GATE2017 ME-1: GA-10

Question

The growth of bacteria (lactobacillus) in milk leads to curd formation. A minimum bacterial population density of $0.8$ (in suitable units) is needed to form curd. In the graph below, the population density of lactobacillus in $1$ litre of milk is plotted as a function of time, at two different temperatures, $25^{\circ}$C and $37^{\circ}$C.

Consider the following statements based on the data shown above:

1. The growth in bacterial population stops earlier at $37^{\circ}$C as compared to $25^{\circ}$C
2. The time taken for curd formation at $25^{\circ}$C is twice the time taken at $37^{\circ}$C

Which one of the following options is correct?

• A. Only i
• B. Only ii
• C. Both i and ii
• D. Neither i nor ii

Comments

I is true as very obvious from the given graph.

II is false as the given graph shown only bacterial growth in milk but curd formation in milk may have other factors too like the purity of milk which might affect the speed of curd formation so II is false.

So, this way I got ans as (a) and as per key it is correct.

Is my analysis for II part correct?

---

For $II$ my reasoing is not considering any other factor :
At around approx $90$ min at $37^o$ Population density is suitable whereas for $25^o$ its approx $130$ min.
Therefore its not twice .

---

@saxena

your reasoning is not correct, entire 1 litre milk will not change into curd instantaneously when bacterial population density will reach 0.8, more info is required for it.

---

Yes ! Thanks nitish though minimal density is achieved way before at $37$ compared to $25$ but cannot comment on twice time ! Correct thank you !

Answer 1

1. The growth in bacterial population stops earlier at $37^∘$C as compared to $25^∘$C - TRUE.
   From the graph it can be seen that the growth stops after $150$ minutes at $37^∘$C while it stops after $180$ minutes at $25^∘$C
2. The time taken for curd formation at $25^∘$C is twice the time taken at $37^∘$C - FALSE.
   From the graph it can be seen that curd formation happens in around $90$ minutes at $37^∘$C and in around $120$ minutes at $25^∘$C

Correct Option: A.

Answer 2

Growth of Bacterial population stops when Bacterial population becomes steady.

It happens after 140 min at 37∘C& at 180 min at 25∘C 180.  it stops earlier at 37∘C

Time taken for curd formation is time required to reach density of 0.8.

At 37∘C time required ≈≈ 90 min

At 25∘C, time required ≈≈ 130 min

Hence only statement -1 is true   2 can not be correct according to above explanation

so A is answer

Answer 3

According to the given graph, Statement-(i) is correct, The time taken for curd formation in $25^{\circ} = 120$ minutes, the time taken for curd formation in $37^{\circ} C= 80$ minutes, hence (ii) is incorrect.

Hence Option A is correct