Plant cells contain organelles, called chloroplasts, where photosynthesis occurs. However animal cells do not have chloroplasts.
Scientists and engineers actively seek evidence to test their ideas — even if the test is difficult. The reason behind is the importance of asking questions based on observations to find more information about the natural effects and proposals. From there, it is ought to determine expected results based on testing, evidence resulting from that experiment will allow testers to find out the solution they are looking for.
An absorption line will appear in a spectrum if an absorbing material is placed between a source and the observer.