Blood is a liquid medium that is the main transporter of heat, nutrients, wastes, gases and other chemicals around the body. Blood is composed of three types of blood cells: red blood cells, white blood cells and platelets, which are all produced in the bone marrow. Erythrocytes (red blood cells) are the most abundant cells in blood. Their primary role is to transport oxygen around the body. Red blood cells contain only a nucleus when they are formed but as the cell develops, it disappears and a red pigment called haemaglobin is formed inside the cell. Because these cells contain no nucleus, they are quite small in size in comparison to white blood cells with a theoretical diameter of 7um (micrometers). Their structure is biconcave, not spherical to increase their surface area. Red blood cells appear red in colour because of the iron protein molecule haemaglobin. The haemaglobin is what assists the red blood cell in transporting oxygen around the body.
Leucocytes (white blood cells) have a primary function of working with the immune system. They protect the body from strange and invading illnesses and are less abundant in blood than red blood cells. They are in theory 50% larger than red blood cells and unlike the red blood cell, they contain a nucleus their whole life span. These cells have no set structure and are usually unusual in shape.
In this experiment, the size of red blood cells will be estimated by viewing a sample of blood through a light microscope and using a field of view to estimate their diameter.
To estimate the size of red blood cells seen with a light microscope.
The size of the red blood cells will have a diameter near to 7um and the white blood cells will be 50% larger.
Risk assessment: Risk | Prevention | 1. Glass slides may break 2. Microscopes are heavy and may cause injury when dropped | 1. Handle all glassware with care and wear safety goggles whilst handling to ensure eyes are safe from shattering glass 2. Carry microscope with two hands, with one hand supporting the base of the microscope to avoid the potential hazard of dropping it |
Materials: * Light microscope * A slide of a blood sample * A calculator * A grid slide
Refer to BIF page 38
1. Field of view x40 = 180um 2. Field of view x100 = 160um 3. Field of view x400 = 400um (160/0.4 = 400)
Table to show the results of estimating the size of red blood cells.
Blood cell | Estimate 1 | Estimate 2 | Estimate 3 | Average | Red Blood Cell | 400/54= 7.4um | 400/58= 6.8um | 400/56= 7.1um | 7.1um | White blood cell | 7.4 x 2= 14.8um | 6.8 x 2-=13.6um | 7.1 x 2= 14.2um | 14.2um |
Observations: * The red blood cells could only be viewed under magnification x400, hence, the field of view was divided by the estimated number of blood cells counted across the diameter. * There were no outlying results * The results reached close to the theoretical value of 7um for the red blood diameter.
Discussion questions: 1. To distinguish between red and white blood cells, one could see that there were many red blood cells in the sample of blood whereas there were only a few white blood cells. The red blood cells appeared to be 50% smaller than the white blood cells and did not contain a nucleus like the white cells. The white cells were irregular in shape whereas the red blood cells were spherical structures. 2. It was evident that the blood sample contained many more red blood cells than white blood cells. The results show that on average, 56 red blood cells were present across the diameter of the slide on magnification x400, where only 2 white cells, which were stained purple, were evident. If there were more white cells than red cells, there would be serious effects such as the risk of a fatal illness such as Leukemia. 3. It was