B4.5.3.3

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

Content

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.

(HT only) The digestion of proteins from the diet results in excess amino acids which need to be excreted safely. In the liver these amino acids are deaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion.


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.

(HT only) Students should be able to describe the effect of ADH on the permeability of the kidney tubules.

(HT only) The water level in the body is controlled by the hormone ADH which acts on the kidney tubules. ADH is released by the pituitary gland when the blood is too concentrated and it causes more water

to be reabsorbed back into the blood from the kidney tubules. This is controlled by negative feedback.

People who suffer from kidney failure may be treated by organ transplant or by using kidney dialysis. Students should know the basic principles of dialysis.

Give examples to show that there are hazards associated with science-based technologies which have to be considered alongside the benefits. Suggest reasons why the perception of risk is often very different from the measured risk (eg voluntary vs imposed risks, familiar vs unfamiliar risks, visible vs invisible hazards).,

Describe and explain specified examples of the technological applications of science. Describe and evaluate, with the help of data, methods that can be used to tackle problems caused by human impacts on the environment.

Translate information between graphical and numeric form