Main Difference – Green Algae vs Cyanobacteria
Green algae and cyanobacteria are two types of photosynthetic organisms that are evolved from algae. Both green algae and cyanobacteria are very diverse organisms that are mainly found in aquatic habitats. Green algae are eukaryotes but, cyanobacteria are prokaryotes. Therefore, the green algae contain membrane-bound organelles along with a nucleus. In contrast, cyanobacteria do not have membrane-bound organelles. The cyanobacteria are also called the blue-green algae. Both green algae and cyanobacteria are photosynthetic organisms that produce their own food by photosynthesis. Some of the cyanobacteria can be heterotrophs as well. The main difference between green algae and cyanobacteria is that green algae contain chloroplasts whereas cyanobacteria do not contain chloroplasts in their cells.
Key Areas Covered
1. What are Green Algae
– Definition, Characteristics, Types
2. What are Cyanobacteria
– Definition, Characteristics, Types
3. What are the Similarities Between Green Algae and Cyanobacteria
– Outline of Common Features
4. What is the Difference Between Green Algae and Cyanobacteria
– Comparison of Common Features
Key Terms: Chlorophyll a, Chlorophyta, Chloroplasts, Cyanobacteria, Green Algae, Heterotrophs, Photoautotrophs
What are Green Algae
The green algae refer to the green colored algae found in freshwater habitats. The green color is from the photosynthetic pigment, the chlorophyll. The chlorophyll a and chlorophyll b are the two types of chlorophyll in green algae. Green algae also contain beta-carotene and xanthophyll. Therefore, green algae are photoautotrophs and the food is stored as starch and fats. Since algae are eukaryotic organisms, they contain membrane-bound organelles in their cells. The genetic material of green algae occurs in the nucleus. Moreover, the photosynthetic pigments are arranged into chloroplasts. A single cell may contain one or more chloroplasts. Green algae can be unicellular, multicellular or living in colonies. Some green algae show a coenocytic growth in which several green algae are composed of a one, large cell, without cross walls. The large cell can be either uninucleated or multinucleated. Some green algae live in symbiotic relationships with fungi, forming lichens.
Green algae, Stigeoclonium is shown in figure 1.
Figure 1: Stigeoclonium
The asexual reproduction of green algae occurs by fission, budding, fragmentation or by the formation of zoospores. The sexual reproduction occurs by the formation of isogamous (both gametes are motile and same size) or anisogamous (female non-motile and male motile) gametes. Most green algae show alteration of generations with a haploid phase and diploid phase in the life cycle. The green algae are classified into two phyla; Chlorophyta and Charophyta. Most Chlorophyta occurs in the marine water, freshwater or subaerial. The Chlorophyta includes Trebouxiophyceae, Chlorophyceae, Bryopsidophyceae (seaweeds), Ulvophyceae (seaweeds), Dasycladophyceae, and Siphoncladophyceae. The Charophyta entirely live in freshwater habitats.
What are Cyanobacteria
The term cyanobacteria refers to any photosynthetic bacteria. Some cyanobacteria can live as heterotrophs. Cyanobacteria can be found in the soil, and in both freshwater and marine water habitats. Cyanobacteria can be either unicellular or multicellular. They form spherical-shaped, filamentous or sheet-like colonies. Some of the colonies of cyanobacteria are covered with sheet-like structures. Though cyanobacteria are a type of prokaryotic organisms, they contain vacuoles inside the cell. The cyanobacteria lack flagella but, they show a gliding movement, which occur by the trichome to change the depth inside the water. Some cyanobacteria are capable of fixing gaseous nitrogen. The photosynthetic pigments in cyanobacteria are chlorophyll a, phycocyanin, and phycoerythrin. Phycocyanin is a blue color pigment and phycoerythrin is a red color pigment. Cyanobacteria store food as starch.
The colonies of nostoc, a cyanobacterium, are shown in figure 2.
Figure 2: Nostoc
The asexual reproduction of cyanobacteria occurs by cell division and the formation of a plate, separating the two cells. Cyanobacteria do not undergo sexual reproduction.
