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Natural Science - Year I

Unit 25: Cell Components and Structures

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Science Weblecture for Unit 25


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Science Lecture for Unit 25: The Cell

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Lecture Outline

Cells as the Fundamental Units of Life

The microscopic observations of the 17th century led to one of the basic tenets of modern biology: all life is based on cellular organization. Further observation of cell life led to a second basic principle: all cells come from existing cells.

All life forms known have one or more cells; while in multicellular organisms, individual cells are specialized and may not survive on their own, in single-celled organisms, such as the protists and bacteria that van Leeuwenhoek observed, the cell contains all the materials and performs all the functions required by a living entity.

Most cells share similar characteristics, but there are major differences between bacteria and protists, and between plant and animal cells. All cells have some kind of membrane or cell wall which keeps the cell contents inside, and which provides a barrier against undesirable chemicals or organism while allowing selected chemicals, such as nutrients, to enter the cell. Inside the cell are several different kinds of self-contained structures.

Cell Components

Some structures provide for the manufacture of cell parts or the protein components needed for them.

Several organelles provide for energy storage and release in the cell.

The shape of the overall cell is maintained by a lattice of microtubules.

Prokaryotes: Bacteria and Archaea

Bacteria and Archaea cells (prokaryotic cells) differ from eukaryotic cells (everything else) in several ways.

Eukaryotes: Protists (single-celled)

Eukaryotic cells are much more complicated than bacteria cells. Even single-celled eukaryotes, —protists like the amoeba and paramecium—have specialized structures for ingesting, metabolizing, and reproducing.

Plant and animal cells, both types of eukaryotic cells, also differ from each other in several ways. Some structures are found only in plant cells:

Animal cells have lysosomes contain enzymes (chemicals) which break down the components of worn-out organelles or used-up proteins, and make the basic chemical components available fore reuse.

By the way, viruses, which are small entities that are capable of rapid reproduction and production of chemicals, are not considered truly living organisms. Viruses do not have cell membranes, nuclei, or organelles. They cannot reproduce without taking over the DNA of the host cell. Nevertheless, viruses have a serious impact on life on earth, causing many diseases, such as the common cold, polio, smallpox, and AIDS.

Use the interactive animation at John Kyrk's biology website to explore the components found in an animal cell and and their functions. If you hover over any component (including the blue stuff that fills the cell), you should see a pop-up description.

Then use the Cell Functions table at the Biology Junction site to identify which types of cells have each component, what the component is like (description), and what function it plays in the organism.

Use information from both sites to answer the questions below.

  • What are the basic chemical components of the cell? Which is present in he largest amount?
  • Which components found in a plant cell are not found in animal cells?
  • Which components found in animal cells are not found in plant cells?
  • What is the function of the following cell structural components (organelles)?
    • Nucleus
    • Chromosome
    • Mitochondrion
    • Chloroplast
    • Endoplasmic Rheticulum
  • Why are most cells small?
  • What are the differences between prokaryotes (bacteria) and eukaryotes (everything else)?

Study/Discussion Questions:

Further Study/On Your Own