Protista
The members of the kingdom Protista are an unusual group of organisms
that were put together because they could not be put under any other
group i.e fungi, animals or plants. The term Protista was first used by
Ernst Haekel in1866. Protists were traditionally subdivided into
several groups based similarities to the higher kingdoms: the
unicellular organism named protozoa, the plant like protophyta( they
were the one celled algae) and the fungus like slime moulds and water
moulds. These groups overlapped with each other, hence they were
replaced by phylogenetic base classifications. They live in almost any
environment that contains liquid water. Many protists such as the algae
are photosynthetic and are vital primary producers in th ecosystems,
particularly in ocean as part of the plankton. Other protists such as
the Kinetoplastids and Apicomplexa are responsible for a range of human
diseases , such as malaria and sleeping sickness.They have membrane
bound organelles and a nucleus.
The characteristic feature of the protists are:
1) They are solitary unicellular, or colonial unicellular eukaryotic organisms.
2) Mostly aquatic, many are planktons. Some are parasites.
3) They have different body shapes
4) he cell wall when pesent contains cellulose, pellicle, shell may be present.
5) cytoplasm contains membrane bound cell organelles. It also manifests streaming movement.Centrioles may be present.The protoplasm is surrounded by a distict plasma membrane made up of lipoproteins.
6)Photosynthetic forms contain chloroplasts with internal thylakoides and act as chief producers of food in the ocean and fresh waters.
7)Nucleus has a typical structure viz: porous nuclear envelope, chromatin material, nucleoplasm and nucleolus.
8)The nucleus is relatively large and prominent and is called as mesokaryon. It is seen to occur in dinoflagellates.
9)The locomotor organs are pseudopodia, flagella and cilia. The arrangement of microtubules in flagella is of 9+2 type. It is composed of a protein called tubulin.
10) Nutrition may be photosynthetic, holozoic, saprobic or parasitic. Some protists exhibit myxotrophic nutrition.i.e photosynthetic and saprobic, as in euglena.
The characteristic feature of the protists are:
1) They are solitary unicellular, or colonial unicellular eukaryotic organisms.
2) Mostly aquatic, many are planktons. Some are parasites.
3) They have different body shapes
4) he cell wall when pesent contains cellulose, pellicle, shell may be present.
5) cytoplasm contains membrane bound cell organelles. It also manifests streaming movement.Centrioles may be present.The protoplasm is surrounded by a distict plasma membrane made up of lipoproteins.
6)Photosynthetic forms contain chloroplasts with internal thylakoides and act as chief producers of food in the ocean and fresh waters.
7)Nucleus has a typical structure viz: porous nuclear envelope, chromatin material, nucleoplasm and nucleolus.
8)The nucleus is relatively large and prominent and is called as mesokaryon. It is seen to occur in dinoflagellates.
9)The locomotor organs are pseudopodia, flagella and cilia. The arrangement of microtubules in flagella is of 9+2 type. It is composed of a protein called tubulin.
10) Nutrition may be photosynthetic, holozoic, saprobic or parasitic. Some protists exhibit myxotrophic nutrition.i.e photosynthetic and saprobic, as in euglena.
Pictures of protists
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| Stentor | Paramecium | Didnium | Kelp |
11) The food reserves may be in the forms of starch, paramylum ( is a
carbohydrate similar to starch), chrysolamilarin (is a storage
polysaccharide), glycogen and fat.
12)The reproduction is both asexually and sexually, although an embryo stage is absent.
13) The asexual reproduction is a rapid multiplcation , occurs by binary fission, multple fission , spore formation, budding , and cyst formation.
14) The primitive forms have been known to exhibit sexual reproduction. Meiosis and syngamy are involved in the sexual reproduction of protists. Meiosis is zygotic and in some gametic.
15) Some protists are parasitic, and some live in the gut of other animals manifesting a symbiotic behaviour. Some protists also act as decomposers.
16) Sexual reproduction is isogamous ( refers to a form of sexual reproduction involving gametes of similar morphology, differing only in allele expression) e.g. Dinoflagellates and slime moulds, or anisogamous( refers to form of sexual reproduction involving the union or fusion of two dissimilar gametes) e.g. Ceratium or oogamy (is the familiar form of sexual reproduction. It is a form of anisogamy [ heterogamy] in which the female gamete is significantly larger than the male gamete and is non-motile ) e.g. Protizoa.
