CELL AS THE BASIC UNIT OF LIFE

CELL AS THE BASIC UNIT OF LIFE


The basic building block of all organisms and the smallest unit of a living thing is called a cell.

KEY POINTS

  • There are two categories of cells: prokaryotic and eukaryotic cells.
  • Cells are specialized with special functions and characteristics.

KEY TERMS

  • prokaryotic: Small cells in bacteria and Archaea that do not contain a membrane-bound nucleus or other membrane-bound organelles.
  • eukaryotic: Having complex cells, in which the genetic material is contained within membrane-bound nuclei.

CELL AS BUILDING BLOCKS

TYPES OF CELLS

MICROSCOPY

KEY POINTS

  • Light microscopes use visible light which passes and bends through the lens.
  • Electron microscopes use a beam of electrons, which is opposed to visible light, for magnification.
  • In comparison to a light microscope thus, electron microscopes allow higher magnification for visualization of a cell's internal structures.

MICROSCOPY

The optics of the microscope's lenses change the orientation of the image that the user sees. A specimen that is facing right when viewed through a microscope will appear upside-down while facing left on the microscope slide, and vice versa. Similarly, if the slide is moved to the left, it will appear to move right, and if moved down while looking through the microscope, it will seem to move up. this occurs because microscopes use two sets of lenses to magnify the image, and thus the system produces an inverted image.

LIGHT MICROSCOPE

Most student microscopes are classified as light microscopes. Visible light passes through the lens to enable the user to see the specimen. The item being viewed is called a specimen. Light microscopes are generally useful for viewing living organisms, but since individual cells are transparent, so their components are not seen unless they are colored with special stains.

Light microscopes are commonly used in graduate college laboratories, which magnifies up to approximately 400 times. Magnification and resolving power are the two specifications that are important in microscopy.

  • Magnification is the process of enlarging an object in appearance.
  • While on the other side, resolving power is used as the ability to distinguish two adjacent structures as separate.

The higher the resolution, the more details, and clearance of the image will also be better. But the magnification is usually increased to 1000 times when oil immersion lenses are used for the study of small items. Scientists, typically use electron microscopes, to gain a better understanding of the structures and functions of cells.

ELECTRON MICROSCOPE

In contrast to light microscopes, electron microscopes use a beam of electrons instead of a beam of light. This allows higher magnifications and, thus, it also provides higher resolving power. Electrons have short wavelengths that move best in a vacuum, so living cells cannot be viewed with an electron microscope.

In a scanning electron microscope, a beam of electrons moves across the cell's surface creating details of its characteristics. In a transmission electron microscope, the beam of electrons penetrates the cells by providing the details of a cell's internal structures. Therefore, electron microscopes are particularly more bulky and expensive than light microscopes.

CELL THEORY

KEY POINTS

  • Theodor Schwann, Matthias Schleiden, and Rudolf Virchow are the three scientists that contributed to the development of cell theory.
  • Cell theory is that all living organisms are made up of one or more cells.
  • The component of cell theory is that the cell is the fundamental unit of all living organisms.
  • Cell theory is that all the new cells come from pre-existing cells.

CELL THEORY

In a 1665 publication called micrographia, experimental scientist Robert Hooke coined the term “cell” when viewing cork tissue through a lens. In the 1670s, van Leeuwenhoek discovered bacteria and protozoa.

By the late 1830s, two scientists Theodor Schwann and Mattias Schleiden were studying tissues and proposed cell theory. The unified cell theory states that; all living things are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells. Later on, Rudolf made contributions to this theory.

Scheilden and Schwann proposed spontaneous generation as the method for cell origination which was later disproven. Rudolf Virchow stated that “Omnis cellula e cellula”…“All cells only arise from pre-existing cells”. Today's scientific community has widely agreed on the parts of the theory that did not have anything to do with the origin of cells. They simply accepted portions of the modern cell theory as follows.

  • In all living things, the cell is the fundamental unit of structure and function.
  • All organisms are made up of one or more cells.
  • Cells arise from other cells through cellular division.

However, Robert Remak had already proposed the idea that all cells come from pre-existing cells; it has been suggested that Virchow plagiarized Remak and did not give him credits. Later on, Remak published observations on cell division, claiming that Schwann and Scheilden were wrong about the generation method. He called that Binary fission, which was first introduced by Dumortier, that how the reproduction of new animal cells was made. Once this tenet was added, the cell theory was completed.

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