How do scientists define animal?

Scientists generally define an animal as a multicellular, eukaryotic, heterotrophic organism that obtains nutrients by ingesting other organisms. Here is a breakdown of each of these characteristics:

1. Multicellular: Animals are made up of multiple cells that are specialized to perform different functions. This allows animals to have a complex body plan and carry out a variety of activities.

2. Eukaryotic: Animal cells have a true nucleus and membrane-bound organelles. This level of cellular organization allows for increased complexity and specialization of cells, enabling animals to perform complex functions.

3. Heterotrophic: Animals cannot produce their own food and must obtain organic matter from other organisms. They are consumers in the food chain and feed on plants, other animals, or both.

4. Ingestion: Animals ingest other organisms or organic matter in order to obtain nutrients. They have specialized structures such as mouths and digestive systems to process and absorb the ingested food.

These characteristics collectively define animals and distinguish them from other organisms such as plants, fungi, and microorganisms.