The Kingdom Protista was set up by Ernst Haeckel in 1866. Eukaryotes are the organism which has a nucleus and is surrounded by other membrane-bound organelles. Protists are eukaryotic cells which are neither animal or plant or fungi. Most protists are unicellular but not all of them. Some protists are multicellular as well. This Kingdom Protista is sometimes known as Junk Drawer because it comprises eukaryotes which does not fit into any other Kingdom.
Protists that the characteristics that are in common with animal cells that also have mitochondria, which are the powerhouse of the cell. Protists which are similar to plant cells have a cell wall and chloroplasts. Photosynthesis is made possible in these cells due to the chloroplasts.
Eukaryotes
Eukaryotes are organisms which have a nucleus and other cell organelles bounded by a plasma membrane. Organelles are internal structures inside a cell which are responsible for several functions, such as production of energy and protein synthesis. Protists are eukaryotic organisms as they have a nucleus and other cell organelles.
Eukaryotes are thought to have evolved between about 1.7 billion and 1.9 billion years ago. The earliest known microfossils resembling eukaryotic organisms date to approximately 1.8 billion years ago.
The eukaryotes have nucleus, nuclear membrane, chromosomes, certain other organelles like Golgi Apparatus and Endoplasmic Reticulum and Lysosomes. All these organelles have several functions.
Characteristics of Kingdom Protista
Protists have a nucleus containing their DNA like all other eukaryotes. They have certain other organelles such as mitochondria and the endoplasmic reticulum. Kingdom Protista has a diverse range of food and reproduction.
Protist Habitats: Protists are generally found in moist and damp areas. They are aquatic organisms found mostly in damp soil, marshes, puddles, lakes, and the ocean. They are mostly parasites that means they live on other organisms while some are free living organisms.
Motility of Protists: Motility means the ability of the organisms to move from place to place. Protists have three types of projection for movement which are flagella, cilia, or pseudopods (false feet).
Protist Reproduction: They reproduce both sexually and asexually. They reproduce by binary fission by existing as haploid cells. Spirogyra is an algae which reproduces sexually.
Protist Nutrition: Protists can either ingest or absorb or make their own organic molecules to get their food.
Protists ingest bacteria and other small particles. They expand their cell wall and cell membrane around the food item, creating a food vacuole. Then enzymes digest the food in the vacuole.
Protists absorb food molecules across their cell membranes by diffusion. These protists are important decomposers.
Protists use light energy to make food by the process of photosynthesis. They are major producers in aquatic ecosystems.
Classification of Protista
The Kingdom Protista is classified into three categories namely Plant-like Protists, Animal-like Protists and Fungi-like protists.
Plant-like Protists: Plant alike are plant-like protists. They are commonly known as Algae. Like plants, they have the ability to photosynthesis. They contain the pigment chlorophyll that collects and converts light into energy. They are plant like and therefore green in color but can also be of red, brown or gold in color.
Red algae are mostly found in tropical marine environments. They often grow on flat surfaces, such as reefs. Though red algae may have a single cell, they are generally multicellular organisms and form a variety of seaweeds.
Green algae are the most commonly found group of algae. They contain chloroplasts and cell walls and are assumed to be the ancestors of plants on land. Green algae may be unicellular or multicellular.
Brown algae are generally found in marine. They are multicellular organisms and create a variety of plant-like species. The most commonly known example of brown algae is the giant kelp, which often grows to over 30m in size.
Fire algae include a set of unicellular organisms called the dinoflagellates. Certain dinoflagellates are bioluminescent means light production and emission by a living organism and can light up the surface of the ocean with a night-time glow. When present in large numbers, they cause a phenomenon known as red tide.
Animal-like Protists: They are called the first animals that are Protozoa. The protozoans are unicellular and heterotrophic which means they depend for food in their surrounding environments. Some animal-like protists on other, smaller microorganisms, which they consume and digest.
Unlike the other types of protists, they do not have chloroplasts and also cell walls. The amoeba, the flagellates, the ciliates, and the sporozoans are the common example of Animal-like Protists.
Amoeba have characterized feature of pseudopodia, or ‘false feet,’ which they use to catch bacteria and smaller protists.
Flagellates have characteristic feature of flagella, or whip, or tail-like structures which they apply to move in themselves through water. Some flagellates are parasitic meaning they feed on living organisms, while others are free-living meaning they don’t feed on living organisms.
Ciliates are surrounded in cilia which are tiny hair-like structures which they use to move around and attract food into their mouths.
Sporozoans are organisms that are parasitic in nature. One common example is Plasmodium, the parasite commonly known for spreading malaria.
Fungi-like protists: Molds are known as Fungus-like protists. Like fungi, they are heterotrophic consumers and absorb nutrients from dead organic matter in their environment. They use spores for reproduction. They differ from true fungi in that their cell walls which contain cellulose instead of chitin. The major types of Fungi-like Protists are slime molds and water molds.
Slime molds are mostly found on rotting logs of wood, where they feed on dead organic matter. These molds are often unicellular but when food is less in amount, can swarm together to form a slimy mass. They are brightly colored blobs and can move very slowly searching for food and, in certain cases, can form one enormous cell which is multinucleated.
Water molds generally live on the surface of water, or in damp soil. Like slime molds, they feed on decaying organic matter. This group comprises several pathogens of plants, including the destructive potato disease known as potato blight.
CONCLUSION
In this article, we have discussed the Eukaryotic Protists. Protists contain several cell organelles such as mitochondria, lysosomes, etc. which have their own unique features. Kingdom Protista is also discussed in the article, where we have discussed the characteristics and different classifications of the Protists in detail. Various examples of different classifications of Protists are also briefly explained in the article.