Microbes in household products — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Which bacteria convert milk into curd?

• A. Baculoviruses
• B. Methanogens
• C. Nitrogen-fixing cyanobacteria
• D. Lactic acid bacteria

Question 2 · difficulty L2 · understanding

Why does bread dough rise after yeast is added?

• A. Yeast releases carbon dioxide
• B. Yeast releases oxygen by photosynthesis
• C. Methanogens produce nitrogen gas
• D. Bacteria remove water from the dough until the dough becomes porous

Question 3 · difficulty L2 · understanding

The bacterium commonly associated with conversion of milk into curd belongs to

• A. Lactobacillus and related lactic acid bacteria
• B. Rhizobium only
• C. Plasmodium
• D. Methanobacterium only

Question 4 · difficulty L2 · understanding

Baker's yeast is useful in bread making because it

• A. produces carbon dioxide during fermentation, causing dough to rise
• B. produces oxygen bubbles by photosynthesis
• C. converts starch directly into protein only
• D. prevents all fermentation

Question 5 · difficulty L3 · understanding

What is the reason behind production of large holes in 'Swiss Cheese'?

• A. The production of large amount of $\mathrm{CO}_2$ by Propionibacterium sharmanii
• B. The production of large amount of $\mathrm{CO}_2$ by Clostridium butylicum
• C. The production of large amount of $\mathrm{CO}_2$ and $\mathrm{H}_2$ by lactic acid bacteria called Lactobacillus
• D. The production of large amount of $\mathrm{CO}_2$ and $\mathrm{H}_2$ by Trichoderma polysporum

Question 6 · difficulty L3 · understanding

Which of the following microbes is NOT involved in the preparation of household products? A. Aspergillus niger B. Lactobacillus C. Trichoderma polysporum D. Saccharomyces cerevisiae E. Propionibacterium sharmanii Choose the correct answer from the options given below:

• A. C and D only
• B. C and E only
• C. A and B only
• D. A and C only

Question 7 · difficulty L3 · application

A traditional batter becomes soft and porous after microbial fermentation. What best explains the texture change?

• A. All starch is removed from the batter
• B. Fermentation gases become trapped
• C. Fermentation eliminates water completely
• D. Microbes convert the starch-rich batter entirely into insoluble cellulose

Question 8 · difficulty L3 · application

Milk is inoculated with a small amount of curd and kept warm. Why does it set faster than uninoculated milk?

• A. The inoculum supplies lactic acid bacteria that multiply and acidify the milk
• B. Curd contains digestive enzymes that evaporate water
• C. The inoculum removes all proteins
• D. Warmth sterilises the milk completely

Question 9 · difficulty L4 · analysis

Milk is inoculated with a suitable starter culture and kept warm. Why does curd formation accelerate?

• A. The starter removes all lactose physically
• B. Warmth alone chemically converts milk proteins into curd without microbial action
• C. The starter supplies active lactic acid bacteria
• D. The bacteria produce methane that solidifies milk

Question 10 · difficulty L4 · application

Why does bread dough expand during yeast fermentation?

• A. CO2 becomes trapped in the dough matrix
• B. Ethanol becomes a solid gas bubble
• C. Oxygen is produced from glucose
• D. Yeast cells turn into air