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 of ba... 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?
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Answer
The correct statement is A: each pair of bases is joined by hydrogen bonds. This is significant as it ensures the integrity of the DNA structure and allows for the precise pairing of complementary bases.
Step 2
Describe how this data provides evidence for base pairing in DNA.
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Answer
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.
Step 3
Calculate the mass of DNA from a haploid human cell.
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Answer
To find the mass of DNA from a haploid human cell, divide the mass obtained from a diploid cell by 2:
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Answer
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.
Step 5
State two variables the student needs to control.
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The volume of buffer solution used in the extraction process.
The duration of the crushing process, to ensure consistent breaking down of the fruit tissue.
Step 6
Give one reason why the student repeated the experiment.
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The student may have repeated the experiment to confirm the reliability and accuracy of the results obtained from the first trial.
Step 7
Compare the outcomes of mitosis and meiosis.
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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.
