Characteristics of Animals
Animals form the kingdom Animalia, one of the largest and most diverse groups of life, ranging from microscopic organisms to blue whales. The characteristics below are what actually define the group biologically, beyond the everyday sense of "creature that moves"; see Characteristics of Plants for how the two major multicellular kingdoms compare, and Characteristics of Living Organisms for the traits all life shares.
Last updated: 8 September 2026
Key characteristics
Multicellular, without cell walls
Animals are made up of many specialised cells, but unlike plant or fungal cells, animal cells have no rigid cell wall, only a flexible outer membrane, which allows for the varied, often mobile body shapes animals have.
Heterotrophic nutrition
Animals cannot produce their own food and must obtain energy by consuming other organisms, whether plants, other animals, or decomposing matter, which distinguishes them from most plants.
Mobility at some life stage
The large majority of animals are capable of self-directed movement, at least during part of their life cycle, using muscles to move toward food, away from danger, or to reproduce.
A nervous system and sensory response
Most animals have some form of nervous system, ranging from simple nerve nets to complex brains, allowing them to detect and respond to their environment, though the complexity varies enormously across the kingdom.
Sexual reproduction, typically
Most animal species reproduce sexually, combining genetic material from two parents, though a number of species are also capable of asexual reproduction under certain conditions.
A defined pattern of growth to adulthood
Animals generally grow from a fertilised egg through a genetically directed developmental sequence to reach a relatively stable adult body form, unlike plants, which often continue open-ended growth throughout life.
Complex, specialised organ systems
Most animals, above the simplest groups, have distinct organ systems, digestive, circulatory, respiratory, and others, working together to keep the organism functioning.
Behavioural responses combining instinct and learning
Animal behaviour ranges from fixed instinctive responses to sophisticated learned behaviour, with more complex nervous systems generally allowing for a greater capacity to learn from experience.
Frequently asked questions
Do all animals have a nervous system?
Nearly all, but not quite all. Sponges, one of the simplest animal groups, lack a true nervous system entirely, coordinating their limited responses through direct cell-to-cell signalling instead.
Are all animals mobile?
Not throughout their entire lives. Some animals, such as adult sponges, corals, and barnacles, are sessile, permanently attached in one place, as adults, even though many of these species have a mobile larval stage earlier in life.
What is the main difference between animals and plants?
The most fundamental differences are nutrition and cell structure: animals obtain energy by consuming other organisms and lack cell walls, while most plants produce their own food through photosynthesis and have rigid cellulose cell walls. See our Characteristics of Plants page for the full comparison.