Cell

In biology, a cell is the basic unit of life - a membrane-bound structure containing the fundamental molecules and organelles needed for life. Some organisms consist of a single cell (e.g. bacteria or yeast), while others are multicellular with specialized cell types that work together in tissues and organs. Cells are categorized as prokaryotic (lacking a nucleus) or eukaryotic (having a nucleus and organelles).

• Cell theory: All living organisms are made of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells.
• Prokaryotes (bacteria and archaea) are unicellular, lack a nucleus, and have 70S ribosomes; Eukaryotes (protists, fungi, plants, animals) have a nucleus, membrane-bound organelles, and 80S cytoplasmic ribosomes.
• Some cells (like bacteria) are independent organisms, whereas in multicellular organisms, cells differentiate and cooperate (e.g., muscle cells vs nerve cells) to maintain the whole organism.

• Cell theory questions - e.g., -What are the tenets of cell theory-- Expect: (1) all living things composed of cells, (2) cell is basic unit of life, (3) cells come from preexisting cells.
• Prokaryote vs. eukaryote ID - If a described cell has no nucleus and a small size (~1-5 -m), it-s prokaryotic. If it has a nucleus and organelles (and ~10-100 -m size), it-s eukaryotic.
• Vital distinction - Viruses are often contrasted with cells: remember viruses are not cells (acellular), reinforcing that cells are the smallest living units (viruses aren-t -alive-).