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A survey of the diverse Kingdom Protista, including amoebas, paramecia, and algae.
What if I told you that in a single drop of pond water, there is a tiny 'junk drawer' filled with creatures that act like animals, plants, and fungi all at once?
The Kingdom Protista is often called the 'junk drawer' of biology. Why? Because it contains eukaryotes (organisms with a nucleus) that don't quite fit into the animal, plant, or fungi kingdoms. Most protists are unicellular, meaning they consist of just one cell, though some, like giant kelp, are multicellular. Because they are so diverse, scientists group them based on how they get their energy: some hunt for food, some make their own food through photosynthesis, and others decompose dead matter.
Quick Check
What is the primary characteristic that all protists share regarding their cell structure?
Answer
They are all eukaryotes, meaning their cells contain a nucleus.
Animal-like protists, also known as protozoans, are heterotrophs, meaning they must eat other organisms to survive. Since they can't make their own food, they have developed incredible ways to move and 'hunt.'
1. Cilia: Tiny, hair-like structures that act like oars (e.g., Paramecium). 2. Flagella: Long, whip-like tails that propel the cell forward (e.g., Giardia). 3. Pseudopods: 'False feet' created by stretching the cell membrane and cytoplasm (e.g., Amoeba).
Imagine an Amoeba spotting a tasty bacteria. 1. The Amoeba extends a pseudopod (false foot) toward the food. 2. It wraps its cell membrane around the bacteria. 3. It pulls the food inside a vacuole to digest it. This process is called phagocytosis.
Quick Check
Which structure would a protist use if it wanted to swim quickly using a whip-like motion?
Answer
A flagellum.
Plant-like protists are commonly called algae. Like plants, they contain chlorophyll and perform photosynthesis to turn sunlight into energy. While they might look like green scum on a pond, they are vital to our survival. Through the chemical reaction:
algae produce roughly of the world's oxygen (). Without these microscopic 'oxygen factories,' we wouldn't have enough air to breathe!
Diatoms are a type of plant-like protist with a beautiful secret: 1. They create shells made of silica, the same material used to make glass. 2. These shells have intricate patterns and holes to allow nutrients in. 3. When they die, their 'glass' skeletons sink to the ocean floor, creating diatomaceous earth used in toothpastes and filters.
Fungus-like protists, such as slime molds, are the recyclers of the microscopic world. Like fungi, they are decomposers that absorb nutrients from dead organic matter. They also reproduce using spores, which are tiny survival cells that can grow into new organisms. However, unlike true fungi, fungus-like protists are able to move at some point in their life cycle, creeping slowly across rotting logs to find food.
In the 1840s, a fungus-like protist called a water mold (Phytophthora infestans) attacked potato crops in Ireland. 1. The protist spread rapidly through wet soil and air. 2. It destroyed the edible tubers, leading to a massive food shortage. 3. This demonstrates how even microscopic 'oddballs' can change human history by affecting our food supply.
Which of the following is an 'animal-like' characteristic of a protozoan?
What percentage of the Earth's oxygen is estimated to be produced by algae?
Fungus-like protists are different from true fungi because they are able to move at some point in their lives.
Review Tomorrow
In 24 hours, try to list the three ways protists move and name one organism that uses each method.
Practice Activity
Draw a diagram of an Amoeba, a Paramecium, and a Euglena. Label their movement structures (pseudopod, cilia, and flagellum) and color the plant-like one green.