Give each cell structure a job
The cell membrane helps control exchange with the surroundings, and ribosomes assemble proteins. In typical animal and plant cell models, a nucleus contains most of the DNA. Different cell types have structures suited to their roles; for example, photosynthetic plant cells contain chloroplasts. Learn the function alongside each label.
Change scale without losing the connection
In animals such as humans, specialized cells work together in tissues. An organ contains several tissue types, and organs cooperate within organ systems. These names describe different scales of organization. A heart is not a single kind of cell made larger, and a single-celled organism does not have this tissue-to-organ hierarchy.
Explain how the parts work together
Begin with a function, then connect it to the structures involved. Identify the scale of every label in a diagram and describe how one part supports another. In humans, circulation carries materials between the lungs, digestive system, and other body tissues. A useful explanation follows those relationships, not only the outline of an organ.
Worked example
From a contracting cell to circulating blood
A cardiac muscle cell can contract. Many cardiac muscle cells work together as tissue in the heart wall. The heart also contains other tissues and functions as an organ that pumps blood. Together with blood and blood vessels, it contributes to the circulatory system. Cell, tissue, organ, and system describe connected scales, not four names for the same structure.