The evolution of the organisms has been occur from the simple organisms and leads to the evolution of the more complex organisms. This complexity arises due to the changing environment of the organisms.
The protozoans are the simplest organisms and all the other animal lineage has been derived from the porifera. The porifera are the cellular organisms that do not have tissue level of organization and simple physiological system. Later, diverse and complex organisms arise from the porifera.
Some molecules can move down their concentration gradients by crossing to the lipid portion of the membrane directly,while others must pass through membrane protein s in a process called Facilitated Diffusion
