Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Today we easily take for granted that living things are composed of cells. Yet it was not always common knowledge and indeed the basic ideas took over 150 years to evolve.
|1965||Robert Hooke noted the cellular structure of cork (dead plant cells).|
|1974||Antonie Van Leeuwenhoek observed living protozoa.|
|1980s||Henri Dutrochet proposed that the cell was not just thestructural unit of living things but the functional unitalso, and that new cells arise from other cells.|
|1983||Barthelemy Dumortier first observed cell division (in plant cells)|
|1837||Jan Purkyne proposed that animal tissues were also composed of cells.|
|1879||Walther Flemming noted that chromosomes 'split' during mitosis.|
|1887||Wilhelm Roux proposed that chromosomes carriedhereditable traits. He was also the first to carry outtissue culture.|
|1904||Theodor Boveri worked with sea urchins embryos and showed that a full set of chromosomes was necessary for normal development.|
|1953||From the early 1900s the chemical structure of chromosomes was gradually clarified and eventually published in 1953.|
As cells grow they take in various raw materials which they use to construct complex biomolecules such as proteins, lipids, DNA andRNA. Cells multiply by binary fission, i.e. they split into two smaller cells, known as daughter cells. During cell division the chromosomes, which are composed of DNA, replicate âˆ’ that is, a copy of each chromosome is formed and one of each goes to each daughter cells.
Structure of Cells
Animal cells such as nerve cells, muscle cells and skin cells are not all alike but they do have some characteristics in common. They typically have an outer cell membrane; inside this there iscytoplasm, a nucleus, mitochondria and other organelles. During the growing stage of a cell the chromosomes (DNA) stay in the nucleus.
Plant cells, in addition to a cell membrane, generally have an outer cell wall which is made mainly of cellulose; often there is a primary and a secondary cell wall. The cell wall of fungal cellscontains chitin, whose structure is similar to that of cellulosealthough it contains amino groups.