Green algae: introduction
Scientifically known as Chlorophyceae or Chlorophyta, green algae represent a heterogeneous group of unicellular and multicellular organisms, with more or less extensive dimensions. Chlorophyceae are green to the eye, thanks to the presence of chloroplasts: the chlorophyll pigments contained therein transform light energy into chemical energy (photosynthetic organisms). The typical coloring of green algae can take on different shades depending on the variety of algae and, above all, on the basis of the composition of pigments: often, in fact, chlorophyll is mixed with other red pigments (hematocroma), or yellow (xanthophylls).
In addition to these colored substances, green algae may contain colorless pigments, known as pyrenoids .
Biological hypotheses
In light of some recent scientific assumptions, it seems that higher plants have evolved from green algae. To confirm this hypothesis it has been observed in the first place that green algae have a nuclear envelope that dissolves during mitosis; also the presence of chlorophyll (of type a and b) and the accumulation of starch inside the plastids (peculiarity of the green algae and of the superior plants) seems to support the theory. Finally, the presence of the fragmoplast (cellular structure that derives from the alignment of the microtubules during the cell division phase) and of a particular photo-respiratory enzyme (the glycolate oxidase) inside the peroxisomes, constitutes a further biological confirmation.
Following these observations, it is almost confirmed that the green algae originated around 300, 000 species of superior terrestrial plants.
Botanical description
Green algae live mainly in fresh water (90%), but some species proliferate in marine environments; in addition, green algae spread in areas with a very high level of humidity, and near other plants.
We have seen that green algae are unicellular and multicellular organisms: approximately 6, 500-9, 000 different species are listed, distinguished by their peculiar characteristics and by reproduction method. Green algae are classified in about 600 different orders.
Chloroplasts are formed from 2-6 thylacoids, fused together; moreover, the organelles used for photosynthesis are devoid of endoplasmic reticulum and starch represents the reserve carbohydrate present inside the plastids.
Cellulose, when present, is located in the cell wall.
The reproduction of green algae - and algae in general - can be vegetative (asexual) or gamica (sexual): the vegetative reproduction, typical of unicellular algae, consists in the simple division of the mother cell into two daughter cells, while the asexual reproduction of the Multicellular algae occurs more often by fragmentation. Sexual reproduction, clearly more complex, consists of the union of two specialized cells, belonging to two different individuals.
Vitamins and mineral salts
The green alga by definition is surely the so-called sea lettuce, scientifically known as Ulva lactuca : it belongs to the family of the Ulvaceae and is a typical alga of the waters of the Mediterranean and cold temperate seas. The leaves, not very large and thin, are fixed to a helical peduncle [taken from //it.wikipedia.org/]. In the eastern regions, sea lettuce is consumed as a food, in the form of soups and salads: with a moderate content of Omega-3, group B vitamins, pro-vitamin A and C, these green algae are particularly rich in mineral salts ( especially calcium and magnesium) and contain all 8 essential amino acids. Sea lettuce is rich in amylaceous polysaccharides and water-soluble amylopectins, with properties similar to the starch contained in potatoes.
Among the most important green algae, we also mention Acetabularia (unicellular model for biological research) and the sea prickly pear ( Halimeda tuna ), whose vulgar name derives from the very particular morphological aspect.
Summary
Green algae: in short
| Green algae: general description | Heterogeneous group of unicellular and multicellular organisms, with more or less extended dimensions. Chlorophyceae are green to the eye, thanks to the presence of chloroplasts |
| Green algae: pigments |
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| Green algae: biological hypotheses | Hypothesis: higher plants evolved from green algae Confirmations:
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| Green algae: botanical description |
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| Green algae: sea lettuce |
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| Green algae: Acetabularia | Single-cell model for biological research |
| Green algae: Halimeda tuna | The common name (prickly pear) derives from the very particular morphological aspect. |
