Investigating the density of blood

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Joe Ainsworth        Page         7/5/2007

Investigating the density of blood

Introduction

I will investigate the relative density of three unknown blood samples by measuring the time taken for drops of simulated blood to fall under gravity through a solution of copper II sulphate. By comparing the two samples I can determine the relative density of them compared to the normal sample.

There are three separate samples of simulated blood and each one will be tested.

  1. Sample 1 will be from a healthy male
  2. Sample 2 will be from the same male after 6 months of regular exercise.
  3. Sample 3 will be from the same male after suspected blood doping.

By analysing the results obtained I should be able to determine the relative density of the blood.

Background scientific knowledge and understanding

I would expect an average healthy male to contain 5-7 litres of blood. Each drop of blood would contain

  • 250 million red blood cells
  • 400,000 white blood cells
  • and 15 million platelets 1

Located with the erythrocytes is haemoglobin. Haemoglobin transports oxygen which is used for respiration. The red blood cells transport the haemoglobin so it can be delivered to wherever needed inside the body, however haemoglobin has a relatively small weight for a respiratory pigment. Haemoglobin molecules are able to pick up oxygen where it is plentiful and transport and release it to where energy levels are low in the body. This is important when exercising or playing a sport when you require a lot of extra oxygen. As cells in tissues are respiring more when exercising they are using up more oxygen, this means the concentration of oxygen in these areas will be low. To continue performing well they require more oxygen. The oxygen in the haemoglobin will now find its way to the tissue and will diffuse from the red blood cell, this method keeps a relatively good consistent supply of oxygen. Haemoglobin weighs very little.

In sample 1, the healthy male will have around 250 million red blood cells in a drop of blood each one containing 300 million haemoglobin molecules to transport oxygen, this droplet of blood would be low in density. The normal value of haemoglobin in a male would be 150gdm-3. In samples 2 and 3 I will expect to see more red blood cells than sample 1, this means that they will contain a larger haemoglobin mass. 2

Sample 2 is from the same healthy male who has been exercising regularly for 6 months. When exercise is taken regularly your body becomes accustom to it and you will find that each time you take regular exercise you will be able to carry on for longer i.e. your stamina will become better. This is because the bone marrow is producing a hormone called EPO (erythropoietin). EPO stimulates bone marrow to make red blood cells and because there are more red blood cells being produced this means more oxygen can be carried hence why stamina increases. For these reasons sample 2 will have a larger mass of red blood cells because the male participates in regular exercise. The blood will be denser with more red blood cells, however the increase in density will not be that dramatic as it takes along time to build up a larger quantity of red blood cells than normal. The density of the blood will be slightly more than that of sample 1 and therefore I expect it to sink faster than sample 1.

Sample 3 has suspected blood doping. There is also a synthetic EPO that can be manufactured which also stimulates the production of red blood cells. In blood doping athletes inject the synthetic hormone into their body a several weeks before a key event or race to increase their red blood cell count. If done correctly, blood doping can increase the haemoglobin level and RBC count by up to 20%. 3

Professional athletes require huge amounts of oxygen in their muscles to perform at the best of their abilities. Increasing the density of red blood cells can theoretically improve performance. It is extremely difficult to differentiate between synthetic EPO and normal EPO. In sample 3 the same male has used blood doping thus greatly increasing his red blood cell count and increasing the mass of his blood more than in sample 2. I expect sample 3 to travel the 90cm3 fastest because of the increase in density of the male’s blood.

Methods

There are a variety of methods I could use to perform my investigation, however not all are appropriate. Here is a list of methods,

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Prediction summary

I will expect to gain different results for each sample. There are a number of factors which will lead to this. From the information of the samples above I can predict that,

  1. Sample 1 will travel the distance the slowest
  2. Sample 2 will travel faster than sample 1 but not quite as fast as the blood from sample 3.
  3. Sample 3 will travel the fastest.

Pilot data

I used the following method when I did my pilot experiment,

  1. I filled three measuring cylinders with the 0.1-3 copper II sulphate solution. ...

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