17) Life cycle may show zygotic meiosis ( e.g. Dinoflagellates and cellular slime moulds.) or gametic meiosis ( e.g. Diatoms and acellular slime moulds.
18) Parasitic protists causes disease such as dysentery, malaria, sleeping sickness.
Major groups of Protista
The kingdom Protista has been broadly divided into three main groups:
1) Photosynthetic protists or protistan algae (Plant Protista)
2)Consumer or decomposer protists ( Advanced Protista)
3) Protozoan Protists (Animal Protists)
Photosynthetic Protists or protistan algae:
They are called protistan algae.They are mainly unicellular eukaryotic algae.hey are also known as protistan algae or plantlike protists. . These organisms are mostly planktonic and represent the phytoplanktons which account for nearly 80% of the total photosynthetic activity in the biosphere. Following are major groups of photosynthetic protists. They include dinoflagellates, diatoms, euglenoides.
Dinoflagellates
These protists belong to a division called Pyrrophyta of algae. They are a well defined group of unicellular, photosynthetic forms. Most of them are flagellated and motile but some forms are non-flagellated.
Dinoflagellates are mostly marine forms. There are some fresh water forms also. Most of the dinoflagellates occur on the surface of water bodies as plankton, imparting characteristic colours to the water. The so-called 'red tide' is due to the characteristic red colour imparted by dinoflagellates belonging to the genus Gonyaulax.
Some dinoflagellates like Noctiluca and Pyrocystis contain phosphorescent granules that make the surface of the sea glow in darkness. This phenomenon is called bioluminescence.
A cell wall may be present or absent. When present it is composed of numerous plates made up of cellulose and is called theca or lorica. The heca contains two grooves , the longitudinal groove is called the sulcus while the ircular groove is called cingulum or annulus or girdle A.Cytoplasm is generally vacuolated and forms numerous radiating strands. The cells usually possess two flagella, differing from each other, arising through the pores in the lorica.
Due to presence of two flagella at right angles to each other , the dinoflagellates show peculiar spinning movement. Therefore they are known as whorling whips.
The nucleus is relatively large and prominent and is called as mesokaryon. The interphase nucleus has condensed chromosomes thereby lacking histones. Cell division occurs through dinomitosis. In this process the nuclear membrane persists. The microtubular spindle is not formed.Chromosomes are acentric and moves while being attached to the inner membrane of the nuclear envelope.There are numerous disc- shaped chloroplasts. They contain chlorophyll-a, chlorophyll-c, α-carotene and Xanthophylls which provide a shade of yellowish brown colour.
Dinoflagellates reproduce asexually by cell division. Some members form zoospores or cysts. Sexual reproduction can be either isogamous (fusion of similar gametes) or anisogamous (fusion of dissimilar gametes). Life cycle may involve either zygotic meiosis as in Ceratium or gametic meiosis as in Noctiluca.
12)The reproduction is both asexually and sexually, although an embryo stage is absent.
13) The asexual reproduction is a rapid multiplcation , occurs by binary fission, multple fission , spore formation, budding , and cyst formation.
14) The primitive forms have been known to exhibit sexual reproduction. Meiosis and syngamy are involved in the sexual reproduction of protists. Meiosis is zygotic and in some gametic.
15) Some protists are parasitic, and some live in the gut of other animals manifesting a symbiotic behaviour. Some protists also act as decomposers.
16) Sexual reproduction is isogamous ( refers to a form of sexual reproduction involving gametes of similar morphology, differing only in allele expression) e.g. Dinoflagellates and slime moulds, or anisogamous( refers to form of sexual reproduction involving the union or fusion of two dissimilar gametes) e.g. Ceratium or oogamy (is the familiar form of sexual reproduction. It is a form of anisogamy [ heterogamy] in which the female gamete is significantly larger than the male gamete and is non-motile ) e.g. Protizoa.
17) Life cycle may show zygotic meiosis ( e.g. Dinoflagellates and cellular slime moulds.) or gametic meiosis ( e.g. Diatoms and acellular slime moulds.
18) Parasitic protists causes disease such as dysentery, malaria, sleeping sickness.
