A Short Exposition of Photosynthesis

Here is a short research paper on photosynthesis, that most wonderful and complex phenomenon that makes life possible. It deserves much deeper treatment that a short, high-school level report, but I hope this will provide a decent starting point on your learning journey. Don’t forget to ask your questions in the forum!


Photosynthesis is the process by which energy from the sun is used to chemically combine carbon dioxide (CO2) with water (H2O) to make oxygen and glucose. Green plants, i.e. plants with chlorophyll, and some other organisms utilize this chemical reaction to make food. Plants are primary producers occupying the lowest trophic level. They support all higher trophic levels and thus their level has the highest biomass. Without photosynthesis, most life on Earth would not exist. (1).

            The majority of photosynthesis in plants takes place in the middle layer of the leaves, or the mesophyll. The cells in the mesophyll are equipped with organelles called chloroplasts, specifically designed for carrying out photosynthesis. Inside the chloroplasts are what resemble stacks of coins. Each coin is called a thylakoid and has a green pigment called chlorophyll in its membrane. The entire stack is a called a granum. The grana are occupy a fluid-filled space called the stroma. (1).

            Photosynthesis is actually a complex series of chemical reactions, some being light-dependent and others being light-independent. The light-dependent reactions take place in the thylakoid membranes where the chlorophyll absorbs light which is converted to adenosine triphosphate (ATP), an energy carrying molecule, and NADPH, an electron carrying molecule. It is here that the oxygen we breathe is created from water as a byproduct and diffuses out through the stomata, tiny pores in the surface layer of leaves letting oxygen diffuse out and carbon dioxide diffuse in. (1).

            Then begin the light-independent reactions that are collectively known as the Calvin cycle. They occur in the stroma and use the ATP and NADPH to fix carbon for use in constructing cells and form three-carbon sugars, glyceraldehyde-3-phosphate, or G3P, molecules,  that link up to make glucose. (1).

            In summary, the heat energy from sunlight ends up stored as chemical energy in the bonds of the sugar molecules that can be metabolized by plants and other organisms. (1). The reaction absorbs heat so it can be described as endothermic. (2).

References


  1. “Intro to Photosynthesis.” (2018). Khan Academy. https://www.khanacademy.org/science/biology/photosynthesis-in-plants/modal/a/intro-to-photosynthesis. Date-accessed: 5/14/2018.

2. Helmenstine, Anne Marie. (2018). “Endothermic Reaction Examples.” ThoughtCo. https://www.thoughtco.com/endothermic-reaction-examples-608179

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