Introduction to Protozoa


INTRODUCTION TO PROTOZOA (Cont.) Characteristics of Protozoa 1.
General morphology: diverse body size & shape 2.
single-celled, eukaryotic 3.
specialized organelles: contractile vacuole 4.
cell motility (locomotion) 5.
nutrition: uptake by cells & intracellular digestion 6.
reproduction and life cycle 

Nutrition in Protozoa •
Most protozoans are heterotrophic: they absorb food from the environment or from host organisms (parasitic) •
Some protozoans can photosynthesize (autotrophic) Food uptake in Protozoa •
by passive diffusion (mainly ions, and small molecules) or active transport across cell membrane •
or by endocytosis: the transport of materials into a cell by means of a coated vesicle 

Food uptake in Protozoa Three types of endocytosis: •
micropinocystosis •
macropinocystosis •
phagocytosis by food vacuoles http://www.youtube.com/watch?v=a4aZE5FQ284 Oral groove & buccal cavity 

http://www.youtube.com/watch?v=W6rnhiMxtKU 

Intracellular digestion: Phagocytosis

after food particle enters the cell, lysosomes (containing digestive enzymes) will fuse in endocytic vesicle or food vacuole and initiate digestion Intracellular digestion: Phagocytosis

product of intracellular digestion will diffuse across the vacuole membrane (absorption) 

Intracellular digestion: Phagocytosis 
exocytosis: the transport of indigestible material out of a cell by fusion of residual vacuole (food vacuole after digestion) with the cell membrane Reproduction and life cycles

Most protozoans reproduce asexually (clonal reproduction or asexual reproduction)

Many can reproduce both asexually and sexually (sexual reproduction)

Life cycles of protozoans are diverse 

Asexual reproduction Most protozoans have clonal (asexual) reproduction by mitosis There are several types of asexual reproduction: •
binary fission •
budding •
multiple fission •
Binary fission = simple mitosis Transverse Longitudinal 

•
Binary fission http://www.youtube.com/watch?v=S1TmU2bb9XA •
Budding = binary fission with unequal division of a cell (one progeny cell is much smaller than the other) 

•
Multiple fission = division of the parent into more than two daughter cells, resulted from multiple divisions of the nucleus before the cell divisions •
In the phylum Apicomplexa, multiple fission is a specialized form, called schizogony •
Schizogony = repeated divisions of the nucleus before the cell divisions = sinh sn vô tính lit sinh •
Schizogony occurs in some parasitic protozoans; e.g species of Plasmodium which cause malaria 

Schizogony in Plasmodium spp Schizogony Schizogony Sexual reproduction Some protozoans have sexual reproduction, meaning a new individual is formed by combining genetic material of two haploid individuals (gametes) 2N Meiosis Diploid individuals 1N Fertilization Zygote 2N 1N Gametes Mitosis 1N Zygote 2N 1N Haploid individuals Fertilization 1N Meiosis 1N Haploid individuals 

Encystment: an extra phase in the life cycle •
Encystment (= kt kén) is the process that the protozoan secretes a thickened envelope about itself and becomes inactive (dormancy) •
The protective cyst is resistant to descication (drying out) or low temperatures, thus encystment enables the cell to survive unfavourable conditions 

Summary * Key characteristics of Protozoa: 1.
General morphology 2.
Cell structure of eukaryote, with emphasis on protozoan cells 3.
Cell motility 4.
Nutrition 5.
Reproduction and life cycles DIVERSITY OF PROTOZOA Important groups of Protozoa 

Diversity of Protozoa PROTOZOA is a diverse group, with over 92,000 species (50% Protista species) Some important groups: •
Phylum Euglenozoa •
Phylum Choanoflagellata •
Phyla Retortamonada & Axostylata •
Order Volvocida (phylum Chlorophyta) •
Phylum Alveolata •
Ameboid protozoans Phylum Euglenozoa 
Key characteristics:

having flagella (usually two) enforced by paraxial rod, located next to the axoneme 