Major groups of Protista
The kingdom Protista has been broadly divided into three main groups:
1) Photosynthetic protists or protistan algae (Plant Protista)
2)Consumer or decomposer protists ( Advanced Protista)
3) Protozoan Protists (Animal Protists)
Photosynthetic Protists or protistan algae:
They are called protistan algae.They are mainly unicellular eukaryotic algae.hey are also known as protistan algae or plantlike protists. . These organisms are mostly planktonic and represent the phytoplanktons which account for nearly 80% of the total photosynthetic activity in the biosphere. Following are major groups of photosynthetic protists. They include dinoflagellates, diatoms, euglenoides.
Dinoflagellates
These protists belong to a division called Pyrrophyta of algae. They are a well defined group of unicellular, photosynthetic forms. Most of them are flagellated and motile but some forms are non-flagellated.
Dinoflagellates are mostly marine forms. There are some fresh water forms also. Most of the dinoflagellates occur on the surface of water bodies as plankton, imparting characteristic colours to the water. The so-called 'red tide' is due to the characteristic red colour imparted by dinoflagellates belonging to the genus Gonyaulax.
Some dinoflagellates like Noctiluca and Pyrocystis contain phosphorescent granules that make the surface of the sea glow in darkness. This phenomenon is called bioluminescence.
A cell wall may be present or absent. When present it is composed of numerous plates made up of cellulose and is called theca or lorica. The heca contains two grooves , the longitudinal groove is called the sulcus while the ircular groove is called cingulum or annulus or girdle A.Cytoplasm is generally vacuolated and forms numerous radiating strands. The cells usually possess two flagella, differing from each other, arising through the pores in the lorica.
Due to presence of two flagella at right angles to each other , the dinoflagellates show peculiar spinning movement. Therefore they are known as whorling whips.
The nucleus is relatively large and prominent and is called as mesokaryon. The interphase nucleus has condensed chromosomes thereby lacking histones. Cell division occurs through dinomitosis. In this process the nuclear membrane persists. The microtubular spindle is not formed.Chromosomes are acentric and moves while being attached to the inner membrane of the nuclear envelope.There are numerous disc- shaped chloroplasts. They contain chlorophyll-a, chlorophyll-c, α-carotene and Xanthophylls which provide a shade of yellowish brown colour.
Dinoflagellates reproduce asexually by cell division. Some members form zoospores or cysts. Sexual reproduction can be either isogamous (fusion of similar gametes) or anisogamous (fusion of dissimilar gametes). Life cycle may involve either zygotic meiosis as in Ceratium or gametic meiosis as in Noctiluca.
Pictures of Dinoflagellates
The nutrition is holophytic or photosynthetic. Symbiotic forms are called Zooxanthellae. The mode of nutrition in Notiluca is holozoic and that of Ceratium is mixotrophic.A colourless Blasodinium is parasitic on animals. A non-contractile vacuole called pusule is present near the flagellar base. Pusule acts an osmoregulatory organ.
The food is stored in the form of starch in the fresh water forms while in the form of oil in the marine forms.
Various types of eye spots can be seen in the dinoflagellates.
Gonyaulax catenella is poisonous to vertebrates.
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| Gonyaulax |
Golden Brown Algae or Diatoms
These protistans
fall under the phylum - Chryosophyta and are commonly called as diatoms.
There are more than 5,000 species of diatoms. Most diatoms exist
singly, although some join to form colonies. They are usually yellowish
or brownish, and are found in fresh- and saltwater, in moist soil, and
on the moist surface of plants They are microscopic, unicellular,
protistans which represent a major part of phytoplanktons both in fresh
water and marine water. Fresh-water and marine diatoms appear in
greatest abundance early in the year as part of the phenomenon known as
the spring bloom, which occurs as a result of the availablity of both
light and (winter-regenerated) nutrients. They are characterized by a
silica shell of intricate and beautiful sculpturing. They reproduce
asexually by cell division. When aquatic diatoms die they drop to the
bottom, and the shells, not being subject to decay, collect in the ooze
and eventually form the material known as diatomaceous earth. Diatoms
can occur in a more compact form as a soft, chalky, lightweight rock,
called diatomite.Diatomite is used as an insulating material against
both heat and sound, in making dynamite and other explosives, and for
filters, abrasives, and similar products. Diatoms have deposited most of
the earth’s limestone, and much petroleum is of diatom origin. The
surface mud of a pond, ditch, or lagoon will almost always yield some
diatoms.Diatoms occur in various shapes and colours. They may be circular, rectangular, triangular, elongated, spindle shaped or filamentous.
