Describe and explain some of the direct and indirect effects of carbon dioxide on organisms?

Carbon dioxide only comprises 0.04 % of the earth’s atmosphere but it is a vital molecule in many processes and effects organisms directly with photosynthesis in plants, body functions causing global warming which then has numerous indirect effects on organisms.  Arguably one of the most important processes in plants is photosynthesis which requires carbon dioxide and water to form glucose and oxygen. Carbon dioxide levels in the atmosphere can have a direct effect on the rate of photosynthesis as it is used within the Calvin cycle in the light independent reaction, the carbon dioxide reacts with Ribulose bisphosphate (RuBP), with the help of the enzyme Rubisco, to produce glyverate-3- phosphate. In turn glycerate-3- phosphate is reduced to Triose phosphate using reduced NADP and energy from ATP from the light dependant reaction. With every 3 turns of the cycle 3 carbon dioxide molecules are fixed to form one new triose phosphate molecule which then leaves the cycle and two combine to form 1 glucose molecule using the glycolysis enzymes in reverse and other triose molecules are used to regenerate the RuBP. Thus without carbon dioxide this process would be unable to continue, which would have direct consequences of no glucose being produced and indirect effects from this. Glucose molecules can be joined by glyosidic bonds to form starch which is the storage molecule in plants and thus is the starting point for all food chains, it is also broken down in the plants and in other organisms during respiration to produce ATP molecules which are used in cellular processes ( active transport through membrane, cell movements ect) as they give out small amounts of energy when they are broken down again to ADP and inorganic phosphate.   During respiration carbon dioxide is released during the link reaction when converting Pyruvate ( the product of glycolysis) to Acetyl group and during the kerbs cycle when turning Citrate ( a 6 carbon compound) into oxaloacetate, removing 2 carbo dioxides each cycle. The carbon dioxide which is formed within the cells then diffuses out by simple diffusing, through the membrane down its concentration gradient and into the blood. In solution (i.e the blood) the carbon dioxide forms a weak acid called carbonic acid which lowers the pH of the blood in humans and in turn causes a change in the tertiary structure of the haemoglobin molecule so that it has a lower affinity for oxygen. This is called the bohr shift (oxygen dissociation curve shifts right) which means the heavily respiring cells get more oxygen so can form more ATP.  It is also important for the excess carbon dioxide in the blood to be removed (to ensure diffusion gradient of cells to the blood is kept high). The low pH in the blood (from increased respiration due to increased metabolic activity) is detected by chemical receptors in the aorta and carotid arteries which has a direct effect of increasing the frequency of impulses to the medulla Oblongata. This in turn increases the frequency of impulses from the medulla oblongata to the Sino atrial node via the sympathetic nervous system. Thus increasing the heart rate, which increases blood flow and removes carbon dioxide faster by transporting more blood to the lungs where it is exhaled into the atmosphere.  Another way carbon dioxide accumulates in the atmosphere is via the carbon cycle when dead or decaying organisms (detritus) are broken down by saprobiotic microorganisms which then respire releasing the carbon dioxide into the atmosphere. Unfortunately, carbon dioxide may indirectly cause adverse effects to the climate in which organisms live. When radiation from the sun reaches the earth’s surface it is reflected back into space, with some being reflected back again to the earth’s surface due to gasses in the atmosphere. Increased levels of carbon dioxide and other greenhouse gases are causing more of this radiation to be reflected back to earth and are preventing it from escaping, so more heat is retained which is leading to rising temperatures and a warmer climate. At first thought an increasing temperature and higher carbon dioxide levels may be considered to have a positive effect by increasing the rate of photosynthesis. However this may not be the case, as the enzyme Rubisco, involved in catalysing the reaction in which RuBP combines with carbon dioxide, also combines with oxygen in a process called photorespiration. Photorespiration increases rapidly at higher temperatures as Rubisco gains a higher affinity for oxygen, meaning the rate of photosynthesis decreases.