Protista

Introduction

Protists are assumed to be the common historical link between plants, animals, and fungi from which these three groups are branched out in the process of evolution. Protists are assumed to be the predecessor to plants, animals, and fungi, and the first eukaryotes. Protozoa, algae, and slime moulds are few examples of the members of the Kingdom Protista, which is a highly heterogeneous collection of microbial eukaryotes.

Kingdom Protista

The eukaryotes that make up the Kingdom Protista are those which do not have much similarities besides a relatively simple organisation. Protists vary in look from each other. Some are tiny and unicellular like an amoeba whereas some are large and multicellular like seaweed. Multicellular protists lack highly specialised tissues or organs.

Protists live in almost every kind of environment that contains water. Many protists, such as the algae, are photosynthetic and are important primary producers in ecosystem. Serious human diseases such as malaria and sleeping sickness can be seen due to other protists.

The German biologist Ernst Haeckel in 1866 first named the Kingdom as ‘Protista’. Protists were traditionally segregated into one of several groups based on similarities to a plant, animal, or fungus: the animal-like protozoa, the plant-like protists and the fungus-like protists.

Characteristics of Protista

• These are eukaryotic and unicellular organisms
• Most of them stay in water at the same time as a few stay in moist places
• They have a membrane-fixed nucleus and different cellular organelles
• They have pseudopodia, cilia, or flagella for movement
• Most of these organisms exhibit aerobic respiration
• They exhibit both the autotrophic nutrition (Euglena) and heterotrophic nutrition (Amoeba)
• They exhibit the asexual mode of reproduction
• They are eukaryotic, as they are eukaryotic hence they have nucleus
• In Protista most have mitochondria
• Protista can be parasites
• Generally Protista prefer aquatic or moist environments

Generally Like all other eukaryotes, protists have a nucleus that contains their own DNA. They also have other organelle which is bound by membrane, such as the mitochondria and the endoplasmic reticulum. In General Most protists have a single cell. Some are multicellular. Because the Protist kingdom is so diverse, their methods of obtaining food and reproducing vary widely.

Classification of Protista

The Protista Kingdom was historically classified into three groups namely the Plant-like protists, Fungi-like protists and Animal-like protists.

Plant-like Protists

Algae are called the plant-like protists. They are a diverse and large group of protists that can photosynthesize as they are autotrophs. Some algae are single-celled like the diatoms whereas some are multicellular such as seaweed. Types of algae include red and green algae and dinoflagellates.

Red algae are generally found in tropical marine environments where they usually grow on flat surfaces such as reefs. Though red algae may be unicellular, they are typically multicellular organisms and form a variety of seaweeds.

Green algae are the most widely found group of algae. They contain chloroplasts and cell walls and are assumed to be the evolutionary ancestors of land plants. Green algae may be one celled or multi celled.

In General Plant-like protists are called algae. They are a large and diverse group. Some algae, like diatoms, have a single cell. Some, such as seaweed, have many cells.

The main reason to call algae a plant-like protist is because they contain chloroplasts and produce food through photosynthesis. However, they do not have many other real plant structures. For example, algae has no roots, stems, or leaves. Some algae also differ in plants by being motile. They may be accompanied by pseudopods or flagella. Although not plants themselves, algae were probably the ancestors of plants

Fungi-like Protists

Moulds are called the fungus-like protists. Slime moulds and water moulds are two major types of fungus-like protists. They feed on decaying organic matter. Fungus-like protists that have various ways of movement and reproduction by forming spores.

Slime moulds are often found on rotting logs where they get to feed on decaying organic matter. These moulds are often single-celled but when food is scarce it can swarm together to form a slimy mass.

Water moulds usually live in moist areas such as the surface of water or in damp soil. Like slime moulds they also feed on decaying organic matter. They contain several plant pathogens, including the potato disease known as potato blight.

In General Fungus-like Protists are once classified as fungi because they produce sporangia. Sporangium (pl., Sporangia) is a plant or fungal structure that produces and contains spores in it. However, slime molds and water fungi, which are the fungi like protists, are now known to be different from fungi.

Smaller, thinner-looking Fungus which are like protists are different from fungi in many ways. The cell walls of protists contain more cellulose than chitin. The fungi have chitin on the cell wall. Fungus-like protists also generally do not have division between their cells as fungido.

Animal-like Protists

Protozoa are commonly called as the animal-like protists.  Most protozoa are single celled. They are animal-like as they are heterotrophs and are capable of moving. Although protozoa are not animals they are assumed to be the ancestors of animals. The amoeba, the flagellates, the ciliates, and the protozoans are some of the examples of protozoans.

Amoeba are recognized by the presence of pseudopodia or ‘false feet,’ which they use to catch bacteria and smaller protists.

Flagellates have flagella or tail-like structures which are used by them to propel themselves through water. Some flagellates are parasitic while others are free-living. 

In General Animal-like protists are called protozoa (meaning ‘first animal’). All protozoans are unicellular and heterotrophic, meaning they want to feed on their surroundings. Some animal-like protists consume other matter, smaller germs, which they swallow and digest through a process known as phagocytosis. Some may eat dead-organic matter.

Conclusion

Plant-like protists produce almost half of the oxygen on the planet through photosynthesis. Other protists decompose and recycle nutrients that are required by the humans to live. All protists contribute to a huge part of the food chain. Protists can be used in medicine and as food additives.

Protists are extremely diversified in terms of biological and ecological characteristics due to its large part in the fact that they are an artificial assemblage of phylogenetically unrelated groups. Protists display highly varied cell structures, various types of reproductive strategies, virtually every possible way of nutrition, and varied habitats. Most unicellular protists are motile, but these organisms use diversified structures for transportation.