The chronicle of the cell dates back to April 1663 and centers around a young researcher called Robert Hooke (1635-1703). As the story goes, Hooke discovered cell while he was working with his new microscope under the directive of the Royal Society of London. Robert Hooke was born at Freshwater on the Isle of Wright and was educated first in London and subsequently in Oxford. In Oxford, Robert Brooke served as an assistant to the pioneering chemist Robert Boyle. When Robert Hooke was still in his 20s, he moved to London with Boyle and there the newly constituted Royal Society hired him as a demonstrator. On March 25, 1663, Robert Hooke was assigned to present a new microscopic demonstration each week. Interestingly enough, from the very first microscopic demonstration, Robert Hooke gave lectures that set a new trend that may rightly be called the contemporary epoch of science.
Robert Hooke was known to be a hard-working young man who was credited with a number of excellent architecture and is also widely recognized for ‘Hooke’s Law’ that elucidates the drawing out of a spring. Barely two weeks after Hooke was assigned to present a new microscopic demonstration at the Royal Society, had he presented a display of how moss looked under a microscope. He also published impressions of the pictures in a significant book ‘Micrographia’ published in 1665. In fact, the drawing of the moss leaflets made by Hooke had a prominent characteristic – each of the leaflets where displayed with such faultless clearness that they showed the minute cells comprising the leaflets and each of these cells matching its neighboring cell resembling bricks comfortably fitted in a wall. A week later, on April 13, Hooke came back with additional study of these tiny forms. In his subsequent presentation, Hooke made an excellent segment of cork from a bottle stopper and demonstrated that these small structures resembling bricks with more specific aspects. In other words, he explained the minute structures of the cork in much more detail. Hooke found them to be akin to minute square rooms and, hence, he named them ‘cells’. Even to this day, this term is extensively used in contemporary biology.
Eventually, all the demonstrations made by Hooke at the Royal Society were brought together in the form of a book called ‘Micrographia’. It is interesting to note that the book proved to be a hefty volume that measured 13 inches in length and weighed three pounds! Although the publication date mentioned in the book is 1665, in fact it had been released in October 1664. Living up to Hooke’s plans and expectations, ‘Micrographia’ immediately turned out to be a best seller and topped the charts in London. In fact, much before Hooke started writing his book, he undertook a market survey to ascertain that no one else would possibly publish a competitive book that may otherwise harm his own prospects. Hooke included several lucid images in ‘Micrographia’ and some of these comprised researches of glaringly recognizable topics, such as a flea and a louse on pages that were so big that actually these pages needed to be folded two times in order to be accommodated within the covers.
Incidentally, Samuel Pepys, who had owned a microscope himself since the day he had joined the Navy Office, was among the many people who bought ‘Micrographia’. Later, Pepys wrote in his personal diary that ‘Micrographia’ was the best book he had ever bought. Pepys further wrote that he remained awake half the night reading this interesting and exceptional book by Hooke. Micrographia proved to be such a popular book and sold like hot cakes that Hooke had to publish its second edition in 1667. The engravings in Micrographia were drawn out of the storeroom some 70 years later and again printed with a new title ‘Micrographia Restaurata’. Even the new title was an instant hit with the people and more editions of ‘Micrographia Restaurata’ were published in 1745 and again in 1780. True copy or facsimile editions of the original book ‘Micrographia’ were published in paperback format during the 20th century and this eventually made ‘Micrographia’ among the most popular and successful books on science that have been published ever.
Soon after the first publication of ‘Micrographia’ and while the book was at the peak of its popularity among the connoisseurs of the British intellectuals, an explorer from the Netherlands called Thonis Leeuwenhoek (1632-1723) sailed all the way to the Thames to meet his business contacts in London. It was common for Leeuwenhoek to evaluate the quality of cloth using a lens and, incidentally, ‘Micrographia’ contained a number of brilliantly implemented plates of cloth under the microscope. These plates of cloth were astonishing and had three-dimensional features something akin to the contemporary scanning electron micrographs. The portrayals in Robert Hooke’s book proved to be a vital motivation for Leeuwenhoek’s inquisitive mind. In the preface of his book ‘Micrographia’, Robert Hooke had explained the process of making a small hand-held microscope using a ground glass (glass that has had its polished surface removed by fine grinding and that is used to diffuse light) bead instead of a lens. According to Hooke, a microscope prepared by this process would offer magnification or enlargement of the objects under it several times more compared to the standard compound microscope that he personally had a preference for. However, the microscope made by using a ground glass bead for a lens had one major hitch and that was they had to be held very close to the eye and, hence, were usually problematic to use.
