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The diatoms (Figure 26.5), members of the Chrysophyta, have organic walls impregnated with silica. The architecture of the diatom wall is exceedingly complex; it always consists of two overlap
 
The diatoms (Figure 26.5), members of the Chrysophyta, have organic walls impregnated with silica. The architecture of the diatom wall is exceedingly complex; it always consists of two overlap
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== The Natural Distribution of Algae: ==
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== The Natural Distribution of Algae ==
    
Most  algae are aquatic organisms that inhabit either fresh water or the Oceans. These aquatic forms are principally free-living, yet certain unicellular marine algae have established durable symbiotic relationships with specific marine invertebrate animals (e.g., sponges, corals, various groups of marine worms) and grow within the Cells of the host Animal. Some terrestrial algae grow in soil or on the bark of trees. Others have established symbiotic relationships with fungi, to produce the curious, two-membered natural associations termed ''lichens'', which form slowly growing colonies in many arid and inhospitable environments, notably on the surface of rocks.
 
Most  algae are aquatic organisms that inhabit either fresh water or the Oceans. These aquatic forms are principally free-living, yet certain unicellular marine algae have established durable symbiotic relationships with specific marine invertebrate animals (e.g., sponges, corals, various groups of marine worms) and grow within the Cells of the host Animal. Some terrestrial algae grow in soil or on the bark of trees. Others have established symbiotic relationships with fungi, to produce the curious, two-membered natural associations termed ''lichens'', which form slowly growing colonies in many arid and inhospitable environments, notably on the surface of rocks.
    
The marine algae play a very important role in the cycles of matter on Earth, since their total mass (and consequently their gross photosynthetic activity) is equal to that of all land plants and is probably much greater. This role is by no means evident, because the most conspicuous of marine algae, the seaweeds, occupy a very limited area of the Oceans, being attached to rocks in the intertidal zone and the shallow coastal waters of the continental shelves. The great bulk of marine algae are uniCellular floating (''planktonic'') organisms, predominantly diatoms and dinoflagellates, distributed through the surface waters of the Oceans. Although they sometimes become abundant enough to impart a definite brown or red color to local areas of the sea, their density is usually so low that there is no gross sign of their presence. It is the enormous total volume of the Earth's Oceans which makes them the most abundant of all photosynthetic organisms.
 
The marine algae play a very important role in the cycles of matter on Earth, since their total mass (and consequently their gross photosynthetic activity) is equal to that of all land plants and is probably much greater. This role is by no means evident, because the most conspicuous of marine algae, the seaweeds, occupy a very limited area of the Oceans, being attached to rocks in the intertidal zone and the shallow coastal waters of the continental shelves. The great bulk of marine algae are uniCellular floating (''planktonic'') organisms, predominantly diatoms and dinoflagellates, distributed through the surface waters of the Oceans. Although they sometimes become abundant enough to impart a definite brown or red color to local areas of the sea, their density is usually so low that there is no gross sign of their presence. It is the enormous total volume of the Earth's Oceans which makes them the most abundant of all photosynthetic organisms.
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== The Nutritional Versatility of Algae==
 
== The Nutritional Versatility of Algae==
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