什麼是藻類

一群主要是水生的、能行光合作用而無法精確定義的有機體。大小不一，從顯微鏡下的單細胞鞭毛蟲，到長達60公尺的大型褐藻。藻類提供了地球上大部分的氧氣，是幾乎所有的水生生物的食物基地，並提供食品和工業產品，包括石油產品。它們的光合作用色素比植物的更為多樣，它們的細胞中具有植物和動物所沒有的特點。隨著新的分類法資訊的發現，藻類的分類也在迅速改變。以前，藻類按它們葉綠體裡的色素分子分成紅藻、褐藻與綠藻三類。現在辨認出的種類遠遠多於這三類，每一種都有共同的色素型別。從演化的意義上看，藻類彼此間的關係並不密切。某些種群與原生動物和真菌的區別只在於它們有葉綠體以及能行光合作用的能力，因此從演化上來看，它們與原生動物或真菌的關係比與其他藻類的關係更為接近。利用藻類的歷史或許與人類的歷史一樣悠久，沿海的居民食用海藻，許多餐館裡都提供藻類食品。它們常見於溪流中「黏滑的」岩石上（參閱diatom），是池塘上綠色光輝之源。

algae

Any of a group of mostly aquatic, photosynthetic organisms (see photosynthesis) that defy precise definition. They range in size from the microscopic flagellate Micromonas to giant kelp that reach 200 ft (60 m) in length. Algae provide much of the earth's oxygen, serve as the food base for almost all aquatic life, and provide foods and industrial products, including petroleum products. Their photosynthetic pigments are more varied than those of plants, and their cells have features not found among plants and animals. The classification of algae is changing rapidly as new taxonomical information is discovered. Algae were formerly classified into three major groups—the red, brown, and green seaweeds—based on the pigment molecules in their chloroplasts. Many more than three groups are now recognized, each sharing a common set of pigment types. Algae are not closely related to each other in an evolutionary sense. Specific groups can be distinguished from protozoans and fungi (see fungus) only by the presence of chloroplasts and their ability to carry out photosynthesis, and thus have a closer evolutionary relationship with the protozoa or fungi than with other algae. Use of algae is perhaps as old as mankind; seaweeds are eaten by coastal societies, and algae are served in many restaurants. They are common on “slimy” rocks in streams (see diatoms) and as green sheens on pools and ponds.