During the subsequent years, taking a cue from the preface in ‘Micrographia’ on making a small hand-held microscope, Thonis Leeuwenhoek himself undertook a series of experiments to make an effective microscope. In due course of time, Leeuwenhoek had refined the design of microscope suggested by Hooke in the preface of his book by means of buffing up his lenses prepared with melted beads of glass. With a view to demonstrate his expertise, Leeuwenhoek once again scrutinized a number of the examples illustrated by Robert Hooke simply to prove that his examinations were of much higher quality compared to the Englishman who actually pioneered the device. In a letter dated June 1, 1674, Leeuwenhoek communicated his findings to the Royal Society in London. Nevertheless, Leeuwenhoek’s grand ‘eureka’ occasion took place in the later part of August that very year. In August 1674, Leeuwenhoek took a trip by boat across a lake called Berkelse Mere, a place where the water is enveloped by rapid growth of micro-organisms during the middle of summer. According to local myths, the growth of microbes was honey dew formed by concentration during the nippy evenings. Hence, Leeuwenhoek gathered a few samples in a glass container and carried them home. On the following day, he began working – scrutinizing the substances collected under the best of his hand-made microscopes.
It is interesting to note that what Leeuwenhoek viewed under his microscopes later changed our perception regarding nature forever. When Leeuwenhoek looked at the subjects through his indigenous microscopes, he was astonished to find innumerable living organisms. While some of these microorganisms remained still gleam in the light, others were swimming around, twisting and twirling before his eyes. Leeuwenhoek continued to watch the acts of these ‘astonishing’ creatures till he eventually became tired. Unfortunately, Leeuwenhoek was not vested with the virtue of drawing and he often lamented that he was unable to sketch the amazing things he viewed under the microscope with a pencil to demonstrated the things to others. Eventually, he hired a limner (an itinerant painter with little formal training) to watch the different specimens under the microscope and prepare meticulous drawing of what he viewed. On his part, the young artist repeatedly became too excited over what he saw through the microscope and had to be often reminded to stop gazing and instead concentrate on drawing the images of what he witnessed. Precisely speaking, it was Leeuwenhoek and his anonymous assistant who were the first people in the world to investigate the amazing world of microorganisms. Leeuwenhoek is credited for discovering protists and algae, polyps and rotifers all by himself. Later, he even went on to explain bacteria! In fact, there is little doubt that it was Leeuwenhoek who presented the world with the new science of microbiology.
Unlike Robert Hooke, the cells described by Leeuwenhoek were not lifeless structures. The new world of microorganisms discovered by Leeuwenhoek comprised innumerable swarming microscopic creatures. When Leeuwenhoek turned an adult, he used ‘Antony’ as his first name and when he gradually became popular among the people, especially the intelligentsia, he added the word ‘van’ to his name to bestow himself with a superior sense of self-esteem. Very soon, Leeuwenhoek had numerous people visiting him, including the rulers of Britain and Russia, who desired to see more of his exceptional work. Over the years, Leeuwenhoek was honored by being elected as a member of numerous top scientific academies. When we talk about cells, it is important to remember that Antony van Leeuwenhoek was the first microbiologist in history. Moreover, the manners in which scientists conduct their experiments today are to a great extent based on the insights or approaches established by Leeuwenhoek himself over three centuries ago. In fact, Leeuwenhoek was brilliantly determined – a self-taught person and always independent. Unlike Robert Hooke again, Leeuwenhoek never ever consented to teach any student or make any public demonstration of his work or give lectures on the subject he had pioneered. In fact, Leeuwenhoek had a simple philosophy – when people were eager to acknowledge what he observed, he did not have enough time to waste explaining them to others. Instead, he could spend his time more usefully be researching new things. He always said, “I know, I am right’. And, there is little scope to doubt his belief.
Leeuwenhoek’s work became so popular that during the second half of the 18th century it was trendy to buy small microscopes to observe the ‘surprises’ in the pond life. These hobbyists were particularly fond of hydra, which was a popular topic those days. They took delight in watching hydra gently expanding its fragile tentacles through the water and taking water fleas into custody by making use of their extremely intricate cells that emit pointed spears at high speed and fasten the prey with filaments that are as tough as wires made of steel. It is interesting to note that the body of this aquatic animal hydra is approximately one centimeter or half an inch long and is made up of a void tube comprising of only two layers of cells.
