Algae - General preview | Study notes Microbiology

Algae are simple, autotrophic organisms, which can synthesize their own food by

means of photosynthesis. Their taxonomy is very confusing. Previously, algae

were classified under the kingdom Plantae, as they possess chlorophyll for

photosynthesis. However, algae are mostly aquatic, and lack true roots, stems,

and leaves, which are not so in plants. Hence, in the modern classification, they

are excluded from Plantae, and categorized under Protists. Their size may range

from few micrometers to several meters. For example, the freshwater

alga Micromonas is about 1 micrometer, whereas the giant marine kelp can grow

to about 60 meters in length. The branch of science that deals with the study of

algae is called phycology, and those who specialize in this study are known as

phycologists.

Blue Green Algae (BGA)

Blue green algae (BGA), also referred to as cyanobacteria, are the simplest forms

of algae. Examples of BGA are Nostoc and Calothrix. As the name suggests, they

are blue green in color, ranging from single-celled organizations to colonial forms.

BGA contain chlorophyll 'a', 'b', and phycobilins. They are prokaryotic in cellular

organizations that resemble bacteria. BGA are considered to be an intermediate

between bacteria and plants. Hence, the name cyanobacteria is assigned to these

species. Since they lack specialized organelles, they photosynthesize directly

through the cytoplasm.

What are Green Algae?

It is a large group of algae, most members of which contain chloroplast.

Chloroplast of these algae contain pigmentsm chlorophyll 'a' and 'b', which give

them a bright green color. Some of them are unicellular and live as a single cells,

while others form a colony or a long filament. Many species of green algae are

motile and they possess flagella, which is a lash-like appendage used for

locomotion. Generally, each cell of a colony possesses two flagella, which help the

entire colony to move. On the other hand, a few species of green algae are

immobile, as they do not contain any flagella. However, it has been observed that

many of the immobile algae pass through a flagellated stage in their life cycle.

Interesting Facts

✦ They are a diverse group of algae that can be found all over the world. They are

often termed as chlorophytes. But chlorophyte is actually a division of green

algae, which includes both freshwater and marine species. There are several

interesting facts about the members of green algae, out of which a few are

enlisted below:

✦ There are about 7000 species of green algae, which can be found in both fresh

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Algae are simple, autotrophic organisms, which can synthesize their own food by means of photosynthesis. Their taxonomy is very confusing. Previously, algae were classified under the kingdom Plantae, as they possess chlorophyll for photosynthesis. However, algae are mostly aquatic, and lack true roots, stems, and leaves, which are not so in plants. Hence, in the modern classification, they are excluded from Plantae, and categorized under Protists. Their size may range from few micrometers to several meters. For example, the freshwater alga Micromonas is about 1 micrometer, whereas the giant marine kelp can grow to about 60 meters in length. The branch of science that deals with the study of algae is called phycology, and those who specialize in this study are known as phycologists. Blue Green Algae (BGA) Blue green algae (BGA), also referred to as cyanobacteria, are the simplest forms of algae. Examples of BGA are Nostoc and Calothrix. As the name suggests, they are blue green in color, ranging from single-celled organizations to colonial forms. BGA contain chlorophyll 'a', 'b', and phycobilins. They are prokaryotic in cellular organizations that resemble bacteria. BGA are considered to be an intermediate between bacteria and plants. Hence, the name cyanobacteria is assigned to these species. Since they lack specialized organelles, they photosynthesize directly through the cytoplasm. What are Green Algae? It is a large group of algae, most members of which contain chloroplast. Chloroplast of these algae contain pigmentsm chlorophyll 'a' and 'b', which give them a bright green color. Some of them are unicellular and live as a single cells, while others form a colony or a long filament. Many species of green algae are motile and they possess flagella, which is a lash-like appendage used for locomotion. Generally, each cell of a colony possesses two flagella, which help the entire colony to move. On the other hand, a few species of green algae are immobile, as they do not contain any flagella. However, it has been observed that many of the immobile algae pass through a flagellated stage in their life cycle. Interesting Facts ✦ They are a diverse group of algae that can be found all over the world. They are often termed as chlorophytes. But chlorophyte is actually a division of green algae, which includes both freshwater and marine species. There are several interesting facts about the members of green algae, out of which a few are enlisted below: ✦ There are about 7000 species of green algae, which can be found in both fresh

or saltwater and also in damp places. ✦ They are considered as the group from which the higher plants evolved on the basis of certain characteristics, and the compounds found in the pigments used for photosynthesis. ✦ Out of all green algae, the members of the order Charales are considered as the closest relatives of higher plants. ✦ Almost all of them contain chloroplast, within which the pigments chlorophyll 'a' and 'b' can be found. These pigments are responsible for imparting a rich green color to these algae. ✦ One of the most well-known types of green algae is volvox. Volvox forms a spherical colony, and each cell of the colony possesses two flagella and a small eyespot. ✦ Chlorella is another well-known green algae, which is usually found inside hydra, ciliates, and some other animals, as an endosymbiont. An endosymbiont is the organism that lives inside the body or cell of another organism and establishes a symbiotic relationship or 'endosymbiosis'. ✦ Green algae of the genera Trebouxia and Pseudotrebouxia are often found to establish symbiotic relationship with fungi. Lichen is the composite organism that results from this symbiotic association. ✦ Spirogyra , Zygnema and Mougeotia are some other common green algae that are often found on the surface of freshwater ponds and ditches. They proliferate rapidly and form a dense mat-like structure on the surface of ponds, which we usually identify as pond scum. ✦ They can reproduce both asexually and sexually, and the mode of reproduction is quite diverse. ✦ In case of asexual reproduction in algae, the parent cell can divide into two similar parts, from which two identical organisms develop, or the parent cell can divide into one or more fragments, which eventually grow as separate organisms. However, some algae have been found to develop motile or non-motile spores for asexual reproduction. ✦ Sexual reproduction takes place through the union of gametes, which can be

carry out photosynthesis for producing energy, as chlorophyll is present in their body. Red algae can absorb blue light, and therefore they can flourish deeper than any other algae in the ocean. They are usually red colored, some other forms are blue or green in color. Red algae cell walls are double-layered, the outer wall is made up of pectic acid and the inner wall is mainly composed of cellulose. Coralline algae, Irish moss, gigartina are some types of red marine algae. Coralline algae is one of the main components of coral reefs. A distinguishing fact about red marine algae is the formation of pit connection. Red algal cells never really undergo the complete phase of cytokinesis, a phase which occurs before mitosis ends. Since cytokinesis remains incomplete, the parent cell does not get divided into two separate daughter cells. When the parent cell undergoes division, a small depression is formed in the wall, which is referred to as a pit, the point where newly formed daughter cells remain in contact with the parent cell. Phaeophyceae (Brown algae) General characteristics  Pheophyceae are called commonly known as brown algae  Photosynthetic pigments: They possesses brown colored photosynthetic pigments fucoxanthin and β-carotenoids in addition to chlorophyll a and c.  Habitat : They are almost marine, very few are fresh water eg.  Thallus: they are multicellular brown algae. No unicellular and colonial (motile or non-motile) brown algae till known.  Storage form of food: laminarin starch, manitol (alcohol) and some store iodine also.  Reproduction: vegetative, asexual and sexual methods  Vegetative : fragmentation.  Asexual: asexual spores (motile zoospores).  Sexual: isogamous or oogamous type gametic fusion.

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