Phylum Euglenozoa 
Key characteristics:

Diverse lifestyle: either free-living (autotrophic or heterotrophic) or parasitic

Reproduction: longitudinal binary fission Phylum Euglenozoa This phylum is divided into two major groups with distinct characteristics: a.
Class Euglenoidea b.
Class Kinetoplastida 

1a Class Euglenoidea 1a Class Euglenoidea

Two thirds of 1000 species are colorless heterotrophs with various kinds of food, i.e organic compounds, bacteria, or other protists

One third are green photoautotrophs (having chloroplasts for photosynthesis), having pigmented eyespot (stigma) 

Class Euglenoidea

Elongate body with a reservoir at anterior end

Contractile vacuoles usually located near the reservoir Class Euglenoidea

having flagella that bear mastigonemes Mastigonemes 

1b Class Kinetoplastida

having or flagella

having undulating membrane flagellum undulating membrane

having kinetoplast = a conspicuous mass of DNA located in a single, large mitochondrion Class Kinetoplastida

Colorless heterotrophs

Of 600 species known, only few are free living, while most are parasitic 

Importance of Kinetoplastida Many parasitic species are causing numerous diseases of human and domesticated animals:

Leishmaniasis disease

Chagas’s disease

Sleeping sickness Leishmania sp causing Leishmaniasis disease 

Trypansoma cruzi causing Chagas’ disease Trypansoma brucei rhodesiense and T b gambiense causing African sleeping sickness 

Trypansoma brucei causing sleeping sickness Phylum Choanoflagellata •
Key characteristics:

having a single flagellum bearing mastigoneme-like filaments

flagellum surrounded by a collar of microvilli 

Feeding in Choanoflagellata •
Flagellum creates water current towards the collar •
The collar then filters food (bacteria or organic particles) Water current Water current Phylum Choanoflagellata

solitary or colonial

free-living or sessile (attached to a substrate), some species have both free-living and sessile stage 

Phylum Choanoflagellata

heterotrophic

asexual reproduction: longitudinal fission * Importance of Choanoflagellata •
This phylum could be a sister group of Metazoa (true animals): 
some higher animals have cells with similar structure (with flagellum and microvilli collar) 
many choanoglagellates are colonial 
DNA evidence 

Phyla Retortamonada & Axostylata •
Most species live in anaerobically in animals’ digestive tract, especially in insects and vertebrates •
These two phyla are not very diverse (700 species) but important because many causes severe disease in animals; some live in insects’ gut (e.g termites), helping to digest cellulose 3a Phylum Retortamonada Key characteristics:

having four to thousands of flagella organized in functional groups

lacking Golgi bodies & mitochondria 

•
many species of Retortamondada can cause diarrhea 3b Phylum Axostylata Key characteristics:

having four to thousands of flagella organized in functional groups

having axostyle (bundle of microtubules)

without mitochondria, but having Golgi bodies Trichomonas 

Importance of Axostylata •
Some live in the gut of termites and other woodeating insects and help the insects to digest cellulose, e.g Trichonympha, Mixotricha •
Some are parasitic, e.g Trichomonas vaginalis living in urogenital track of humans Trichonympha causing STD 
... in Protozoa •
Most protozoans are heterotrophic: they absorb food from the environment or from host organisms (parasitic) •
Some protozoans can photosynthesize (autotrophic) Food uptake in Protozoa. .. 4.
Nutrition 5.
Reproduction and life cycles DIVERSITY OF PROTOZOA Important groups of Protozoa 

Diversity of Protozoa PROTOZOA is a diverse group, with over 92,000 species (50% Protista... means of a coated vesicle 

Food uptake in Protozoa Three types of endocytosis: •
micropinocystosis •
macropinocystosis •
phagocytosis by food vacuoles http://www.youtube.com/watch?v=a4aZE5FQ284