Way back in December 1702, Leeuwenhoek conducted research on hydra and his assistant limner drew the images of how the animal appeared under the microscope. Much later, during the 1740s a young academic called Abraham Trembley (1710-1784) picked up hydra as the object of his research. Trembley was appointed the tutor of two juvenile children of Count Bentinck of The Hague in the Netherlands at a very young age of 30 years and he regularly used the microscope in his classes. Like Leeuwenhoek, even young Trembley was awestruck by the microscopic organisms. He examined these microorganisms minutely and drew them perfectly. Subsequently, Trembley embarked on a series of remarkable experimentations and today when one looks back at them, they find them absolutely amazing for that period.
What was remarkable about Trembley’s experiments is the fact that he pioneered the science of tissue grafting. Through his experiments, Trembley demonstrated that the hydra was able to redevelop itself even from petite tissue sections. It was Trembley who was the first person in the world to show the way to stain tissues, the manner in which an animal with no eyes was able to act in response to light and also explained the cytoplasm – an essential ingredient of every type of cells. In fact, all cells are composed of cytoplasm. Today, very few people remember Trembley or his achievements. People have almost forgotten this pioneering scientist, so much so that his name does not figure in most of the reference books on biology. In 1744, the interesting experiments conducted by Trembley were published in a book form under the title “Memoires d’un genre des polypes d’ eau douce” in Geneva. “Memoires d’un genre des polypes d’ eau douce” is a wonderful book, complete with details of extraordinary experiments conducted by Trembley. Anyone going through this book will realize that it contains numerous indications regarding great things that would happen in the field of cell biology in future.
The growing curiosity among the people regarding hydra ultimately resulted in the creation of the first effective bench microscope. In fact, microscopes were available since the 1660s either as a useful device or a novelty. People proficient in utilizing the microscope, for instance Robert Hooke and other pioneers, made good use of the instrument and conducted numerous interesting experiments with it. The professional or pre-eminent microscopes were made of brass, but compared to the machines we use today, even they were just something more than just curious. On the other hand, the ordinary or low-power microscopes were made with wood and cardboard and were aimed by means of a rudimentary clamp set on a pillar. In fact, these microscopes were not developed on any design that could be improved upon to make something useful for important research work. However, people’s growing interest in hydra changed the scenario. In fact, Trembley used hand-held lenses to observe his specimens. Habitually, Trembley used to put the hand lens and the specimens in a small pool of water locked in the palm of his cupped hand and stage-managed them using a bristle.
If you intend to watch this frail and small animal under a bench microscope, you require a metallic instrument that can be aimed quietly without any harsh shaking that would otherwise result in the hydra contracting into a ball-like structure. Thus, to observe the hydra, it was necessary to design a wide stage that was big enough to bear a watch glass confining the specimens. In addition, it was also necessary for the instrument to provide a practical amount of enlargement to enable the observers to view each detail minutely.
Composition of the cell
The cell is among the most fundamental elements of life. In fact, there are several million kinds of cells that are different from each other. A number of cells are organisms by themselves, for instance, the minuscule amoeba and the bacteria cells. On the other hand, there are cells that operate as a small part of a large organism, such as the cells that forms the composition of our body. In fact, a cell is the least element of life in our body. For instance, there are several types of cells in our body – skin cells, stomach cells, brain cells, liver cells, name an organ and there are specific cells composing it.
Each type of cell present in our body, rather composing our structure, has different and exceptional features and functions. Nevertheless, all of them have a number of identifiable resemblances. Each cell possesses a ‘skin’ or outer coating that is known as plasma membrane that guards it from the external situations. In fact, the cell membrane controls the interchange or passage of water, nutrients and wastes inside and out of the cell. The working parts of the cell are all located inside the cell membrane. The nucleus is at the center of the cell containing the DNA or genetic code of the cell that synchronize with synthesis of proteins. Apart from the cell nucleus, several organelles are present within the cell that includes minute structures that assist in performing the routine functions of the cell. Ribosome, which partakes in the synthesis of protein, is one such important organelle present inside the cell. The motivation period of synthesis of protein occurs in the nucleus of the cell. When this phase is concluded, the mRNA departs from the nucleus and passes through the ribosome of the cell where the conversion takes place. The mitochondrion is another significant organelle of the cell. Occasionally, the mitochondria (plural for mitochondrion) are denoted as the power generating units of the cells as numerous reactions taking place in mitochondria generate energy that the body uses to carry out its normal functions. In addition to the ribosome and mitochondrion, lysosomes are also very important in the cell’s life. Basically, lysosomes are organelles that enclose enzymes which help in the absorption of nutrient molecules and other substances into the body.