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| Types of Diatoms |
The cell body of a diatom is called as a frustule. It is bound by a cell
wall composed of cellulose impregnated with silica forming
characteristic ornamentations. The cell wall has two overlapping halves
called valves or theca that fit together like the two parts of a soap
box. The upper valve is called as epitheca and the lower valve is called
as hypotheca.
A flagella is absent except in the reproductive stages. The cells may exhibit gliding type of movement with the help of mucilage secretion.
The cell has a large central vacuole in which the diploid nucleus lies suspended with the help of cytoplasmic strands. Disc-like chloroplasts are present containing the pigments
They have chlorophyll a and c, fucoxanthin and xanthophyll.
Diatoms reproduce commonly by binary fission which involves simple cell division. During this process, each daughter individual retains one half of the parent cell and the other half is newly synthesized. What is retained, always becomes the epitheca of the daughter cell and what is newly synthesized will be the hypotheca. As a result, during each fission, one of the two daughter individuals becomes progressively smaller in size.
They may show gliding moement with the help of mucilage. The cell has a large central vacuole. The single large nucleus is suspended in the entral vacuole with help of cytoplasmic strands.
Photosynthetic pigments contain chlorophyll-a, Chlorohyll-c, β- carotene, fucoxanthin, diatoxanthin, diadinoxanthin. The food reserve in the form form of oils and lecosin or chrysolaminarin (polysaccharide, β-1,3 glucan), Volutin globules (proteinaceous in nature) are also present.
The common mode of multiplication is by binary fission.Each daughter retains one valve of the parent as epitheca and secretes a new hypotheca. Cnsequently one of the daughters is slightly smaller than the parent. Over the generations here is a gradual reduction in size. The normal size is restored by the formation of rejuvenescent cells (auxophores). The sexual reproduction varies from isogamy to oogamy. However the meiosis is gametic.
The diatoms are unususal because their vegetative cells are typically diploid. They resemble the dinoflagellates in having fucoxanthin. They are very important photosynthesizers.A 60 ton blue whale may have 2 tonnes of planktons in the gut which is mostly diatoms.
The silicious frustules of diatoms do not decay very easily. They pile up at te bottom of water reservoirs and form big heaps called diatomic or diatomaceous earth.
Euglenoid Flagellates
Euglenophyta: small phylum of the kingdom protista, consisting of mostly unicellular aquatic algae. Some euglenoids contain chloroplasts with the photosynthetic pigments; others are heterotrophic and can ingest or absorb their food. Reproduction occurs by longitudinal cell division. Most live in freshwater. The most characteristic genus is Euglena, common in ponds and pools, especially when the water has been polluted by runoff from fields or lawns on which fertilizers have been used. There are approximately 1000 species of euglenoids.
Euglenophyta: small phylum of the kingdom protista, consisting of mostly unicellular aquatic algae. Some euglenoids contain chloroplasts with the photosynthetic pigments; others are heterotrophic and can ingest or absorb their food. Reproduction occurs by longitudinal cell division. Most live in freshwater. The most characteristic genus is Euglena, common in ponds and pools, especially when the water has been polluted by runoff from fields or lawns on which fertilizers have been used. There are approximately 1000 species of euglenoids.
The apical end bears an invagination having three parts- cystosome , cytopharynx and reservoir. An orange red eye spot or stigma contains red pigment called astaxanthine. It is also found in crustaceae. The euglenoides have two flagella, one is ususally shorter.
They can also perform creeping movements by expansion and contraction of their body. The phenomenon is called metaboly.
The nutrition is mixotrophic i.e. Holophytic an saprobic.The photosynthetic pigments present are chlorophyll-a, Chlorophyll-b, β-carotene, xanthophylls. They store their carbohydrates as paramylum bodies. Under favourable conditions they multiply by Binary fission.Sexual reproduction has not been proved yet. Under unfavourble periods they perennate as cysts.They are the connecting links between plants and animals. e.g. Euglena, phacus, Peranema, Astasia etc.
Other Algae
The word algae represents a large group of different organisms from different phylogenetic groups, representing many taxonomic divisions. In general algae can be referred to as plant-like organisms that are usually photosynthetic and aquatic, but do not have true roots, stems, leaves, vascular tissue and have simple reproductive structures. They are distributed worldwide in the sea, in freshwater and in moist situations on land. Most are microscopic, but some are quite large, e.g. some marine seaweeds that can exceed 50 m in length.
