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What is a mutation? A mutation is a change in the DNA sequence of an organism - AQA - GCSE Biology - Question 7 - 2022 - Paper 1
Question 7
What is a mutation? A mutation is a change in the DNA sequence of an organism. This can involve alterations in the base code or nucleotide sequence, which may affec... show full transcript
Worked Solution & Example Answer:What is a mutation? A mutation is a change in the DNA sequence of an organism - AQA - GCSE Biology - Question 7 - 2022 - Paper 1
Step 1
How many algal cells are in the 0.2 mm × 0.2 mm square in Figure 9?
Answer
To determine the number of algal cells in the specified area, count the cells that are completely contained within the 0.2 mm × 0.2 mm square without touching the top or right sides. Based on the counting grid, there are 16 algal cells within the specified area.
Step 2
Calculate the number of algal cells in 1.0 mm³ of undiluted pond water. Use the scientist’s second count of 14 cells.
Answer
To calculate the number of algal cells in 1.0 mm³ of undiluted pond water, first find the volume of diluted pond water used:
- Volume of sample = 0.2 mm × 0.2 mm × 0.1 mm = 0.004 mm³.
Since the scientist counted 14 cells in the 0.004 mm³ of diluted pond water, the concentration can be expressed as:
ext{Cells per mm³ of diluted pond water} = rac{14}{0.004} = 3500 ext{ cells/mm³}.
Given that the dilution factor was ¼, we multiply the count by 4 to find the undiluted concentration:
ext{Cells in 1 mm³ of undiluted pond water} = 3500 imes 4 = 14000 ext{ cells/mm³}.
Step 3
Suggest why the scientist diluted the pond water before placing it on the special slide.
Answer
Diluting the pond water makes it easier to count the algal cells by reducing the cell density. This ensures that the cells are more spread out, which minimizes overlap and allows for accurate counting.
Step 4
Explain how the use of the thin coverslip would affect the results for the cell count.
Answer
Using a thin coverslip instead of a thick one may cause the liquid to pull the coverslip downwards slightly. This could result in a smaller volume being counted and may lead to an underestimation of the algal cell count, as some cells may be obscured or less visible.