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
Question 8
8 (a) James Watson and Francis Crick built a model that showed that DNA has a double helix structure.
(i) Which statement about DNA is correct?
A each pair o... show full transcript
Worked Solution & Example Answer: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
Step 1
Which statement about DNA is correct?
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The correct statement about DNA is A: each pair of bases is joined by hydrogen bonds. This is fundamental to the structure of DNA, as hydrogen bonds between complementary bases (A-T and G-C) maintain the stability of the double helix.
Step 2
Describe how this data provides evidence for base pairing in DNA.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The data from Figure 13 shows that the percentages of adenine (A) and thymine (T) are approximately equal, as well as the percentages of guanine (G) and cytosine (C). This suggests that A pairs with T and G pairs with C in the DNA structure, providing empirical evidence for the base pairing rule.
Step 3
Calculate the mass of DNA the scientist should obtain from a haploid human cell.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To find the mass of DNA in a haploid human cell, we divide the diploid mass by 2. 0.0062 nanograms ÷ 2 = 0.0031 nanograms. Since 1 nanogram = 1000 picograms, this is equal to 3.1 picograms.
Step 4
State why ethanol is used.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Ethanol is used to precipitate the DNA from the solution. When ethanol is added, it decreases the solubility of DNA, allowing it to be separated and visible.
Step 5
State two variables the student needs to control when using this method to compare the mass of DNA from these two fruits.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The amount of fruit used in each extraction should be the same to ensure a fair comparison.
The extraction time should be consistent for both fruits to avoid discrepancies in yield due to time variation.
Step 6
Give one reason why.
97%
121 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The student repeated the experiment to ensure the results were reliable and reproducible, thus confirming the data obtained.
Step 7
Compare the outcomes of mitosis and meiosis.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Mitosis results in two genetically identical daughter cells, maintaining the same chromosome number as the parent cell. In contrast, meiosis produces four genetically diverse daughter cells, each with half the chromosome number (haploid), essential for sexual reproduction.
