Which characteristics correctly describe prokaryotic cells? (select all that apply.)
a. have no nucleus
b. have a nucleus
c. have membrane-bound organelles
d. have no membrane-bound organelles

Before the can be observed by using a transmission electron microscope, cells are sliced into very thin sections. what disadvantage does this procedure present in the study of cellular parts

What is the difference between the conducting zone and the respiratory zone of the respiratory system? the conducting zone is a series of cavities and tubes that move air to the respiratory zone where gases exchange with the bloodstream. the conducting zone exchanges gases between the lungs and the alveoli and the respiratory zone is a series of cavities and tubes that move air to the conducting zone. the conducting zone moves oxygen into the cells and the respiratory zone takes carbon dioxide away from the cells. the conducting zone moves oxygen into the bloodstream and the respiratory zone takes carbon dioxide away from the bloodstream.

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled