Do All Cells Look the Same?

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson is on different types of cells in living things. In this lesson we'll discuss the major categories of cells and give examples of how different cells look.

What Is a Cell?

If you look down at your body, you'll see some skin, hair, maybe your eyes and ears if you're looking in a mirror. What you don't see is the microscopic parts that make up your body. Although your skin seems like a seamless coating on your muscles, it is actually made of tiny little units called cells.

Cells are the basic units of life and make up all living things. Millions of cells arrange themselves into tissues, which is what your skin is made of. Other living things, like bacteria, plants, and fungi are also made of cells. Since all cells have different jobs, they tend to look very different!

Today we'll go over the main two categories of cells, eukaryotes and prokaryotes, and give examples of cell shape in each.

Prokaryotic Cells

Prokaryotic cells are the simplest type of cell. They do not have a nucleus or any compartments, called organelles. Bacteria are the only type of prokaryotic cell. Although bacteria may all seem the same to you, there are actually very different types of bacteria, which can be categorized into three major shapes:

  1. Spherical bacteria are called cocci (singular: coccus). If cocci assemble together in a clump, we call them staphylococci. If they assemble into a chain, they're known as streptococci. If they come in a pair, they're called diplococci.
  2. Some bacteria are oblong, known as bacilli.
  3. Spiral shaped bacteria are called spirilla.

Shapes of bacteria
shapes of bacteria

Examples of Prokaryotic Cells

A well known bacillus is the rod-shaped E. coli. Some E. coli are good for us, like ones in our stomach that help us digest food. Others, however, can be deadly. The common bacteria in cases of food poisoning is E. coli O157:H7. This bacteria invades the intestinal lining of our digestive system, making us very sick with diarrhea and vomiting.

E. coli is a type of bacillus that can cause food poisoning

Methicillin-resistant Staphylococcus aureus (MRSA) is an extremely deadly staphylococcus bacteria. These small clumped spheres are resistant to many antibiotics, meaning the medicine doesn't work against the bacteria anymore. MRSA infections frequently occur in hospitals and the number of treatments possible is limited.

Structure of MRSA under a microscope

Eukaryotic Cells

Eukaryotic cells are the ones we are most familiar with because they are what we have! These cells have a nucleus and small compartments called organelles that do different jobs in the cell. This allows these cells to have more complex functions compared to prokaryotes. While prokaryotes are single cells, eukaryotic cells assemble into multicellular organisms, like plants, animals, and fungi. The cells in multicellular organisms specialize to do a particular job, and so all look very different.

Eukaryotic cells versus prokaryotic cells
eukaryote vs. prokaryote

Examples of Plant Cells

Some plant cells, called parenchyma cells, are unique in that they can make their own food using chloroplasts, which give plants their green color. They are usually shaped like boxes, surrounded by a thick barrier called the cell wall. They also have giant water storage tanks, called vacuoles, that help plants stand up straight.

Other plant cells, like xylem cells are elongated cells specialized for transporting water throughout the plant.

Diagram of typical plant cell such as the parenchyma cell
plant cell

Examples of Animal Cells

Animal cells are incredibly diverse. Red blood cells actually lose their nucleus at maturity to let the cell have more hemoglobin, a protein necessary for carrying oxygen. Their concave shape also allows them to squeeze through the tiniest blood vessels, called capillaries.

Red blood cells under a microscope
red blood cells

Neurons, or brain cells, also look very different from all other cells. They have a circular cell body with tiny protrusions called dendrites that pick up signals from other neurons. Protruding from the cell body is a long filament called an axon, which extends to where the neuron needs to send signals. Some extend from the top of our spine all the way down to our toes, sometimes measuring two meters long!

Structure of a neuron

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