Bacterial cell has a Cytoplasm and Membrane surrounded by a cell wall

Yeast is a single celled organism. Yeast cells have a Nucleus, cytoplasm, cell membrane and surrounded by a cell wall

Cells are living things; so they need to replace substances that are used up like oxygen and food but remove substances that accumulate like carbon dioxide and waste products. They pass through cell membranes by diffusion.

A net movement occurs from a region of high concentration to a region of low concentration. For example, oxygen required for respiration process passes through all membranes by diffusion.

Diffusion can take place automatically without need for energy.