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Introduction of cells

The Cell Theory

  • living organisms are composed of cells

Discrepancies (exceptions to the cell theory)

  • organisms or parts of organisms that do not consist of typical cells.

Organisms consisting of only one cell carry out all functions of life in that cell.

  • Metabolism: chemical reactions inside the cell, including the cell respiration to release energy
  • Reproduction: producing offspring either sexually or asexually
  • Growth: an irreversible increase in size
  • Response: the ability to react to changes in the environment
  • Excretion: getting rid of the waste products of metabolism
  • Nutrition: obtaining food, to provide energy and the materials needed for growth
  • Homeostasis: keeping conditions inside the organism within tolerable limits

Limitations on cell size

The surface area to volume ratio is important in the limitation of cell size.

  • Substances move into and out of cells through the plasma membrane at the surface of the cell rate of substances across the membrane depends on SA
  • if the ratio is small (elephant):
    • substances will not enter the cell as quickly as they are required
    • waste products will accumulate because they are produced more rapidly than excreted
    • cells may overheat because the metabolism produces heat faster than it is lost over the cell surface

Multicellular Organisms

Multicellular organisms have properties that emerge from the interaction of their cellular components.

  • organisms consisting of a single mass of cells, fused together, are multicellular
  • example of a multicellular organism: Caenorhabditis elegans
    • the adult body is 1mm long and is made up of exactly 959 cells.
    • it feeds on the bacteria that cause decomposition
    • has a mouth, pharynx, intestine, and anus
    • hermaphrodite (contains both male and female reproductive organs
    • has neurons

Emergent properties

  • individual cells in a group can organize themselves and interact with each other to form a living organism with distinctive overall properties. (1+1>2)
  • properties that arise from the interaction of component parts

Cell differentiation in multicellular organisms

Specialized tissues can develop by cell differentiation in multicellular organisms.

  • the development of cells in different ways performs different functions
  • a group of cells specialize in the same way to perform the same function is called tissue
  • becoming specialized makes the cell more efficient than they had many different roles
  • thus multicellular organisms are able to carry out multiple and complex functions because different cells responsible for different jobs

Gene expression and cell differentiation

Differentiation involves the expression of some genes and not others in a cell's genome

    • differentiated cells get exactly the same set of genes
    • 25000 genes in the human genome are all present in every body cell
    • gene is being expressed means gene is being used, which can switch specific gene to make a protein or other gene product
    • cell differentiation happens because a different sequence of genes is expressed in different cell types
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