Cell Sizes and Shapes

Cells are dramatically variable, both in size and in shape, and that variability tracks both the organism they belong to and the specific job the cell has to do within that organism. Bacterial cell shape ranges from round (cocci) to rectangular/rod-shaped forms; viral 'shapes' (really, the shape of their protein envelope) range from round to hexagonal to a distinctive 'T'-shape; fungal cells range from globular to elongated cylinders, and fungal spores show yet more shape variety of their own. Within plants and animals, individual cell shape is closely tied to the specialised tissue the cell belongs to - parenchyma, mesophyll, palisade, tracheid, fibre, and epithelium cells, among others, each have their own characteristic shape suited to their function. Grouping upward from the single cell gives the levels of biological organisation: cells with a similar structure that work together form a tissue; tissues working together for a shared purpose form an organ; organs working together form an organ system; and organ systems working together in a coordinated way form a complete organism. Cell size spans an enormous range, from viruses at roughly 0.004-0.1 micrometres and mycoplasma at 0.15-0.3 micrometres, through bacteria (0.5-5 micrometres) and blue-green algae (1-60 micrometres), up to typical plant cells at 10-100 micrometres, …