Plants & Human Affairs - Introduction
Cherries.wmf (7140 bytes) Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;

Introduction to Plants and Human Affairs

 I. What is a Plant?

A. The 5 or 6 (or More?) Kingdom System
    Traditionally, biologists recognized 5 major groups (or kingdoms) of organisms. This system of classification was originally formulated by Robert Whittaker at Cornell, and then championed by Lynn Margulis (Boston Univ.). However, recent studies indicate that there are others including a specialized group of bacteria, methane producers, that are called Archaebacteria). Thus, commonly recognized kingdoms are: Plantae, Animalia, Protista (single-celled or simple organisms), Monera (bacteria, includes blue-green algae), Fungi (mushrooms and molds, mycelium), and Archaebacteria (methane producers, extremeophiles, salt & heat lovers - halophytes and thermophiles).

B. Characteristics of the Plant Kingdom

  • Non-motile (stationary)
  • Photosynthetic (autotrophs vs. heterotrophs). Most plants have chlorophyll, a green pigment. Plants are considered producers - because they can produce their own food (organic nutrients) from simple raw materials in the environment. And they serve as the basis for the food chain. Heterotrophs are consumers; herbivores are primary consumers; carnivores are secondary consumers.
  • There are some "non-photosynthetic" plants that rely on other plants to obtain their organic nutrients. Thus, these plants are heterotrophs and usually parasitic. A good example is dodder (Cuscuta sp), which inserts a root-like structure (called a haustorium) into the host plant and essentially sucks water and nutrients from the host. These plants are detrimental to their host. Indian pipes (Monotropa sp) are completely white, but not directly parasitic. Instead, a fungus serves as a bridge between the roots of the Indian pipe and a host plant, transferring nutrients from host to Indian pipe. This mode of nutrition is called mycotrophic. Epiphytes, like Spanish moss (Tillandsia) and bromeliads, are plants that live on other plants.  They use the host solely for support.  Carnivorous plants are typically photosynthetic but supplement their nutrients with animals - carnivory in plants appears to be an adaptation to survival in nutrient poor environments
  • Eukaryotic - cells with a nucleus and other membrane-bound structures (vs. prokaryotic, like bacteria with no nucleus and no membrane bound structures)
  • Cells with walls of cellulose. Members of other kingdoms also have walls (i.e., fungi, bacteria), but they have a different chemical composition.
  • Alternation of generations – plants spend part of life in a haploid phase and part in a diploid phase. As an analogy, our haploid phase would be egg/sperm which are short-lived cells with a single goal while the rest of our bodies would be diploid. Depending on the plant, they can spend their life as a haploid or some fraction. The more advanced the plant, the less important the haploid stage.
  • Continuous growth throughout entire life
  • Localized growth - restricted to meristems (at tips of roots/shoots) which are the only regions of a plant in which cells are able to divide.

C. Summary
    Plants are non-motile, photosynthetic autotrophs that have cell walls and undergo alternation of generations.

II. Plant Diversity

A.  Types of plants

  • Angiosperms - produce flowers, fruits and seeds (has a pre-formed embryo with nutrients - I like to think of a seed as a baby in a suitcase with its lunch).  ca. 250,000 species.  Most important group to humans (see III).
  • Gymnosperms - cones, seeds
  • Mosses & relatives - spores (smaller than a seed, no pre-formed embryo inside, no stored food), no vascular tissue (xylem - water & mineral transport; phloem - nutrient/food transport)
  • Ferns & relatives - spores, vascular tissue
  • Algae (some are included in Protista)

B.  Cladogram (in class)

III. Why are plants important? or, Have you thanked a plant today?

A. Plant products
    A quick look at the list below should prove the importance of plants in our lives. For more information about any of these topics, check any book on economic botany. One of my favorites is Plants for People by Anna Lewington which examines our reliance on plants from the time we wake up until we go to bed.

    Among the ways in which people use plants are: (1) Energy (food, fossil fuels); (2) Nutrients (vitamins, etc.); (3) Liberate oxygen; (4) Prevent oil erosion; (5) wood products (paper, fuel, shelter, furniture); (6) beverages (coffee, tea, beer, wine); (7) fibers/textiles; (8) drugs/medicines; (9) latex/rubber; (10) pitch, turpentine, resins; (11) essential oils (spices, perfumes); (12) aesthetic appeal (gardens, houseplants, landscaping); (13) purify air; (14) food preservation (fermentation); (15) nitrogen fixation; (16) influence course of human history (i.e., spice trade); (17) symbolize events in life (marriage, death, etc.); (18) important in music and art; (19) religious significance; (20) beauty aids cosmetics, soaps; (21) mental stability (horticultural therapy); (22) oils, waxes, gels, tannins

B. The Saupe Challenge
    Virtually every aspect of our lives is impacted by plants! In fact, I challenge you to think of product or aspect of your life that is not directly, or indirectly, impacted by plants

IV. Trying to improve on Mother Nature

A. Synthetic Substitutes
    Some plant products have been replaced by a variety of synthetic substitutes. These include:

  • fossil fuels - wind/solar/nuclear power
  • medicinal plants - synthetic drugs
  • cotton and other natural fibers) - rayon, nylon, polyester
  • natural rubber - synthetic
  • real maple syrup - flavored corn syrups (ick!)
  • natural vegetable dyes - coal tar derivatives
  • wood - plastics
  • edible wild plants - crops

B. Rationale for synthetics
    Replacement of plant products with synthetics is a product of "civilization." Among the reasons are: (1) lower cost; (2) uniformity of product; (3) ease of obtaining; (4) ensures supply; and (5) mass production.

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Last updated:  09/01/2008 / � Copyright  by SG Saupe