Learn about the requirements to enter Kingdom Protista, one of the five kingdoms of life. Discover and read about the organisms that can be found there.
What Is Kingdom Protista?
Imagine you are cleaning or organizing around your house. To assist in this process, you separate your items into categories to help you locate them later.
Maybe you have a box for books, a drawer for school supplies, and a cubby for electronics. You start to realize, however, that you have a bunch of extra bits and pieces that do not fit into any of your other groups. So, you create a special container for them: your ‘other’ container.
This is pretty much what happened with Kingdom Protista.All the life on planet Earth is organized into five kingdoms based on whether or not the organism is single-celled, how it obtains energy, and how (or if) it moves. Kingdom Protista is the hodge-podge category. It contains the protists, or the organisms that do not fit into any of the other categories.Protista is Greek for the very first.
These organisms were traditionally considered the first eukaryotic forms of life, predecessors to the organisms in the plant, animal, and fungus kingdoms. Eukaryotes are organisms whose cells have membrane-bound organelles. This is opposed to prokaryotes, single-celled organisms lacking a nucleus.
Characteristics of Protists
Protists are eukaryotic organisms that cannot be classified as a plant, animal, or fungus. They are mostly unicellular, but some, like algae, are multicellular.
Kelp, or ‘seaweed,’ is a large multicellular protist that provides food, shelter, and oxygen for numerous underwater ecosystems. Even though kelp resembles a plant, it is not classified into Kingdom Plantae because it lacks the cellular complexity of plant cells.Protists can be heterotrophic, which means they obtain the energy they need to live by consuming other organisms. Or, they can be autotrophic, which means they obtain energy from the environment through photosynthesis, the process of capturing light energy and storing it in carbohydrates.Protists primarily live in water, though some live in moist soil. They can be found almost anywhere on Earth where there is liquid water, even in humans.
Classification of Protists
Protists are grouped by how they move and how they obtain nutrients.
They are arranged into three main categories: animal-like protists, plant-like protists, and fungus-like protists.The animal-like protists are also known as protozoans, which is Latin for ‘first animals.’ All protozoans are single-celled heterotrophs and are categorized based on their movement.
Paramecia are examples of protozoans that use cilia, or tiny hairs, to propel themselves through the water. Amoebas are able to change their shape and move through extensions of cytoplasm called pseudopodia, Greek for ‘false feet.’ The plasmodium is the parasite that causes malaria. It cannot move on its own, but rather depends on its host for locomotion.The plant-like protists are commonly referred to as algae and can be either single- or multi-celled.
Algae contain chlorophyll and carry out the process of photosynthesis. Diatoms are single-celled algae that excrete a cell wall made of silica. They are one of the most common types of autotrophic plankton. When they die, their silica skeleton is harvested and utilized for a variety of purposes, including as a filter for alcohol and a gentle abrasive in toothpaste. An algal bloom of Volvox, a single-celled protist that lives in colonies, is the cause of green water in your fish tank.The fungus-like protists are the slime molds and water molds. They are mostly single-celled organisms that live in the moist soil of forest floors and compost piles.
These heterotrophs absorb nutrients from decaying organic matter and move in the same fashion as amoebas by extending and pulling with pseudopodia. A parasitic water mold was responsible for the Great Potato Famine in Ireland that killed almost one million people in the 1800s.
Kingdom Protista contains the protists, or all the organisms that do not fit into the other kingdoms of life. Protists can be heterotrophic or autotrophic, mobile or immobile, single-celled or multi-celled, solo or a member of a colony. They are categorized into three main categories based on how they obtain nutrients. The animal-like protists consume other organisms, the plant-like protists perform photosynthesis, and the fungus-like protists break down dead and decaying matter.
When you reach the end of this lesson, see if you can accomplish these goals:
- Characterize the organisms in Kingdom Protista
- Enumerate the three main categories of protists and cite examples of each