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Do Animal Cells Have Cell Walls?
Understanding the difference between cell walls and cell membranes, and why they are present or absent in various cell types.
Table of Contents
One of the first science lessons we learn is that cells are the smallest units, or the “fundamental” units, of life on earth. We also learn that single cells were the first signs of life that sprung from the primordial soup of life in the Archean era.
Eventually, as life on earth evolved, so too did the complexity of life forms. Life on earth evolved from simple single-celled organisms into bacteria, protists, and fungi. From fungi, life further branched into plants and animals as well. As life on earth diversified, one thing remained the same. It was still made of the same stuff: cells!
How did cells cope with the diversification of life?
At first, there was only one type of cell, the primitive prokaryotic cell. The very first life forms on earth were single-celled prokaryotes such as bacteria and archaea.
Single-celled organisms eventually made way for multicellular life such as protists, fungi, plants, and animals. These more complex organisms were made of eukaryotic cells.
Does this mean all eukaryotes have the same kind of cells?
While all eukaryotes are made of cells that have a defined nucleus, this doesn’t mean that all eukaryotic cells are exactly the same. Generally, we can differentiate eukaryotic cells into two kinds: those with cell walls and those without.
What is a cell wall?
Simply put, a cell wall is a well-defined boundary that separates the cell from other entities around it. Depending on the type of organism, the cell wall composition varies quite a bit. For example, fungi cells have chitin, a nitrogen-containing protein, in their cell wall. On the other hand, plant cell walls have a different mixture of molecules, including cellulose, pectin, and lignin.
Similarly, depending on the type of organism, the cell wall can even be made up of different numbers of layers. For example, plant cell walls are usually bi-layered and have an inner, thinner, and flexible primary layer and an outer, thicker, and more rigid second layer. On the other hand, fungal cells generally have three layers in their cell wall.
These differences in cell wall composition reflect the unique functions and properties of different types of cells, and they play important roles in protecting and supporting the cell. For example, lignin, a molecule found in plant cells, has a very specific role to play. Lignin provides rigidity to the cell wall. Another instance of the same can be seen in the cell walls of some protists. Protist cell walls generally have some amount of calcium and silica that help provide structure to the cells.
So, we can conclude that most life forms on earth do, in fact, generally have cell walls. However, there is one notable exception to this rule: animals. Animal cells do not have a cell wall at all. Rather, animal cells only possess a cell membrane.
What is a cell membrane?
A cell membrane, or a plasma membrane, is pretty much the same as a cell wall, except for a few key differences. In terms of function, the cell wall and the cell membrane both serve the same purpose: they define the cell’s boundary. The key difference between a cell wall and a cell membrane is porosity . The cell membrane is a porous and less strongly-defined boundary than a cell wall.
The cell membrane is also unlike cell walls in the sense that it has a fixed composition across all animal cells. It is always a bilayer. The two layers are always made of molecules known as phospholipids , a type of fat. Another cool fact about the cell membrane is that it allows animal cells to be flexible and fluid. In fact, it’s the cell membrane that is primarily responsible for the diversity in sizes and shapes of animal cells. For example, muscle cells are spindle-shaped, and red blood cells are spherical and caved in towards the center.
Why don’t animal cells need cell walls?
Animals can move around. Compare this to plants and fungi that stay rooted in position. Animals don’t lack cell walls as much as they don’t really need them. Animal cells need to work a little differently than other cells. This comes down to the fact that, as animals keep moving around, their cells need to be capable of responding to the changing stimuli around them.
Animal cells forgo having rigid cell walls to speed up or better facilitate cell-to-cell communication. This lets animal cells work together as cohesive units. They’re capable of communicating with one another to form comprehensive and quick responses to their surroundings.
Conclusion
Animal cells do not have cell walls, but this is more of an adaptation than a drawback. Animal cells use their cell membrane to better manage faster cell-to-cell communication.
The lack of a cell wall also makes a lot of sense if we consider cell arrangement within animals. Individual animal cells generally have a lot more breathing room than plant cells. If you’ve ever observed somatic plant cells, like onion root-tip cells, under a microscope, you’d have noticed that plant cells are packed super close to one another.
The rectangular plant cells have virtually no gap between one another. On the other hand, animal cells are circular and loosely packed. Their shape and arrangement, coupled with the flexibility gained by just having a cell membrane, help animal cells maximize the extent of their cell-to-cell communication.
Readability: 61.2
Flesch Kincaid Grade Level: 7.9
Glossary
Prokaryotes: Cells or organisms made of cells that are characterized by their lack of organized nuclei.
Eukaryotes: Cells or organisms made of cells that are characterized by their organized nucleus.
Porosity: A property of a substance that defines the number of empty spaces within it.
Somatic: Any cell that is not a reproductive cell and forms a part of the body of a multicellular organism.
Phospholipids: fats that contain phosphorus
References
Do animal cells have a cell wall? | AAT Bioquest. (n.d.). https://www.aatbio.com/resources/faq-frequently-asked-questions/do-animal-cells-have-a-cell-wall
Pedersen, T., & Dutfield, S. (2022, January 18). What is the difference between prokaryotic and eukaryotic cells? livescience.com.
https://www.livescience.com/65922-prokaryotic-vs-eukaryotic-cells.html
Molecular Expressions Cell Biology: Animal Cell Structure. (n.d.).
https://micro.magnet.fsu.edu/cells/animalcell.html
Swami, A. (2023, March 12). Understand the Key Differences between Plant and Animal Cells: A Comprehensive Guide. RS Creator.
https://awbi.org/differences-between-plant-and-animal-cells/
Author
Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.
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