SINGLE CELLED EUKARYOTES

Presented by-Hasnahana ChetiaM.Sc BT IInd sem,G.U.

What are Eukaryotes?

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried.

NOMENCLATURE The single celled eukaryotes are classified under

the kingdom “PROTISTA”. It is a being a paraphyletic group. They are first eukaryotes, having a well

organized nucleus and complex membranous organelles.

Protozoa; some unicellular algae,phycomycetes; myxomycetes and yeasts come under this kingdom.

The term protista was first used by Ernst Haeckel in 1866.

The simplest protist is “Amoeba”.

CHARACTERISTICS They are microscopical, unicellular

eukaryotes. They are unicellular or colonial forms

without distinct division of labor. They generally live in water. They maybe heterotrophic or autotrophic. They may use pseudopodia, flagella or

cilia for locomotion. They showed mitosis and meiosis.

TYPES OF PROTISTS

ANIMAL-LIKE PROTISTS

There are four phyla of Animal-like Protists classified by how they move-

1.Zooflagellates – flagella.2.Sarcodines - extensions of cytoplasm

(pseudopodia).3.Ciliates – cilia.4.Sporozoans - do not move.

Zooflagellates

They move using one or two flagellaabsorb food across membrane, eg-Leishmania

Fig. Leishmania

Sarcodines(Amoeba,Foraminiferans, Heliozoans)

They moves using pseudopodia (false feet),which are like extensions of the cytoplasm --ameboid movement.

They ingest food by surrounding and engulfing food (endocytosis),creating a food vacuole.They reproduce by binary fission.contractile vacuole - removes excess watercan cause amebic dysentery in humans - diarrhea and stomach upset from drinking contaminated water

Fig. Amoeba

Fig. Foraminiferan

Fig. Heliozoa

Ciliates Paramecium- They move using cilia;has

two nuclei: macronucleus, micronucleus;food is gathered through food vacuole;anal pore is used for removing waste;contractile vacuole removes excess water;reproduces asexually (binary fission) or sexually (conjugation);paramecia are always the same shape,like a shoe. Fig. Paramecium

Sporozoans

They do not move on their own.They are parasitic.Plasmodium falciparum and Plasmodium vivax are sporozoans, infects the liver and blood and causes malaria. 

Fig. Plasmodium vivax 

Plantlike Protists: Unicellular Algae

They contain chlorophyll and carry out photosynthesis.

There are four phyla: euglenophytes, chrysophytes, diatoms, dinoflagellates.

Their accessory pigments help absorb light, and give them a variety of colors.

Euglenophytes

Euglena- They live in water,have

2 flagella for movement,use chlorplasts for photosynthesis, but turn into heterotrophs if kept in the dark,has an eyespot used for sensing light and dark pellicle - like a cell wall, helps maintain their shapes.

Fig. Euglena

Chrysophytes-Yellow-green algae, "golden plants“.

Diatoms-produce thin cell walls of silicon.

Dinoflagellates-Often have two flagellaluminescent.

Fig. Chrysophytes

Fig.Diatoms

Fig. Dinoflagellates

Yeasts

Yeasts are eukaryotic, mostly unicellular micro-organisms.Most reproduce asexually by budding, although a few do so by mitosis. They are phylogenetically diverse and are placed under phyla Ascomycota and Basidiomycota. Yeasts are chemorganotrophs. They usually reproduce by budding or by meiosis and spore formation (under stress conditions).

Fig. Yeast

Nutrition in Protists

Nutrition in some different types of protists is variable. In flagellates, for example, filter feeding may sometimes occur where the flagella find the prey. Other protists can engulf bacteria and digest them internally, by extending their cell membrane around the food material to form a food vacuole. This is then taken into the cell via endocytosis usually phagocytosis; sometimes pinocytosis.

Nutritional types in protist metabolism

Nutritional type s

Source of energy

Source of carbon

Examples

Phototrophs  Sunlight  Organic compounds or carbon fixation

 Algae, Dinoflagellates or Euglena

Organotrophs Organic compounds

 Organic compounds 

Apicomplexa, Trypanosomes or Amoebae

Reproduction

Some protists reproduce sexually (conjugation), while others reproduce asexually (binary fission).

Some species, for example Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually.

Usefulness of Protists Protists form a broad base across the

bottom of the food chain, and they supply approximately one-half of the world’s oxygen.

Protists, along with bacteria and fungi, are responsible for decomposing and recycling nutrients.

Euglena are used to help treat sewage because of their unique ability to switch from an autotrophic to a heterotrophic nutritional mode, helping to maintain oxygen levels in the balance.

Trichonympha which lives in the digestive system of termites and produces cellulase, an enzyme that enables termites to digest wood.

Products derived from protists are used in treatment of ulcers, high blood pressure and arthritis.

Role as pathogens

Some protists are significant pathogens of both animals and plants; for example Plasmodium falciparum and P. vivax, which causes malaria in humans, and Phytophthora infestans, which causes potato blight. Balantidium Coli and Entamoeba Histolytica causes severe dysentry in animals, eg-pigs and humans. Mastigophorites that belong to the genus trypanosoma,causes African Sleeping Sickness, a disease which often leads to death.

REFERENCES http://biology.clc.uc.edu/courses/bio106/p

rotista.htm http://answers.yahoo.com/question/index

?qid=20061030191849AA5001g http://www.blurtit.com/q658222.html http://single%20celled%20euk/Introductio

n%20to%20the%20Protists.htm http://www.zephyrus.co.uk/index.html http://users.rcn.com/jkimball.ma.ultranet/

BiologyPages/P/Protists.html