Cell Theory Exceptions & Differentiation

Topic 1: CellsExceptions to Cell

Theory & 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

Past paper question

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.