Question

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.

A bacterium divides into two every 30 minutes, and every new bacterium does the same. Starting with 1 bacterium in a sweet left on the table, how many bacteria will there be after 3 hours?

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?