Plant like Protists the Algae

Algae (singular: Alga) are widely distributed in various habitats such as oceans, freshwater ponds, lakes, streams, hot springs, polar ice, moist soil, trees, and rocks. They play a significant role in photosynthesis, accounting for 50 to 60% of global photosynthetic activity. Algae can exist as unicellular, filamentous, or multicellular forms. Filaments are composed of multicellular structures called coenocytes, which lack cross-walls, while multicellular algae, such as seaweeds, have a branched or leaf-like body structure called thallus, which lacks roots, stems, leaves, and vascular tissues. The photosynthetic pigments found in algae include chlorophyll "a", yellow and orange carotenoids, xanthophyll, and phycoerythrin.

The life cycle of algae exhibits a wide range of variations. With the exception of red algae (Phylum Rhodophyta), all algae have forms with flagellated motile cells at least in one stage of their life cycle. Algae differ from plants in that their sex organs are unicellular, the zygote is not protected by the parent body, and no embryo is formed.

Algae are classified into six phyla, each with its unique features and examples, as outlined in the following table.  

Classification of the Photosynthetic Protoctists

Note: "Chlorophyll a" and "chlorophyll b" are the primary pigments used in photosynthesis, while "chlorophyll c" and "chlorophyll d" are secondary pigments found in some algae. Fucoxanthin and phycobilins are additional pigments found in certain algae.