Essential Idea:
The evolution of multicellular organisms allowed
cell specialisation and cell replacement
Understandings:
- According to the cell theory, living organisms are composed of cells
- Organisms consisting of only one cell carry out all the functions of life in that cell
- Surface area to volume ratio is important in the limitation of cell size
- Multicellular organisms have properties that emerge from the interaction of their cellular components
- Specialised tissues can develop by cell differentiation in multicellular organisms
- Differentiation involves the expression of some genes and not others in a cell’s genome
- The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses
Applications:
- Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae
- Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism
- Use of stem cells to treat Stargardt’s disease and one other named condition
- Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby and from an adult’s own tissues
Skills:
- Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells
- Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs