Реферат: What Is A Cell Essay Research Paper
What Is A Cell? Essay, Research Paper
What is a Cell?
The English scientist Robert Hooke who used a makeshift microscope of his own invention to examine a variety of objects, including a thin piece of cork, made the first observations of cells in 1665. Noticing the rows of little boxes that made up the dead wood’s tissue, Hooke created the term “cell” because the boxes reminded him of the small cells the monks in the monastery lived in. While Hooke was the first to study and describe cells, he did not realize their importance. At about the same time, the Dutch maker of microscopes Antoni van Leeuwenhoek prepared for the invention of one of the best microscopes of the time. Using his invention, Leeuwenhoek was the first to study, draw, and describe a lot of living organisms, including bacteria in saliva, one-celled organisms in pond water, and sperm. Two centuries passed, however, before scientists understood the true importance of cells.
Modern ideas about cells appeared in the 1800s, when better light microscopes allowed scientists to observe more details of cells. Working together, the German botanist Matthias Jakob Shleiden and the German zoologist Theodor Schwann recognized the basic likeness between plant and animal cells. In 1839, they planned the new idea that all living things are made up of cells.
During the 1800s, scientists began to understand some of the chemical processes in cells.
In the 1920s, the ultracentrifuge was developed. The ultracentrifuge is a tool that spins cells or other things in test tubes at high speeds, which causes the heavier parts of the substance to fall to the bottom of the test tube. This device allowed scientists to separate the fairly heavy mitochondria from the rest of the cell and study their chemical reactions. By the late 1940s, scientists were able to explain the role of mitochondria in the cell. Using refined techniques with the ultracentrifuge, scientists subsequently isolated the smaller organelles and gained an understanding of their functions.
While some scientists were studying the functions of cells, others were examining details of their structure. They were aided by a crucial technological development in the 1940s: the invention of the electron microscope, which uses high-energy electrons instead of light waves to view specimens. New generations of electron microscopes have provided resolution, or the differentiation of separate objects, thousands of times more powerful than that available in light microscopes. This powerful resolution revealed organelles such as the endoplasmic reticulum, lysosomes, the Golgi apparatus, and the cytoskeleton. The scientific fields of cell structure and function continue to complement each other as scientists explore the enormous complexity of cells.
Another busy area in cell biology concerns programmed cell death, or apoptosis. Millions of times per second in the human body, cells commit suicide as an essential part of the normal cycle of cellular replacement. This also seems to be a check against disease: when mutations build up within a cell, the cell will usually self-destruct. If this fails to occur, the cell may divide and give rise to mutated daughter cells, which continue to divide and spread, gradually forming a growth called a tumor. This unregulated growth by cells can be benign, or harmless, or cancerous,
This may threaten healthy tissue. The study of apoptosis is one thing that scientists explore in an effort to understand how cells become cancerous.
Scientists are also discovering exciting aspects of the physical forces within cells. Cells use a form of architecture called tensegrity, which enables them to withstand battering by a variety of mechanical stresses, such as the pressure of blood flowing around cells or the movement of organelles within the cell. Tensegrity stabilizes cells by evenly distributing mechanical stresses to the cytoskeleton and other cell components. Tensegrity also may explain how a change in the cytoskeleton, where certain enzymes are anchored, initiates biochemical reactions within the cell, and can even influence the action of genes. The mechanical rules of tensegrity may also account for the assembly of molecules into the first cells. Such new insights made some 300 years after the tiny universe of cells was first glimpsed show that cells continue to yield fascinating new worlds of discovery.