Photosynthesis and Respiration

Photosynthesis and Respiration

Photosynthesis refers to the process by which plants having green coloring matter, convert light energy from the sun into chemical energy in the form of sugar. This energy is stored in the sugar molecules in the form chemical bonds (Stein, 2014). The process of photosynthesis takes place in two basic steps: the light dependent and light independent stages. In the light dependent stage, energy excites the electrons on the chloroplast; as a result, the electrons move to an acceptor called nicotinamide adenine dinucleotide phosphate (NADP) which turns to NADPH. Water splits into hydrogen and oxygen. Moreover, the energy carrier ADP turns to ATP in readiness for stage two of the process. The main products at the end of light dependent stage are ATP, oxygen, NADPH. The second stage involves the products from the first stage without the use of light. This stage uses both the energy and the electrons in the ATP and NADPH to form sugar from carbon dioxide gas. The first stage occurs in the membranes while the second stage occurs in the stroma. It is worth noting that oxygen is the main byproduct of photosynthesis.

Unlike photosynthesis, respiration uses oxygen and sugars to produce energy. There are two forms of respiration. These include aerobic and anaerobic. Aerobic respiration is a form of cellular respiration, which utilizes oxygen to generate energy in the form of ATP and carbon dioxide as a byproduct (Pearson Education, 2014). The raw materials are sugar and oxygen, which are the main products of photosynthesis. However, in anaerobic respiration or fermentation, oxygen is not used and other chemicals accept electrons. Mostly, anaerobic respiration occurs in red blood cells and bacteria. It produces lactic acid, low ATP, alcohol, and carbon dioxide gas. Since it uses sulfates, nitrates, and sulfur as electron acceptors, which have smaller reduction potentials than oxygen, it is very inefficient, and produces less energy. Through photosynthesis, the plants manufacture sugars. These sugars are broken down in the cells of organisms the absence of oxygen to produce energy, lactic acid, and carbon dioxide gas.

According to Richard (2013), enzymes are very important for most biological processes. Enzymes have active sites where food substrates adhere. Enzymes catalyses reactions by offering an alternative route that requires lower activation energy. This particular mode of action resembles the catalysts. The interaction between enzymes and substrates takes three main steps. In the first step, the enzyme collides with the substrate in the right direction, orientation, and with sufficient energy. The second step involves the locking of the enzyme and the food substrate to form enzyme-substrate complex. This complex is an intermediate between the food substrate and the product. Finally, the enzyme-substrate complex breaks and forms the desired product leaving the enzyme free and unused, just like chemical catalysts remain chemically unchanged. However, cells regulate activities of enzymes (Richard, 2013). There are several ways of regulating the enzyme activity by the cells. Firstly, the cells can control the food substrate availability. The lower the concentration of the substrate, the slower the enzymatic activity, and the converse is always true. Secondly, in most cells, product inhibition takes place. In this process, some parts of a highly concentrated product bind on the active sites of enzymes, and thus inhibit further catalysis. Thirdly, the concentration of hydrogen ions plays a key role in enzyme regulation. Since enzymes are sensitive to changes in hydrogen ion concentration, the cells can easily alter the concentration of hydrogen ions to inhibit the enzymatic process. Other processes include protonation of active sites, and covalent modifications.

 

References

Pearson Education. (2014). Cell respiration. The Biology Places. Retrieved from http://www.phschool.com/science/biology_place/biocoach/cellresp/intro.html

Richard, S. (2013). How enzymes work. Bio-topics. Retrieved from http://www.biotopics.co.uk/other/enzyme.html.

Stein, C. (2014). Photosynthesis. Science Links. Retrieved from http://biology.clc.uc.edu/courses/bio104/photosyn.htm

 

 

 

 

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