Difference Between Protozoa and Algae

Main Difference – Protozoa vs Algae

Protozoa and algae are two types of animals that belong to the kingdom Protista. Both protozoa and algae are eukaryotic organisms. Therefore, they consist of a membrane-bound nucleus. Both types can be unicellular. But, algae can also be multicellular. The main difference between protozoa and algae is that protozoa are heterotrophic, animal-like organisms whereas algae are autotrophic, plant-like organisms. This means protozoa ingest organic molecules by phagocytosis while algae produce their own food by photosynthesis.

Key Areas Covered

1. What are Protozoa
      – Definition, Structure, Mode of Nutrition
2. What are Algae
      – Definition, Structure, Mode of Nutrition
3. What are the Similarities Between Protozoa and Algae
      – Outline of Common Features
4. What is the Difference Between Protozoa and Algae
      – Comparison of Key Differences

Key Terms: Algae, Aquatic Habitats, Autotrophs, Flagella, Heterotrophs, Protista, Protozoa

What are Protozoa

Protozoa refer to single-celled animals that belong to the kingdom Protista. Though most protozoa are free-living, some of them infect higher animals. Protozoa can obtain a variety of shapes due to the absence of a cell wall. The free-living vegetative form of protozoa is called the atropohozoite whereas the resting form is called a cyst. The cyst of the protozoa is analogous to the spore of bacteria. Since protozoa are eukaryotic organisms, they contain a membrane-bound nucleus. Some protozoa may contain more than one micronuclei. The excess water in the cell is removed by the contractile vacuoles. Food vacuoles can also be identified in protozoa. Amoeba, ciliates, flagellates, and sporozoans are examples of protozoa. A flagellate is shown in figure 1.

Figure 1: Flagellate

Protozoa are heterotrophic animals and obtain food by phagocytosis. The digestion occurs inside a food vacuole by the lysosomal enzymes. Flagella, cilia, and pseudopodia are used for the locomotion by protozoans.

What are Algae

Algae refer to a small, non-flowering, aquatic plant, which contains chlorophyll but lacks a true stem, root, leaves and a vascular system. Some algae are unicellular, and they are microscopic. They are called microalgae. This includes cyanobacteria (blue-green algae) as well as green, red, and brown algae. Other algae can be multicellular, which are known as macroalgae. Macroalgae are mainly seaweeds such as kelp, which grow about hundred feet in length.

Figure 2: Seaweed

Most microalgae are autotrophic, and they produce their own food through photosynthesis. Some algae show a heterotrophic growth, by living in the dark with the use of sugars. Another type of algae may use both of the above growth modes, and this is called the mixotrophic growth. Algae produce 70% of the oxygen in the atmosphere through photosynthesis.

Similarities Between Protozoa and Algae

Both protozoa and algae belong to the kingdom Protista.
Both protozoa and algae are eukaryotes.
Both protozoa and algae contain a membrane-bound nucleus and organelles.
Both protozoa and algae can be unicellular organisms.
Both protozoa and algae can be found in aquatic habitats.
Both protozoa and algae can reproduce through mitotic division.
Both protozoa and algae consist of flagella.
Both protozoa and algae represent the foundation of food chains.

Definition

Protozoa: Protozoa are single-celled animals that belong to the kingdom Protista.

Algae: Algae are small, non-flowering, aquatic plants containing chlorophyll but lack a true stem, root, leaves and a vascular system.

Related to

Protozoa: Protozoa are animal-like organisms.

Algae: Algae are plant-like organisms.

Methods of Obtaining Energy

Protozoa: Protozoa are heterotrophs.

Algae: Algae are autotrophs.

Significance

Protozoa: Protozoa ingest food particles by phagocytosis.

Algae: Algae produce their own food by photosynthesis.

Chlorophyll

Protozoa: Protozoa do not contain chlorophyll.

Algae: Algae contain chlorophyll.

Cell Wall

Protozoa: Protozoa do not have a cell wall.

Algae: Algae have a cell wall made up of cellulose.

Resting Unit

Protozoa: The resting unit of protozoa is the cyst.

Algae: The resting unit of algae is the spore.

Examples

Protozoa: Amoeba, Plasmodium, Euglena, Paramecium, Entamoeba histolytica, and Leishmania are the examples of protozoa.

Algae: Seaweeds, green algae, red algae, brown algae, and cyanobacteria are examples of algae.

In Humans

Protozoa: Protozoa like Plasmodium can cause diseases such as malaria in humans.

Algae: Algae may produce toxins, which are toxic to humans.

Importance

Protozoa: Protozoa serve as the foundation of most aquatic food chains.

Algae: Algae produce 70% of the oxygen in the atmosphere.

Conclusion

Protozoa and algae are two types of organisms that belong to the kingdom Protista. Protozoa are unicellular, animal-like organisms. Algae are unicellular or multicellular plant-like organisms. Therefore, protozoa are heterotrophs while algae are autotrophs. The main difference between protozoa and algae is their mode of nutrition.

References:

1. General Characteristics of Protozoa. Cliff Notes, Available here.
2. “What are Algae?” Algae Basics – All About Algae, Available here.

Image Courtesy:

1. “Giardia muris trophozoite SEM 11643” By CDC/ Dr. Stan Erlandsen (Public Domain) via Commons Wikimedia
2. “410893” (Public Domain) via Pixabay