CORE Biology (Short Course) - 9221 OxfordAQA

Control Of Water And Ion Content Of The Body

Overzicht

Breathe onto a cold window and a patch of mist appears. That water was inside you a moment earlier, and nothing you decided put it there. Spend an afternoon working in the sun and your shirt dries into a faint pale crust, which is what stays behind when the water in sweat evaporates and the dissolved salts do not. Neither loss asked your permission and neither of them ever stops.

This lesson follows water, dissolved ions and a little waste out of the body by the three routes that carry them: the lungs, the skin and the kidneys. You will learn exactly which substance leaves by which door, why two of those doors cannot be closed however short of water you are, what the small word excess is doing in the phrase excess water is removed via the kidneys, and how to set a day of intake against a day of losses accurately enough to work out a volume nobody measured.

Doelstellingen

  1. Water leaves the body via the lungs when we breathe out and the skin when we sweat. Excess water is removed via the kidneys in the urine.
  2. Urea and ions are lost via the skin when we sweat. Excess ions are removed via the kidneys in the urine.

Mindmap

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Lesnotitie

Water and dissolved ions arrive with everything you eat and drink, and a little more water is made inside your own cells every second by aerobic respiration. They leave again by several routes at once. The amount held in the body has to stay inside a narrow band, because a cell surrounded by liquid that is too dilute takes in water and swells, while a cell surrounded by liquid that is too concentrated loses water and shrinks. You met that behaviour as osmosis in the Transport In Cells lesson, and the water content and the ion content of the body are two of the internal conditions the Homeostasis lesson lists as being held steady.

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  1. By which route is water lost from the body but ions are not? A. The lungs B. The skin C. The kidneys D. The liver Answer: A
  2. Which substances are lost from the body in sweat? A. Water only B. Water and glucose only C. Water, ions and a small amount of urea D. Ions and urea only Answer: C
  3. What is removed from the body by the kidneys in the urine? A. All of the water and all of the ions in the body B. Excess water and excess ions C. Excess water only D. Excess ions only Answer: B
  4. What decides how much water is lost from the skin? A. How much water the body has to spare B. How many ions there are in the food eaten that day C. How hot the body is D. How fast the person is breathing Answer: C
  5. In one day a woman takes in 2600 cm3 of water in total and loses 1100 cm3 by routes other than urine. The water content of her body does not change. What volume of urine does she produce? A. 1100 cm3 B. 1500 cm3 C. 2600 cm3 D. 3700 cm3 Answer: B

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