Earth Science: Plants and Fungi – Seedless Plants
Mosses, ferns, as well as many algae species do not pro- duce flowers and are therefore unable to create seeds. Instead, they reproduce by means of spores.
Many seed- less plants display so-called alternate generations, where both types of reproduction—sexual and asexual—alternate from generation to generation.
Earth Science: Biology – Plants and Fungi – Algae
Algae are eukaryotic organisms that normally live in water and practice photosynthesis. The best known species are brown, red, and green algae. Reproduction in all three groups can be either sexual or asexual.
Algae do not form a true family group; however, they can be categorized according to their physical and chemical composition as well as the reserve substances and photosynthetic pigments they produce. Multicellular, primarily marine brown algae can become rather large, as for example the giant bladder kelp that can reach a length of up to 197 feet (60 m) and grow up to 19.7 inches (50 cm) a day.
At locations with nutrient-rich, relatively cold ocean currents, such as along the North American Pacific coast, this kelp forms huge underwater forests, so-called kelp forests, which provide a valuable habitat for numerous animals.
On the other hand, smaller brown algae species are found in nearly all of the world’s oceans, where they normally grow attached to the ocean substrate by means of an attachment organ. The brown or olive green coloration, displayed by many of the approximately 2,000 species, comes from dark fucoxanthin color pigments that cover the green chlorophyll. Most of the 4,000 to 4,500 single- or multicelled red algae species can also be found in the sea.
Special pigments enable them to survive down to a depth of 590 feet (180 m). Apart from chlorophyll, they also carry the pigments phycocyanin and phycoerythrin; the latter is responsible for the red coloration. With the aid of these pigments, shortwave sun- light penetrating to deep-water layers can still be used for photosynthesis.
The diverse group of green algae can be divided into single-celled and filamentous species; these can be branched or un- branched. There are also species with a leaflike structure. Colony formation has also been observed in some species. Green algae occur primarily in freshwater and their pigment content is similar to that of higher plants. Almost all forms have chloroplasts containing chlorophyll, which gives these algae their green coloration.
UTILIZATION OF ALGAE
Algae harvested at natural locations are mainly used for the production of iodine, bromine, vitamins, mineral substances, and proteins. Further- more, they can function as binding and thickening agents in food production and livestock feed supplements.
In biotechnical facilities in Israel, Japan, Australia, and some other countries, fast growing unicellular algae are cultivated as food supplements and as ingredients for cosmetics.