Each colony starts as one bacterium. Every time bacteria reproduce, the number of bacteria in each colony doubles. (a) Calculate the number of bacteria in a colony after five hours, if each bacterium reproduces every 30 minutes. (2) (b) Some bacteria are pathogens: (ii) Explain why antibiotics can be used to treat bacterial infections. (2) (iii) A rod-shaped bacterium is 0.005 mm long. A student draws the rod-shaped bacterium. The bacterium in the drawing is 80 mm long. Calculate the magnification of this drawing. (2)

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Each colony starts as one bacterium - Edexcel - GCSE Biology - Question 3 - 2023 - Paper 1

Question 3

Each colony starts as one bacterium. Every time bacteria reproduce, the number of bacteria in each colony doubles. (a) Calculate the number of bacteria in a colony... show full transcript

Worked Solution & Example Answer:Each colony starts as one bacterium - Edexcel - GCSE Biology - Question 3 - 2023 - Paper 1

Step 1

Calculate the number of bacteria in a colony after five hours

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Answer

To find the number of bacteria in the colony after five hours, we can use the formula for exponential growth:

Let the initial number of bacteria be $N_0 = 1$ . Every 30 minutes, the population doubles, so:

the number of doublings in 5 hours = ( \frac{5\text{ hours} \times 60\text{ minutes}}{30\text{ minutes}} = 10 ) doublings.

The formula becomes:

$N = N_0 \times 2^{n} = 1 \times 2^{10} = 1024$

Thus, the number of bacteria in the colony after five hours is 1024.

Step 2

Explain why antibiotics can be used to treat bacterial infections

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Answer

Antibiotics are used to treat bacterial infections because they specifically target and kill bacteria or inhibit their growth. They work by disrupting critical processes in bacterial cells, such as:

Cell wall synthesis: Many antibiotics (like penicillin) prevent bacteria from forming their cell walls, which are essential for their structural integrity.
Protein synthesis: Some antibiotics inhibit the bacterial ribosomes, which are crucial for producing proteins vital for growth and reproduction.
DNA replication and repair: Certain antibiotics interfere with enzymes involved in DNA replication, leading to bacterial cell death.

Because human cells do not have these structures, the antibiotics selectively affect bacterial cells without harming human cells.

Step 3

Calculate the magnification of this drawing

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Answer

To calculate the magnification of the drawing, we can use the formula:

$\text{Magnification} = \frac{\text{Size of image}}{\text{Actual size}}$

In this case:

Size of image = 80 mm
Actual size of bacterium = 0.005 mm

Thus, substituting the values gives:

$\text{Magnification} = \frac{80 \text{ mm}}{0.005 \text{ mm}} = 16000$

Therefore, the magnification of the drawing is 16000.

Each colony starts as one bacterium - Edexcel - GCSE Biology - Question 3 - 2023 - Paper 1

Worked Solution & Example Answer:Each colony starts as one bacterium - Edexcel - GCSE Biology - Question 3 - 2023 - Paper 1

Calculate the number of bacteria in a colony after five hours

Explain why antibiotics can be used to treat bacterial infections

Calculate the magnification of this drawing

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