A pressure cooker reduces cooking time for food because a)boiling point of water involved in cooking is increased b)the high pressure inside the cooker crushes the food material c)cooking involves chemical changes helped by a rise in temperature d)heat is more evently distributed in the cooking space

A pressure cooker doesn't allow for anything (even gases) to escape at any significant amounts (unless the pressure inside gets too high and you hear that whistleing noise).With heat, the gases inside want to expand, but because they are restricted to the volume of the pressure cooker they can't, so pressure builds up.In addition, when a liquid, lets say water in this case, is heated under normal pressure its temperature won't go above 100C, because any water molecule that has higher energy leaves the liquid and goes into gas phase.Now, applying pressure to water, will increase the boiling point (for example from 100C to 110C)Reason: When any liquid is under higher pressure it is less likely to go in the gaseous phase.The pressure cooker works with these principles, because usually when you cook water in an open pot, the boiling point of water restricts the temperature to a 100C. A pressure cooker uses the pressure to keep the water in the liquid form even though it is far above the boiling point, and hence the temperature is far above 100C.Because the pressure build up inside causes higher cooking temperatures thus reducing cooking times