capillary毛细管教材课程.ppt

Unit 13 Period 1 Reading The Properties of Water Water is a liquid at room temperature, and it has a relatively high freezing point. The reason why water can dissolve most substances on earth is that water has high heat capacity. Like all the other substances, water gets smaller (contract 缩小) when it freezes. Pure water has a higher freezing point and lighter than salt water. The salinity of the earth’s oceans is about 3.5%. When water freezes, its density increases. Other recourses such as oil, gas, gold etc is as precious as a drop of rain. Because water is polar gets expand decreases Nothing is as precious as --- Find out some basic facts about life in the oceans Basic facts about life in the oceans from the opening paragraph : Life on earth began in the oceans about three billion years ago; 99% of the living space on earth is in the oceans; There are about five million (known) species in the oceans; Life in the oceans ranges from tiny plankton to giant whales. Life first appeared in the blue seas. Natural selection A diverse world 99% of the living space on earth is in the oceans. Why? Because the chemical structure of water makes it an excellent medium (substance /surroundings) for life. How many species and how rich? Five million ranging from the tiniest plankton all the way up to giant sharks and whales. Water is an excellent medium for life.Why ? Water is a liquid at room temperature and has a relatively high freezing point; All living creatures need food to survive, but on many occasions the nutrients become available to living things only when they are dissolved by water. Water is polar, it can break down both solids and gases. Why? Water’s unique chemical structure Oxygen Atom Hydrogen Atom A polar molecule We can get a lot of nutrients by drinking soup. Plants can pull water up their roots via a capillary(毛细管) process. Can you give some other examples which are also resulted from water’s unique chemical structure? The salinity of