Q3. Calculating the number of Lactobacillus in a 1-litre curd packet:
Your friend Ravi has been given a powerful microscope, 1 litre of curd packet and lots of distilled
water. Ravi was asked to think of a way to calculate the number of Lactobacillus bacteria present in
the curd packet. Ravi chose multiple methods and in the end, he was successful in calculating it.
Method 1: Ravi took 1 millilitre of curd and then he put it on a slide. He said that he will count the
number of bacteria in 1 millilitre and then he will multiply the count by 1000. He started to observe
the Lactobacillus. What is the problem that he will face in this method?
Method 2: Ravi took 0.1 millilitres of curd this time instead of one 1 millilitre. He said that he will
count the number of bacteria in 0.1 millilitres and then he will multiply the count by 10,000. He
started to observe the Lactobacillus. What is the problem that he will face in this method?
Method 3: Both of the above methods did not work. Ravi suddenly remembers that he has lots of
distilled water. This time Ravi took 0.1 millilitres of curd and mixed it in 10 litres of distilled water.
He then took 1 millilitre of the distilled water that was mixed with the curd. He could count the
number of bacteria in this 1 millilitre of a water drop. After this, he used simple maths to tell the
number of bacteria in 1 litre of curd. Why do you think that this method is better?