How Carbon Dioxide May Affect Organisms Directly and Indirectly

How carbon dioxide may affect organisms directly and indirectly
Carbon dioxide is a molecule that is essential to the survival of nearly all organisms on our planet, as in some way or another they rely on carbon dioxide or its products to provide them with respiratory substrates. However, as I will elaborate later, carbon dioxide also has adverse effects on organisms.
Carbon dioxide primarily affects all organisms as it is essential for the process of photosynthesis, in which organic compounds vital to a plant’s growth , and essential as food for a primary consumer , are synthesized. In photosynthesis carbon dioxide diffuses through the stomata on the underside of a plant, into the mesophyll layer of the leaf and finally into the photosynthesizing cells of a plant. In these cells it is accepted by Ribulose Bisphosphate (RuBP) as part of the light independent reaction. The RuBP and carbon dioxide then split into two molecules of Glycerate-3-phosphate (GP) and then are reduced by reduced NADP with ATP as an energy source, into two molecules of triose phosphate (TP). These molecules are then converted into glucose and other organic substaces. These organic substances directly influence the growth rate and yield of the plant, meaning carbon dioxide (and it’s concentration) are directly linked to plant growth.
Carbon dioxide also influences plant growth through water intake and loss. To receive carbon dioxide a plant must open its stomata to allow diffusion of the gas into its leaves. However when a plant does this it also results in loss of water, as water vapour diffusing out of the leaves. Lost water however is drawn up through the xylem through a process called transpiration. Water is able to move in opposition to gravity due to the negative pressure of the vessels, and the cohesion-tension property of water, which allows water molecules to “stick together” and influence the movement of another water molecule. If it is a sunny day, and the carbon dioxide concentration is high outside the plant, the plant will open its stomata to receive high amounts of carbon dioxide and therefore maximise photosynthesis. However, due to it being a sunny day, this will result in a great deal of water loss from the plant through transpiration. Water is a vital reactant in the light dependant reaction of photosynthesis as it undergoes photolysis by light, producing protons to reduce NADP and electrons to reduce oxidised chlorophyll, ensuing the continuation of the process. However water loss will mean this can happen less frequently, so photosynthesis slows down.
Carrying on with the theme of frequency, carbon dioxide has an effect on the frequency a human heart beats, and thus a human’s capacity for exercise. During respiration, carbon dioxide is produced both in the link reaction and the krebs cycle, as carbon compounds lose carbon atoms. This carbon dioxide diffuses out of the respiring cells into the capillaries. Here the carbon dioxide dissociates into carbonic acid, decreasing the pH of the blood. This change in pH could be harmful, as it could denature proteins in the body, by breaking hydrogen bonds and changing the tertiary structure of proteins, rendering them ineffective, as in the case of an enzyme, the shape of the active site would be altered, and no substrate would be able to bind with it. The pH change is detected by chemoreceptors in the walls of the carotid arteries; the carotid arties increase the frequency of impulses to the heart rate increase centre of the medulla oblongata. This causes the frequency of impulses along the sympathetic nerve to the sinoatrial node to increase. This means the heart contracts at a faster rate, meaning more carbon dioxide in the blood is pumped from the capillaries of respiring tissues into the vena cava, the right side of the heart and ultimately into the pulmonary arteries. Here the carbon dioxide diffuses out of the blood, increasing the blood’s pH, releasing carbon dioxide into the atmosphere.
The concentration of carbon dioxide in the atmosphere, if too high, affects every living organism in the planet in an adverse way. Carbon dioxide is a greenhouse gas; This means that as radiation from the sun (mostly infra-red radiation) enters our atmosphere and is reflected off the surface of the planet, it is unable to leave the atmosphere as it is reflected again back towards the planet by these greenhouse gases. This effectively traps heat energy from the sun within our atmosphere, and results in the change of our planet’s climate known as global warming. The effects of global warming on living organisms are many. The increased climate will cause the polar ice caps to melt, resulting in loss of habitats for many species, causing them to become extinct, altering the earth’s ecosystems. The melted ice will cause sea levels to rise, flooding many areas with salt water, again reducing biodiversity and destroy fertile land, making crop cultivation difficult. The conditions of areas closer to the poles will also become more humid and hot, causing the migration of many organisms adapted to these temperatures. This includes insects and other organisms that are hosts for various tropical diseases that could cause epidemics in countries ill-equipped to deal with these diseases.
From these points you can see carbon dioxide is a molecule that affects us all. In too low concentrations life will be unable to continue as photosynthesis will occur at too low a rate, and at too high concentrations, it causes the increase of global temperature, which could kill us all.