Biology Assessment Study Sheet. Estimating the size of Red Blood Cells

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1 Biology Assessment Study Sheet Perform a first-hand investigation using a light microscope and prepared slides to gather information to estimate the size of red and white blood cells and draw scaled diagrams of each. Estimating the size of Red Blood Cells AIM: To observe prepared slides of human blood and estimate the size of red and white blood cells to draw a scaled diagram HYPOTHESIS : diagram MATERIALS: pre-prepared slides of human blood, light microscope, mini-grid (ruler) with millimetres, paper, pencil, ruler, calculator Method: RISK Infection due to use of human blood Microscopes are heavy and may injure is dropped PRECAUTION Take care when handling blood samples, only use pre-prepared slides Grasp microscopes firmly by the neck and base 1. Ensure the microscope is securely on the bench and everything is in working order 2. Rotate the noise piece so that the lowest power objective is in position 3. Obtain a slide and, making sure it is the correct way up with the cover slip on top, put it on the stage and hold it in place with the stage clips. 4. Switch on the microscope light and adjust the light intensity 5. Using the coarse focus nob and watching from the side of the microscope, wind the stage up until the tip of the low power objective lens is 5mm from the slide 6. Look through the eyepiece and use the coarse focus knob to slowly move the stage downwards to bring the specimen into focus 7. Use the fine focus knob to bring the specimen into sharp focus. If necessary move the slide around so that it is in the centre of the field. 8. Place the mini-grid on the microscope stage and move it so that the edge of the grid line is against the side of the field of view (circle) 9. Place clear glass slide on stage and small minigrid on top. 10. Place the prepared slide of a blood smear on the microscope stage under low magnification. 11. Use the low and high-power objective to locate the specimen, once it is in focus, rotate the high power objective into place 12. Distinguish between the numerous small red blood cells and the few, larger white blood cells 13. Count or estimate the approximate number of red blood cells that would fit across the diameter (imaginary centre line) of the field of view. 14. Using these number and the known diameter for the field of view, calculate the size of each blood cell by dividing the diameter of the field of view by the number of cells which fit across it.

2 15. Repeat this process three times within different fields of view to determine an average size for red blood cells 16. Record the results 17. Draw a scaled diagram of both the red blood cell and white blood cells ensuring to include the magnification and a scale in micrometers. Table 1.0 Estimated sizes of red and white blood cells Estimated number of red blood cells Size of RBC (micrometers μm) DISCUSSION: Trial 1 Trial 2 Trial μm 7.8μm 7.14μm Trial 1 Trial 2 Trial 3 Average size of one cell μm Average size of one cell Estimated number of white blood cells Size of WBC (micrometers μm) μm 13.7μm 12.5μm 13.03μm This scientific investigation aimed to estimate the size of red and white blood cells using a light microscope. By measuring the field of view and the diameter, we were able to approximate the average size of both red and white blood cells in micrometers. After concluding the experiment it was apparent that my results coincided with my hypothesis that red blood cells were smaller in average as 7.44μm in comparison to white blood cells 12.89μm. There was a disparity of 5.59μm in average size. The red blood cell was small, round and biconcave Red colour of blood is due to the presence of a complex protein molecule called haemoglobin. Their function is to transport respiratory gases; mainly oxygen. They have no nuclei and only live for 3 months before being destroyed in the liver or spleen. There 5-6 million in every millimetre of blood. White blood cells are also known as leucocytes, are irregularly shaped. They have the function to defend against disease; the main types being phagocytes and lymphocytes It is biconcave in structure which improves the diffusion of oxygen as it increases the surface to volume ratio, no nucleus as after entering into the blood stream after being formed in the bone marrow, each red blood cells has lost its nucleus Red cells make up less that 50% of blood and the white cells and platelets together make up less than 1% Red blood cells also known as erythrocytes are the most abundant, evidenced within the high power microscope field, there are hundred of red blood cells and only one or two white cells visible. Leucocytes are also produced in the bone marrow and are larger than red blood cells around 5-% bigger. They staining method in preparing a slide, the nucleus appears purple in colour. Less abundant and are about 1.5 times the size of red cells.

3 Platelets are fragments of function is to make the blood cells. No nucleus marrow old cells and their blood clot. Smallest and made in the bone 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. RELIABILITY There was a low level of reliability during this experiment. Whilst we used the trials to attain averages, the entire investigation relies on estimation and human error would have greatly impacted on the results. Despite this the results coincide with scientific knowledge and other student s results which suggest that the average size of red blood cells ranges between 6-8 micrometers and white blood cells are typically between 7-21 micrometers. The ruler was also easily knocked and was not as accurate say if a microgram was used and open to human interpretation, so a margin of error must be taken into consideration. Further repetition of the experiment using more scientifically accurate materials may have increased the reliability of the results. Suggested improvements : repeated numerous times with more scientifically accurate equipment smaller measuring device RELIABILITY The investigation possesses moderate validity, reduced by the human fallacies in the procedure itself. There was little precision in the material used, margin of er

4 Size of Red & White Blood Cells _Maintaining_a_Balance_by_Faisal_Abdul.pdf AIM: Perform a first hand investigation to estimate the size of red and white blood cells and draw diagrams HYPOTHESIS: White blood cells are larger than red blood cells MATERIALS: pre-prepared slides of human blood, light microscope, mini-grid, paper, pencil, ruler RISK ASSESSMENT METHOD: 1. Set up the compound microscope and place a small ruler on the stage 2. Focus on lower power objective (x10) and use your ruler to calculate the field of view 3. Observe the prepared blood slide under the microscope and observe under low power (x10) and high power objective (x40) 4. Use the establishes field to work out the size of the red and white blood cells

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