Red blood cells and haemoglobin
The function of the red blood cells is to transport oxygen around the body. Oxygen is carried in red blood cells because it binds with a protein on the red blood cell. This protein is called haemoglobin. A haemoglobin molecule consists of four polypeptide chains, with a haem prosthetic group at the centre of each chain. Each haem group contain one iron atom, and one oxygen molecule binds to each iron atom. This forms oxy-haemoglobin. As there are four iron atoms within the haemoglobin molecule four oxygen molecules are able to bind. Red blood cells have specific features (listed below) that make it efficient in absorbing and transporting respiratory gasses:
- They are small in size - This enables the haemoglobin molecules to be close to the surface, allowing oxygen to be picked up and released rapidly, as the diffusion pathway is shorter.
(This is because of diffusion = (surface area x difference in concentration) / length of diffusion path.)
- Red blood cells are biconcave discs. This unique shape creates more surface area and therefore the red blood cell can carry more haemoglobin. This shape also lends to the red blood cell being efficient at gaseous exchange.
- Red blood cells do not contain any organelles (e.g. a nuclei or mitochondria.). This allows more space inside the cell for haemoglobin.
As stated earlier haemoglobin is the protein that is responsible for the oxygen – carrying property of the red blood cells. When saturated with oxygen it is called oxy-haemoglobin. After haemoglobin releases oxygen to the body tissues, it reverses its function and picks up carbon dioxide, which is a product of tissue respiration, for transport to the lungs, where it is expired. In this form, it is known as carb-oxy-haemoglobin. The process of the haemoglobin binding with the oxygen molecules is called loading or associating and the process of releasing oxygen is called unloading or dissociating.
Haemoglobin has a quaternary structure. The primary structure consists of four polypeptide chains, these chains coil up into a helix and then fold into a precise shape (which is important as if the oxygen can’t find the iron molecules within the structure then oxygen will not be able to bind with the haemoglobin.) all four polypeptides are linked together in a spherical shape (almost spherical shape). Each polypeptide has a haem group containing the iron ions. The iron ions are Fe2+ and can therefore bind with 2 oxygen molecules. This results in one haemoglobin molecule being able to carry four oxygen molecules.
Haemoglobin readily associates with oxygen (binds with oxygen), when gaseous exchange takes place and readily dissociates with oxygen when in contact with tissues that need oxygen. This happens because haemoglobin can change its affinity for oxygen, depending on the conditions of the environment it is in:
- High levels of carbon dioxide means the haemoglobin will more readily dissociate with the oxygen molecules (the bohr effect)
- Low levels of carbon dioxide means the haemoglobin will more readily associate with oxygen.
There are two types of haemoglobin ones that have a high infinity for oxygen (bind with oxygen more easily but release it less readily) and ones that have low affinity for oxygen (take up oxygen less easily but release more readily.). There is a correlation between the type of organism, where its lives and the ratio of high to low affinity haemoglobin molecules. These are displayed on graphs called oxygen disassociation curves. This is a graph of partial pressure of oxygen against saturation of haemoglobin with oxygen. The further the curve on the graph is to the left (the lower the partial pressure of oxygen) the greater the affinity of haemoglobin for oxygen and the further to the right the curve (the higher the partial pressure of oxygen) the lower the affinity of haemoglobin for oxygen.
To combine properly with oxygen, the red blood cells must contain adequate haemoglobin; this, in turn, depends on the amount of iron in the body. The organism derives its store of iron by absorption from the gastrointestinal tract. The organism conserves and constantly reuses the supply of iron. A deficiency of haemoglobin caused by a lack of iron leads to anaemia.
What is altitude training?
The main aim of altitude training is to increase red blood cells and haemoglobin mass. This improves the ability of blood to carry oxygen as it increase vo2 max and aerobic performance.
describes altitude training as ‘a way to encourage the body to produce more red blood cells, which help improve endurance when performing activities at lower altitudes’. The purpose of altitude training therefore seems to be to increase the number of red blood cells within the blood. It is used by endurance athletes as it means oxygen can be carried to muscles more efficiently as there are more red blood cells available to carry the oxygen.
The high altitudes mean that the atmospheric pressure around the individual is lower than what it is at sea level. This lower atmospheric pressure results in the oxygen pressure gradient between the lungs and the blood is reduced. This causes an increase in oxygen, which is detected by specialised cells in the kidneys and so the hormone erythropoietin is released. This hormone stimulates red blood cell production. The hormone enters the bone marrow and bind with the erythropoietin receptors on the stem cells. The stem cells then divide and form new red blood cells, which are then released into the blood stream.
