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.
All cells have a cell membrane. its basically what protects the cells from getting toxins that are sometimes entering your body. without a membrane on all cells, you would get sick a lot!!
It is D. <span>Packets of stored energy are converted to chemical energy in glucose.</span>
Answer: because the flu is not liquid it is air born even in your body it is airborn so it floats through your orgons and through any thing in its way even through the heart
Explanation:
Answer:
eukaryote
Explanation:
That small, dark circle in the center of the cell is the nucleus .Prokaryotes do not have nucleus.