Similarities Between Green Algae and Cyanobacteria
- Both green algae and cyanobacteria are evolved from algae.
- Both green algae and cyanobacteria are diverse organisms.
- Both green algae and cyanobacteria occur in terrestrial and aquatic habitats.
- Both green algae and cyanobacteria can be photosynthetic organisms.
- Some of the green algae and cyanobacteria live symbiotically.
- Both green algae and cyanobacteria can be either unicellular or multicellular.
- Both green algae and cyanobacteria contain vacuoles.
- Both green algae and cyanobacteria store food as starch.
Difference Between Green Algae and Cyanobacteria
Definition
Green Algae: Green algae refer to any green color algae found in freshwater habitats.
Cyanobacteria: Cyanobacteria refer to any photosynthetic bacteria, which often form colonies in the form of filaments, spheres or sheets and occur in diverse environments.
Type
Green Algae: Green algae are eukaryotes.
Cyanobacteria: Cyanobacteria are prokaryotes.
Membrane-bound Organelles
Green Algae: Green algae consist of membrane-bound organelles.
Cyanobacteria: Cyanobacteria lack membrane-bound organelles.
Chloroplasts
Green Algae: Green algae contain one or more chloroplast per cell.
Cyanobacteria: Cyanobacteria do not contain chloroplasts.
Photosynthetic Pigments
Green Algae: Green algae contain chlorophyll a, chlorophyll b, carotenoids, and xanthophyll as photosynthetic pigments.
Cyanobacteria: Cyanobacteria contain chlorophyll a, phycoerythrin and phycocyanin as photosynthetic pigments.
Under the Light Microscope
Green Algae: Green algae can be identified by the presence of chloroplasts in the cells.
Cyanobacteria: Cyanobacteria exhibit a homogeneous color throughout the cell.
Mode of Nutrition
Green Algae: Green algae are photoautotrophs.
Cyanobacteria: Cyanobacteria are either photoautotrophs or heterotrophs.
Nitrogen Fixation
Green Algae: Green algae do not fix gaseous nitrogen.
Cyanobacteria: Cyanobacteria are involved in the nitrogen fixation by utilizing gaseous nitrogen as a nutrient.
Storage of Nutrients
Green Algae: Green algae have less ability to store nutrients.
Cyanobacteria: Cyanobacteria show an efficient storage of nutrients.
Swimming
Green Algae: Green algae can swim through water.
Cyanobacteria: Cyanobacteria cannot swim but, they can alter their buoyancy, changing the depth in water.
Asexual Reproduction
Green Algae: The asexual reproduction of green algae occur by fission, budding, fragmentation or by the formation of zoospores.
Cyanobacteria: The asexual reproduction of cyanobacteria occurs by cell division and the formation of a plate, separating the two cells.
Sexual Reproduction
Green Algae: The sexual reproduction of green algae occurs by the formation of gametes.
Cyanobacteria: Cyanobacteria do not undergo sexual reproduction.
Examples
Green Algae: Chlamydomonas, Ulva, Spirogyra, Chlorella, and green seaweeds are examples of green algae.
Cyanobacteria: Nostoc, Anabaena, Oscillatoria, and Spirulna are examples of cyanobacteria.
Conclusion
Green algae and cyanobacteria are two variants of algae. Green algae are eukaryotes and cyanobacteria are prokaryotes. Both green algae and cyanobacteria are mainly photosynthetic organisms. Green algae contain chloroplasts but cyanobacteria lack chloroplasts. Thus, the main difference between green algae and cyanobacteria is the presence or absence of chrloroplasts in the cell.
Reference:
1.“The Seaweed Site: information on marine algae.” Seaweed.ie :: Chlorophyta, Available here. Accessed 18 Sept. 2017.
2. Arjun, K. “Complete information on the important characteristic features of Cyanobacteria.” PRESERVE ARTICLES, Available here. Accessed 18 Sept. 2017.
Image Courtesy:
1. “Stigeoclonium sp zugespitzte seitenzweige” By Kristian Peters – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “CyanobacteriaColl1.” By Christian Fischer (CC BY-SA 3.0) via Commons Wikimedia
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