[Biology Class Notes] on Desmids Pdf

All the algae are eukaryotic organisms, each cell of the organisms contains a nucleus and other structures (organelles) enclosed within membranes. The algae live only in moist environments, mostly aquatic, and contain chlorophyll, which helps to synthesis their own food. Desmid is a unicellular microorganism, it comes under the green algae family Mesotaeniaceae and Desmidiaceae. Sometimes desmid placed under the family of order Zygnematales. Desmids are usually developing in standing freshwaters. As it is a unicellular organism it is impossible to view a single desmid. But can view the largest representatives in the naked eye. This green alga comprises 40 genera with 5000 species.  

View of Desmids Under Microscope

The desmid’s microscopical view is indispensable. Desmids under microscope can magnify from 40 to 400x for a clear view. it is easy to find the species type. All desmids look green in colour. Each cell consists of two half cells with similar images. The two half cells are connected by a bridge-like structure. It contains a nucleus, which can be noticed only with the specific dyes. The nucleus present in the middle of the desmids contains a transparent and denser nuclear structure. The globular nucleus turns and develops into a globose, vacuole-like structure. The shape of the semi cells changes. It looks like a disc or spindle shape and ranging from more or less globular. 

The cell wall of the mixed desmids are smooth and have distinct patterns of tubercles, granules, or spines. The desmids have a rich cell wall and not in combination with deep semicellular incisions. These algae usually appear with an elegant appearance. While exploring desmid algae to sunlight for photosynthesis, Desmids secrete mucilage from pores in the cell wall. With the help of mucilage, it can move towards light or avoid too bright light. It also acts as a protective layer

Desmids Reproduction

Usually, Desmids can reproduce both through sexual and asexual reproduction. 

Asexual Reproduction

Desmids reproduce asexually like amoeba through the simple cell division method. The two semi cells are connected together with a centre called an isthmus. Usually, cell division occurs in the region of the isthmus, each half of the semi cells is divided into two halves and developed into an individual organism.

Sexual Reproduction 

In many cases, desmids look like it reproduces in an asexual manner. While watching closely, it is proven that the desmids are reproducing through sexual reproduction. But, it does not have sperm or gametes. The cells of desmids change like an amoeba. Sexual reproduction of desmid algae occurs through a process of conjugation.  Here, each half crawls out of its shell to fuse with a mate. Sometimes, the zygote is formed, only when the “male” amoeba reaches into the shell of the “female”. This process is the same as the reproduction of Spirogyra algae. Here, the fused cells do not remain the same in a giant pile of cytoplasm. It develops into orb-like objects. The zygote formed are developed into spore-like structures. The zygote formed is surrounded by the evacuated shell. It developed into a distinct structure. In desmids, the sexual cell division takes place, and the new daughter cell algae emerged from the zygospore. 

Desmids Location

Polluted/dirty water does not support the reproduction of mixed desmids and cannot help the growth of desmids. This is due to the absence of nutrient-rich conditions in the water. The freshwater vegetations have rich nutrients and support the growth of desmids and boost reproduction. So, the desmids are widely grown in lakes, pits, aquariums..etc. The development of desmid are based on other systems like climate, nutrient conditions, and geology influence species composition, but in macrophyte plant composition, water level, wetlands, and degree of mixing with other water bodies 

Desmids in Food Web

Desmid is a well-known aquatic species. It plays an important role in aquatic ecosystems. The desmids are the type of unicellular biomass algae. It acts as an important food source for many invertebrates. The desmids are the potential food source for zooplankters like Cladocera and Copepods. The daphnids use planktonic mixed desmids as a food source. The Dplanktonic desmids are a rich potential food source. As the desmid has a low population density, it plays a minor role in the pelagic food web. In particular, where desmids grow in a submerged substrate as a green film that can be view through the naked eye, they are acting as a feed for the large numbers by grazers like rotifers, worms, midge larvae, etc.