Which has higher air pressure—warm air or cold air? how do you know?

The one with higher air pressure is Warm Air.  The reason why is because when you boil water, the water always makes the lid rise.  This is because Warm Air has more activity in its atoms and molecules, so it is moving around more, which in turn means that there is more pressure.  

Hope I helped.  :)

Probably a mushroom or a tomato plant