Level 14 Guiding Question: How are plants sustainable?
Characters which distinguish the classes. It must be pointed out, however, that there are many exceptions to these characters in both groups, and that no single character in the list below will infallibly identify a flowering plant as a monocot or dicot.The table summarizes the major morphological differences between monocots and dicots; each character is dicussed in more detail below.
Number of cotyledons -- The number of cotyledons found in the embryo is the actual basis for distinguishing the two classes of angiosperms, and is the source of the names Monocotyledonae ("one cotyledon") and Dicotyledonae ("two cotyledons"). The cotyledons are the "seed leaves" produced by the embryo. They serve to absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis.
Number of cotyledons -- The number of cotyledons found in the embryo is the actual basis for distinguishing the two classes of angiosperms, and is the source of the names Monocotyledonae ("one cotyledon") and Dicotyledonae ("two cotyledons"). The cotyledons are the "seed leaves" produced by the embryo. They serve to absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis.
- Number of flower parts -- If you count the number of petals, stamens, or other floral parts, you will find that monocot flowers tend to have a number of parts that is divisible by three, usually three or six. Dicot flowers on the other hand, tend to have parts in multiples of four or five (four, five, ten, etc.). This character is not always reliable, however, and is not easy to use in some flowers with reduced or numerous parts.
- Leaf veins -- In monocots, there are usually a number of major leaf veins which run parallel the length of the leaf; in dicots, there are usually numerous auxillary veins which reticulate between the major ones. As with the number of floral parts, this character is not always reliable, as there are many monocots with reticulate venation, notably the aroids and Dioscoreales.
- Stem vascular arrangement -- Vascular tissue occurs in long strands called vascular bundles. These bundles are arranged within the stem of dicots to form a cylinder, appearing as a ring of spots when you cut across the stem. In monocots, these bundles appear scattered through the stem, with more of the bundles located toward the stem periphery than in the center. This arrangement is unique to monocots and some of their closest relatives among the dicots.
- Root development -- In most dicots (and in most seed plants) the root develops from the lower end of the embryo, from a region known as the radicle. The radicle gives rise to an apical meristem which continues to produce root tissue for much of the plant's life. By contrast, the radicle aborts in monocots, and new roots arise adventitiously from nodes in the stem. These roots may be called prop roots when they are clustered near the bottom of the stem.
- Secondary growth -- Most seed plants increase their diameter through secondary growth, producing wood and bark. Monocots (and some dicots) have lost this ability, and so do not produce wood. Some monocots can produce a substitute however, as in the palms and agaves.
Level 14 Investigation: Comparing Monocots and Dicots
Download and print the lab sheet below. Follow the directions and after our garden tour answer the questions that are on the lab sheet.
Comparing Monocots & Dicots Lab
Level 14 Videos: What are differences between Monocots and Dicots?
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Level 14 Elaborate: So how can you categorize plants?
Download the make believe plants and color and cut them out spread them out on your lab station. organize the them by anatomical parts, flowers, leaf shapes etc. Remember to classify them always ask a yes or no question so that every one can get the same results as you. You are making a dichotomous key. Watch the Videos below so that you can make your own key.
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Level 14 Review: Do you know all of the plant parts and their function?
Take the time to study the vocabulary and concepts by playing the games and review activities.
Level 14 Summary: Unit Test
The test will be posted here on test day!