How are plants classified? It’s a fairly straight-forward question one might assume would produce a straight-forward answer, but in fact there are many grey zones. There are four basic criteria that allow scientists to classify an organism as a plant. First, the organism in question must have a cell wall that uses cellulose. This cell wall provides mechanical strength, a protective barrier, an expandable frame, and exoskeleton for turgor pressure changes, and is made of cellulose. The second criteria is the cell must be able to store starches. Specifically store them in organelles known as plastids. These plastids may be for only storage production or can actually produce certain chemicals depending on the type of plant. The third criteria is the organism must contain both plasmodesmata and phragmoplasts. Plasmodesmata are channels which connect adjacent cells protoplasts to one another. The protoplast of a plant cell is the fluid in the cell similar to the cytoplasm in an animal cell. Phragmoplasts mediate cell separation during mitosis. They provide the scaffolding needed that allows a clean separation to occur properly. The fourth and final criteria to be classified as a plant is the organism must undergo photosynthesis and contain chlorophyll a and b. Each type of chlorophyll absorbs a different wavelength of light. Many organisms are able to fit one two or three of these criteria and some all. Ultimately it comes down to the scientist's interpretation of the organism. Some believe that only land plants should be considered while others believe some green algae should be included as they do meet all the criteria.
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