1.1: Cell Theory, Cell Specialization & Cell Replacement
Understandings:
· Living organisms are composed of cells
· Single-celled organisms carry out all functions of life in that cell.
· Surface area to volume (SA-V) 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 into 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.
Mission 1: Cells, Cells & More Cells!
Mission Objectives. You should be able to...
1. Explain cell theory and identify exceptions to cell theory.
2. List and describe the seven life functions.
3. Calculate surface area to volume ratio and explain how this relates to cell growth.
4. Explain the difference between differentiation and specialization.
5. Calculate magnification of images of structures and ultrastructures in drawings and micrographs.
6. Explain why stem cells are so unique and significant.
Mission Objectives. You should be able to...
1. Explain cell theory and identify exceptions to cell theory.
2. List and describe the seven life functions.
3. Calculate surface area to volume ratio and explain how this relates to cell growth.
4. Explain the difference between differentiation and specialization.
5. Calculate magnification of images of structures and ultrastructures in drawings and micrographs.
6. Explain why stem cells are so unique and significant.
There are three principles that make up cell theory. They are:
1. all organisms are composed of one or more cells 2. cells are the smallest units of life 3. all cells come from pre-existing cells All organisms exist as a unicellular or multicellular organism. All organisms carry out the seven life functions. These functions include:
Page 5 in your text defines each of these functions. Reproduction & Differentiation
Cells have the ability to produce rapidly and the resulting cells go through a differentiation process to produce required cell types that are necessary for the life of the cell. This process is the result of specific genes being present. As a result, each cell contains the genetic information needed for the production of the complete organism. See the figure to the right. Some cells lose their ability to reproduce once they become specialized. Neurons and muscle cells are good examples. Epithelials, or skin cells, retain their ability to reproduce. Cancer cells are cells that undergo extremely rapid reproduction with little or no differentiation, leading to a mass (a tumor) with no useful function to the organism. |
Cell Size
Cells are tiny objects that do not grow past a certain point. This may seem strange, considering that growth is one of the major life functions. Cell size is limited by the surface area-to-volume ratio (SA-VR). The rate of heat and waste production and the rate of resource consumption are functions of a cell's volume. Chemical reactions of life occur inside a cell and the size of the cell affects the rate of those reactions. The surface of the cell, the membrane, controls what materials move in and out of the cell. A cell with a higher SA-VR is able to move more materials in and out of the cell, for each unit volume of the cell. Examine the images to the left. As the width of a cell increases, the SA also increases, but at a much slower rate than the volume. Examine Table 1.2 on page 9 in your text. Surface area increases by a factor determined by squaring the radius, but volume increases by a factor determined by cubing the radius. Because of this, cells are limited in the size they can reach and still be able to carry out life functions. Therefore large organisms do not have large cells; they have more cells. Below the image, there is a video about how to calculate SA/V and what it means. |
Calculating magnification. If you want to calculate the actual size of a specimen under a microscope, you need to know the diameter of the 'scope's field of vision. This can be calculated and the size of the specimen can be determined. Drawings and photographs are often enlarged. Below is a video describing how to calculate magnification of specimens using the MIA formula.
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Stem Cells
Stem cells are cells that retain their ability to divide and differentiate into various cell types. When they divide, they produce daughter stem cells, which enables the continued production of a specific tissue type. There are two types of stem cells: adult and embryonic. Medical scientists saw the possibilities of using stem cells to treat certain human diseases such as Parkinson's disease and Alzheimer's, which are conditions caused by the loss of brain cells. Stem cells can also be used to treat forms of diabetes, bone marrow treatments and other medical conditions. Read more about stem cells from the National Institute of Health. |