Q.Onion cells have no chloroplast. How can we tell that they are plant cells?

The cell wall is the outermost, actively growing protective covering of a cell, present in bacteria, fungi and plants but completely absent in animal cells - the single feature most consistently used to tell a plant cell from an animal cell. Its chemistry differs by group: peptidoglycan in bacteria, chitin and fungal cellulose in fungi, cellulose/galactans/mannans in algae, and cellulose, hemicellulose, pectin, lignin, cutin, suberin and silica in plants. A mature plant cell wall has three distinct regions laid down in order - the outermost middle lamella (calcium/magnesium pectate, cementing adjacent cells), the primary wall (a loose, elastic network of cellulose microfibrils in a hemicellulose/pectin/glycoprotein matrix), and the thick, inelastic secondary wall (laid during maturation, itself divided into three sub-layers S1, S2, S3 with differently oriented microfibrils). Channels called plasmodesmata run thro …