Download - Cell Theory Exceptions & Differentiation
Functions of Life
All systems classified as “living” must be able to do the following on their own:Reproduce + Pass on genesEvolve + Respond + Adapt to their
changing environmentMetabolize nutrients + Excrete
WasteGrow + Develop over timeMaintain Homeostasis
The Cell Theory
Once we know something is living, we also know it must follow the Cell Theory:All living things are made of
cells.Cells are the most basic unit of
life.Existing cells come from pre-
existing cells.
Exceptions to Cell Theory1. Mitochondria & chloroplasts
2. Viruses
Tissues and organisms not made of typical cells:
3. Skeletal muscle
4. Giant algae
5. Aseptate fungi
What two things set stem cells apart from “regular cells?
Self-renewal
The ability to go through numerous cycles of cell division while maintaining the undifferentiated state
Potency
Stem cells are undifferentiated and have the capacity to differentiate down different paths into specialized cell types.
This requires stem cells to be either totipotent or pluripotent to be able to give rise to any mature cell type
Adult stem cells have been used for many years to treat leukemia through bone marrow transplants.
The bone marrow contains cells that differentiate into the different types of blood cells.
Link to TOK!Why is stem cell research controversial?
On what basis do people object to it?
Differentiation
Cells become specialized for different functions by the process of differentiation
Gives an advantage to multicellular organisms by allowing for a division of labor
Emergent propertiesWhen units of biological material are put together,
the properties of the new material are not always additive, (equal to the sum of the properties of the components).
Instead, at each level, new properties and rules emerge that cannot be predicted by observations and full knowledge of the lower levels. Such properties are called emergent properties (Novikoff, 1945).
Life itself is an example of an emergent property. For instance, a single-celled bacterium is alive, but if you
separate the macromolecules that combined to create the bacterium, these units are not alive. Based on our knowledge of macromolecules, we would not have been able to predict that they could combine to form a living organism, nor could we have predicted ALL of the characteristics of the resulting bacterium.