What is this incredible object? Would it surprise you to learn that it is a human cell? The cell is actually too small to see with the unaided eye. It is visible here in such detail because it is being viewed with a very powerful microscope. Cells may be small in size, but they are extremely important for life. Like all other living things, you are made of cells. Cells are the basis of life, and without cells, life as we know it would not exist. You will learn more about these amazing building blocks of life when you read this section. If you look at a living matter with a microscope — even a simple light microscope — you will see that it consists of cells. Cells are the basic units of the structure and function of living things. They are the smallest units that can carry out the processes of life. All organisms are made up of one or more cells, and all cells have many of the same structures and carry out the same basic life processes. Knowing the structure of cells and the processes they carry out is necessary to understanding life itself.
The first time the word cell was used to refer to these tiny units of life was in 1665 by a British scientist named Robert Hooke. Hooke was one of the earliest scientists to study living things under a microscope. The microscopes of his day were not very strong, but Hooke was still able to make an important discovery. When he looked at a thin slice of cork under his microscope, he was surprised to see what looked like a honeycomb. Hooke made the drawing in the figure below to show what he saw. As you can see, the cork was made up of many tiny units, which Hooke called cells. Soon after Robert Hooke discovered cells in cork, Anton van Leeuwenhoek in Holland made other important discoveries using a microscope. Leeuwenhoek made his own microscope lenses, and he was so good at it that his microscope was more powerful than other microscopes of his day. In fact, Leeuwenhoek’s microscope was almost as strong as modern light microscopes. Using his microscope, Leeuwenhoek was the first person to observe human cells and bacteria. 
By the early 1800s, scientists had observed the cells of many different organisms. These observations led two German scientists, named Theodor Schwann and Matthias Jakob Schleiden, to propose that cells are the basic building blocks of all living things. Around 1850, a German doctor named Rudolf Virchow was studying cells under a microscope when he happened to see them dividing and forming new cells. He realized that living cells produce new cells through division. Based on this realization, Virchow proposed that living cells arise only from other living cells. The ideas of all three scientists — Schwann, Schleiden, and Virchow — led to cell theory, which is one of the fundamental theories unifying all of biology. Cell theory states that:
Starting with Robert Hooke in the 1600s, the microscope opened up an amazing new world — the world of life at the level of the cell. As microscopes continued to improve, more discoveries were made about the cells of living things. However, by the late 1800s, light microscopes had reached their limit. Objects much smaller than cells, including the structures inside cells, were too small to be seen with even the strongest light microscope. Then, in the 1950s, a new type of the microscope was invented. Called the electron microscope, it used a beam of electrons instead of light to observe extremely small objects. With an electron microscope, scientists could finally see the tiny structures inside cells. In fact, they could even see individual molecules and atoms. The electron microscope had a huge impact on biology. It allowed scientists to study organisms at the level of their molecules and led to the emergence of the field of cell biology. With the electron microscope, many more cell discoveries were made. Figure \(\PageIndex{3}\) shows how the cell structures called organelles appear when scanned by an electron microscope.
Although cells are diverse, all cells have certain parts in common. These parts include a plasma membrane, cytoplasm, ribosomes, and DNA.
These parts are common to all cells, from organisms as different as bacteria and human beings. How did all known organisms come to have such similar cells? The similarities show that all life on Earth has a common evolutionary history.
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To learn more about cell theory, and its history, watch the video below. LICENSED UNDER Answer Hint: The term ‘cell’ was coined by a European scientist who observed the dead cork cells under his microscope and later compared it with the compartments or cavities of a honeycomb. Complete answer: Robert Hooke was a European scientist in the Royal Society of London. He built a microscope in 1665 to examine the thin sections of cork he had cut with a penknife. He observed a number of tiny boxlike structures that resembled honeycomb. He named these structures as ‘cells’.The word ‘cell’ originated from a Latin word ‘cellula’ which means little room. Though Robert Hooke didn’t realize that they were dead, he did notice in the cells of other plant tissues that were filled with’ juices’. But his discovery was limited due to the magnification power of his microscope which was 30X i.e it could magnify an object only 30 times its size. The discovery of the cell was carried forward by Anton van Leeuwenhoek. He was a Dutch textile merchant and produced lenses that could magnify an object up to 300 times. This made him the first one to study the living cells ranging from sperm cells to blood cells to single-celled organisms such as algae. But his observation was again restricted by the limited resolving power of his lenses though he did send letters to the Royal Society of London dictating his exciting findings. Resolving power of a lens is its ability to distinguish between two extremely closely present objects in a specimen. This hindered the possibility to properly deduce the internal compartments of a cell. This problem was solved in the 1800s when the compound microscope was invented. Later, by using this technology, Robert Brown declared the presence of a rounder structure in every cell. This was named as ‘nucleus’.So, the correct answer is ‘Robert Hooke.’ Note: In a compound microscope, there are two lenses - an eyepiece and an objective lens. Here, one lens i.e. an eyepiece magnifies an image created by the second lens i.e objective. This served the dual purpose by enhancing magnification as well as a better resolution. This made the possibility of seeing structures that were as tiny as 1μm clearly. |
Who first used the term cell
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