Cyanobacteria resemble the eukaryotic algae in many ways, including morphological characteristics and ecological niches, and were at one time treated as algae, hence the common name of blue-green algae. Cyanobacteria may be unicellular or filamentous. Many have sheaths to bind other cells or filaments into colonies.

Blue-green algae are a type of photosynthetic bacteria known as cyanobacteria. They are called blue-green algae because they contain pigments that give them a bluish or greenish color. When it comes to their resemblance to other organisms, blue-green algae resemble more closely to red algae and bacteria.

1. Blue-green algae and red algae:
Blue-green algae and red algae share some similarities in terms of their pigments and photosynthetic abilities. Both groups contain pigments called phycobiliproteins, which allow them to photosynthesize in deep water where other pigments cannot absorb light effectively. This adaptation enables them to live in environments with low light penetration, such as the deep ocean.

Additionally, both blue-green algae and red algae lack flagella, which are whip-like structures that some other algae possess. This shared characteristic suggests a closer evolutionary relationship between blue-green algae and red algae.

2. Blue-green algae and bacteria:
Blue-green algae are classified as bacteria due to their prokaryotic nature. They lack a true nucleus and organelles, similar to other bacteria. This classification is based on their cellular structure and genetic characteristics.

Furthermore, blue-green algae and bacteria both use similar mechanisms for energy production. They perform photosynthesis using chlorophyll and other pigments, similar to green algae and plants. However, blue-green algae have additional pigments called phycobilins, which give them their characteristic bluish or greenish color.

Conclusion:
In conclusion, blue-green algae resemble more closely to red algae and bacteria. They share similarities in terms of pigments, photosynthetic abilities, and cellular structure. While blue-green algae have some similarities with green algae and brown algae, their close resemblance is with red algae and bacteria.

Blue-greens are more akin to bacteria which have similar biochemical and structural characteristics. Blue-green algae possess photosynthetic pigments like phycoerythrin and  does not have flagellated gametes similar to  red algae