Introduction
Cellular respiration and photosynthesis are vital reactions in living organisms since without the two; there would be no life on earth. Cellular respiration involves a set of metabolic reactions that take place in cells of living organisms thereby converting nutrients like sugar into adenosine triphosphate (ATP) (Osterhoudt & Barhydt, 2010). On the other hand, photosynthesis involves the conversion of carbon dioxide into organic compounds by the photoautotroph in the presence of sunlight. Most animals attain their energy requirements through cellular respiration while on the other hand; photosynthesis is performed by most plants that can make their food. These two reactions usually complement each other even though they occur in reverse. For instance, in cellular respiration process, glucose and oxygen yield carbon dioxide and water whereas carbon dioxide and water yield glucose and oxygen in photosynthesis.
The link between cellular respiration and photosynthesis and specific organelles within the eukaryotic cell
Respiration takes place mainly in the organelle called mitochondrion within the cell. Almost all respiratory activities occur in different parts of the mitochondrion in multiple simultaneous steps except glycolysis. Glycolysis takes place in the cell cytoplasm which includes the cytosol and the organelles that reside in it inside the cell. After the glycolysis, the produced pyruvate is transferred into the mitochondria where it is used for the subsequent process. The pyruvate is utilized during the Krebs cycle to create energy
Photosynthetic cells contain special pigments that absorb light energy. Different pigment responds to various wavelengths of visible light (Hopkins, 2006). The primary pigment used in photosynthesis is the chlorophyll, and it reflects green light and absorb red and blue lights most strongly. Photosynthesis takes place in the chloroplast of plants as it is where the chlorophyll is found. The chlorophyll is located within the thylakoid membrane. The space between thylakoid and the chloroplast membrane is called the stroma.
Stages of cellular respiration
Steps in cellular respiration involve the enzymatic synthesis of glucose (C6H12O6) to produce cellular energy (ATP) with oxygen (O2). There are usually three stages of cell respiration (Osterhoudt & Barhydt, 2010).
[C6H12O6 + 6O2 ® 6 CO2 + 6H2O + 38 ATP]
Stage 1 (Glycolysis): This involves ten process occurring in the cytoplasm, and it involves the conversion of a glucose molecule into a 3-carbon molecule, two molecules of pyruvic acid. Glycolysis is anaerobic and occurs whether oxygen is available or not. Each glucose molecule yields 2 ATP and 2 NADH (nicotine adenine dinucleotide). NADH is co-enzyme that is a carrier for H+ ions which are produced during the oxidation of glucose. Eventually, the pyruvic acid disperses into the mitochondrion’s inner compartment. In this section, a transition reaction takes place thereby preparing pyruvic acid for the following step of respiration
Stage 2 (Citric Acid Cycle): This phase takes place in the inner matrix of the mitochondrion. Here, the acetyl group separates from the co-enzyme A and goes into the reaction cycle. This type of reaction is aerobic hence it can only take place when there is oxygen. It yields a net of 2 ATP from each molecule of glucose. Alongside the 2 ATP, the process yields six NADH and two FADH2. The conversion of glucose to CO2 (oxidation) is completed in this stage.
Stage 3 (Electron Transport System): This step takes place in the inner mitochondrial membrane, and it involves of a chain of enzymes. There is a release of electrons from NADH and FADH2. As they pass along the set of enzymes, they provide the energy used in the process by which H+ ions are moved from the inner to the outer mitochondrial membranes. This process is called Chemiosmosis and it explains how the electron transport chain produces ATP. The enzymes controlling the steps in the chain, embedded in the cristae membrane, are proton pumps. There is then a backflow of H+ ions through a particular pore in the membrane. This process drives the ATP synthesis. In this stage, a total of 34 ATP is yielded from each glucose molecule. At the end of electron transport, 6 H2O are formed when O2 and the electrons combine.
Stages of Photosynthesis
The process of photosynthesis takes place in the chloroplast of a plant, as well as in eukaryotic single-celled algae and several photosynthetic prokaryotes (Hopkins, 2006)
Stage 1(Light absorption): This is the first step. In this stage, the chlorophylls which is attached to proteins found in the thylakoid membrane absorbs the light. The energy generated from the light absorbed is used to take out electrons from water to form oxygen. It is also used to relocate the electrons to quinine (CoQ), a primary acceptor of electrons.
