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Unifying features of plants
To characterize the features that define plants as different from other eukaryotes is almost impossible since every feature has exceptions, but usually these exceptions are among plants that have lost the feature or are among the algae on the boundary between protists and plants.
• They are photosynthetic and obtain all their nutrients from inorganic sources, i.e. they are autotrophic and the start of a food chain. Many protists, particularly among the plankton, are also photosynthetic. A few plants derive all or part of their nutrients from other organisms (Topics M6, M7) but these are closely related to other, photosynthetic, flowering plants.
• The photosynthetic pigment is chlorophyll, and in all plants except some algae, there are two forms, a and b, contained within chloroplasts.
• The cells have a cell wall made predominantly of the polysaccharide cellulose, and a vacuole in addition to the cytoplasm.
• There is an alternation of diploid and haploid generations . Often one of these is much reduced and may not live independently.
Vegetative structure and physiology is similar throughout the seed plants (flowering plants, conifers and some smaller groups) and there are many similarities with other vascular plants as well, but the reproductive structures differ markedly. Larger algae and bryophytes differ more fundamentally in vegetative and reproductive structure .
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