Difference Between Cyanobacteria and Algae

The key difference between cyanobacteria and algae is that cyanobacteria are a group of prokaryotic bacteria while algae are small eukaryotic plant-like organisms.

Photosynthesis is an extremely important process that converts the energy of sunlight into chemical energy of carbohydrates. Hence, it is the process that allows certain organisms to make their own foods, and these organisms are known as photoautotrophs. Likewise, green plants, algae and cyanobacteria are three types of photoautotrophs. Among these three types, cyanobacteria are prokaryotes, which are bacteria. On the other hand, green plants and algae are eukaryotic organisms. When considering cyanobacteria and algae, they are microscopic organisms, unlike green plants. However, cyanobacteria and algae differ from each other mainly by the cellular organization. The aim of this article is to explain the difference between cyanobacteria and algae.

CONTENTS

1. Overview and Key Difference
2. What are Cyanobacteria
3. What are Algae
4. Similarities Between Cyanobacteria and Algae
5. Side by Side Comparison – Cyanobacteria vs Algae in Tabular Form
6. Summary

What are Cyanobacteria?

Cyanobacteria are a group of bacteria. Their speciality is the ability of photosynthesis. They appear in blue-green colour, and they are also called blue-green bacteria. Cyanobacteria use carbon dioxide as the source of carbon. Moreover, photosynthesis first evolved in bacteria. Hence, it is highly probable that photosynthesis is first evolved in cyanobacteria. Thus, blue, green bacteria are present in the surface layers of seawater as well as in the surface layers of fresh water. They are also present on shaded soil, rocks, mud, wood and even on some living organisms.

Most of the cyanobacteria are unicellular forms. But some get together to form filaments which are enclosed by mucous. Two good examples for this situation are Anabaena and Spirulina. Cyanobacteria are different from most other bacteria. More or less they resemble plants and algae as they can produce oxygen from water during photosynthesis. Photosynthetic pigments of cyanobacteria are present on photosynthetic membranes. Photosynthetic membranes run throughout the cytoplasm. Chlorophyll a is one of the main photosynthetic pigments present in cyanobacteria. Also, they contain phycocyanin, which is a blue-green pigment. Cells of blue-green bacteria are more often larger than those of other bacteria.

Figure 01: Cyanobacteria

Moreover, some cyanobacteria can fix nitrogen from the atmosphere into ammonia. Ammonia then involves in the amino acid synthesis in them. For this purpose, cyanobacteria possess a special cell called heterocysts. Anabaena and Nostoc are two types of nitrogen-fixing cyanobacteria.

What are Algae?

Algae are the simplest plant-like organisms found in the aquatic environment, and resemble higher plants by the presence of chlorophyll and being photoautotrophic. The very primitive algae were unicellular, but with evolution, they developed into multicellular forms, which had vertical and horizontal systems. Even now algae are found in association with damp soil and aquatic environments, both freshwater and marine.

There are different groups of algae. In past classification systems, algae are included into 6 groups. Those are chlorophytes including green algae, euglenophytes, pyrrophyts, chrysophytes, phaeophytes including brown algae and rhodophytes including red algae. Algae as a group of plants show a wide variation in morphology. They are not only microscopic but also macroscopic. Their plant body could be unicellular, uninucleate, or unicellular multinucleate or multicellular multinucleate forms. Almost all of the multicellular forms show an undifferentiated body called thallus. The shape of the plant body could be filamentous, thalloid, globe-like, flattened or heterotrichous forms.

Figure 02: Algae

Some algae are motile while some are not motile. Some are attached to a substrate with the help of a holdfast. Algae show different colours because they contain different combinations of pigments. Unicellular forms show greater variation in their size and shape of the chloroplast. Colony forms of algae are common in freshwater bodies. These are aggregations of cells having fixed number of cells. Reproduction in algae is complex because they show vegetative reproduction as well as sexual reproduction.

What are the Similarities Between Cyanobacteria and Algae?

• Cyanobacteria and algae are photosynthetic organisms.
• Thus, they can convert sunlight into carbohydrates and, they both contain chlorophyll a.
• Furthermore, both are mostly aquatic organisms.
• Also, they are primary producers of the aquatic environments.
• Besides, there are unicellular members in both groups.

What is the Difference Between Cyanobacteria and Algae?

Cyanobacteria are a group of prokaryotic bacteria that can photosynthesize. On the other hand, algae are small plant like eukaryotic organisms. This is the key difference between cyanobacteria and algae. Furthermore, cyanobacteria are unicellular while algae are mostly unicellular while there are several multicellular forms as well. Thus, it is a significant difference between cyanobacteria and algae. One more difference between cyanobacteria and algae is that the cyanobacteria belong to kingdom Monera while algae belong to kingdom Protista.

Moreover, cyanobacteria do not possess membrane-bound organelles and a nucleus. But, algae possess membrane-bound organelles and a nucleus. Therefore, it is an additional difference between cyanobacteria and algae. Most importantly, cyanobacteria can fix atmospheric nitrogen while algae are not able to fix nitrogen. Hence, this is also a difference between cyanobacteria and algae.

Below infographic on the difference between cyanobacteria and algae shows these differences comparatively.

Summary – Cyanobacteria vs Algae

Cyanobacteria and algae are photosynthetic organisms. However, cyanobacteria are prokaryotic organisms while algae are eukaryotic organisms. This is the key difference between cyanobacteria and algae. Furthermore, cyanobacteria do not have a true nucleus and membrane-bound organelles. But, algae have a true nucleus and membrane-bound organelles such as chloroplasts, mitochondria, etc. Also, cyanobacteria contain chlorophyll a, phycocyanin and phycoerythrin while algae contain chlorophyll a and b, carotenoids and xanthophylls. This is the summary of the difference between cyanobacteria and algae.

Reference:

1. “Cyanobacteria.” NeuroImage, Academic Press. Available here  
2. Vidyasagar, Aparna. “What Are Algae?” LiveScience, Purch, 4 June 2016. Available here  

Image Courtesy:

1.”Cyanobacterium-inline”By Kelvinsong – Own work, (CC BY-SA 3.0) via Commons Wikimedia  
2.”Algae Algonquin”By Mykola Swarnyk – Own work, (CC BY-SA 3.0) via Commons Wikimedia  

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