Answer: Because it is harder to draw breath in. And the cold
Explanation: At higher altitudes, it becomes more dangerous, and you can develop altitude-related illnesses such as HAPE and HACE. I read a book called<em> Into Thin Air</em>, and in the book the author goes into detail on the details/complications of climbing Mt.Everest and oxygen needs. Mountain climbers use canisters of oxygen called <u>Supplemental Oxygen.</u>
Although the actual questions are missing from your ask, here's how you can tell.
If the study will be messed up (added bias) through interaction with the subjects the study should be observational. For example if a biologists wanted to study the eating habits of wild birds in the tropics, they would need to do an observational study. if they did a controlled experiment, the birds will change their eating habits based on human interaction, thus making the study invalid.
If the study requires specific measurements, close monitoring, or contact and interaction with the subjects the study should be a controlled experiment. For example, if a scientist wanted to test out a new drug, the health of patients would need to be closely monitored.
Answer:
There are two kinds of cellular communication: communication between cells is called intercellular signaling, and communication within a cell is called intracellular signaling.
Explanation:
