Which of the following statements about transmembrane proteins is correct? they usually have one or more helical regions spanning the membrane bilayer. they are always inserted with the amino terminus on the lumenal side and the carboxyl terminus in the cytosol. they are always inserted with the carboxyl terminus on the lumenal side and the amino terminus in the cytosol. the signal sequences are always cleaved off. they can cross the membrane only once.

Which statements best describe the differences or similarities between a comparative investigation and an experimental investigation? check all that apply. experimental investigations are best for showing cause-and-effect relationships, while comparative investigations do not necessarily show this type of relationship. comparative investigations are often impractical and unrealistic, while experimental investigations are the most practical and realistic kinds of investigations. comparative investigations allow for the use of a wide range of variables but do not have a control group, while experimental investigations involve variables that can be controlled. both experimental investigations and comparative investigations are designed to answer scientific questions. both experimental investigations and comparative investigations focus on making observations rather than collecting new data.