| Themes > Science > Zoological Sciences > Animal classification > Polygenetic Tree of Kingdom Animalia > Animalia |
Animals are members of the kingdom Animalia, which are all multicellular organisms whose cells are bound only by a plasma membrane and not by a cell wall of cellulose. They obtain energy by acquiring and ingesting their food, unlike plants, which use photosynthesis to manufacture their nutrients. In animals, the cells are organized into tissues and specialized tissue systems that permit them to move freely in search of food or allow nonmotile, or fixed, animals to draw food toward themselves. A developed nervous system with sensory and motor nerves enables animals to receive environmental stimuli and to respond with specialized movements. |
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