Lab 5 Green Plant I

last updated July 29, 2002
Introduction   General Links
Dicot     Bean
Determinant growth
Monocot
Corn
Pigments
Rf
Spectrophotometry
Assignment Quiz Questions
Green is the dominant color of vegetation throughout most of the growing season. The characteristic green color of plants is due to the pigment chlorophyll which is abundant in the leaves of plants.
 
Bean (Animated GIF)
Of the 350,000 different species of plants, more than 70% are flowering plants (Angiosperms). We will therefore use flowering plants in our study of the typical green plant. Angiosperms differ from all other plants because they bear flowers, which are their specialized reproductive organs, and produce seeds which are enclosed in fruits.

Plants belonging to the Angiosperms form two classes, the monocotyledonous plants, or Monocots, and the dicotyledonous plants, or Dicots. You will study one example of each to learn the structure of the vegetative plant body. In addition, you will examine properties of pigments found in chloroplasts.

DICOT - EXTERNAL STRUCTURE

We will use the common bean plant, a dicot that is relatively easy to grow, to introduce you to the external structure of flowering plants. As the name dicot indicates, these plants have two cotyledons. Cotyledons are seed leaves. In addition, Dicots often have leaves with veins arranged in a network of branches and one central, major root known as a tap root.

Bean plants of different ages are provided so you can examine the maturation process and also so that you can make observations on the location and rates of growth. The older plants may have lost leaves or other parts which still are present on younger plants, and they also may have produced flowers, fruits (beans) and parts not yet developed in younger plants.

Bean -

  • Bean seed showing hilum
  • Bean plants - U. Wisconsin


  • MONOCOT - EXTERNAL STRUCTURE

    We will use cornZea mays, known as maize in much of the world, as our example of a monocot. Corn is of tremendous economic importance, and as you probably know may grow very tall ( as high as an Elephant's eye ). We have corn seeds and seedlings 1,2,3,4 and 5 weeks old available for study.

    Monocots often have leaves with veinsarranged in a parallel pattern and the root sytem is often shallow and fibrous. As the name monocot implies, these plants have only a single cotyledon. In corn and other grasses, the cotyledon remains within the seed in the ground. There it digests stored food of the seed and makes it available to the growing seedling.

    In lilies, onions and other monocots the single cotyledon comes above ground and is green and leaf-like in appearance.
    The young leaves of corn and other grasses are protected by a hollow sheath, the coleoptile, as they emerge through the soil. Growth of the coleoptile stops soon after it is exposed to light, but the leaves continue to grow and soon break through the coleoptile's tip.

    Corn -

  • Corn - grain   grain - treated with I2KI
  • Corn - earlyh development U. Wisconsin


  • Links to General Information about Plants and Photosynthesis

    GROWTH OF STEMS OF BEAN SEEDLINGS


    Information on growth of bean seedlings and growth curves.

    There are two main patterns of growth, determinant, and indeterminant.

    Organisms with determinant growth, grow only until they have reached a mature size, which usually is genetically predetermined.

    For example, most humans grow relatively rapidly until about the age of puberty, at which time they have reached an adult size (often 5 to 6 feet tall). The adults maintain this height throughout the remainder of their lives.
    Organisms with indeterminant growth continue to grow throughout their lives. There is no point at which growth is completed.
    For example, a pine tree becomes several feet taller every spring throughout its lifetime. Growth stops only when the tree is damaged by a storm, fire, disease, or when the tree is harvested for timber. Although the stem of a plant may thus continue to grow taller through its life, older regions closer to the ground may have completed growth while younger regions near the apical bud where growth is initiated in stem tips continue to increase in length.
     

    Pigments and Chromatography

    SEPARATION AND IDENTIFICATION OF LEAF PIGMENTS


    Separation of Pigments

  • Paper chromatography Plant extract
  • Chromatography
  • Animation of paper chromatography - Kean
  • Paper Chromatography
  • Paper Chromatography
  • Chromatography information   - references
  • Pigments  German text
  • Thin layer   thin layer
  • links to separations introductory theory   biological chromatography chemical separations  types of chromatography
  • ink - theory and simple diagrams

  • The technique of chromatography is used widely to separate the individual components of a mixture of related substances -- for example a mixture of amino acids, or one of sugars. The term chromatography refers to the fact that after separation, the individual substances may be visualized as spots of color, either because of their own natural color, or more commonly by causing them to react with reagents to yield a colored product.

