Cells and cellular organization

 Cell theory.

All organisms are composed of cells, some of a single cell some of many cells. Recall the hierarchy of life, the levels of organization mentioned earlier. The basic  unit which can be called “living” is the cell, which may form a single celled organism (e.g.,  Chlamydomonas , Yeast) or a multicellular plant or animal. The cell is the basic structural and functional unit of life. The level of organization of matter represented by a cell shows all the characteristics of life. Any stage below level of a cell cannot be considered living, whether it is a single celled organism or multicellular  plant or an animal.

History and presentation of Cell theory

•    Robert Hooke (1663), while trying to understand why, cork which is a solid substance can float, examined thin slices using a microscope and found that they are      made up of ‘pores’ and coined the term ‘cells’ to describe the pores.

•    Anton Van Leeuwenhook (1650), a contemporary of  Robert Hooke was the first to describe and record  living single celled organisms,  Euglena  & bacteria

•    Matthias Schleiden (1831), a botanist, studying plant tissues concluded that all plants are made up of cells.

 •    Theodore Schwann (1839), a zoologist and Shleiden (1832), concluded that animal tissues are  also made up of cells.

•    Schleiden and Schwann presented the  ‘Cell Theory’ which included the following.

1.       All organisms are composed of one or more cells.

2.        The basic structural and functional unit of organisms is the cell.

3.       All cells arise from pre-existing cells.                                               

                                                                                                                             

Organization of cells

                    •    Two kinds of cellular organization - Prokaryotic and Eukaryotic

                    •    The differences between prokaryotic cells and eukaryotic cells.

                    •    Bacteria and Archaebacteria have prokaryotic cells. All the other organisms have

                        eukaryotic cells.

                    •    Prokaryote cells, in comparison to eukaryotic cells, are small in size, have no

                        organized nucleus, no membrane bound organelles, have 70 s ribosomes, flagella

                        are simple without microtubules and not bound by membrane, have no endoplasmic

                        reticulum and cytoskeleton, Peptidoglycan present in cell wall of bacteria and

                        polysaccharides and proteins present in Archaebacteria

                    •    Features of different cellular organizations illustrated by diagrams, electron

                        micrographs or electronic sources.