Carbohydrates, proteins, and lipids are important molecules that make up the structure of the cell membrane. They help move materials into and out of the cell through the cell membrane In what way is the cell membrane like a security guard?

The cell membrane only alows certian materials to move through the membrane. Just like a security guard the membrane sorts through the good stuff and lets it past, but if someone or something bad comes along the security guard stops it. Just like the cell membrane.  

the answer is d p: cell, q: organ, r: organ system, s: tissue