The diagram represents red and white blood cells seen under a light microscope - HSC - SSCE Biology - Question 13 - 2005 - Paper 1

To determine what X, Y, and Z represent on the scale, we need to analyze the size of red and white blood cells observed under a light microscope.

Step 1: Understanding the size of blood cells

Typically, red blood cells have an average diameter of about 7-8 μm while white blood cells are larger, ranging from 10-20 μm. Given that the diagram scales these cells, the options must reflect realistic measurements for microscopic measurements.

Step 2: Comparing options

• (A) 0, 10, 20 m: This scale is too large; red and white blood cells cannot be measured in meters.
• (B) 0, 10, 20 μm: This range is plausible for the cell sizes observed.
• (C) 0, 50, 100 μm: 50 μm is larger than typical cell sizes, hence less realistic for this context.
• (D) 0, 50, 100 mm: This scale is far too large for blood cells.

Conclusion

Among the given options, (B) 0, 10, 20 μm is the most appropriate as it correlates with the actual dimensions of red and white blood cells under a light microscope.