LAB 7: PLANT ANATOMY AND PHYSOLOGY
Growth and development are shared properties of life that occur in all organisms. However, these basic processes occur quite differently in plants and animals. As you would expect, there are major differences with respect to the changes that occur between the time of fertilization and the appearance of the characteristic form for any given plant or animal.
Development in plants is indeterminate, whereas in animals it is determinate. That is, in plants development continues throughout the life, with new organs, tissues, and cells forming perpetually. For example, in a great redwood tree, some cells and tissues near the base of the tree may be more than 2,000 years old, while in the tips of its branches new cells, tissues, and organs continue to form and differentiate into their final structures.
Theoretically there is no limit to the growth of this tree. Conversely, an animal becomes complete (i.e., determined) early in its life—although cells continue to divide, all cell/tissue differentiation takes place early in embryonic development. After an animal matures, no further differentiation occurs. Much of the activity of plants is mediated by signaling molecules called Hormones.
Another major distinction between plants and animals is that in plants cell division occurs in localized regions, whereas in animals it occurs throughout the entire immature organism. A special kind of rapidly dividing, undifferentiated tissue called meristem is the site of plant tissue growth and differentiation. Apical meristems (on the stem and root tip) lead to primary (i.e., vertical) growth, whereas the two forms of lateral meristems lead to secondary growth (horizontally, in girth).
In order to understand the growth and development of plants and to comprehend the relation between their structure and function, it is necessary to study their anatomy. In this lab session we will begin looking at plant tissues with an examination of plant roots, stems, and leaves.
1. What is xylem, what does it do, and where is it found in the plant?
2. What if phloem, what does it do, and where is it found in the plant?
3. How do the structures of the roots, stem, and leaves reflect their unique functions?
4. What are the gibberellins and what is their effect on plants?
Flowering plants are divided into two major groups called the monocotyledons (a.k.a. monocots, for short) and dicotyledons (dicots). The differences in the number of seed leaves or cotyledons (food storage organs) in the plant embryo—one in the monocots and two in the dicots—provide the most familiar distinction between (and the names of) these groups.
Other differences are based on 1) the leaf venation pattern (parallel in monocots; reticulate in dicots), 2) the vascular bundle arrangement in the stem (peripheral and arranged in a cylinder in dicots; scattered in monocots); 3) the presence (in dicots) or the absence (in monocots) of a vascular cambium; 4) the numerical arrangement of floral parts (three in monocots; four or five, or multiples thereof, in dicots); and 5) the number of pores in pollen grains (one in monocots, three in dicots).
The first part of the lab gives you an opportunity to become familiar with the structure of the major plant organ systems. In this part you will sketch several labeled drawings you make from slides and specimens rather than from photographs or diagrams in your lab manual. Please examine all of the live and preserved specimens (monocots and dicots), prepared microscope slides, models (particularly useful), and demonstrations. A summary of lab materials is given below:
Tap root (e.g., carrot) demonstration
Fibrous root (e.g., bean) demonstration
Adventitious root (e.g., Coleus leaf cutting) demonstration
Prop root (e.g., corn) demonstration
Root hairs (radish)—demo or wet mount
Root tip model
Prepared slides: Allium (onion) root tip (longitudinal section=ls)
Ranunculus (buttercup) root slide (cross section=xs or cs)
Monocot (e.g., corn) stem parts, demo or wet mount
Dicot (e.g., geranium) stem parts, wet mount
Apical stem tip model
Prepared slides: Coleus stem tip and bud (apical meristem)
Medicago (alfalfa) dicot stem slide (xs)
Zea (corn) monocot stem slide (xs)
Celery and Carnation stems in dye solutions (started 2 days before lab)
Dicot (e.g., bean, geranium or Zebrina [wandering Jew]) leaf, wet mount (for stomata)
Dicot leaf model
Prepared slides: Zea (corn) monocot leaf
Syringa (lilac) dicot leaf
In the second part of the lab you will be provided with the following materials and will need to design and perform an experiment to demonstrate the role of gibberellins in early plant development. You will be provided with the following materials:
Radish and corn seeds, both sprouted and dry (unsprouted)
Soil, trays or pots for sproting
Place in light and dark for spouting
Have your instructor approve your hypothesis, and experimental design, then set up the experiment.