Top 100,000 Why Questions Students Most Want to Know - (Volume A)

Author: None
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Publish Date: 2006-09-01
Features: Why can electric eels generate strong electric currents? Electric eels are the most powerful fish, known as "water lines," and can generate 300 volts or even 800 volts of current when threatened. Many people have been stunned by electric eels and even drowned as a result. The electric organ of an electric eel consists of many "electroplasts." Its electric organ is distributed in the muscles on both sides of the body, with the tail as the positive electrode and the head as the negative electrode. The current flows from the tail to the head. When an electric eel is stimulated, it generates a strong electric current. Stunning fish or other organisms with electricity is the primary method electric eels use to hunt. The amount of electricity released by electric eels can easily kill animals smaller than them, and sometimes even larger animals. Why is the amphioxus considered the ancestor of fish? According to research, amphioxus appeared as early as 500 million years ago and has retained its primitive characteristics to this day, providing living evidence for the study of fish origins and the evolutionary history of invertebrates. As a result, amphioxus has become a highly valuable fish species. Amphioxus are 3–5 cm long, with strange anatomy, a slender and laterally compressed body, and pointed heads. They are pink and translucent, allowing their muscles to be clearly seen as parallel rows. Amphioxus lack scales, paired fins, and a vertebral column. A single, beating ventral heart tube serves as the heart, and they have no eyes, ears, or noses. Their digestive organs are not yet differentiated. Apart from the mouth and pharynx, which are still distinguishable, they have a single rectum leading to the anus. Amphioxus often swim to the shallow sea bottoms of river confluences with the tides, have almost no self-defense ability, but possess remarkable burrowing skills and can generally live for three to four years. Surveys show that amphioxus are distributed in places like Fujian, Qingdao, and Taiwan in China, with Liu Wudian in Tongan County, Fujian being the most famous. It is said that the name "Wenchang" originates from "Wenchang Emperor." Amphioxus have great value in studying the process of animal evolution. They are the ancestors of fish but differ from fish, representing a transitional species between invertebrates and vertebrates. Why do crabs spit foam? When buying crabs, people often prefer those with hard shells and a lot of foam. Why is this? Crabs, like fish, are crustaceans that breathe through gills and live in water. Unlike fish, crabs' gills are not located on the sides of their heads but on the upper sides of their bodies, consisting of many soft, sponge-like gill filaments covered by hard shells. Crabs often crawl onto land to search for food and do not dry out when out of water. This is because their gill filaments store a lot of water. Even when out of water, they can continue to breathe as if they were in water, inhaling air and then expelling it from the sides of their mouthparts. Since they inhale a lot of air, and the contact area between their gills and the air is large, the water in their gills mixes with the air and is expelled as countless bubbles, which accumulate and form foam in front of their mouths. Why can squids spray ink? Squids are mollusks with an ink sac in their stomachs filled with "ink." When the ink flows out, it turns the surrounding water black, which is why many people call them "cuttlefish."