Tảo không có gametangia đa bào như thực vật. Chúng chứa chất diệp lục, nhưng cũng chứa các sắc tố quang hợp khác. Những sắc tố này cung cấp cho các màu sắc đặc trưng tảo và được sử dụng để phân loại tảo vào phyla khác nhau. Các đặc điểm khác được sử dụng để phân loại tảo là năng lượng dự trữ lưu trữ và các thành phần vách tế bào. | synthesizing organisms. Many forms of algae look like plants but they differ in many ways. Algae do not have roots stems or leaves. They do not have the waxy cuticle plants have to prevent water loss. As a result algae must live in areas where water is readily available. Algae do not have multicellular gametangia as the plants do. They contain chlorophyll but also contain other photosynthetic pigments. These pigments give the algae characteristic colors and are used to classify algae into various phyla. Other characteristics used to classify algae are energy reserve storage and cell wall composition. Members of the phylum Euglenophyta are known as euglenoids. These organisms are both autotrophic as well as heterotrophic. There are hundreds of species of euglenoids. Euglenoids are unicellular and share properties of both plants and animals. They are plant-like in that they contain chlorophyll and are capable of photosynthesis. They do not have a cell wall of cellulose as do plants instead they have a pellicle made of protein. Euglenoids are like animals in that they are motile and responsive to outside stimuli. One particular species Euglena has a structure called an eyespot. This area of red pigments is sensitive to light. An Euglena can respond to its environment by moving towards areas of bright light where photosynthesis best occurs. In conditions where light is not available for photosynthesis euglenoids can be heterotrophic and ingest their food. Euglenoids store their energy as paramylon a type of polysaccharide. Members of the phylum Bacillariophyta are called diatoms. Diatoms are unicellular organisms with silica shells. They are autotrophs and can live in marine or freshwater environments. They contain chlorophyll as well as pigments called carotenoids which give them an orange-yellow color. Their shells resemble small boxes with lids. These shells are covered with grooves and pores giving them a decorated appearance. Diatoms can be either radially or .
