Theory: The red blood cell is shaped like a biconcave disc. This cell has a large surface area to volume ratio as a means of increasing diffusion. The typical cell has a size of 7 µm which makes it only able to move in single file in the capillaries as the diameter of the capillary is about 7m as well. As a result, this maximizes area for diffusion to take place. The membrane of the red blood cell is thin so that rapid diffusion can take place and pliable so that one will be able to squeeze through the capillaries since they are similar in diameter. Some of the organelles within the red blood cell include mitochondria and endoplasmic reticulum. It however, does not contain a nucleus. The benefit of having little number of organelles is that more haemoglobin molecules can be packed into the red blood cell (280 million Hb molecules per red blood cell). The role of the red blood cell is to transport 02 and CO2 to some extent. The oxygen transporting component is haemoglobin. The function of haemoglobin is to rapidly pick up O2 in the lungs and rapidly release it into the tissue. The property which allows haemoglobin to function this way is its high affinity for O2 at higher O2 tensions and its low affinity for O2 at lower O2. These properties are effectively taken advantage of in the lungs and tissue.
Between men and women, there are usually 5 million red blood cells per cubic centimetre of blood at sea level.
Aim: To identify the number of red blood cells in blood samples under a light microscope.
Apparatus & Material:
- Light microscope
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Slides (5cm 2cm)
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Cover slips (2m 2cm)
- 3 Blood samples
- Micropipette
Diagram:
Method:
- Take one of the blood samples and using the micropipette place 0.1 ml a drop of blood on the slide.
- Using another slide the drop should be spread evenly over the non-frosted area on the slide( if slide has no frosted areas on either side, over a suitable, similar region for each slide).
- Place a cover slip over the area of the blood and view under the light microscope at high power.
- Count the number of red blood cells present.
- Repeat steps 1 to 4 for the other blood samples.
Variables:
Controlled Variable:
- The size of the slides, i.e. the area that the drop of blood should be spread across for viewing under light microscope
- Drop of blood from each sample( 0.1 ml from micropipette).
Manipulated Variable:
- The different samples of blood used.
Responding Variable:
- The number of red blood cells counted from each slide.
Results
Table 1.0 shows results recorded when number of red blood cells were counted under light microscope.
Expected Results: It would be expected that Sample C would contain the most number of red blood cells followed by Sample B then followed by Sample A.
Interpretation: In men and women, there are usually 5 million red blood cells per cubic centimetre of blood at sea level. However, with aerobic exercise, studies have shown that the number of red blood cells increases. In addition, studies have also shown that with an increase in altitude the oxygen concentration increases and in humans, the numbers of red blood cells increase to accommodate this change. Therefore Sample A would be expected to have the least number of red blood cells since the male had not undergone aerobic exercise and was living at sea level. Sample B would then expected to have more red blood cells than Sample A but less than sample C since the male had undergone exercise at only sea level compared to in the mountains in Sample C.
Limitations:
- The blood samples may contain more blood cells than can be counted as a result the red blood cell density should be used to compare blood cell concentrations.
- Red blood cells don not live for more than 120 days.
Precautions:
- In each sample under the microscope, the red blood cells should be counted over the same area. The use of a graticule can be used to ensure this.
Improvements: Erythropoietin is a hormone that is secreted by the kidney that controls the number of red blood cells. It stimulates the bone marrow to produce red blood cells and therefore the levels of erythropoietin in the blood can be measured to ensure the results are accurate.