Stage 2 (Electron Transport): In this step, there is the movement of electrons from quinine through a sequence of molecules the thylakoid membrane. They ultimately reach the NADP+, the ultimate electron acceptor. This reduces NADP+ to NADPH.
Stage 3 (ATP generation): Here, protons move down from the lumen in thylakoid to the stroma. It couples the movement of protons to the separation of adenosine triphosphate from Pi and ADP.
Stage 4 (Carbon fixation): The ATP4- and NADPH formed stages two and three give the energy and electrons required for the synthesis of CO2 and H2O into polymers of six-carbon sugars.
It is important to note that from steps 1-3, the reactions generating ATP and NADPH directly depend on light and are thus called the light reactions of photosynthesis. In stage 4, the processes are indirectly dependent on light and thus referred to as dark reactions. Chlorophyll absorbs the energy from sunlight and transforms it into chemical energy. The chemical energy is usually in terms of electron carrier molecules. Furthermore, the chemical energy from the light-dependent reaction assembles carbohydrate molecules from carbon dioxide.
Comparison between cellular respiration and photosynthesis
Cellular respiration involves glucose decomposition into water and carbon dioxide as well as energy, and it occurs in mitochondria Glycolysis (cytoplasm) as compared to photosynthesis that takes place in the chloroplast and involves the combination of carbon dioxide and water in the presence of sunlight to form glucose and oxygen. In cellular respiration, reactants are C6H12O6 and 6O2 whereas, in photosynthesis, reactants are 6CO2 and 12H2O and light energy. Sunlight is not required in cellular respiration whereas photosynthesis can only take place in the presence of sunlight. Oxygen is absorbed, and carbon dioxide is usually released in cellular respiration whereas carbon dioxide is absorbed and oxygen is released in photosynthesis. In cellular respiration, the products released are6CO2 and 6H2O and energy (ATP) whereas the released products in photosynthesis are C6 H12 O6 (or G3P) and 6O2 and 6H20.
Interaction and interdependence between cellular respiration and photosynthesis
The interaction between cellular respiration and photosynthesis play a fundamental role in life since they complement each other by ensuring that the products of one process are the reactants of the other. Photosynthesis is the process that produces the glucose used in cellular respiration to make adenosine triphosphate. This glucose is then transformed into carbon dioxide. In photosynthesis, water is decomposed into oxygen while in cellular respiration; water is created through a combination of oxygen and hydrogen. Besides, photosynthesis requires carbon dioxide and produces oxygen while cellular respiration needs oxygen and produces carbon dioxide. Living organisms use the oxygen released for respiration
Importance/Significance of cellular respiration
The ATP made by cellular respiration has a diverse functionality in the life of an organism. Among the cell works of ATP are chemical, mechanical, and electrochemical. In addition to that, ATP is used in undergoing reactions and also used to run cells. In the absence of ATP energy, no cell would be able to function. However, only the anaerobic part of cellular respiration is vital to every living thing since aerobic respiration is only essential for organisms that have oxygen and mitochondria.
Importance/Significance of photosynthesis
Both plants and animals synthesize proteins and fats from carbohydrates thereby rendering glucose a primary source of energy for all living creatures (Ridge, 2002). The released oxygen is a byproduct of photosynthesis, majorly of phytoplankton. It is the major source of the atmospheric oxygen essential for respiration in animals and plants. Animals then produce carbon dioxide which is essential to plants. It is, therefore, worthwhile to conclude that photosynthesis is the vital source of life for all living things since it provides the energy that is required for the metabolic processes in plants and animals.
References
Hopkins, W. (2006). Photosynthesis and respiration. New York: Chelsea House.
Osterhoudt, G. & Barhydt, J. (2010). Cell respiration and cell survival. New York: Nova Biomedical Books.
Ridge, I. (2002). Plants. Oxford: Oxford University Press.
