|MadSci Network: Botany|
Hello Andy! Sorry to take so long in answering your question! :} A plant grows when new cells are produced, and there are localized regions within a plant for cell production. These areas are called the meristems. The most easily noticed meristem is the shoot apical meristem on plants; it is the tip of the plant stem. The apical meristem looks like a cap, with new cells dividing underneath it and pushing it forward (or in this case, upwards). There is another apical meristem on the tip of each root. There are also lateral meristems found in a bud(s) at each node along the stem. There are chemicals, auxins, that the apical meristem produces which prevent the lateral buds from growing. When you prune a flower bush, you are chopping off the apical meristems so that the lateral buds start to grow out and you end up with a many-flowered bush. As for algae they are not considered plants - they have their own taxonomic division as Protists. There are six different subgroups (phyla) of algae. Three of these six phyla are single-celled organisms, so they would produce more algae simply by dividing. Red, brown and some green algae are also known as seaweeds. These are multicellular organisms that actually form plant-like structures but they are not as complex as the stem, roots and leaves of real plants. For instance, green algae can form large structures (like sea lettuce) but the cells found in any part of the organism are pretty much all alike instead of being differentiated into stem, roots, etc. Algal growth is in the form of a filament either with new cells developing from the end of the last cell in the filament, or with cells dividing between two other cells within a filament. The most complex algae are the brown algae (the kelps). These actually have differentiated cells to transport material internally and some kelps actually have a meristem-like growth area but again, the structures that an algae develop are not as complex as that found in plants. Thanks for waiting for my answer! Evelyn Sites of interest: Algae photos http://www.sonoma.edu /biology/algae/algae.html Drawing and photos to describe a plant meristem: http://ww w-plb.ucdavis.edu/courses/plb105/Students/Rice/stems/meristem.html Text references: An Evolutionary Survey of fungi, algae and plants. J.C.Semple & B.Kendrick, Dept of Biology, University of Waterloo. 1992. Life. R.Lewis, Wm.C. Brown Publishers, Dubuque, IA. 1992. David Hershey adds: Woody plants have a vascular cambium, which lies underneath the bark and is responsible for the increase in stem and root diameter. Grass plants have an intercalary meristem at the base of each leaf which allows the leaf to regrow after mowing, even though the leaf tip has been removed. It operates differently than an apical meristem. An intercalary meristem is more like squeezing toothpaste out of tube because growth occurs at the base. With an apical meristem, it is more like stacking blocks because growth occurs just behind the tip. Kelps (a type of algae) and bulbs, such as daffodils and onions, also have intercalary meristems at the base of their leaves. References Grass Structures - Mechanisms for Growth Kelp
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