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Cell Theory (1.1/1.5)

Cell Scale: http://learn.genetics.utah.edu/content/cells/scale/

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1.1 Introduction to cells

Nature of science:

Looking for trends and discrepancies—although most organisms conform to cell theory, there are exceptions. (3.1)

Ethical implications of research—research involving stem cells is growing in importance and raises ethical issues. (4.5)

Understandings:

According to the cell theory, living organisms are composed of cells.

Organisms consisting of only one cell carry out all 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.

Specialized 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 and skills:

Application: Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.

Application: Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.

Application: Use of stem cells to treat Stargardt’s disease and one other named condition.

Application: 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.

Skill: 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)

Guidance:

Students are expected to be able to name and briefly explain these functions of life: nutrition, metabolism, growth, response, excretion, homeostasis and reproduction.

Chlorella or Scenedesmus are suitable photosynthetic unicells, but Euglena should be avoided as it can feed heterotrophically.

Scale bars are useful as a way of indicating actual sizes in drawings and micrographs.

International-mindedness:

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.

Theory of knowledge:

There is a difference between the living and the non-living environment. How are we able to know the difference?

Utilization:

The use of stem cells in the treatment of disease is mostly at the experimental stage, with the exception of bone marrow stem cells. Scientists, however, anticipate the use of stem cell therapies as a standard method of treating a whole range of diseases in the near future, including heart disease and diabetes.

Aims:

Aim 8:There are ethical issues involved in stem cell research, whether humans or other animals are used. Use of embryonic stem cells involves the death of early-stage embryos, but if therapeutic cloning is successfully developed the suffering of patients with a wide variety of conditions could be reduced.

Essential idea: Eukaryotes have a much more complex cell structure than prokaryotes.


1.5 The origin of cells

Nature of science:

Testing the general principles that underlie the natural world—the principle that cells only come from pre-existing cells needs to be verified. (1.9)

Understandings:

Cells can only be formed by division of pre-existing cells.

The first cells must have arisen from non-living material.

The origin of eukaryotic cells can be explained by the endosymbiotic theory.

Applications and skills:

Application: Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth.

Guidance:

Evidence for the endosymbiotic theory is expected. The origin of eukaryote cilia and flagella does not need to be included.

Students should be aware that the 64 codons in the genetic code have the same meanings in nearly all organisms, but that there are some minor variations that are likely to have accrued since the common origin of life on Earth.

Theory of knowledge:

Biology is the study of life, yet life is an emergent property. Under what circumstances is a systems approach productive in biology and under what circumstances is a reductionist approach more appropriate? How do scientists decide between competing approaches?

Aims:

Aim 6: Pasteur’s experiment can be repeated using modern apparatus.

Essential idea: Cell division is essential but must be controlled.



Stargardt’s Disease Websites:

Leukaemia Websites
Watch the following video:

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