This is a bit of a trick question! Both a paramecium and an Elodea plant cell are considered organisms, just at different levels of organization. Here's why:

* Paramecium: A paramecium is a single-celled organism. It's a complete living being capable of independent survival, reproduction, and carrying out all the essential life processes.

* Elodea plant cell: An Elodea plant cell is a single cell within a larger, multicellular organism (the Elodea plant). It's a specialized part of the plant, performing a specific function.

In short, the difference is in the level of organization:

* Paramecium: A complete organism

* Elodea plant cell: Part of a larger organism

To be considered an organism, something must be able to:

* Maintain homeostasis: Regulate its internal environment.

* Respond to stimuli: React to changes in its surroundings.

* Reproduce: Create offspring.

* Grow and develop: Increase in size and complexity.

* Obtain and use energy: Carry out metabolism.

Both paramecia and Elodea plant cells meet these criteria, but at different scales.