What is Protozoa? ????
Answers
Explanation:
Protozoa is the single cell organisms .They come in many shapes and sizes regarding from an Ameoba which can change its shape to paramacium with it's fixed shape & complex structure . They live in a wide variety of moist habitats including fresh water, marine environment & the soil.
Protozoans are single-celled eukaryotes which are either free-living or parasitic in nature. They come in different sizes and shapes. They live in a wide variety of habitat including freshwater, marine environments. They are heterotrophic in nature. Protozoa are microscopic and have complex internal structure.
Habitat-
Protozoa are found in the aquatic environment. They live in freshwater or oceans. Some are free-living and some are parasitic in plants and animals. Mostly they are aerobic but some are anaerobic and present in the rumen or human intestine.
Some of the species are found in extreme environments like hot springs. Some of them form resting cyst to overcome dry environments.
Size and Shape-
The size and shape of Protozoa vary greatly, from microbial (1µm) to large enough and can be seen by the naked eye. The shell of unicellular foraminifera can have a diameter of 20 cm.
They lack the rigid cell wall, so they are flexible and found in various shapes. Cells are enclosed in a thin plasma membrane. Some of the species have a hard shell on the outer surface. In some of the protozoans especially in ciliates, the cell is supported by Pellicle, which may be flexible or rigid and give organisms the definite shape and help in locomotion.
Cellular Structure-
They are unicellular having a eukaryotic cell. The metabolic functions are performed by some specialised internal structures.
- They mostly have one membrane-bound nucleus in the cell
- The nucleus has diffused appearance due to scattered chromatin, the vesicular nucleus contains a central body called endosome or nucleoli. Nucleoli of apicomplexans have DNA, whereas amoeboids lack DNA in their endosome
- Ciliates have micronucleus and macronucleus
- The plasma membrane encloses the cytoplasm and other locomotory projections like flagella, pseudopodia and cilia
- Some of the genera have a membranous envelope called pellicle, which gives a definite shape to the cell. In some of the protozoans, epibiotic bacteria attach to the pellicle by their fimbriae
- The cytoplasm is differentiated into outer ectoplasm and inner endoplasm, ectoplasm is transparent and endoplasm contains cell organelles
- Some of the protozoa have cytostome for ingesting food. Food vacuoles are present, where ingested food comes. Ciliates have gullet, a body cavity which opens outside
- The central vacuole is present for osmoregulation, that removes excess water
- Membrane-bound cell organelles, like mitochondria, Golgi bodies, lysosomes and other specialised structures are present
Nutrition-
Protozoa are heterotrophic and have holozoic nutrition. They ingest their food by phagocytosis. Some of the protozoan groups have a specialised structure called cytostome for phagocytosis.
The pseudopodia of amoeboids help in catching the prey. Thousands of cilia present in ciliates drive the food-laden water into the gullet.
The ingested food comes to the food vacuole and gets acted on by lysosomal enzymes. The digested food gets distributed throughout the cell.
Locomotion-
Most of the protozoa species have flagella, cilia or pseudopodia. Sporozoa, which don’t have any locomotory structure, have subpellicular microtubules, which help in the slow movement.
Life Cycle-
The life cycle of most of the protozoa alternates between dormant cyst stage and proliferating vegetative stage, e.g. trophozoites.
The cyst stage can survive harsh conditions without water and nutrients. It can remain outside the host for a longer duration and get transmitted.
The trophozoite stage is infectious, and they feed and multiply during this stage.
Reproduction-
Mostly they reproduce by asexual means. They multiply by binary fission, longitudinal fission, transverse fission or budding.
꧁Hopes so that this will help you,꧂