    Chromatographic procedures have been developed for a variety of specific purposes. In general, a sample of a solution containing the mixture of substances to be separated is applied to a supporting medium. A suitable solvent is then made to move through the medium, and carries with it the mixture of components to be separated. Different components of the mixture travel at different speeds, depending on their affinity for the medium and their solubility in the solvent.

    Spotting the chromatogram

     
     
     
     

    One of the simplest chromatographic techniques is that of Paper Chromatography, in which the supporting medium is filter paper. In today's laboratory you will separate plant pigments by paper chromatography.
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    Chromatography apparatus

    Identification of Pigments


    The predominant pigment in the leaves of green plants is chlorophyll, which occurs in two slightly different chemical forms called chlorophyll a and chlorophyll b. Most leaves contain at least two additional types of pigments, carotenes and xanthophylls, which are ordinarily not visible because they are masked by the more abundant chlorophyll.

    The pigments you are working with were extracted from leaves of English Ivy (Hedera helix). Ivy leaves were cut into small pieces and placed in acetone. The liquid was saved and tissue debris was discarded. Most students are able to separate and identify four pigments from Ivy.
     

    In the solvent system which you used, carotenes move the fastest, followed in turn by xanthophylls, chlorophyll a and chlorophyll b. Besides their location on the chromatogram, pigments can be identified by their characteristic colors:

    Pigment Color
    carotenes orange to yellow 
    xanthophylls yellow or grayish
    chlorophyll a green to blue-green 
    chlorophyll b green to yellowish-green

    Rf
    The ratio of the distance traveled by a particular substance to the distance traveled by the solvent, both measured from the original spot, constitutes the so-called ratio of fronts, or Rf, for that substance. This value is constant for a given set of conditions, but changes when the conditions are changed, for example if a different solvent is used. Visit this link for help calculating Rf .
     


    Questions

    1. What are the major functions of stems and leaves?
    2. What structural adaptations do they have for these functions?
      Hint: If the job of a root is to anchor a plant , having broad roots, with many branches, each attached to soil particles allows it to perform the job of holding the plant in place.
    3. What selective advantages might be associated with the differences in vegetative structure that you observed?
    4. Hint: Compare the leaf and stem structure of bean with the leaf and stem structure of corn, then try to associate the differences with the growing conditions (environment) to which each plant is most suited.
    5. Suggest a procedure to measure growth rate more precisely and accurately than the method we used.
    6. Hint: We measured 5 separate plants. Each individual plant was of a different age, from 1 week to 5 weeks. We made measurements only on one occasions, and measured 3 stem regions (hypocotyl, 1st internode, and second internode).
    7. If you did not use chromatography, how else might you separate a mixture of pigments?
    8. Hint: Think of another procedure that can isolate the individual pigments based on physical or chemical or biological properties.
    9. How might you determine if a stain on the clothing of a victim found near the seashore was from an angiosperm, such as spinach, rather than from a seaweed, such as Ulva?
    10. Hint: Algae and angiosperms contain a number of different photosynthetic and accessory pigments, sometimes in varying amounts and sometimes with slight chemical differences.
     


    Assignment

    Check with your own instructor to learn the assignment for your section. The instructions here apply to students in sections 01, 02, 03 and 04 taught by Dr. Reid.

    Do the exercise as written. Record all observations, make all measurements, and answer the questions as directed in lab exercise 5.

    The Assignment consists of  four separate activities. Please submit them together at one time, with your name and section number on each, and organized in the following sequence.

    1. Chromatogram  (color, Rf, pigment name)
    2. Absorption spectrum (graph) of photosynthetic pigments
    3. Growth Curve  - Graph of hypocotyl, 1st and 2nd internode + hypothesis and evaluation of hypothesis of determinant growth pattern
    4. Label diagram of bean