What are the Different Types of Cells?
From a human egg cell--which is large enough to be seen with the naked eye--to unimaginably tiny, free-living bacteria, cells can come in a huge variety of shapes, sizes, and functions. The human body alone has around 200 different types of cells, and that’s just in one type of organism!
On the most basic level, scientists divide cells into the categories of prokaryotic and eukaryotic. Both kinds of cell have a cellular membrane and an internal fluid called cytoplasm. However, prokaryotic cells have their genetic material as a free-floating bundle in their cytoplasm, while eukaryotic cells enclose their genetic material in a membrane called the nucleus.
Prokaryotic organisms are always unicellular (single-celled) and are either bacteria or archaea. Most eukaryotic organisms are multicellular, but some, like algae and protozoa, are unicellular. Some algae have single-celled bodies that can be up to ten feet long!
Eukaryotic cells also have other membrane-bound structures called “organelles” that help carry out jobs within the cell. The vast majority of eukaryotic cells have a type of organelle called “mitochondria”, which helps the cell make energy from food.
Plant cells also have another type of organelle called a “chloroplast”. Chloroplasts allow plants to photosynthesize, or take the energy from sunlight and make it into energy. Chloroplasts are what give plant cells the green color that we associate with plant life.
Another important difference between plant and animal cells is that plant cells have cell walls in addition to their cell membranes. These walls are made from cellulose and give plant cells a fixed, square shape, rather than a loose, circular shape like most animal cells. Cell walls are what allow plants to stand rigid and upright without muscles or bones to hold them up.
Fungi cells also have cell walls, but they are composed of a different material called “chitin”. Although fungi may superficially resemble plants, they are actually much more closely related to animals and their cells are more similar to animal cells. The cells of animals and fungi both have only mitochondria to generate energy, because they only get energy from breaking down other living organisms rather than from sunlight.
Even within a single organism there are many different kinds of cells with different jobs. In the human body, cells range from long, skinny nerve cells that send electrical messages to donut-shaped red blood cells that carry oxygen throughout the body and everything in between. Sexually reproducing organisms (including humans) also have a special kind of cell called “gametes”. Gametes only contain half of the organism’s genetic code and are meant to combine with a gamete from another member of their species in order to produce offspring.
Vierschilling, Andrea (photographer). (2016).Waterweed Plant Cell [photography]. Retrieved from https://pixabay.com/photos/waterweed-plant-cell-mikroskopieren-1582259/