Arrange the following from smallest to largest: a) organism b) atom c) molecule d) cell e) organ

To arrange the items from smallest to largest, we look at the size scale of biological structures:

1. Atom: Atoms are the basic building blocks of matter and are the smallest unit in this list.
2. Molecule: Molecules are made up of two or more atoms bonded together, making them larger than atoms.
3. Cell: Cells are the basic units of life, composed of various molecules and organelles, thus larger than molecules.
4. Organ: Organs are made up of different types of cells working together to perform specific functions, making them larger than individual cells.
5. Organism: An organism is a complete living entity that can be made up of many organs and systems, making it the largest in this list.

So, the correct order from smallest to largest is: atom, molecule, cell, organ, organism.