Some human structures and their functions are listed below. in a single-celled organism such as an amoeba, all these functions can be performed by

As amoeba is a unicellular organism all the physiological processes are performed by the single cell.

Explanation:

The food is captured by the pseudopodia and after entering into the body it forms food vacuole. Then the food is broken down by enzymatic activities within the food vacuole and the simplified food absorbed by the cytoplasm.

The remaining undigested food is expelled by the plasma membrane. This is done by rupture of the cell membrane and the waste products diffused out of the plasma.  

Most of the time the food captured by amoeba is absorbed more and less waste is formed.

Amoeba reproduces the process of binary fission. It is a type of asexual reproduction where the body is divided into 2, 4, 8 then 16 and so on.. many cells. These small amoeboid cells grow and become new organisms.  

As it is a single-cell organism, nutrition, assimilation, excretion, the reproduction process occurs at a fast rate.