BIO - 1ST PART

TOPICS TO PONDER:

  1. Cell Theory

  2. Microscopy

Cell Theory

          About 150 years passed before scientists were able to organize the observations made by Hooke and van Leeuwenhoek into a unified theory. In 1838, the German botanist Matthias Schleiden, discovered that all plants are composed of cells and a year later, a German zoologist Theodore Schwann, discovered that all animals are also made up of cells. Several years after the discovery of Schleiden and Schwann, in 1855, Rudolf Virchow, a German physician, discovered that cells came from pre-existing cells after he worked on how diseases affect the living organisms.

The observations made by these three scientists together comprised the cell theory which includes the following three tenets:

  1. all living organisms are made up of one or more cells;

  2. cells comprise the smallest unit of life; and 

  3. cells come only from pre-existing cells.

  • refers to the idea that cells are the basic unit of structure in every living thing

  • one of the foundations of biology

PEOPLE:

  • 1838 - Matthias Schleiden concluded that all plant parts are made up of cells

  • 1839 - Theodor Schwann stated that all animal tissues are composed of cells.

  • 1855 - Rudolf Virchow concluded that all cells come from pre-existing cells

  • 1831 - Robert Brown discovered the cell nucleus while looking at a plant

  1. Matthias Schleiden, - German botanist who discovered that all plants are composed of cells

  2. Theodore Schwann- German zoologist discovered that all animals are also made up of cells.

  3. Rudolf Virchow - In 1855, a German physician, discovered that cells came from pre-existing cells after he worked on how diseases affect the living organisms.

  4. Antonie van Leeuwenhoek - (1674) was the first person to see live cells in 1665 using a microscope

  5. Robert Hooke - coined the word “cell” , pioneered microscopic research

MICROSCOPY

  • Almost all cells cannot be seen with the naked eye, and it was the invention of the microscope in the 16th century that paved the way for the discovery of the cell.

The Early Microscope

          The earliest simple microscope was described as mere a tube with a plate for the object to be studied at one end and a lens at the other end. This microscope gave a magnification of ten times the actual size of the object. Even with its very low magnifying capacity, it was considered a monumental development because through its use, people at the time were able to visualize sperm cells and single-celled "animals" or animalcules.

Figure 1.1 A replica of the Janssen microscope.

  •   In 1597, Hans Janssen and his son, Zacharias Janssen, while experimenting with several lenses in a tube, discovered that the combination of two lenses in particular arrangement was the secret to better visualization and magnification of of objects. One lens was positioned at the eyepiece of the microscope, and the second lens was  put near the sample to be studied. It is believed that this particular arrangement of the lenses was based on the reverse of a telescope. This explains why these instruments were two feet long and extremely heavy (Figure 1.1). Nevertheless, they invented what would become the prototype for the compound microscope.

          More and more people took interest in observing things far smaller than could be perceived by the naked eye. Many optical workshops were set up throughout Europe by 1625

  • Hans Janssen & Zacharias Janssen(son) - discovered that two lenses was the secret for better magnification and visualization of objects.

    • One lens - eyepiece of the microscope

    • Second lens - was put near the sample to be studied

  • Janssen microscope - reverse of a telescope that is why it is two feet long and extremely heavy.


17th-Century Microscopes and the Discovery of the Cell

Figure 1.2 Hooke's microscope

         

The microscope was later modified in the 17th century by Robert Hooke, an English scientist and a mechanical genius who pioneered in microscopic research. He is widely recognized as the English Father of Microscopy. One of his greatest discoveries was the cell which looked like a small monastery rooms, hence the name. What he actually saw ware dead plant cells.

  To combat dark specimen images, Hooke designed an ingenious method of concentrating light on his specimens, as shown in the illustration. He passed light generated from an oil lamp through a water-filled glass flask to diffuse the light and provide a more even and intense illumination for the samples. Even with all the intricate details involved with this microscope, it still fell short in optical performance when compared to the simple Leeuwenhoek microscope.

  • Robert Hooke - English Father of Microscopy

    • discovered “cell”

    • to combat dark specimen images, he designed ingenious method of concentrating light on his specimen.

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17th-Century Microscopes and the Discovery of the Cell

Figure 1.3 A replica of Antonie van Leeuwenhoek's microscope.

          Antonie van Leeuwenhoek, a Dutch maker of microscopes, was the first person to see live cells in 1665 using a microscope that he himself made. He was able to grind and polish purer glass - rather than poor quality, greenish glasses commonly used in his time - into a lens. He mounted a double-convex lens between brass plates. His microscope was capable of giving 270 times magnification, which was exceedingly greater than those of the early compound microscopes which had 20 to 30 times magnification. Through his microscope, he made pioneering discoveries on protozoa, red blood cells, capillary systems, and the life cycle of insect. His invention also paved that way for the development of the world's first practical microscope.

  • Antonie Van Leeuwenhoek - the development of the world's first practical microscope.

    • first person to see live cells in 1665 using a microscope that he himself made.

    • polish purer glasses, greenish glasses, double-convex lens, 270 times magnification.

    • Pioneering discoveries of Protozoa, red blood cells, capillary systems, and the life cycle of insect.

          Half a century after the invention of the compound microscope , both Hooke and Leeuwenhoek realized that lenses with very short focal lengths were the key to more magnification. This idea led to the discovery of using double convex or spherical lenses, which improved both resolution and magnification of the compound microscope. Using this microscope, many discoveries in biology ware made especially in the field of microbiology. The discovery of two infectious bacteria, tubercle and cholera bacilli by Robert Koch, a German physician and microbiologist, was among monumental discoveries in microbiology.

  • Robert Koch - discovered two infectious bacteria, tubercle and cholera bacill

Electron Microscope

Figure 1.4 Scanning Electron Microscope

          Modern electron microscopes which now have greater magnifying power and greater resolution, can magnify objects up to 500 000 times their actual size. An electron microscope uses beams of accelerated electrons as a source of illumination. Electron microscope use electrostatic and electromagnetic lenses in forming the image by controlling the electron beam to focus it at a specific plane with reference to the specimen. 

MODERN ELECTRON MICROSCPE

  • 1931 - first prototype of electron microscope was built by two German engineers, Ernst Ruska and Max Knoll