Does the Root or Stem Form First in a Pea Plant?
The seeds of a pea plant germinate when conditions are right, just as the seeds of other plant species. Likewise, there is a logical order in which the tiny plant emerges from its protective seed coat.
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The Seed
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Peas are dicots. Their seeds have two cotelydons, or food storage structures. The embryo sits between the cotelydons and the entire seed is surrounded by a hard covering called the testa.
The Embryo
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The embryo is made up of the radicle, which will become the first root, and the plumule. which will form the first green shoot. If you look at a pea seed under the microscope the plumule will look like two tiny leaves.
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Germination
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The testa has a tiny hole called the micropyle which draws water into the seed and eventually splits the testa. The radicle emerges first, pushing downward to push the first root into the soil.
Root Hairs
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Seeds carry a limited amount of stored energy so it is important for the root to anchor itself and start to draw in nutrients. Tiny root hairs extend from the outer layer of root cells to increase the amount of water and nutrients drawn into the plant.
The Stem
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Once the root is anchored the first green stem emerges, holding the first leaves. The plumule protects the tender leaves from breakage by rising backward from the cotyledons and not straightening up until the stem has broken through the soil.
Growth
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Once the tiny shoot is above ground the process of photosynthesis can take place. Plants use a green substance called chlorophyll to take carbon dioxide and the energy of the sun to make sugars and starches they can use for food. Until photosynthesis is in full swing, the tiny pea plant will be sustained by its root structure.
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- Photo Credit Image by Flickr.com, courtesy of Biology Big Brother
