2 while NAD is reduced to NADH.
The NADH is also used by electron transport chain to further produce ATP as part of the oxidative phosphorylation. For the full oxidization, two acetyl-CoA are metabolized by the Krebs cycle producing H2O and CO2 as the waste product. In the absence of oxygen, the fermentation of the pyruvate molecule occurs.
References
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Campbell, Neil A., Lawrence G. Mitchell, Jane B. Reece. (1999). Biology: Concepts and Connections, 3rd Ed. Benjamin/Cummings Publ. Co., Inc. Menlo Park, CA.
Marchuk, William N. (1992). A Life Science Lexicon. Wm. C. Brown Publishers, Dubuque, IA.
