bio111

• The scientific study of cells- their structures, functions, and activities is called cytology.
• The cell is the smallest unit of life.
• In 1590, Francis and Zacharias Janssen constructed the first compound microscope.
• The cell as a structural unit was first observed by Robert Hooke in 1665 in thin slices of cork and other plant tissues.
• At about the same time (1674) the Dutch lensmaker Leeuwenhoek reported seeing "animalcules" or single-celled organisms through his microscope.
• Marcello Malphigiani used a microscope to examine and describe thin slices of animal tissues from brain, liver, kidney, spleen, lungs, and tongue.
• In time, the quality of microscopes improved, leading to the concept of the cell theory gaining currency in the scientific world in the early 1800s.
• Theodor Schwann, a zoologist, wove the various loose ends into a coherent theory which proposed that all organisms are composed of cells and the product of cells.
• In 1831, Robert Brown described and named the nucleus of the cell.
• At the end of the decade Purkinje proposed using the term protoplasm to describe the living material within the cell.
• Thomas Huxley later called protoplasm the "physical basis of life".
• Another advancement came about when Rudolf Virchow stated an important principle: All cells arise from pre-existing cells.
• Louis Pasteur's experiment marked the end of a belief in spontaneous generation theory and the establishment of the principle of biogenesis.
• Plant cells are encased in an outer protective and supporting structure called the cell wall.
• The cell wall is composed of the polysaccharide cellulose in the form of threadlike structure called fibril.
• The first portion of the cell wall laid down by a young cell is the primary wall.
• Between the walls of adjacent cells is an intercellular layer called middle lamella which contains pectin.
• The middle lamella binds the cells together.
• The cells of the more woody portion of plants form an additional layer called secondary wall.
• This is located internal to the primary wall and contains lignin which adds stiffness and rigidity to cell walls.
• Mitochondria are round or filamentous structures with predominantly fat-protein composition, found in all cells, with an outer layer covering the mitochondrial surface, and the inner surface much folded and forming projections called cristae that extend into the interior fluid or matrix.
• The cristae is the site of protein synthesis for respiration.
• Many cells bear specialized structures of locomotion called cilia or flagella, which are vibratile extensions of the cell surface.
• The nuclear membrane has a double unit membrane structure and communicates with an internal membrane network, the endoplasmic reticulum by minute pores, which may facilitate an exchange of materials between the nucleus and the cytoplasm.
• The most conspicuous protoplasmic structure is a spherical or ellipsoid body called the nucleus, which is the reproductive, metabolic, and dynamic center of the cell.
• Cells without nuclei are called procaryotic cells in contrast to those with nuclei called eucaryotic cells.
• Chromosomes are principal nuclear structures which consists of DNA and proteins, and are conspicuous only during cell division.
• The mitochondria, as the respiration centers, have been aptly called the "powerhouse of the cell".
• The cell membrane, also known as the plasma membrane or plasmalemma, is the living boundary between the external and internal environment of the cell.
• The Golgi apparatus, discovered by Camilo Golgi, consists of flattened sacs which appear as parallel membranes, cluster of small, tightly packed vesicles and large clear vacuoles.
• The soluble portion of the cytoplasm, the cytosol, has a very high protein concentration exceeding 20%, most of which are enzymes required in metabolism.
• In the matrix of the mitochondria are a number of enzymes of the Krebs cycle, salts, water.
• The cytoplasm, a transluscent, colorless, viscous mass, is where most of the organelles of the cell are situated.
• The functions of the Golgi apparatus have not yet been completely defined but some investigators believe that they play an important role in secretion (cellulose) and provide a temporary storage area and repackaging center for substances like proteins and lipids.
• The nucleolus (little nucleus) is a highly compact and darkly staining spherical body which consists largely of RNA and proteins, and is believed to be the site of ribosomal manufacture.
• Mitochondria are the principal sites for cellular respiration.
• Some unicellular organisms such as bacteria and blue-green algae do not show a distinctive separation of nuclear and cytoplasmic constituents.
• Chromoplastids are yellow or red in color and owe their color to the presence of various carotenoids and are responsible for the color of ripening fruits and autumn leaves.
• Microtubules are the thickest, consisting of a chain of proteins wrapped in a spiral to form a tube, and radiate from an area near the nucleus, providing intracellular support in non-dividing cells.
• Chloroplastids are the green plastids containing the light-sensitive pigment chlorophyll and are the centers of photosynthetic activity.