Figure 9 shows a diagram of a red blood cell from a turtle and a diagram of a red blood cell from a human - Edexcel - GCSE Biology Combined Science - Question 5 - 2018 - Paper 1

To find the magnified length of the red blood cell:

1. Use the formula for magnification:

   $ext{Magnification} = \frac{ ext{Magnified length}}{ ext{Actual length}}$

2. Rearranging gives:

   $ext{Magnified length} = ext{Magnification} \times ext{Actual length}$

3. Plugging in the values:

   $ext{Magnified length} = 400 \times 20.5 \text{ µm}$

   $= 8200 ext{ µm}$

   Thus, the length of the magnified image is 8200 µm.

To find the actual width of the human red blood cell:

1. Use the magnification formula again:

   $ext{Magnified length} = \text{Magnification} \times \text{Actual width}$

2. Rearranging gives:

   $\text{Actual width} = \frac{ ext{Magnified length}}{ ext{Magnification}}$

3. Using the values:

   $\text{Actual width} = \frac{3.08 ext{ mm}}{400}$

   $= 0.0077 ext{ mm}$

   To convert this to nanometers (1 mm = 1,000,000 nm):

   $0.0077 ext{ mm} = 0.0077 \times 10^6 ext{ nm}$

   $= 7700 ext{ nm}$

   In standard form, the actual width is 7.7 x 10³ nm.