OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What happens to urine production during dehydration?

1. The kidneys produce less concentrated urine

2. The kidneys stop producing urine

3. The kidneys reabsorb more water, producing concentrated urine

4. The kidneys excrete all water from the body

The correct answer is: The kidneys reabsorb more water, producing concentrated urine

During dehydration, the body experiences a reduction in the availability of water. In response, the kidneys play a crucial role in conserving water in order to maintain homeostasis. When the body is dehydrated, the kidneys increase the reabsorption of water from the filtrate back into the bloodstream. This process is regulated by the antidiuretic hormone (ADH), which signals the kidneys to retain more water. As a result, the urine produced becomes more concentrated, containing higher levels of solutes relative to the volume of water, which is a mechanism to reduce water loss from the body. The other options do not accurately reflect the physiological response to dehydration. For example, the kidneys do not stop producing urine entirely, as this would be detrimental to bodily function and waste removal. Similarly, the kidneys do not produce less concentrated urine during dehydration; rather, they work to concentrate the urine. Lastly, the idea that the kidneys excrete all water is unfounded, as some level of waste and solute excretion is still necessary for health. Therefore, the correct response highlights the body's adaptive strategy to conserve water during conditions of dehydration.