That’s a great question. The correlation between structure and function is one of the major themes of biology.

Biology textbooks often start the cell chapter with pictures of an “animal cell” and a “plant cell.” Then students think all animal cells are sort of round and all plant cells are sort of square. But drawing one animal cell to represent all animal cells is like drawing one animal to represent all animals. What would you draw? A worm? A sponge? A fly? So the textbook artists do the best they can, but it’s an impossible job. Plant cells are a bit more similar in shape because their cell walls limit their shape a bit, but they have distinctly different cell types too.

The job (function) of a cell can determine its size, shape, proportions and position of organelles, inclusions in the membrane, and many other characteristics (structure). Some properties are more obvious than others. For example, if a nerve cell is going to carry a message from your spinal cord to your big toe, it can’t be a sphere. It has to have a long, thin arm (the axon) that looks and acts rather like a wire. The main part of the cell is up in the spinal cord and contains all the organelles it takes to keep the cell alive and doing its job. It also has receptors to pick up chemical messages that started off in your brain.

The red blood cells are much more passive. Like all cells, they start off with a nucleus, but when the red blood cells of mammals (like us) mature, they lose their nucleus. They are basically bags of hemoglobin (the molecule that helps carry oxygen and carbon dioxide). If they were spheres, they could hold more hemoglobin, but they need a larger surface area so that the gases can diffuse in and out of the cell. In other words, if they were a sphere, the oxygen would have to travel too far to get to hemoglobin in the middle of the sphere. Instead, the red blood cells are shaped like doughnuts that don’t quite have a hole in the middle. This keeps all of the hemoglobin close to the membrane where the gases enter and leave. The red blood cells are exactly the size that allows them to travel through our smallest blood vessels (capillaries) single file. Sickle cell disease disrupts the shape of red blood cells, but that’s a different story.

Try this yourself. Look at picture of a skeleton muscle cell and compare it to another type of cell (a gland cell, fat cell, etc.). What do you notice about the shape? Which has a lot of mitochondria? Are there lots of organelles for making proteins (ribosomes, rough endoplasmic reticulum, Golgi body)? Are there a lot of lysosomes for breaking down wastes? What is that sarcoplasmic reticulum doing?

In biology, structure determines function. It has been hypothesized that due to the acclamation of non-coding DNA, DNA that does not code for a protein, in the mammalian genome, a nucleus would occupy too much space in a mammalian red blood cells and an anucleate red blood cell, a cell that without a nucleus, is better suited for transporting gas. As such, the mammalian mature red blood cell does not have a nucleus.

There are too many to list here. Cells have anatomy and organelles of their own, and the organelles that a cell possesses are necessary for its function. A cell that serves a structural component needs to have a heavy cell wall or at least be encased in proteins or other chemicals that give it structural strength. A cell used in photosynthesis will have plastids such as chloroplasts that contain chlorophyll. A cell used to store energy will have starch or lipid bodies inside of it. These are examples just in plants.

Muscle cells are long, because they have long muscle fibers in them.

Blood cells are sort of round, so they can go through small blood vessels and capillaries without getting stuck.

Red blood cells [erythrocytes] have an unusual shape called 'bi-concave.' They're like an O-ring with a covering over it [the cell membrane], so there's no hole going through the center. They can fold up when they go through capillaries. People with sickle cell anemia have red blood cells that are stiff and curved, so they don't go through capillaries easily, but they give some protection from malaria.

White blood cells are sort of spherical, with bumps sticking out - they interact with all sorts of molecules and viruses and bacteria in the body.

Schwann cells in the brain are flat cells that wrap around neurons [nerve cells] to keep the electrical currents in the neurons from leaking to the wrong cells.

Thanks for your interesting question.