Maintaining water and nitrogen balance in the body (biology only)

Students should be able to explain the effect on cells of osmotic changes in body fluids.

Water leaves the body via the lungs during exhalation.

Water, ions and urea are lost from the skin in sweat.

There is no control over water, ion or urea loss by the lungs or skin.

Excess water, ions and urea are removed via the kidneys in the urine.

If body cells lose or gain too much water by osmosis they do not function efficiently.

Students should be able to describe the function of kidneys in maintaining the water balance of the body.

The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water.

Knowledge of other parts of the urinary system, the structure of the kidney and the structure of a nephron is not required.

Students should be able to translate tables and bar charts of glucose, ions and urea before and after filtration.