Structural Characteristics:
* Eukaryotic Cells: Animal cells, like plant and fungal cells, possess a nucleus and membrane-bound organelles.
* Multicellularity: Animals are multicellular organisms, meaning they are composed of many cells that work together to form tissues, organs, and organ systems.
* Heterotrophy: Animals obtain nutrients by consuming other organisms (plants, animals, or decaying matter). They cannot produce their own food through photosynthesis like plants.
* Movement: Most animals exhibit movement at some stage in their life cycle, whether through muscle contractions, cilia, or flagella.
* Lack of Cell Walls: Unlike plants and fungi, animal cells lack rigid cell walls, giving them flexibility and allowing for complex movement.
* Specialized Tissues: Animals possess specialized tissues like muscle, nerve, and connective tissue, which contribute to their complex body organization.
Functional Characteristics:
* Digestive System: Animals have a specialized digestive system to break down food and absorb nutrients.
* Nervous System: Most animals have a nervous system that coordinates responses to stimuli and allows for complex behavior.
* Reproductive Strategies: Animals reproduce sexually, although some can reproduce asexually.
* Development: Animals undergo a process of development, with many going through embryonic stages and metamorphosis.
* Adaptation and Evolution: Animals have evolved diverse adaptations to survive in different environments.
Distinguishing Animals from Other Life Forms:
* Plants: Animals differ from plants by their heterotrophic mode of nutrition, lack of cell walls, ability to move, and complex nervous systems.
* Fungi: Animals differ from fungi by their multicellularity (most fungi are single-celled), lack of cell walls, and ability to move.
* Bacteria and Archaea: Animals are eukaryotes, while bacteria and archaea are prokaryotes, lacking a nucleus and other membrane-bound organelles.
* Viruses: Viruses are not considered living organisms, as they lack the ability to reproduce independently and require a host cell.
It's important to note that these characteristics are not absolute and some exceptions exist. For example, there are some species of animals that are sessile (don't move), and some fungi are multicellular. However, these characteristics provide a general framework for understanding how animals are differentiated from other life forms.