Cells are the basic components of every living organism. They provide structure for the body, take in nutrients from food that is consumed, convert those nutrients into energy, store the body’s genetic material and carry out some specialized functions. Today, as a bunch of cells ourselves, we’re going to explore these building blocks of us.
The History of Cells
The word cell has been derived from the Latin word cella, meaning a small room. It was first used in the context of biological organisms in the 17th century by Robert Hooke, who, using a primitive microscope looked at a thin slice of cork. He saw empty spaces contained by walls, which reminded him of the tiny rooms occupied by monks. The cell theory, which states that all organisms are composed of at least one cell, that cells are the fundamental unit of structure and function in all living organisms, and that all cells come from cells that pre-existed was developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann.
People have studied cells for centuries. Understanding how cells work both in healthy and diseased states has enabled us to cure diseases, cross-breed species and produce genetically modified organisms, but most importantly, the study of cells allows for a glimpse into how exactly all living things live.
But how do cells work? What are they composed of? To answer that question, we first have to differentiate two types of cells: prokaryotic and eukaryotic.
Prokaryotic cells, in short, are cells that do not contain a nucleus – the structure that holds the cell’s genetic material. Instead, their DNA is organized into a single, circular chromosome located in the cytoplasm and it is called the nucleoid (meaning nucleus-like). Their organelles, which are structures specialized to perform specific functions, are not membrane-bound and most prokaryotes have a cell wall protecting the cell membrane.
Eukaryotic cells do contain a nucleus and have membrane-bound organelles, each dedicated to a specific task. Eukaryotic organisms include plants, animals, fungi, slime moulds, protozoa, and algae. DNA in the nucleus is organized into linear chromosomes and it is separated from the cytoplasm by a membrane. Organelles of a eukaryotic cell include the mitochondria, which are responsible for producing energy; ribosomes, which synthesize proteins; the Golgi apparatus, which is responsible for intracellular transport and lysosomes, which contain enzymes capable of breaking down proteins, nucleic acids, lipids, and carbohydrates.
Plant and Animal Cells
However, there are quite a few differences in the structure of the eukaryotic, animal and plant cells. Firstly, animal cells are generally smaller than plant cells and they come in different
shapes and sizes, whereas plant cells tend to be cube-shaped. Animal cells are not protected by a cell wall, which in plant cells is formed of cellulose. In an animal cell, there are many vacuoles – organelles responsible for storing organic and inorganic molecules, whereas in a plant cell there is a singular, large vacuole. Both cell types have mitochondria, but only plant cells have chloroplasts – organelles, where the process of photosynthesis is carried out.
There is also one other difference between plant and animal cells, which is crucial especially to the development of medicine: most plant cell types are capable of differentiation – the process where a cell changes from one cell type to another. Most animal cells, on the other hand, are specialized, meaning that they have a specific role in our bodies that they cannot change. That is, however, not the case with stem cells.
What are Stem Cells?
Despite what the name may suggest, these cells are neither scientists nor mathematicians, but they are an amazing feat of engineering in our body. In short, they can divide over and over again to produce more undifferentiated cells that are then able to change into specialized cells. They provide new cells for the body as it grows and replaces cells that have been damaged or lost due to disease, injury or genetic conditions. This is crucial because some cells in the body, such as red blood cells, are unable to divide. Stem cells exist in embryos and throughout the adult body. They are intensively researched because of their potential in using them to replace damaged tissues or even create organs.
Cells with similar functions that work together to perform a shared function are organized into tissue. There are four main types of tissue: muscle, epithelial, connective and nervous. Tissues are organized into organs, groups of organs are called systems and systems are organized into… well, us.
Written by: Marta Luterek
Marta Luterek is volunteering for Voyager Space Outreach to write Blog posts on Space/STEM oriented topics.