The algae have chlorophyll and can manufacture their own food through the process of photosynthesis. Recently they are classified in the kingdom of protiste, which comprise a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms that have cells with a membrane-bound nucleus.
Almost all the algae are eukaryotes and conduct photosynthesis within membrane bound structure called chloroplasts, which contain DNA. The exact nature of the chloroplasts is different among the different lines of algae.
Cyanobacteria are organisms traditionally included among the algae, but they have a prokaryotic cell structure typical of bacteria and conduct photosynthesis directly within the cytoplasm, rather than in specialized organelles.
Glenophyta: small phylum of the kingdom protista, consisting of mostly unicellular aguatic algae. Some euglenoids contain chloroplasts with the photosynthetic pigments; others are heterotrophic and can ingest or absorb their food. Reproduction occurs by longitudinal cell division. Most live in freshwater. The most characteristic genus is Euglena, common in ponds and pools, especially when the water has been polluted by runoff from fields or lawns on which fertilizers have been used. There are approximately 1000 species of euglenoids.
Phaeophyta: phylum of the kingdom protista consisting of those organisms commonly called brown algae. Many of the world's familiar seaweeds are members of phaeophyta. Like the chrysophytes brown algae derive their color from the presence, in the cell chloroplasts, of several brownish carotenoid pigments, as fucoxathin. With only a few exceptions, brown algae are marine, growing in the colder oceans of the world, many in the tidal zone, where they are subjected to great stress from wave action; others grow in deep water. There are approximately 1500 species of phaeophyta.
Rhodophyta: phylum of the kingdom protista consisting of the photosynthetic organisms commonly known as red algae. Members of the division have a characteristic clear red or purplish color imparted by accessory pigments called phycobilins. The red algae are multicellular and are characterized by a great deal of branching, but without differentiation into complex tissues. Most of the world's seaweeds belong to this group. Although red algae are found in all oceans, they are most common in warm-temperate and tropical climates, where they may occur at greater depths than any other photosynthetic organisms. Most of the coralline algae, which secrete calcium carbonate and play a major role in building reefs, belong here. Red algae are a traditional part of oriental cuisine. There are 4000 known marine species of red algae; a few species occur in freshwater. e.g Batrachospermum.
Cyanobacteria: phylum of prokaryotic aquatic bacteria that obtain their energy through photosynthesis. They are often referred to as blue-green algae, even though it is now known that they are not related to any of the other algal groups, which are all eukaryotes. Cyanobacteria may be single-celled or colonial. Depending upon the species and environmental conditions, colonies may form filaments, sheets or even hollow balls. Some filamentous colonies show the ability to differentiate into three different cell types. Despite their name, different species can be red, brown, or yellow; blooms (dense masses on the surface of a body of water) of a red species are said to have given the Red Sea its name. There are two main sorts of pigmentation. Most cyanobacteria contain chlorophyll a, together with various proteins called phycobilins, which give the cells a typical blue-green to grayish-brown colour. A few genera, however, lack phycobilins and have chlorophyll b as well as a, giving them a bright green colour.
Unlike bacteria, which are heterotrophic decomposers of the wastes and bodies of other organisms, cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis. Cyanobacteria are thus autotrophic producers of their own food from simple raw materials. Nitrogen-fixing cyanobacteria need only nitrogen and carbon dioxide to live: they are able to fix nitrogen gas, which cannot be absorbed by plants, into ammonia (NH3), nitrites (NO2) or nitrates (NO3), which can be absorbed by plants and converted to protein and nucleic acids.
Cyanobacteria are found in almost every conceivable habitat, from oceans to fresh water to bare rock to soil. Cyanobacteria produce the compounds responsible for earthy odors we detect in soil and some bodies of water. The greenish slime on the side of your damp flowerpot, the wall of your house or the trunk of that big tree is more likely to be cyanobacteria than anything else. Cyanobacteria have even been found on the fur of polar bears, to which they impart a greenish tinge. In short, Cyanobacteria have no one habitat because you can find them almost anywhere in the world. e.g. Nostoc, Anabaena.
Xanthophyceae: These are yellow green algae.The pigments are chlorophyll 'a' and 'b' β -carotene, anthophyll. The stored food is oil and leucosin. Cell wall is pectocellulose. e.g.vaucheria.
