Cell Theory:
Cell Theory is composed of three parts
- All living organisms are composed of cells
- These cells form the smallest unit of life
- Cells come from previous cells
The cell theory was made up by the discoveries of many scientists. Antonie Van Leeuvenhoek was famous for inventing the microscope which allowed humans to examine the makeup of living organisms. It has been found that all organisms are made up of cells. Although sometimes these cells have might have slight differences in its structure. Theodor Schwann discovered that animals were made up of cells and likewise, another scientist named Matthias Schleiden found that plants were also made up of these cells. Finally, Rudolf Virchow found that cells came from pre-existing cells. And so these discoveries formed the Cell Theory.
Experiments in the lab have yet to discover anything smaller than a cell that can live independently. Unicellular organisms are therefore the smallest organisms that are able to living independently. Examples of unicellular organisms would be Amoeba, paramecium, euglena and bacterium.
Whether an organism is unicellular or multicellular, they will share these 7 characteristics:
- Movement: all living things have some sort of movement whether it is external or internal
- Reproduction: offspring need to be produced either sexually or asexually
- Response: the interaction and reaction to the environment
- Growth: growth in size, organelles, or shape of organisms.
- Respiration: energy production using substances from the environment
- Excretion: removal of waste
- Nutrition: exchange of materials with environment
Surface Area to Volume Ratio:
The ratio of surface area to Volume can influence the survival of a cell. The exchange of materials between the cell and the environment often occurs through diffusion where molecules in a high concentration move to an area of low concentration. Cells with a large volume will decrease the concentration of molecules within the cell and cripple the diffusion process. As a cell grows the SA/V ratio decreases until the SA is so small that there won't be enough materials diffusing in to support the enlarged volume because the enlarged volume will equate to a greater number of metabolic reactions. When a cell reaches this point, it has to divide to restore the SA/V ratio.
Specialization of Cells in Multicellular Organisms
The cells of a multicellular organism contain the same identical genome which forms its genetic instruction. Different parts of the genome, genes, will be activated via chemical signals so that each cell will perform a specific function. This process is called differentiation. The genes that are activated are packaged in an accessible and expanded form called euchromatin. The inactivate genes are packed in a condensed form called heterochromatin Differentiated cells that have differing functions will have different areas of heterochromatin and euchromatin.
Stem cells have not been differentiated, but can be excited to become a specialized cell. Stems cells by themselves can also replicate to form more differentiable cells. Because of the stem cells ability to differentiate, it has become a valuable tool in therapeutics. Stem cells can be taken from embryos or the placenta of the mother. Sometimes it can be found in some adult tissue. Stems cells can then be used to replace damaged or diseased cells by exciting and differentiating certain genes within the cell. After it s differentiated, the cell can be implanted into the patient. The immune system must be suppressed to prevent any rejection of the 'foreign cell' and then it needs to be monitored to ensure that it doesn't become cancerous.
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