Although 0 db is often referred to as the lower threshold of human hearing, it is important to realize that the human ear is not equally sensitive to all frequencies of sound. In other words, a particular noise may sound louder or softer depending on the frequency of the sound wave being transmitted. Because of this variation, scientists have defined a unit of loudness, called a phon, to represent the intensity of sound waves with a frequency of 1000 hz: a 60-phon sound is one that is perceived by the human ear to have the same loudness as a sound wave with an intensity of 60 db and a frequency of 1000 hz.

Why do you think electric energy for households is generally supplied by power plants instead of by an electric generator at home.

Afood web shows who eats who in any given habitat. every living thing, from one-celled algae to giant blue whales, needs food to survive. each food web is a possible pathway that energy and matter can follow through the habitat. a food web begins with producers: organisms that convert sunlight into usable chemical energy. the food web is completed by the decomposers who turn organic wastes, such as decaying plants, into inorganic materials, such as nutrient-rich soil. decomposers complete the cycle of life, returning nutrients to the soil or oceans for use by producers. in this food web, identify the decomposer.

Spider crabs live in the shallow regions of the ocean floor. algae tend to grow on the surface of spider crabs. the algae provide the crabs protection from predators by camouflaging them. the spider crabs give the algae shelter. what does this description suggest? 1. the algae are parasites of the spider crabs. 2. the algae and the spider crabs have a mutualistic relationship. 3. the spider crabs are commensals, and the algae are parasites. 4. the spider crabs benefit from the algae living on them. 5. the spider crabs are parasites of the algae.