The body is very sensitive to increases in CO2 and so this is an indicator of the need for oxygen. The levels of oxygen in the arterial blood vary very little, even during exercise, but the CO2 levels vary in direct proportion to the level of exertion. The heavier the exercise the greater the CO2 concentration. During exercise there is also an increase in lactic acid levels. Any changes in the level of CO2 or lactic acid concentration in the blood lowers its pH. Chemoreceptors can detect very small changes in pH. They send nerve impulses along the phrenic and thoracic to the diaphragm and intercostals muscles. This stimulates an increase in breathing rate.
The amount of oxygen in the atmosphere is the same at high altitudes as it is at sea level, about 21% or 10kPa, and in the lungs about 5.3kPa. This means that the haemoglobin will become only about 70% saturated in the lungs. Less oxygen will be carried around the body, and the person may begin to feel breathless and ill. The respiratory problems associated with living at high altitude are a result of the reduced atmospheric pressure and as there is not enough oxygen to replace the CO2 after it has been flushed out of the lungs the chemoreceptors often fail to register that anything is wrong, and the brain becomes starved of oxygen. The reduced pressure also means that it is more difficult to load haemoglobin with oxygen. Above about 600m the pressure is inadequate to load haemoglobin effectively. Some human settlements exist at these altitudes and the inhabitants become acclimatised. Acclimatisation involves:
-
Adjustment of blood pH- the reduced loading of haemoglobin leads to deeper breathing in an attempt to compensate for lack of oxygen in the blood. This leads to excessive removal of CO2 and a raised blood pH. ;
- Increased oxygen uptake;
- Improved transport of oxygen to the tissues- this is the result of;
- increased red blood cell concentration- this may rise from 45% to 60% of the total blood volume;
- increased haemoglobin concentration in red blood cells- this may rise by 20%.
- Changes in haemoglobin affinity for oxygen.
Changes in haemoglobin affinity for oxygen and increased oxygen uptake do not have any effect on the density of blood but an increase in red blood cell concentration results in an increase in blood density.
Null hypothesis:
There will be no difference in density between the three samples of blood.
Alternative hypothesis:
By using my background knowledge I am able to predict that (C) will reach 10 cm3 faster than (b) and (c), and sample (b) will reach the 10cm3 mark faster than (a). This prediction is based on the fact that blood density increases when training at a high altitude due to the increased red blood cell concentration. However there will not be much difference in density between (a) and (b) as background knowledge states that there is no increase in density in blood after regular exercise; regular exercise results in an increase in efficiency of oxygen use around the body.
Method:
To work out the molarity of copper sulphate rearrange the formula no.of moles = MV/1000, to M = no.of moles x V/1000.
Calculate the number of moles of copper sulphate by using this formula;
no.of moles = mass/Mr.
So, no.of moles = 24.96/160 (CuSO4 = 64 + 32 +16X4)
= 0.156 moles.
∴M = 0.156 x 1000/1000
= 0.156 (0.2M)
Procedure:
-
Fill three 100cm3 measuring cylinders with the 0.2M copper sulphate solution, and label the cylinders a, b and c.
- Using a syringe take a small amount of sample A and release a small drop into the measuring cylinder.
- Start the timer as soon as the drop touches the 100cm mark and stop the timer when the drop reaches the 10cm point.
- Record the results in an appropriate table and repeat the above a further 9 times to gain an average.
- Repeat the above procedure with samples B and C, and record the results.
Risk assessment:
- Goggles must be worn at all times to protect the eyes as you will be handling harmful products throughout the experiment.
- Care should be taken when handling copper sulphate as it maybe irritating to eyes and skin.
- Care should be taken when handling the syringes as they are sharp objects and can cause injury.
- To avoid accidents, wipe any spillages immediately and keep large objects, such as seats, out of the way.
Time taken for drop to fall between 100cm3 and 10cm3 (s)
Analysis and conclusions:
The T test is used to test the difference between two unpaired independent samples.
This statistical test was used to analyse the data as it is used to test the statistical significance of continuous variables.
The mean can be calculated by using the following equation:
χ = χ1+χ2……χn = ∑ χ
n n
Where n is the sample size.
So for sample A:
χ = 121.5=12.15
10
For sample B:
χ = 118.2=11.82
10
For sample C:
χ = 78.7=7.87
10
The variance of each sample is then calculated by using the following equation:
σ2 = ∑ χ2- χ2
n
So for sample A:
σ2 = 1485.35 –12.152
10
= 0.9125
For sample B:
σ2 = 1415.64 - 11.82 2
10
= 1.8516
For sample C:
σ2 = 628.17 - 7.872
10
= 0.8801
The null hypothesis is that there is no difference between the two means and the alternative hypothesis is that there is a difference between them.