The aim of this experiment is to either prove or disprove the hypothesis that altitude training increases the bloods efficiency of carrying oxygen around the body. Also to prove or disprove the null hypothesis that altitude training has no effect on the bloods capability to transport oxygen around the body.
This experiment involves comparing three samples of blood:
- A – Represents the blood taken from a healthy adult male who lives at sea level
- B – Represents the blood taken from the same male after six months of regular aerobic exercise
- C – Represents the blood taken from the same male after he spent three months undergoing aerobic training at altitude. (altitude training for three months)
The densities of each sample of blood will be investigated because in order for the blood to be more efficient at carrying oxygen the composition of the blood must have changed. As haemoglobin is the component of blood which transports oxygen to the organs and around the body it is an increase in these that would cause the blood to become more efficient at carrying blood, hence the density of the blood would increase. The densities of blood will be investigated by measuring the rate at which drops of blood fall through 100cm3 of copper (II) sulphate solution. The longer it takes for the blood drops to fall through the 100cm3 copper (II) sulphate solutions, the lower the density of the blood. I predict that sample A will take the longest to pass through the copper (II) sulphate solution because blood density would be of norm and whereas exercise increases blood density and so does altitude training (from background information) so drops of blood from B and C will fall more quickly . I predict that sample C will fall more quickly through the solution because it is off higher density due to the increase of haemoglobin from the altitude training. (See background information.)
Method
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First label three 100cm3 measuring cylinders with sample A sample B and sample C.
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Next fill each one with copper (II) sulphate until the meniscus is 5 cm above the marked 100cm3 line.
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Fill one of the 1cm3 syringes (fitted with long needle) with blood from sample A.
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Drop 1 drop of blood from the syringe into the measuring cylinder when the meniscus of this drop reaches the 100cm3 marked lines immediately start timer.
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Observe and time how long it takes for the drop to reach the 0cm3 marked line. When it reaches the 0cm3 line stop the timer.
- Record time in table and repeat steps 3-5 till ten consistent results are obtained.
- Repeat steps 3-6 for sample B and C remembering in step 3 to add blood from the sample being observed.
- Plot a graph of time taken (s) against result number (e.g. reading 1 was 2.43s so plot 2.43s against, result 2 was 2.45s so plot 2.45s against 2). Plot results from all three blood samples on the same graph making it easier to compare them.
- Next compare results A and B to result C by using the chi- square statistic, using first A as expected and then B as expected.
- Then compare the critical values obtained for both comparisons of A vs. C and B vs. C to the number stated in the degrees of freedom table.
- If the critical number are larger than the stated degrees of freedom value then the null hypothesis can be rejected if not accept null hypothesis.
Results
Anomaly results repeated following results used in averages instead:
- A3 – 11.16, A7 – 11.28
- B3 – 9.53
- C2 – 7.21 , C4 – 7.39
My results show that blood sample C was indeed the densest as it dropped through the copper (II) sulphate solution the quickest at an average of 7.28s. The slowest average time taken for the blood drop to fall through the 100cm3 copper (II) sulphate solutions was 11.24s and was of blood sample A , making this the least dense of the three samples. This proves my prediction correct as blood A did indeed take the slowest.
Chi square (C2) – blood sample A vs. blood sample C (with A as the expected)
Chi square (C2) – blood sample B vs. blood sample C (with B as the expected)
Table from for degrees of frequency
Comparing two sets of data so df= 1 which gives value of 3.84 both sets of data are higher than the degrees of freedom value , so I can reject my null hypothesis and state that altitude training does have an effect on the density of blood and the haemoglobin as more red blood cells are present in the blood.
. Also the null hypothesis of altitude training having no significant effect on the density of blood and its ability to carry oxygen can be rejected.
Overall altitude training does increase the density of blood as more red blood cells are present in the blood.
Evaluation
I feel my experiment gave reliable results, which were consistent with the facts that were stated in the background information. Moreover the chi squared statistical test showed that results gained were not down to chance.
If I did this experiment again I would use blood samples from both female and males and maybe from different age groups. This would increase the validity of my results as the sample size would be larger. This data would also eliminate the possibility that the blood sample could have been contaminated or adjusted. The only problem with these alterations is that it may be considered unethical to take blood from children to test for density changes. In terms of reliability, I think that my results were reliable because I decided to take 10 repeat readings for each blood type.
A limitation to this experiment was apparatus. I feel it may have been better to use data loggers or even record the drop falling this would help obtain more precise and accurate readings. Also I could not say that each drop was off the same volume at the start as each drop could not really have been measured. Next time maybe a measured volume of blood could be used to drop and therefore the results would be more reliable and would reduce error of results due to volume of blood in each drop.
Because the results demonstrate the expected results I feel that they are reliable and that the experiment was a success.
