In women, the first division of meiosis produces one daughter cell that has almost all of the cytoplasm - AQA - A-Level Biology - Question 3 - 2018 - Paper 3

The correct process is 'Crossing over'. This process allows for the alleles to be recombined during meiosis.

First, we calculate the radius of the polar body, which is half its diameter: ( r = \frac{10.4 , \text{μm}}{2} = 5.2 , \text{μm} ).

Using the volume formula, we find:

$V = \frac{4}{3} \pi (5.2)^3 = \frac{4}{3} \times 3.14 \times 140.608 = 589.73 \, \text{μm}^3$

Next, we use the density of the mitochondria to calculate the total number:

Number of mitochondria = Volume of polar body × Density = ( 589.73 , \text{μm}^3 \times 0.08 , \text{mitochondria/μm}^3 = 47.18 \approx 47 ) mitochondria.

The treatment prevents inheritance of mitochondrial diseases by removing the nucleus from an egg cell of a woman with faulty mitochondria and replacing it with a nucleus from a polar body of a healthy woman. This way, the egg cell created will have normal mitochondria from the healthy donor egg, reducing the chances of passing on faulty mitochondria.

One reason is that if the mitochondria are faulty, they produce little or no ATP, which is essential for cellular processes. Without enough ATP, essential enzyme-catalyzed reactions cannot occur efficiently, drastically reducing cellular function and energy production.