Answer:
C. active transport, because protein pumps are needed to move substances against a concentration difference
Explanation:
There are two major types of transport in living cells namely: passive transport and active transport. The passive transport moves molecules down a concentration gradient and hence, do not need energy (ATP) to occur. However, on the other hand, ACTIVE TRANSPORT moves substances against their concentration gradient, thus, require energy input.
Active transport makes use of PROTEIN PUMPS to achieve this process. Hence, in this case where Alexis is using models of the cell membrane to compare the types of cellular transport. The model that shows a molecule entering through a protein pump is modelling ACTIVE TRANSPORT.
