Question

The white or greenish cotton-like growth seen on stale bread is a kind of bacterium.

Cooked dal kept outside overnight in summer often smells bad by morning, but in winter it may stay fine. Explain why. Give one sign that food has spoiled.

Equal samples of fresh milk were kept at four temperatures for 1 day, and the number of bacterial colonies grown from each was counted (see bar graph). (a) At which temperature did bacteria grow most? (b) How many times more colonies were there at 37 °C than at 4 °C? (c) What advice would you give a shopkeeper about storing milk, and why?

Distinguish between unicellular and multicellular organisms with two examples each. How does a single-celled organism like Paramecium manage all its life activities?