在托福阅读真题中有关于水藻的托福阅读文章，针对这道托福考题，前程百利小编来为大家普及一下关于水藻的背景知识，这样有助于考生在面对这类题目时方便作答，同时希望大家对背景知识不要太过依赖，重点还是在于原文章的信息。
水藻(Seaweed)相关背景：
Seaweed, any red, green, or brown marine algae that grow on seashores. They are anchored to the sea bottom or to some solid structure by rootlike holdfasts that perform the sole function of attachment and do not extract nutrients as do the roots of higher plants.
Seaweeds often form dense growths on rocky shores or accumulations in shallow water. Many show a well-established zonation along the margins of the seas, where the depth of the water is 50 metres (about 165 feet) or less. The types of seaweed growing near the high-water mark, where plants are often exposed to air, differ from those growing at lower levels, where there is little or no exposure. Fucus, Macrocystis, Nereocystis, and Laminaria are widely distributed in colder zones and are absent from tropical waters.
Brown algae commonly found as seaweeds include kelps and Fucus. Among the kelps are the largest algae; certain species of Macrocystis and Nereocystis of the Pacific and Antarctic regions exceed 33 metres (100 feet) in length. Laminaria, another kelp, is abundant along both Pacific and Atlantic coasts. Gulfweed (Sargassum;) is common as free-floating masses in the Gulf Stream and the Sargasso Sea.
Red alga seaweeds include dulse (Rhodymenia), Gelidium, Chondrus, and laver (Porphyra). Various species of Chondrus (see Irish moss) carpet the lower half of the zone exposed at low tide along rocky coasts of the Atlantic.
Ulva species, commonly called sea lettuce, are among the relatively few green algal seaweeds.
Ecology
Two specific environmental requirements dominate seaweed ecology. These are the presence of seawater (or at least brackish water) and the presence of light sufficient to drive photosynthesis. Another common requirement is a firm attachment point. As a result, seaweeds most commonly inhabit the littoral zone and within that zone more frequently on rocky shores than on sand or shingle. Seaweeds occupy a wide range of ecological niches. The highest elevation is only wetted by the tops of sea spray, the lowest is several meters deep. In some areas, littoral seaweeds can extend several miles out to sea. The limiting factor in such cases is sunlight availability. The deepest living seaweeds are some species of red algae.
A number of species such as Sargassum have adapted to a fully planktonic niche and are free-floating, depending on gas-filled sacs to maintain an acceptable depth.
Others have adapted to live in tidal rock pools. In this habitat seaweeds must withstand rapidly changing temperature andsalinity and even occasional drying.
以上就是关于托福阅读背景知识的介绍，考生可在平常托福考试复习中多留意托福阅读背景知识，以帮助自己应对各种背景下的托福阅读文章。
