Examining_Blood_Cells

First hand investigation 5.3.1 Examining blood cells Aims: • To observe prepared slides of human blood and describe the visible cells • To estimate the size of red blood cells and white blood cells • To draw scaled diagrams of red and white blood cells Hypothesis: On close examination of blood there should be differences in the size and shape of cells, indicating that blood is made up of a number of different components Material: • Prepared slides of human blood • Light microscope • Graph paper photocopied onto transparency PART A – MAKING OBSERVATIONS Method: 1. Draw up a table like table 5.3.2 2. Examine the blood smears provided and use the labelled diagrams provided to try to identify at least three different types of blood cells 3. Record your observations of a red blood cell and as many different white blood cells as you can identify Results Type of blood cells shape Other distinguishing features Red blood cells Circle Light pink/purple; very small White blood cells Curvy Darker in colour; larger PART B – ESTIMATING SIZE Method: 1. Draw up a table like table 5.3.3 2. Place graph paper under low power (10x) and calculate the diameter of your field of view in millimetres (mm). Then multiply this measurement by 1000 to convert it to micrometers) 3. Now calculate what your field of view in high power will be. (if using the 40x lens, your field of view will be one-quarter of what it was under 10x. If using the 100x lens, the field view will be one-tenth) 4. Place the prepared blood slide under low power and focus. Then switch to high power. Move the slide around to find some different types of cells 5. For each type of cell you can identify, estimate: a) The number of cells of that type that could fit across the diameter of the field of view b) The size (µm) of one cell of that type 6. Record your estimates in table 5.3.3 Results: Type of blood cell Diameter of field (µm) Estimated number of cells that could fit across diameter Estimated size of one cell (µm) PART C – DRAWING SCALE DIAGRAMS Method: 1. Choose one red blood cell and one white blood cell to draw. You will be drawing these side by side to show the sizes of the cells relative to one another 2. Refer to the cell measurements you made earlier to decide on a suitable scale for your diagram. 3. Draw the white blood cell to scale. Use a ruler to draw the scale you used underneath 4. Draw the red blood cell, using the same scale. Label the cells Discussion Questions: 1. Identify the most common type of cell you observed in the blood preparation Red blood cells 2. Outline why this cell is the most common The red blood cell is the most common because it contains and is rich in oxygen, something our body needs 3. Explain why there is more than one type of white blood cell in blood. There is more than one type of blood cell because each type of white blood cell has a specific job and fights foreign material such as: fungi, parasites etc. 4. Using your diagrams as a guide, identify the size of a red blood cell relative to a white blood cell The white blood cell is relatively larger than the red blood cell