When you study the cells, you will find that there are several dissimilar kinds of cells. One major difference between the cells is the dissimilarity between the plant and animal cells. Several dissimilarities are found in these two types of cells. Although both, the plant cells and the animal cells, possess the structures discussed above, some extra or specialized formations are present in the plant cells. Most of the animals possess a skeleton that provides their body with a definite structure as well as support. Although the plants do not possess any skeleton, they do not simply slum over like a large sponge mass. This is primarily owing to the fact that the plants have an exceptional firm cell structure known as the cell wall. The cell wall present in the plant cells is an unyielding formation formed on the exterior of the cell membrane and is basically created with polysaccharide cellulose. In fact, the cell wall provides the cells with a definite form that assists the cells to support separate parts of a plant. Besides the cell wall, the plant cells also enclose an organelle known as chloroplast that enables the plants to collect energy from sunlight.
Dissimilar forms of cells
It is interesting to note that diverse families of cells exist in the biological world. It is most possible that in your day-to-day life you will come across a variety of cells ranging from single cell microorganisms like bacteria and fungus to cells that form a minute part of plants and animals. Nevertheless, what you may be viewing is most of the time the multifaceted arrangements formed by dissimilar cells.
Fundamentally, there are two major clusters of cells – prokaryotic cells and eukaryotic cells. These two groups of cells are not only at variance in their appearance, but also in their makeup, reproduction and metabolism. Nevertheless, all the existing cells belong to any of the five living realms. And hence the maximum dissimilarity is found among the cells belonging to the different life kingdoms. Fundamentally, the five living kingdoms include protista, monera, fungi, plantae and animalia. All the cells belonging to the five live realms may be categorized into two groups – prokaryotic cells and eukaryotic cells.
Prokaryotic cells are those whose nucleus is not bound by a membrane. This category of cells derives their name from the Greek term ‘prokaryotes’ denoting before nuclei. The prokaryotic cells possess a small number of internal structures that are clearly noticeable when viewed under a microscope. Cells belonging to the monera kingdom, for instance bacteria and cyanobacteria, which are also known as the blue-green algae, all come under the prokaryotic category.
The prokaryotic cells and eukaryotic cells differ considerably. The prokaryotic cells not only have a nucleus that is not bound by a membrane, but even do not have chromosomal DNA. As a substitute for the chromosomal DNA, the genetic information of prokaryotic cells is found in a spherical ring known as plasmid. Basically, the cells of bacteria are miniscule, almost of the size of an animal mitochondrion – approximately one to two µm in diameter and about 10 µm in length. Characteristically, the prokaryotic cells have three main forms – rod shaped, spiral and spherical. In addition, unlike the eukaryotic cells, the prokaryotic cells do not go through complicated reproductive processes. On the contrary, bacterial cells that belong to the prokaryotic category reproduce by means of binary fission.
Although bacteria are considered to be a pathogen, they also carry out numerous significant roles on our planet. They are useful as decaying agents, instrumental in fermentation and also perform a pertinent function in our digestive system. In addition, bacteria are occupied in numerous nutrient cycles, for instance the nitrogen cycle that helps to return nitrate into the soil for the plants. Dissimilar to eukaryotes that rely on oxygen for their metabolic processes, the prokaryotic cells possess a dissimilar range of metabolic functions. For instance, a number of bacterium use sulfur in place of oxygen to carry out their metabolic processes.
Eukaryotic cells derive their name from a Greek word that denotes ‘genuinely nuclear’. Barring monera, these cells encompass all of the life kingdoms. In other words, a eukaryotic cell is one that encloses compartments bound by a membrane within which particular metabolic processes occur. Among the different compartments bound by the membrane of the eukaryotic cells, the nucleus is the most significant as it accommodated the DNA of the eukaryotic cell. In fact, the nucleus of the eukaryotic cell gives it its name that literally means ‘true nucleus’. In addition to the nucleus, the eukaryotic cells also enclose other specific structures within their membranes and these are known as organelles. Organelles are actually minute formations present inside the cells and execute specialized tasks. Normally, the eukaryotic cells are 10 to 100 micrometers in diameter, which means they are ten times bigger in size compared to the prokaryotic cells.
The plant cell is an important member of the eukaryote family or category of cells. Although the plant cells basically operate almost in the same way as any other eukaryotic cells, they possess three distinctive structures or formations that make them different from other eukaryotic cells. In fact, cell walls, plastids and vacuoles are only found in the plant cells.