Iv'e written this essay for biology but need an idea of where I'm at in terms of marks. does anyone know how to mark an essay?
the title is:
Carbon dioxide may affect organisms directly or indirectly. Describe and explain these effects.
Carbon dioxide is a molecule becoming evermore present in today's atmosphere - now making up 0.04%. It is made up of one carbon atom and 2 oxygen atoms. Although it is vital for many biological processes, it can have some negative impacts, as described in my essay below.
Firstly, the process of carbon sequestration involves capturing CO2 from the atmosphere and putting it in long term storage. Biologic sequestration involves the use of plants to capture this CO2 via photosynthesis and store it as carbon in the stems and roots (as well as in the soil). CO2 is useful for plant organisms and affects them directly- it is used to bind with Ribulose bisphosphate (RuBP) the light independent reaction of photosynthesis to form a six carbon intermediate in the Calvin cycle. This molecule is unstable however, and therefore breaks down into 2x stable 3-carbon molecules of Glycerate-2-phosphate. This is then converted to Triose phosphate via a reduction reaction; ATP is hydrolysed to ADP+Pi and an electron is donated to NAD to form reduced NAD. One carbon molecule is released and Ribulose bisphosphate is regenerated as a 5-carbon molecule. To form one molecule of Glucose, the cycle has to repeat six times as only one molecule of carbon is released every time
CO2 can also have indirect negative effects on aquatic ecosystems. Carbon dioxide released from biologic sequestration into the atmosphere often diffuses into the oceans through direct chemical exchange. This CO2 then dissolves in the salt water and forms carbonic acid. This makes the slightly alkaline water become a little more acidic (the pH is lowered). Therefore there is a higher concentration of hydrogen ions (H+). The impacts on ecosystems is huge; firstly, carbonic acid reacts with carbonate ions in the water to form bicarbonate. This is detrimental because carbonate ions are used by many plank-tonic species to create their calcium carbonate shells. With less carbonate available, the animals need to expend more energy to create these shells (via the hydrolysis of ATP) - as a result, the shells are often thinner and more brittle.
CO2 also has direct implications on more complex organisms like humans. For example, during intense levels of exercise, anaerobic respiration can be used as a last resort to provide an essential "boost" of energy from ATP (although it only produces 2 molecules of ATP via glycolysis, whereas aerobic respiration produces approximately 38). it is used as oxygen levels in the blood are not sufficient for aerobic respiration to take place in respiring tissues. This causes the increase of CO2 in the blood which is then detected by chemo-receptors in the medulla oblongata and in carotid arteries. This in turn increases the frequency of nerve impulses sent to the sino-atrial node (SAN) which then passes these impulses to the atrioventricular node (AVN) which directs the impulse down the muscle walls of the heart and up the septum (to stop the pooling of blood) from the purkinje fibers. This causes the sympathetic nervous system to increase the heart rate and therefore respiratory rate. This increases levels of oxygen in the blood, which therefore increases pH again and lowers the concentration of CO2.
If this process was to not occur, the low pH of the blood would indirectly affect enzyme activity.If the CO2 concentration is too high, then it may cause the active site of enzymes in the blood to become denatured- as the primary structure changes which alters the tertiary structure due to increased vibrations putting strain on the structural bonds like disulphide bridges. This would cause the active site to no longer be complementary to its substrate and therefore no enzyme-substrate complexes would form; hence the enzymes would be non-functional.
this took me an hour to hand write (i typed it up to put it on here)
also if you have any topic ideas please let me know as i could only think of these ones