Ho= μ1=μ2
H1= μ1≠μ2
Using the following :
Z= χ1- χ2 – (μ1-μ2)
σ2 1 + σ2 2
n1 n2
Where (μ1-μ2) is the population mean
However, we are assuming that there is no difference therefore μ1-μ2 =0
Therefore Z= χ1- χ2
σ2 1 + σ2 2
n1 n2
A two-tailed test is used at the 5% level
If Z > 1.96 or <-1.96 Ho is rejected
If Ho is rejected we can conclude that there is evidence at the 5% level of a difference in population means.
If Ho is accepted the Z value must lie between –1.96 and 1.96.
So when testing samples A and B:
Z= 12.15- 11.82
0.9125 + 1.8516
10 10
= 0.6272678228
When testing samples B and C:
Z= 11.82 - 7.87
1.8516 + 0.8801
10 10
= 7.557542433
When testing samples A and C:
Z= 12.15 - 7.87
0.9125 + 0.8801
10 10
= 10.10885746
Conclusion
For samples A and B Z (0.6272678228) lies between 1.96 and –1.96.
For samples B and C Z (7.557542433) is larger than 1.96.
For samples A and C Z (10.10885746) is larger than 1.96.
Therefore the null hypothesis is accepted for sample A and B, whilst the null hypothesis is rejected for sample B and C and also for sample A and C.
Based on these results the alternative hypothesis is accepted. Sample C did reach the 10cm point faster than sample B and A, and this can be explained using the background information. Mock blood sample C represents blood from a person who has undergone 3 months of aerobic training at altitude. Research has shown that when a person undergoes training at altitude the concentration of red blood cells increases to overcome the consequences of respiring in an environment where there is a low partial pressure of oxygen. CO2 is flushed out of the lungs therefore chemoreceptors fail to register any problems. Respiratory problems are overcome when the person returns to normal partial pressures of oxygen, however if the person remains at altitude they can become ‘acclimatised’. This is when the concentration of red blood cells increases to ensure that more oxygen will reach the muscles and tissue, hence there is an increase in the density of blood.
Sample A was predicted to fall at the slowest rate when compared with samples B and C, this was based on the fact that sample A (blood from a healthy male living at sea level) should have 45%-60% less red blood cells as a person who has trained at altitude for a period of time usually has an increase of about 45-60% in the number of red blood cells. Thus sample A would have a lower density and therefore fall at a slower pace. Regular aerobic exercise increases the efficiency of oxygen disposition and the binding of haemoglobin with oxygen, however it does not have any effect on the density of blood as there is no increase in the number of red blood cells. Although CO2 and lactic acid is produced the body does not produce more red blood cells to allow more oxygen to get to the muscles and tissue. This is because chemoreceptors are activated due to the presence of lactic acid which cause a change in pH (they are very sensitive to any changes in pH) and the activation causes an increase in breathing rate therefore there is no need for production of extra red blood cells, so there is no increase in blood density. This explains why the rate at which sample B falls is very similar to the rate at which sample A falls. The blood density of both samples should almost be identical.
Evaluation:
No major anomalies were found in the results apart from the fourth trial of solution C. This may have occurred due to the release of a large amount of the sample in that trial which would have increased the weight of the drop and caused it to reach the 10cm point quicker. As human errors such as this were expected a large number of trials were performed to minimise the consequences of these errors and so increase the reliability of the results. The main sources of error in the experiment were found to be:
- The copper sulphate solution- insufficient mixing of the copper sulphate results in crystals of copper sulphate remaining in the bottom of the cylinder which results in an inaccurate solution which in turn will affect the rate at which the drop falls.
- Human error- reflex actions such as activating and stopping the timer will cause inaccuracies in the results due to hand-eye coordination. Also the size of the drops released through the syringe may vary from trial to trial due to varying pressure applied in the different trials, so this too will affect the final result.
- Point at which the drop is released- the height from which the sample is dropped will vary each time due to human error, and also the point from which it is dropped will affect the end result. The way in which the syringe is held will affect the amount of pressure applied which will then have an affect on how much of the sample is released.
Modifications:
The above sources of error, when considered individually, appear as not having a major influence over the results but if all these errors take place during the experiment then together they are found to be quite significant and can be the major cause of anomalous results. To increase the reliability of the results and in order to gain valid results, these errors will have to be overcome or reduced.
The first error mentioned above could be overcome by using a solution that has been prepared by a qualified technician.
Working in pairs may reduce human error; by having one person releasing the sample whilst the other activates the timer.
Finally by using a clamp stand to hold the syringe in place will ensure a consistent height from which the sample is dropped as well as a consistent position in which the syringe is held.
