8 (a) James Watson and Francis Crick built a model that showed that DNA has a double helix structure - Edexcel - GCSE Biology - Question 8 - 2019 - Paper 1

The data in Figure 13 shows that the percentages of adenine (A) and thymine (T) are equal, as well as the percentages of cytosine (C) and guanine (G). This complementary base pairing is crucial for the stability of the DNA double helix, as adenine pairs with thymine through two hydrogen bonds, and cytosine pairs with guanine through three hydrogen bonds.

To find the mass of DNA from a haploid human cell, divide the mass obtained from a diploid cell by 2:

ext{Mass from haploid} = rac{0.0062 ext{ nanograms}}{2} = 0.0031 ext{ nanograms}

Then convert to picograms:

$0.0031 ext{ nanograms} imes 1000 = 3.1 ext{ picograms}$

Ethanol is used to precipitate the DNA, as it reduces the solubility of DNA in the solution, allowing for easier separation and visualization of the DNA strands.

1. The volume of buffer solution used in the extraction process.
2. The duration of the crushing process, to ensure consistent breaking down of the fruit tissue.

The student may have repeated the experiment to confirm the reliability and accuracy of the results obtained from the first trial.

Mitosis results in two genetically identical daughter cells, each with the same number of chromosomes as the parent cell, which is essential for growth and tissue repair. In contrast, meiosis produces four genetically diverse daughter cells with half the number of chromosomes, which is crucial for sexual reproduction and genetic variation.