What is the physical description of algae?

Question

Just algae in general. Thanks!

Answer 1

Algae (sing. alga) are a large and diverse group of simple plant-like organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are considered "plant-like" because of their photosynthetic ability, and "simple" because they lack the distinct organs of higher plants such as leaves and vascular tissue. Though the prokaryotic Cyanobacteria (commonly referred to as Blue-green algae) were traditionally included as "algae" in older textbooks, many modern sources regard this as outdated and restrict the term algae to eukaryotic organisms. All true algae therefore have a nucleus enclosed within a membrane and chloroplasts bound in one or more membranes.Algae constitute a paraphyletic and polyphyletic group:they do not represent a single evolutionary direction or line, but a level or grade of organization that may have developed several times in the early history of life on Earth.

Algae lack leaves, roots, and other organs that characterize higher plants. They are distinguished from protozoa in that they are photosynthetic. Many are photoautotrophic, although some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have reduced or lost their photosynthetic apparatus.

All algae have photosynthetic machinery ultimately derived from the cyanobacteria, and so produce oxygen as a byproduct of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria.The study of marine and freshwater algae is called phycology or algology.Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and non-motile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the life cycle of a species, are

Colonial: small, regular groups of motile cells

Capsoid: individual non-motile cells embedded in mucilage

Coccoid: individual non-motile cells with cell walls

Palmelloid: non-motile cells embedded in mucilage

Filamentous: a string of non-motile cells connected together, sometimes branching

Parenchymatous: cells forming a thallus with partial differentiation of tissues .Algae is commercially cultivated as a nutritional supplement. One of the most popular microalgal species is Spirulina (Arthrospira platensis), which is a Cyanobacteria (known as blue-green algae), and has been hailed by some as a superfood.Other algal species cultivated for their nutritional value include; Chlorella (a green algae), and Dunaliella (Dunaliella salina), which is high in beta-carotene and is used in vitamin C supplements.Rhodophyta, Chlorophyta and Heterokontophyta, the three main algal Phyla, have life-cycles which show tremendous variation with considerable complexity. In general there is an asexual phase where the seaweed's cells are diploid, a sexual phase where the cells are haploid followed by fusion of the male and female gametes. Asexual reproduction is advantageous in that it permits efficient population increases, but less variation is possible. Sexual reproduction allows more variation but is more costly because of the waste of gametes that fail to mate, among other things. Often there is no strict alternation between the sporophyte and gametophyte phases and also because there is often an asexual phase, which could include the fragmentation of the thallus.