Consumer Decomposer Protists:
Slime Moulds
Consumer Decomposer protists are slime moulds. They are connecting link between animal and fungi. They are also known as Myxomycota (Mac Bride,1897). Some authors also describe them protistan fungi. They have cell membrane without cell walls. They do not have chlorophyll. As they have no chlorophyll they can’t produce their own food. So they depend on outside source for it. They reside in decaying environment. They have different colors and have amoeba like structure. They have saprotrophic mode of nutrition. Reproduction can be sexual or asexual type. They also produce spores. Slime Mould is divided into two types cellular and acellular.
The spores have the cellulose cell wall. They have phagotrophic or saprotrophic nutrition. Bot asexual and sexual modes of reproduction are found. Hey produce spores within sporangia. Asexual reproduction takes place through binary fission , plasmotomy, spores, cyst and sclerotium.
The slime moulds resemble both protozoa and true fungi. They resemble protozoa in the amoeboid plasmodial stage and are similar to the true fungi in the spore formation stage.
(a)Acellullar Slime Mould (Plasmodial slime mould)
A plasmodial slime mold involves numerous individual cells attached to each other, forming one large membrane. This "supercell" a syncytium is essentially a bag of cytoplasm containing thousands of individual nuclei. The somatic bodies are free-living, multinucleate, naked diploid protoplasmic masses called plasmodia.Cellular slime molds spend most of their lives as individual unicellular protists, but when a chemical signal is secreted, they assemble into a cluster that acts as one organism.
Slime molds as a group, are polyphylectic. They were originally represented by the subkingdom Gymnomycota in the Fungi kingdom and included the defunct phyla Myxomycota, Acrasiomycota and Labrinthulomycota.In fungi, the assimilative stages are mycelium and yeast, both of which are surrounded by a rigid cell wall and obtain their food by means of absorption. These are some of the reasons why mycologists no longer recognize slime molds as being fungi. Now, slime molds have been divided between several supergroups and not one of them is included in the kingdom Fungi.
The slime moulds are holocarpic and polycentric. The sporangium usually contains a network of fine threads called capillitium. Acellular slime moulds exist as slime masses on decaying leaves and timber.Locomotion is with help of pseudopodia like in amoeba.The sexual reproduction is isogamous. e.g. Physarella and Physarum.
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| Life Cycle of a Typical Cellular Slime Mould |
2. Sporen 10. Haplophase
3. Germination 11. Myxamoebae Plasmogamy
4. Meiosis 12. Swarm Cells (N)
5. Fructifications 13. Older Plasmodium (2N)
6. Myxamoeba 14. Young Plasmodium (2N)
7. Cell Division 15. Karyogamy
8. Beginning of Fruiting 16. Zygote (2N)
Each sporophore bears one or more sporangia (= fruiting bodies). Each sporangium is surrounded by a hard and brittle wall-¬like layer, the peridium.
(ii) Formation of Spores. The numerous diploid nuclei in the sporangium undergo meiotic division. The multinucleate protoplasm of the sporangium undergoes cleavage to form uninucleate tiny segments.
Each uninucleate tiny segment becomes rounded and secretes a cell wall to become spore. The sporangium also develops a system of threads called capillitium.
(b) Cellular slime mould:( Comunal slime moulds)
These spend most of their lives as separate amoeboid cells; however, upon the release of a chemical signal, the individual cells aggregate into a great swarm. Up to 125,000 individual cells aggregate and flow together, forming a multicellular mass called a pseudoplasmodium that resembles a slug and crawls about ingesting food in the same way as a plasmodial slime mold, before settling in a location with acceptable warmth and brightness. Each of the spores s released from a fruiting body develops becomes a single amoeboid cell, feeding individually until starving cells release a chemical signal that causes them to aggregate into a new pseudoplasmodium, and the process is repeated. Anisogamous sexual reproduction takes place.In sexual reproduction, two haploid amoeboid cells fuse, then engulf surrounding amoeboids to form a single organism called a macrocyst. The macrocyst then undergoes meiosis and mitosis and releases haploid individuals.
Cellular slime molds are of great interest to cell and developmental biologists because they provide a comparatively simple and easily manipulated system for understanding how cells interact to generate a multicellular organism. There are two groups of cellular slime molds, the Dictyostelida and the Acrasida, which may not be closely related to each other.
