What is the circulatory system

The circulatory system carries blood to every part of your body. Your heart beats to pump blood all throughout your body. Blood is very important because it keeps your body warm and helps it to move. When the heart pulls in and pumps out blood, the arteries transport it to different locations in your body. The artery is basically a tube that transports the blood.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.