Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
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Question: Freshwater below Earths surface is called groundwater. The water infiltrates, or seeps down into, the ground from the surface. How does this happen? And where does the water go? Water infiltrates the ground because soil and rock are porous. Between the grains are pores, or tiny holes. Since water can move through this rock it is permeable. Eventually, the water reaches a layer of rock that is not porous and so is impermeable. Water stops moving downward when it reaches this layer of rock. Look at the diagram in Figure 13.11. It shows two layers of porous rock. The top layer is not saturated; it is not full of water. The next layer is saturated. The water in this layer has nowhere else to go. It cannot seep any deeper into the ground because the rock below it is impermeable. The top of the saturated rock layer in Figure 13.11 is called the water table. The water table isnt like a real table. It doesnt remain firmly in one place. Instead, it rises or falls, depending on how much water seeps down from the surface. The water table is higher when there is a lot of rain and lower when the weather is dry. An underground layer of rock that is saturated with groundwater is called an aquifer. A diagram of an aquifer is shown in Figure 13.12. Aquifers are generally found in porous rock, such as sandstone. Water infiltrates the aquifer from the surface. The water that enters the aquifer is called recharge. Most land areas have aquifers beneath them. Many aquifers are used by people for freshwater. The closer to the surface an aquifer is, the easier it is to get the water. However, an aquifer close to the surface is also more likely to become polluted. Pollutants can seep down through porous rock in recharge water. An aquifer that is used by people may not be recharged as quickly as its water is removed. The water table may lower and the aquifer may even run dry. If this happens, the ground above the aquifer may sink. This is likely to damage any homes or other structures built above the aquifer. One of the biggest aquifers in the world is the Ogallala aquifer. As you can see from Figure 13.13, this aquifer lies beneath parts of eight U.S. states. It covers a total area of 451,000 square kilometers (174,000 square miles). In some places, it is less than a meter deep. In other places, it is hundreds of meters deep. The Ogallala aquifer is an important source of freshwater in the American Midwest. This is a major farming area, and much of the water is used to irrigate crops. The water in this aquifer is being used up ten times faster than it is recharged. If this continues, what might happen to the Ogallala aquifer? The top of an aquifer may be high enough in some places to meet the surface of the ground. This often happens on a slope. The water flows out of the ground and creates a spring. A spring may be just a tiny trickle, or it may be a big gush of water. One of the largest springs in the world is Big Spring in Missouri, seen in Figure 13.14. Water flowing out of the ground at a spring may flow downhill and enter a stream. Thats what happens to the water that flows out of Big Spring in Missouri. If the water from a spring cant flow downhill, it may spread out to form a pond or lake instead. Lake George in New York State, which is pictured in Figure 13.15, is a spring-fed lake. The lake basin was carved by a glacier. Some springs have water that contains minerals. Groundwater dissolves minerals out of the rock as it seeps through the pores. The water in some springs is hot because it is heated by hot magma. Many hot springs are also mineral springs. Thats because hot water can dissolve more minerals than cold water. Grand Prismatic Spring, shown in Figure 13.16, is a hot mineral spring. Dissolved minerals give its water a bright blue color. The edge of the spring is

Answer: top of an underground rock layer that is saturated with water


Question: To be a good aquifer, the rock in the aquifer must have good: porosity: small spaces between grains permeability: connections between pores To reach an aquifer, surface water infiltrates downward into the ground through tiny spaces or pores in the rock. The water travels down through the permeable rock until it reaches a layer that does not have pores; this rock is impermeable (Figure 1.1). This impermeable rock layer forms the base of the aquifer. The upper surface where the groundwater reaches is the water table. Groundwater is found beneath the solid surface. Notice that the water table roughly mirrors the slope of the lands surface. A well penetrates the water table. For a groundwater aquifer to contain the same amount of water, the amount of recharge must equal the amount of discharge. What are the likely sources of recharge? What are the likely sources of discharge? What happens to the water table when there is a lot of rainfall? What happens when there is a drought? Although groundwater levels do not rise and fall as rapidly as at the surface, over time the water table will rise during wet periods and fall during droughts. In wet regions, streams are fed by groundwater; the surface of the stream is the top of the water table (Figure 1.2). In dry regions, water seeps down from the stream into the aquifer. These streams are often dry much of the year. Water leaves a groundwater reservoir in streams or springs. People take water from aquifers, too. Groundwater meets the surface in a stream (Figure 1.2) or a spring (Figure 1.3). A spring may be constant, or may only flow at certain times of year. Towns in many locations depend on water from springs. Springs can be an extremely important source of water in locations where surface water is scarce. A well is created by digging or drilling to reach groundwater. It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is. When the water table is close to the surface, wells are a convenient method for extracting water. When the water table is far below the surface, specialized equipment must The top of the stream is the top of the water table. The stream feeds the aquifer. A spring in Croatia bubbles to the surface and feeds the river Cetina. be used to dig a well. Most wells use motorized pumps to bring water to the surface, but some still require people to use a bucket to draw water up (Figure 1.4). An old-fashioned well that uses a bucket drawn up by hand.

Answer: the surface of a stream is


Question: So what happens to your bodys wastes? Obviously, you must get rid of them. This is the job of the excretory system. You remove waste as a gas (carbon dioxide), as a liquid (urine and sweat), and as a solid. Excretion is the process of removing wastes and excess water from the body. Recall that carbon dioxide travels through the blood and is transferred to the lungs where it is exhaled. In the large intestine, the remains of food are turned into solid waste for excretion. How is waste other than carbon dioxide removed from the blood? That is the role of the kidneys. Urine is a liquid waste formed by the kidneys as they filter the blood. If you are getting plenty of fluids, your urine should be almost clear. But you might have noticed that sometimes your urine is darker than usual. Do you know why this happens? Sometimes your body is low on water and trying to reduce the amount of water lost in urine. Therefore, your urine gets darker than usual. Your body is striving to maintain homeostasis through the process of excretion. Urine helps remove excess water, salts, and nitrogen from your body. Your body also needs to remove the wastes that build up from cell activity and from digestion. If these wastes are not removed, your cells can stop working, and you can get very sick. The organs of your excretory system help to release wastes from the body. The organs of the excretory system are also parts of other organ systems. For example, your lungs are part of the respiratory system. Your lungs remove carbon dioxide from your body, so they are also part of the excretory system. More organs of the excretory system are listed below ( Table 1.1). Organ(s) Function Lungs Skin Remove carbon dioxide. Sweat glands remove water, salts, and other wastes. Removes solid waste and some wa- ter in the form of feces. Remove urea, salts, and excess wa- ter from the blood. Large intestine Kidneys Component of Other Organ Sys- tem Respiratory system Integumentary system Digestive system Urinary system

Answer:
what organ of the excretory system removes solid waste?