Answer:
1. Homeostasis is the maintenance of a constant internal environment.
2. Bacteria play a variety of roles in the environment, including decomposition, nitrogen fixation, and soil formation.
3. Single-celled organisms maintain homeostasis by regulating their internal environment, while multicellular organisms maintain homeostasis by regulating the environment around them.
4. The levels of organization in multicellular organisms are cells, tissues, organs, and systems.
5. A cell receptor is a protein that binds to a specific molecule, usually a hormone or neurotransmitter, and initiates a cellular response.
Step-by-step explanation: