Essential idea: The evolution of multicellular organisms allowed cell specialization and cell replacement.
The above image shows totipotent stem cells. These unspecialised cell will be divide and some will become the cells that form heart muscle, neurones in the brain and lymphocytes in the blood. These three types of specialised human cells are structurally very different and perform certain functions much more efficiently than an unspecialised cell, such as the embryonic cells above, could.
Another advantage that multicellular organisms have over unicellular organisms is that severe damage to a cell does not mean the end of an organism. Stem cell persist through the life of a multi-cellular organism, this enables organisms to digest severely damaged cells and replacement them, i.e. wounds can be healed.
Another advantage that multicellular organisms have over unicellular organisms is that severe damage to a cell does not mean the end of an organism. Stem cell persist through the life of a multi-cellular organism, this enables organisms to digest severely damaged cells and replacement them, i.e. wounds can be healed.
Understandings, applications and Skills:
| 1.1.U1 | According to the cell theory, living organisms are composed of cells. |
| 1.1.U2 | Organisms consisting of only one cell carry out all functions of life in that cell. [Students are expected to be able to name and briefly explain these functions of life: nutrition, metabolism, growth, response, excretion, homeostasis and reproduction.] |
| 1.1.U3 | Surface area to volume ratio is important in the limitation of cell size. |
| 1.1.U4 | Multicellular organisms have properties that emerge from the interaction of their cellular components. |
| 1.1.U5 | Specialized tissues can develop by cell differentiation in multicellular organisms. |
| 1.1.U6 | Differentiation involves the expression of some genes and not others in a cell’s genome. |
| 1.1.U7 | 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. |
| 1.1.A1 | Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae. |
| 1.1.A2 | Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism. [ Chlorella or Scenedesmus are suitable photosynthetic unicells, but Euglena should be avoided as it can feed heterotrophically.] |
| 1.1.A3 | Use of stem cells to treat Stargardt’s disease and one other named condition. |
| 1.1.A4 | 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. |
| 1.1.S1 | 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. (Practical 1) [ Scale bars are useful as a way of indicating actual sizes in drawings and micrographs.] |
[Text in square brackets indicates guidance notes]
Starter
Presentation and notes
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The presentation is designed to help your understanding. The notes outline is intended to be used as a framework for the development of student notes to aid revision.
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Use the BioK Quick Quiz on 1.1 Introduction to cells (as directed) to check your understanding of the topic
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Weblinks
Cell theory
Cell theory summarised and evidence for it by Click4Biology. Click here for the playlist which looks at other related aspects of this sub-topic (n.b. these videos match the old IBO syllabus, but still contain lots of relevant detail)
Cell theory summarised and evidence for it by Click4Biology. Click here for the playlist which looks at other related aspects of this sub-topic (n.b. these videos match the old IBO syllabus, but still contain lots of relevant detail)
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Stem cells
Embryonic stem cells a video tutorial by the Khan Academy Human embryonic stem cells by Sunamas Inc. What are stem cells? by Craig Kohn (TED Ed) Stem cell therapy Stem-cell based therapies by the Howard Hughes Medical Institute A new stem cell therapy is being developed to treat Diabetes by Prof Doug Melton |
SA:Vol and the limitation of cell size
a nice lab demonstration of how small cells are more efficient than larger ones |
Nature of science:
Looking for trends and discrepancies—although most organisms conform to cell theory, there are exceptions. (3.1) [Addressed by 1.1.A1]
Ethical implications of research—research involving stem cells is growing in importance and raises ethical issues. (4.5) [Addressed by 1.1.A4]
Ethical implications of research—research involving stem cells is growing in importance and raises ethical issues. (4.5) [Addressed by 1.1.A4]
International-mindedness:
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Stem cell research has depended on the work of teams of scientists in many countries who share results thereby speeding up the rate of progress. However, national governments are influenced by local, cultural and religious traditions that impact on the work of scientists and the use of stem cells in therapy.
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The video to the right is a talk by Manu Prakash. Manu was born in Meerut, India, but now he is a bioengineer working at Stanford University in the USA. The research done by his team has lead them to invent a 50 cent microscope which could help to save the lives of millions throughout the developing world. If you are interested get involved by contacting Foldscope.
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Theory of knowledge:
There is a difference between the living and the non-living environment. How are we able to know the difference?
