Highlights
Protista includes organisms which are neither plants nor animals. Protists are eukaryotes that mean they have membrane-bounded nucleus and organelles. Some protists are plant-like as they have chloroplast.
These plant-like protists do photosynthesis for the production of their food so are autotrophs. These attributes make them similar to plants but they don’t have proper roots, stems, leaves or other plant structures. So, they are called algae.
Some organisms which were initially classified into kingdom Animalia such as euglenoids, dinoflagellates are now also classified into protists.
There are also some fungi like protists as they have structures that look like hyphae and are not photosynthetic but also some of them have their initial life phase look like fungi. These include slime molds or water molds. Here is the detailed article:
Plants and Fungi Like Protista
Plant-like protists are called algae. They include single-celled diatoms and multicellular seaweed. Like plants, algae consist of chlorophyll and make food by photosynthesis. Types of algae consist of red and green algae, euglenoids, and dinoflagellates.
They are protists that absorb their food from dead raw material. They are classified into 2 groups, slime molds, and water molds. The majority of fungus-like protists utilize pseudopods, (” false feet”) to move around.
The Algae: Plant-like protists
Algae (singular alga) are photosynthetic protists, performing probably 50 to 60 percent of all the photosynthesis on earth (plants represent most of the rest).
Algae differ from the plants in their sex organs which are unicellular and the zygote is not protected by the parent body. A plant zygote, on the other hand, grows into a multicellular embryo that is protected by adult tissue.
Algae show an amazing variety of growth types. Some are unicellular; others are filamentous. Filaments are made up either of distinct cells or coenocytes (multinucleate structures that lack cross-walls), still others (e.g. seaweeds) are multicellular and intricately branched or set up in leaf-like extensions. A body that is not differentiated into real roots stems and leaves and lacks xylem and; phloem is called a thallus.
In addition to green chlorophyll a, yellow and orange carotenoids, which are photosynthetic pigments are found in all algae, other algal phyla have a range of other pigments (such as xanthophylls and phycoerythrin) that are likewise crucial in photosynthesis. Classification into phyla is mostly based on their pigment composition.
Algal life cycles reveal extreme variation, however, all algae other than members of the phylum Rhodophyta (red algae) have formed with flagellated motile cells in at least one stage of their life process.
Almost all algae are aquatic. When actively growing, algae are restricted to moist or damp environments, such as the ocean; freshwater ponds, lakes, and streams; warm springs; polar ice; moist soil, trees, and rocks.
(I) The Euglenoids
Euglenoids have at various times been classified in the plant kingdom (with algae) and in the animal kingdom (in protozoans). Based on molecular information, euglenoids are thought to be carefully related to zooflagellates. They are plant-like in their pigments. Nevertheless, some photosynthetic euglenoids lose their chlorophyll when grown in dark and get their nutrients heterotrophically by ingesting raw material. Other types of euglenoids are constantly colorless and heterotrophic.
Euglenoids have special evolutionary significance as they look like plants and green algae in having comparable pigments and, on the other hand, are also related One of the most uncommon protists to zooflagellates.
(ii) Dinoflagellates
Among the most unusual protist phyla is that of dinoflagellates. Most dinoflagellates are unicellular. Their cells are frequently covered with shells of interlocking cellulose plates impregnated with silicates. Environmentally, dinoflagellates are one of the most essential groups of producers (2nd just to diatoms) in the marine community. Dinoflagellates are known to have occasional population explosions or blooms. These flowers often color the water orange, red or brown and are called red tides.
(iii) Diatoms
The cell wall of each diatom includes 2 shells that overlap where they find it together, just like a petri dish. Silica is deposited in the shell, and this glasslike material is set in elaborate patterns. Diatoms are the significant manufacturers in the marine (marine and freshwater) environments because of their very great deals. Diatoms are really crucial in the water food cycle.
(iv) Brown Algae
Brown algae include the giants of the protist kingdom. All brown algae are multicellular and varied from a couple of centimeters to around 75 meters in length. The biggest brown algae, called the kelps are hard and tough in appearance. They have leaflike blades, stemlike stipes, and rootlike anchoring holdfast. Brown algae prevail in cooler marine waters, particularly along rocky shorelines in the intertidal zone.
(v) Red Algae
The multicellular body type of red algae is commonly made up of complicated interwoven filaments that are fragile and feathery. A couple of red algae are flattened sheets of cells. A lot of multicellular red algae connect to rocks or other substances by a basal holdfast. Some red algae integrate calcium carbonate in their cell walls from the ocean and participate in building coral reefs along with coral animals.
(vi) Green Algae
Green algae have pigments, energy reserve products, and cell walls that are identical to those of plants. Green algae are photosynthetic, with chlorophyll a, chlorophyll b, and carotenoids present in the chloroplasts. Their primary energy reserves are saved as starch. Most green algae have cell walls with cellulose. Because of these and other similarities it is usually accepted that plants arose from ancestral green algae. Proof from RNA sequencing also shows that green algae and the plants form a monophyletic family tree.
Chlorella is a unicellular non-motile green alga. Its environment is freshwater ponds and ditches. It is easily cultured and has actually been utilized as a speculative organism in a research study on photosynthesis as well as being investigated as an alternate source of food.
Importance of Algae
Algae have great economic and ecological significance for us. Some algae such as kelps are edible and may be utilized to conquer the shortage of food on the planet. Marine algae are likewise a source of numerous helpful compounds like algin, agar, carrageenan, and bactericides. Algae are major manufacturers of the water community; thus, they play a basic function in food chains, providing food and oxygen to other organisms.
Fungi like Protists
Some protists superficially look like fungi because they are not photosynthetic and some have actually bodies formed of threadlike structures called hyphae. However, fungus-like protists are not fungi for a number of factors. A lot of these protists have centrioles and produce cellulose as a significant element of their cell walls, whereas fungi do not have centrioles and have cell walls of chitin.
(i) Slime molds or Myxomycota
The feeding stage of a slime mold is a plasmodium, a multinucleate mass of cytoplasm that can grow to 30 cm (1 feet) in size. The plasmodium, which is slimy in look, streams over damp, decaying logs and leaf litter. It frequently forms a network of channels that cover a big surface area. As it creeps along, it consumes bacteria, yeasts, spores, and decaying raw material.
Throughout damaging conditions, slime mold kinds resistant haploid spore by meiosis within stalked structures called sporangia. When conditions become favorable again, spores germinate into biflagellate or amoeboid reproductive or swarm cells that unite to form a diploid zygote. Zygote produces multinucleate plasmodium, each nucleus being diploid. The plasmodial slime mold Physarum polycephalum is a model organism that has actually been used to study numerous essential biological processes, such as development and differentiation, cytoplasmic streaming, and the function of the cytoskeleton.
Water molds or Oomycotes
Oomycotes reveal close relations with the fungi and have a comparable structure, however are now regarded as a more ancient group. Their cell walls contain cellulose, not chitin. Their hyphae are aseptate (without cross-walls). Oomycotes consist of a variety of pathogenic organisms, including Phytophthora infestans, which have played infamous roles in human history.
Phytophthora infestans were the cause of the Irish potato famine of the 19th century. It causes a disease commonly called late blight of potatoes. Because of several rainy, cool summer seasons in Ireland in the 1840s, the water mold increased unchecked, triggering potato tubers to rot in the fields. Since potatoes were the staple of Irish peasants’ diet, lots of people (250,000 to more than 1 million) starved to death. The scarcity triggered a mass migration out of Ireland to such countries as the United States.
