Nutrient agar heated at 80degC used for -

Ans. is 'a' i.e., Spore germination* Heating for 20 minutes at 80 degrees centigrade destroyes vegetative cells and activates the spores for germination.About options a & c* Microorganisms can be grouped into broad (but not very precise) categories, according to their temperature ranges for growth.# Psychrophiles (cold-loving) can grow at 0degC, and some even as low as -10degC; their upper limit is often about 25degC.# Mesophiles grow in the moderate temperature range, from about 20degC (or lower) to 45degC.# Thermophiles are heat-loving, with an optimum growth temperature of 50deg or more, a maximum of up to 70degC or more, and a minimum of about 20degC.# Hyperthermophiles have an optimum above 75degC and thus can grow at the highest temperatues tolerated by any organism. An extreme example is the genus Pyrodictium, found on geothermally heated areas of the sea bed. It has a temperature minimum of 82deg, optimum of 105deg and growth maximum of 110degC.