Q4. Give examples to prove that microbes release gases during metabolism. (NCERT Exercise 2, page 159.)
Idli and dosa dough puffs up because its bacteria release CO2; the large holes in Swiss cheese are made by CO2 from a bacterium (NCERT page 151). Methanogens also release methane with CO2 and H2 while growing anaerobically on cellulosic material, which is the basis of biogas (NCERT Section 8.4, page 155).
Q5. Why is a little curd added to fresh milk when making curd at home?
It is the inoculum or starter: it contains millions of lactic acid bacteria, which multiply at suitable temperatures and convert the milk to curd (NCERT page 151).
Q6. How does curd improve on milk as food?
Its nutritional quality is better, because the lactic acid bacteria increase its vitamin B12 (NCERT page 151).
Q7. What role do lactic acid bacteria play in our stomach?
A very beneficial one: they check disease-causing microbes (NCERT page 151).
Q8. Name three foods, other than dairy products and dough, that are made by fermenting with microbes.
Foods made by fermenting fish, soyabean and bamboo-shoots; toddy is a drink made by fermenting palm sap (NCERT page 151).