Botany/Plant cells

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Chapter 2. Plant Cells


Introduction[edit]

A loupe (left) and a hand-lens (right) - tools used by botanists in the field

A cell is a very basic structure of all living systems, consisting of protoplasm within a containing cell membrane. Only entities such as viruses—literally on the boundary between non-living chemicals and living systems—lack cells or basic cell structure. All plants, including very simple plants called algae, and all animals are made up of cells, and these are organized in various ways to create structure and function in an organism. Biologists recognize two basic types of cells: prokaryotic and eukaryotic. Prokaryotic cells are structurally more simple. They are found only in single-celled and some simple, multicellular organisms (all bacteria and some algae, which all belong to Bacteria and Archaea domains). Eukaryotic cells are found in most algae, all higher plants, fungi, and animals (Eukarya domain). Thus, differences between these two cell types are critical to how an organism is classified, and an important consideration in the evolutionary sequence of life on the planet Earth.

Plant Cell Structure[edit]

Nearly all cells are too small to be seen with the unaided eye. As always there are some exceptions, but generally magnification is required to detect a cellular structure. In plants, a good hand-lens or loupe (see photo at right) will sometimes suffice, but in working with cells or observing how cells are organized to form tissues and structures, a high power microscope is used.

Also note that the textbook, Cell Biology, is available at WikiBooks and can be used as a more detailed reference. You should read the Introductory Chapter (all subsections) at this time.

Questions:

  1. Can you think of reasons why macroscopic organisms are multicellular? (Macroscopic means large, in the sense of "not microscopic")

Basic Cell Function[edit]

You should, by now, have a general appreciation for the complexity of cellular structure. Improvements in microscopy, especially development of the Electron microscope, have revealed that cells are not merely membranous sacks containing fluid of gel-like consistency. The degree of organization of the cytoplasm into organelles and their membranes should have you convinced that much (perhaps most) of what is really going on around you on this planet is occurring at a scale that is simply inaccessible to your eyes. And while you cannot be expected to directly observe chemical reactions at a molecular scale, contemplate that you cannot, even with powerful optics, directly observe most of the structure where these reactions are somehow controlled to produce outcomes favorable to life—indeed, are life. Hopefully, as you acquire knowledge and become a biologist—a botanist—you will learn to recognize the relevant phenomena by their macroscopic expressions (that which you can readily observe with the unaided eye).

To appreciate basic cell function, it is necessary to first list the processes or outcomes that cells must accomplish to further existence. More specialized functions will be discussed under plant cell structure, as our interest must eventually focus on plants. For now, recall that in your reading you have already encountered these several basic abilities of cells:

  • Metabolism involves taking in of raw material to use in building cell components and breaking down of other molecules to provide energy for various growth processes; byproducts may be released.
  • Protein biosynthesis by transcription of DNA to RNA and then translation to protein, used in growth or released for use elsewhere by the organism.
  • Reproduction by cell division.

Now explore each in turn. Think initially of a single-celled organism with no special abilities, only a "will" to stay alive and perpetuate itself. Remember, the environment will not be kind. The cell must grow and reproduce to counter the tendency of outside forces to breakdown molecular structure and destroy life. Then consider the situation where a cell is part of a multicellular organism, and may be performing more limited and specialized functions.

Questions:

  1. Have you been able to discern a relationship between genes and basic cell function? If so, is this also a basic cell function, and where do we list it?

Plant Cell Specializations[edit]

We will learn about the cells of algae and other organisms (e.g., bacteria and fungi) traditionally covered within Botany in later chapters on those organisms (Chapters 5 - 7). Here, we concentrate on the cells of plants.

The simplest type of plant cell is called a parenchyma cell and most of the basic metabolic and reproductive processes of the plant occur in these cells. A term for parenchyma cells with chloroplasts, is chlorenchyma cells. Other plant cell types that we shall be considering are:

  • Collenchyma ~ living cells with thickened walls for increased support
  • Sclerenchyma ~ lignified dead cells forming fibers for increased support
  • Epidermal ~ surface covering
  • Cork
  • Xylem tracheid ~ single long (up to 1 mm) thin cells for transporting water and support
  • Xylem vessel ~ cells form individual elements in an even longer (up to 1 meter in extreme cases) tube for transporting water
  • Meristematic cells ~ growth

Laboratory Exercises for Chapter 2 >>
Discussion of questions for Chapter 2 >>>


Botany Study Guide ~ Wiki Contents Table
Section I

Chapter 1 - Introduction ~ Chapter 2 - Plant cells
Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs
Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology