How do you distinguish between representatives of different kingdoms of nature?

The main criteria for dividing living organisms into three kingdoms is their way of feeding. Thus, organisms of the animal kingdom feed on already existing organic substances (heterotrophic) and accept them in solid form. Plants, on the other hand, accept dissolved inorganic substances and synthesize organic substances from them (autotrophically). Mushrooms, on the other hand, occupy the middle position: they eat like animals, only heterotrophically, but they eat, like plants, exclusively in dissolved form.