There is a complete absence of flagellated cells. Presence of wall less uninucleate myxamoebae. Formation of pseudoplasmodium by the aggregation of myxamoebae.The myxamoebae secretes acrasin (cAmp) and show chemotactic movements.They are holocarpic and monocentric. Capillitia are lacking in the sporangium.the sprangia also does not posses any cover., instead they have cellulosic wall around the spores.
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| Life Cycle of a Typical Cellular Slime Mould |
1. Division 6. Spore
2. Amoeboid Cells 7. Sporangium
3. Pseudo Plasmodium 8. Stalk
4. Myxamoeba 9. Substratum
5. Spore Germination
iii) Formation of Sporangium.
The aggregated cells of pseudoplasmodium differentiate and migrate to form a stalked sporocarp. The sporocarp bears a sporangium at its terminal end.
The sporangium of cellular slime moulds is naked. The stalk may remain upright or become slightly bent.
(iv) Formation of Spores.
The cells present inside the sporangium become rounded and become surrounded by the cellulose wall to form the spores.
Each spore is an void, haploid, uninucleate mass of protoplast covered by a cellulose cell wall. The spore germinates to produce a single naked amoeba-like cell called myxamoeba.
Protozoan Protists
Animal-like protists are called protozoans ("first animals") because it is thought that they are the evolutionary history of animals. They share many common traits with animals. All of the animal-like protists are heterotrophs; they are unable to make their own food. But unlike animals, they are unicellular. Since they can’t make their own food they must be able to move through their environment and catch their food.
The animal-like protists are divided into four groups based upon their means of mobility and manners for catching their food. They are divided into: protists with pseudopods, protists with cilia, protists with flagella, and parasitic protists.
They belong to the phylum Protozoa in Animal Kingdom . Therfore it is discussed in zoology.
2. Amoeboid Cells 7. Sporangium
3. Pseudo Plasmodium 8. Stalk
4. Myxamoeba 9. Substratum
5. Spore Germination
iii) Formation of Sporangium.
The aggregated cells of pseudoplasmodium differentiate and migrate to form a stalked sporocarp. The sporocarp bears a sporangium at its terminal end.
The sporangium of cellular slime moulds is naked. The stalk may remain upright or become slightly bent.
(iv) Formation of Spores.
The cells present inside the sporangium become rounded and become surrounded by the cellulose wall to form the spores.
Each spore is an void, haploid, uninucleate mass of protoplast covered by a cellulose cell wall. The spore germinates to produce a single naked amoeba-like cell called myxamoeba.
Protozoan Protists
Animal-like protists are called protozoans ("first animals") because it is thought that they are the evolutionary history of animals. They share many common traits with animals. All of the animal-like protists are heterotrophs; they are unable to make their own food. But unlike animals, they are unicellular. Since they can’t make their own food they must be able to move through their environment and catch their food.
The animal-like protists are divided into four groups based upon their means of mobility and manners for catching their food. They are divided into: protists with pseudopods, protists with cilia, protists with flagella, and parasitic protists.
They belong to the phylum Protozoa in Animal Kingdom . Therfore it is discussed in zoology.
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| External image of didinum |
Economic Importance of Algae:
1) They form a source of food for human beings and other non- living organisms.e.g. Porphyra, Nostoc,Ulva,Laminaria etc. Are used as food in different countries.
2)Many algae are also eaten by fish.
3)The Blue-green algae present in the soil increases the fertility of the soil by fixing atmospheric nitrogen; e.g. Nostoc, Anabaena.
4) Algae are the source of agar-agar used in laboratories as clture medium of fungi and bacteria e.g. Gelidium.
5) Algae are a source of iodine e.g. Laminaria.
Salts of Alginic acid obtained from algae are used in cosmetics and textile industries.
1) They form a source of food for human beings and other non- living organisms.e.g. Porphyra, Nostoc,Ulva,Laminaria etc. Are used as food in different countries.
2)Many algae are also eaten by fish.
3)The Blue-green algae present in the soil increases the fertility of the soil by fixing atmospheric nitrogen; e.g. Nostoc, Anabaena.
4) Algae are the source of agar-agar used in laboratories as clture medium of fungi and bacteria e.g. Gelidium.
5) Algae are a source of iodine e.g. Laminaria.
Salts of Alginic acid obtained from algae are used in cosmetics and textile industries.
I was trying to identify a type of diatom and although I didn't find a similar image here, the information about diatoms was very informative and helpful - written in a manner that a non-scientist can understand.
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