KINGDOM PROTOCTISTA (UNICELLULAR EUKARYOTES)
Protoctista is unicellular eukaryotes. Protozoa and diatoms and algae are included in it.They have membrane-bound organelles such as nucleus with chromosomes enclosed in the nuclear membrane, mitochondria, chloroplast (in photosynthetic protoctists only), Golgi bodies and endoplasmic reticulum.Mitochondria are the respiratory organelles.Protoctists are either photosynthetic, parasitic or saprotrophic.For locomotion, protoctists may have cilia or flagella (Fig.) having 9 + 2 microtubules unlike those of bacteria, which have the 9 + 1 arrangement of microtubules.They reproduce both asexually and sexually.Some protoctists are beneficial to humans while others are harmful.Classification of Protoctista
The kingdom Protoctista includes –
1. Phylum Protozoa which has the following four classes :
(i) Rhizopoda: Example Amoeba
(ii) Flagellata: Example Euglena
(iii) Ciliata: Example Paramecium
(iv) Sporozoa: Example Plasmodium
2. Phylum Bacillariophyta: Example diatoms
The algae belong to
3. Phylum Chlorophyta: Example Chlorella
4. Phylum Phaeophyta: Example Brown algae
5. Phylum Rhodophyta: Example Red algae
6. Phylum Oomycota: Example Phytophthora
Some examples of Protoctists1. Amoeba
Amoeba is commonly found in the mud in freshwater ponds and ditches containing decaying leaves.
It has blunt pseudopodia for locomotion.It captures food by pseudopodia to form a food vacuole.It has a contractile vacuole for osmoregulation
Reproduction: Sexual reproduction is absent in Amoeba. Asexual reproduction is by binary fission.
Amoeba structure
Male Anopheles cannot cause malaria as it feeds on plant juices and not human blood.
4. Euglena — A freshwater Flagellate
Euglena is abundantly found in stagnant waters such as pools, ponds, ditches etc. containing decaying organic matter.
As seen in the, the organism has the following parts.
Pellicle — elastic body covering made up of protein.
Cytostome and Reservoir — the cell mouth leading into a tubular cytopharynx which opens into a vesicle called reservoir.
Stigma — a prominent red pigment spot. It is sensitive to light.
Contractile Vacuole — for osmoregulation.
Flagellum — for propulsion in water.
Chloroplast — contain green coloured chlorophyll for photosynthesis.
Reproduction — is by binary fission.
5. The Diatoms
The diatoms are found in both fresh and saltwater and in moist soil.Thousands of species of diatoms form food for aquatic animals.Diatoms are either unicellular, colonial or filamentous and occur in a wide variety of shapesEach cell has a single prominent nucleus and plastids. They produce shells (cell walls) containing silica.
6. Other Algae
Algae can be unicellular e.g. Chlamydomonas or multi-cellular like SpirogyraAlgae can prepare their own food by photosynthesis as they contain chlorophyll. Some algae have other pigments also e.g. blue pigment (Phycocyanin), a brown pigment (Fucoxanthin) or a red pigment (Phycoerythrin). Depending on the pigment present, the algae are called blue, green, brown or red algae.Structurally the algae have a definite cell wall, cell membrane, a nucleus, cytoplasm and chloroplast. The chloroplast is cup-shaped in Chlamydomonas and ribbon-shaped in Spirogyra. Pyrenoid bodies are attached to chloroplasts.
Colour of the Red Sea is due to the dominant occurrence of a red alga.
Usefulness of AlgaeProvide food for fish as part of phytoplankton (organisms floating on the water surface)These are rich sources of vitamins A and E.Many marine forms are important sources of iodine, potassium and other minerals.Blue-green algae increase the soil fertility by fixing atmospheric nitrogen.Some algae can fix atmospheric nitrogen, so they are a source of natural fertilizer for the plants.A group of algae (diatoms) deposit silica in their walls. After their death, these algae are preserved as fossils. Their deposits in large amounts are used as flters, and for the lining of furnaces.
