Why does osmosis differ from the diffusion of gases

This can be answered with the help of describing osmosis and diffusion in plants. The motion of molecules through the semi-permeable membrane is osmosis. In diffusion, motion of molecules is direct and does not need a semi-permeable membrane.

Explanation:

In plants, osmosis help plants to absorb water from soil. Diffusion is the process by which carbon dioxide diffuses to the leaves and then to the cells. The genetic modifications in some of the plants can help in survive and adopt the osmosis in a very dry environment. They develop defense methods to handle the water loss. Some plants in a permanent dry environment like desert have special structures like reduced leaves,  sunken stomata, and so on to conserve water.Osmosis happens only in liquid medium. Diffusion happens in any medium - solid, liquid, and gases.