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星期天,芳芳见妈妈给金鱼换水,金鱼在水里自由自在地游着。芳芳问:“妈妈,金鱼在水里为什么不会淹死?”妈妈听了芳芳的提问,就把爸爸刚买回的一条鲜鱼拿来,对芳芳说:“金鱼和一般鱼一样,头部两边各有一块鳃盖。”说着,妈妈剪去鱼的鳃盖,又说:“你看,里面有鲜红的鳃,鱼就是用鳃呼吸的。它把水吸进口腔,经过鳃吸取水中氧气,然后从鳃盖两侧吐出二氧化碳。鱼,能在水里呼吸,所以在水里不会淹死。”接着,妈妈又把鱼剖开,对芳芳讲:“你再看看,鱼肚里有一个白色的气囊,叫做鳔。鳔有前后两节呢。鱼吸气时鳔变大,水对它的浮力增大,就游上来了,呼气时鳔变小,浮力减小,就会下沉。
Sunday, Fang Fang see my mother to change the goldfish, goldfish swim freely in the water. Fang Fang asked: “Mom, why goldfish drowned in the water?” Mother heard the Fangfang question, put my father just bought a fresh fish brought to Fangfang, said: “Goldfish and fish in general , With a gill cover on each side of the head. ”Then, mother cut off the fish’s gill cover and said:“ You see, there are bright red gills, the fish breathe through the gills. The gills inhale the oxygen in the water and then spit out the carbon dioxide from the sides of the gill cover. The fish, breathing in the water, will not drown in the water. ”Then the mom cut the fish again and said to Fangfang:" Look at it again Look, there is a white fish in the balloon, called 鳔. 鳔 there are two before and after it. When the fish inhalation 鳔 become larger, the buoyancy of water on it increases, to swim up, expiratory 鳔 smaller, buoyancy reduction Small, it will sink.