iCell is a free, educational iPad app that gives students an inside look at the structures that make up living cells. By exploring interactive 3D simulations, you can examine and learn about various cell components. Brief textual descriptions of each feature are accessible, at a level of difficulty of your choosing. The app doesn't provide any references or suggestions for additional reading, and would benefit from a greater diversity of cell types. But it is free, and if you're interested in the subject matter, it's worth a download.

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Design and Features
The app's design and operation are the essence of simplicity. The main screen is a triptych depicting three images of cells, labeled as Animal, Bacteria, and Plant. Tapping one of these options brings up a three-dimensional rendition of a representative cell. (In the case of bacteria, which are single-celled although they can cluster, the entire organism is shown.) You can rotate it using a finger, and stretch or pinch it to zoom in or out.

The cells are translucent, and various cell structures (organelles) are visible within. (The plant cell is shown without the opaque cell wall, though you can add it by touching the appropriate button in the screen's upper right corner.) Tapping on a structure zooms in on it, and also displays a brief textual description. By default, you get the Basic description, but you can switch to an Intermediate or Advanced description by touching the appropriate button in the screen's lower left corner.

The Basic description is suitable for elementary-school students getting their first exposure to cell biology, while the Advanced description provides information useful to high-school or beginning college students. For example, the Basic description of the mitochondrion states that "It is known as the 'power house' of the cell and produces energy to fuel the cell's activities." The Advanced description provides much more detail on the mitochondrion's structure and function: It describes it as "a double membrane organelle where cellular respiration takes place" and notes that molecules such as glucose and oxygen are converted into useable energy in the form of ATP (adenosine triphosphate). It concludes by stating that the mitochondrion contains its own circular DNA and replicates independently from the rest of the cell. The Intermediate description provides more detail than the Basic description, but not as much as the advanced.

Testing and Evaluation
In testing the app, I clicked on all the cell components (aka organelles) and read through all the descriptions. For each item I would start with the Basic description, and then read the Intermediate, and finally the Advanced; I found this process helpful in my comprehension of the material.

The app lacks social media integration. Also, it lacks any links, references, or other suggestions for material to further explore the subject. Another downside is that the diagrams are very generalized, with just a single example of a plant cell, an animal cell, and a bacterium, while in reality they have diverse forms, not all of which have the same components. For instance, the Bacteria diagram shows an organism with flagella, whip-like tails that help propel it, and describes their function. Not all bacteria have flagella, however, and many bacteria are surrounded by cilia—much shorter strands—which are not shown or described in the app.

Conclusion
The iCell app is a useful educational tool for learning about living cells, providing a three-dimensional look inside several representative cells to reveal and describe important structures. It lacks any references or suggested readings, so it is best used in a classroom context or if you already have books on cell biology. The app would benefit from a wider variety of cells, as not all animal cells, plant cells, or bacteria have all the same components. But even as is, this free app is worth downloading by students or anyone who wants to learn a bit about cell biology.