Courtesy: Master of Science in Microbiology (M.Sc.Microbiology)

Eukaryotes

Eukaryotic cells contain membrane bound organelles, such as mitochondria, a nucleus, and chloroplasts. Prokaryotic cells probably transitioned into eukaryotic cells between 2.0 and 1.4 billion years ago. This was an important step in evolution. In contrast to prokaryotes, eukaryotes reproduce by using mitosis and meiosis. Sex appears to be a ubiquitous and ancient, and inherent attribute of eukaryotic life. Meiosis, a true sexual process, allows for efficient recombinational repair of DNA damage  and a greater range of genetic diversity by combining the DNA of the parents followed by recombination. Metabolic functions in eukaryotes are more specialized as well by sectioning specific processes into organelles.# ISO certification in India

The endosymbiotic theory holds that mitochondria and chloroplasts have bacterial origins. Both organelles contain their own sets of DNA and have bacteria-like ribosomes. It is likely that modern mitochondria were once a species similar to Rickettsia, with the parasitic ability to enter a cell. However, if the bacteria were capable of respiration, it would have been beneficial for the larger cell to allow the parasite to live in return for energy and detoxification of oxygen. Chloroplasts probably became symbionts through a similar set of events, and are most likely descendants of cyanobacteria. While not all eukaryotes have mitochondria or chloroplasts, mitochondria are found in most eukaryotes, and chloroplasts are found in all plants and algae. Photosynthesis and respiration are essentially the reverse of one another, and the advent of respiration coupled with photosynthesis enabled much greater access to energy than fermentation alone..# ISO certification in India

Protozoa

Paramecium tetraurelia, a ciliate, with oral groove visible

Protozoa are largely defined by their method of locomotion, including flagella, cilia, and pseudopodia. While there has been considerable debate on the classification of protozoa caused by their sheer diversity, in one system there are currently seven phyla recognized under the kingdom Protozoa: Euglenozoa, Amoebozoa, Choanozoa sensu Cavalier-Smith, Loukozoa, Percolozoa, Microsporidia and Sulcozoa. Protozoa, like plants and animals, can be considered heterotrophs or autotrophs. Autotrophs like Euglena are capable of producing their energy using photosynthesis, while heterotrophic protozoa consume food by either funneling it through a mouth-like gullet or engulfing it with pseudopods, a form of phagocytosis. While protozoa reproduce mainly asexually, some protozoa are capable of sexual reproduction. Protozoa with sexual capability include the pathogenic species Plasmodium falciparum, Toxoplasma gondii, Trypanosoma brucei, Giardia duodenalis and Leishmania species..# ISO certification in India

Ciliophora, or ciliates, are a group of protists that utilize cilia for locomotion. Examples include Paramecium, Stentors, and Vorticella. Ciliates are widely abundant in almost all environments where water can be found, and the cilia beat rhythmically in order to propel the organism. Many ciliates have trichocysts, which are spear-like organelles that can be discharged to catch prey, anchor themselves, or for defense. Ciliates are also capable of sexual reproduction, and utilize two nuclei unique to ciliates: a macronucleus for normal metabolic control and a separate micronucleus that undergoes meiosis. Examples of such ciliates are Paramecium and Tetrahymena that likely employ meiotic recombination for repairing DNA damage acquired under stressful conditions.

The Amebozoa utilize pseudopodia and cytoplasmic flow to move in their environment. Entamoeba histolytica is the cause of amebic dysentery. Entamoeba histolytica appears to be capable of meiosis.

Unicellular algae

A scanning electron microscope image of a diatom

Unicellular algae are plant-like autotrophs and contain chlorophyll. They include groups that have both multicellular and unicellular species:

• Euglenophyta, flagellated, mostly unicellular algae that occur often in fresh water. In contrast to most other algae, they lack cell walls and can be mixotrophic (both autotrophic and heterotrophic). An example is Euglena gracilis.
• Chlorophyta (green algae), mostly unicellular algae found in fresh water. The chlorophyta are of particular importance because they are believed to be most closely related to the evolution of land plants.
• Diatoms, unicellular algae that have siliceous cell walls. They are the most abundant form of algae in the ocean, although they can be found in fresh water as well. They account for about 40% of the world’s primary marine production, and produce about 25% of the world’s oxygen. Diatoms are very diverse, and comprise about 100,000 species.
• Dinoflagellates, unicellular flagellated algae, with some that are armored with celluose. Dinoflagellates can be mixotrophic, and are the algae responsible for red tide. Some dinoflagellates, like Pyrocystis fusiformis, are capable of bioluminescence..# ISO certification in India