Concept:A cell wall is a rigid outer layer that provides support and protection. It is absent in animal cells.Explanation:Cell walls are present in bacteria, plants, and fungi but not in humans or other animals.Human cells are animal cells and lack a cell wall; they are surrounded only by a cell membrane.Bacterial cells have a cell wall made of peptidoglycan.Plant cells have a cell wall made of cellulose.Fungal cells have a cell wall made of chitin.Answer:Humans