That depends on the kind of waste. If a cell is doing cellular respiration, it is producing carbon dioxide. CO₂ can just diffuse out of the cell and into the fluid around the cell by diffusion, moving from an area where there’s a lot of it to where there is less of it. Diffusion is a passive process. It happens because molecules are always moving around randomly. If they are small enough and not too polar, they can go right through the cell membrane. If they are bigger or polar, they can move through tubes in the cell membrane. That’s call facilitated diffusion. Salts, sugars, and some proteins can move this way.

Really big waste can be “spit out” by the membrane in a process called “exocytosis.” ‘Exo’ means out, and ‘cyto’ means cell. The wastes are in little bags made of membrane (vesicles). When the bags hit the cell membrane, they start to become a part of the membrane. This releases the wastes to the outside of the cell. The process uses energy as the cell uses contracting fibers to change the cell shape and move things.

The cell can also pump out certain wastes using active transport. Active transport uses special proteins to throw out the wastes. This costs energy.

What kinds of wastes might different types of cells make?

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Cells excrete it by putting in internal containers called vacuoles and pushing them to the outside.