Your question is rather unclear but from what I can tell either there were not an even amount of Petri dishes or some of them were left open while others were not.
Paper, pencils, spoons, trash cans, etc
The two upper chambers are the atria or auricles. They are the left and right atriums
The brain recieves stimuli. Your brain does a lot of things for you. It is one of the busiest organs in your body. Your brain stimulis can enjoy various brain stimulis games to keep your brain healthy and sharp. if it stays healthy, everything follows after.
Explanation:
Melanin is the pigment which absorbs UV light and it is present in skin and gives black colour to it.As we can see africans usually have black skin as they have to face direct uv light.
