Water pollution comes from many sources. One of the biggest sources is runoff. Runoff moves over the surface of the land and picks up chemicals such as fertilizer (contains vital nutrients such as nitrogen, phosphorous, and potassium - NPK) from agricultural fields, lawns, and golf courses. It carries the chemicals to bodies of water. The added nutrients from fertilizer often cause the excessive growth of algae, creating algal blooms which are temporary phenomena because the large population of algae use up the available nutrients (Figure 2.4c). When the algae die, the decomposing bacteria use up oxygen in the water so that other aquatic organisms cannot survive. This has occurred over large areas of the ocean, creating dead zones, where low oxygen levels have killed all ocean life. A very large dead zone exists in the Gulf of Mexico. Measures that can help prevent these problems include cutting down on fertilizer use. Preserving wetlands also helps because wetlands filter runoff.
When deep-water waves move into shallow water, they change into breaking waves. When the energy of the waves touches the ocean floor, the water particles drag along the bottom and flatten their orbit (Fig. 4.18 B). Transitional waves occur when the water depth is less than one-half the wavelength
Protists belong to the group eukaryotes (having their DNA enclosed
inside the nucleus). They are not plants, animals or fungi but they act like
one. They can be in general subgroups such as unicellular algae, protozoa and
molds. They thrive in environments with little sunlight. But they are not
plant-like organisms. The answer is letter B.
