#Infodump 5

Protozoa

A wide range of organisms are described as protozoans, these are unicellular eukaryotes and considered to be a subkingdom of Protista. As, mentioned in the previous infodump, Antonie Van Leeuvenhoek was the first person to discover protozoas, since then more than 50,000 species have been described.

Protozoans have a variety of shapes and are known to exhibit mainly two forms of life: free living (seawater, freshwater, aquatic), parasitic (endoparasite or ectoparasite)

Exceptions: there are some which are commensals. Some protozoa, ex: Euglena, are photosynthetic.

Structure: They have an enclosed nucleus as all other eukaryotes. The nucleus is vesicular (except ciliates) and has a scattered chromatin giving it a diffused appearance. The ciliates have micronucleus (centre of all metabolic activities) and macronucleus (storage of germline genetic material.

They are motile and can move by the means of various locomotory structures like pseudopodia, cilia and flagella. These structures are also covered by the plasma membrane surrounding the microbe.

Protozoan organelles are similar to the organs of higher animals. In some protozoas such as trypanosomes and Giardia, the outer surface layer is sufficiently firm enough to maintain a distinct shape and is termed as pellicle. The cytoplasm in most protozoa is differentiated into ectoplasm (transparent outer layer) and endoplasm (inner layer enclosing organelles). For the ingestion of fluids and solid particles some protozoa possess a cytosome (part of cell specialised for phagocytosis) or cell “mouth”. In some organisms such as Naegleria and Balantidium contractile vacuoles are present for osmoregulation.

Protozoans can be divided into four major groups:

Amoeboid protozoan: These protozoans utilise pseudopodia for locomotion and are usually found in fresh water, sea water or moist soil. They are mostly free living but some are parasitic. Example: Amoeba, Entamoeba

Flagellated protozoans: They use flagella (long whip-like structure) for locomotion live in aquatic environment or could be parasitic, commensal, symbionts. Example: Trypanosoma (causes sleeping sickness).

Ciliated protozoans: They locomote via cilia (small, slender hair-like structure) and predominantly found in aquatic environment, some are parasites. Example: Paramoecium

Sporozoans: They do not possess any special locomotory structures. They are known to exhibit an infectious spore-like stage in their life cycle. They are all endoparasites. Example: Plasmodium (agent causing malaria).

Algae

These are photosynthetic eukaryotes of variable size and form. Their size ranges from microscopic unicellular form (Chlamydomonas) to colonial forms (Volvox). Kelps (a type of algae) are known to form massive plant bodies. Algae are thallophytic, that is, their vegetative body is not organised into roots, stem and leaf).

Algae are commonly found in either marine or fresh water habitat as well as on moist stones, wood and soil. These organisms are sometimes also known to form associations with fungi (lichen) and animals (ex: on hair of sloth and polar bears).

Reproduction: Algae can reproduce by vegetative, asexual and sexual methods. Vegetative reproduction is via fragmentation where the parent body breaks into fragments (two or more) and individual fragments develop into a new thallus. Spores are responsible for the asexual reproduction of algae. These spores are released from the parent body which germinate and give rise to a new plant. In case of sexual reproduction there are three types: Isogamous (fusion of two similar sized gametes), Anisogamous (fusion of dissimilar sized gametes) and Oogamous (fusion of small motile male gamete with large non-motile female gamete).

All algae are known to contain either chlorophyll a, b, c and/or d. Algae can be classified on the basis of pigment present into three classes: Chlorophyceae (green algae), Phaeophyceae (brown algae) and Rhodophyceae (red algae).

Chlorophyceae: The members of Chlorophyceae contain the pigment chlorophyll-a, chlorophyll-b, carotene and xanthophyll. Due to the dominant presence of chlorophyll-a and chlorophyll-b they are usually grass green in colour hence are commonly called green algae. Their cell wall is composed of cellulose. Example: Chlamydomonas, Chara, Volvox.

Phaeophyceae: The members of Phaeophyceae, commonly known as brown algae, contain the pigment chlorophyll-a, chlorophyll-c, carotenoids and xanthophyll. Depending on the presence of the xanthophyll fucoxanthin their colour can range from olive green to various shades of brown. Their cell wall is composed of cellulose and algin. Example: Laminaria, Sargassum, Fucus.

Rhodophyceae: Red algae is the common name of the members of Rhodophyceae which contain the pigments r-phycoerythrin, r-phycocyanin, chlorophyll-a and chlorophyll-d. Due to the dominant presence of r-phycoerythrin they have a distinctive red colour. Their cell wall is composed of cellulose, pectin and poly-sulphate esters. Example: Porphyra, Gelidium, Gracilaria.