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On a hot day, what would you expect to happen to the volumes of sweat and urine which are excreted?

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(A) The volume of sweat would decrease, and the volume of urine would increase.

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(B) The volume of sweat would increase, and the volume of urine would decrease.

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(C) The volumes of both sweat and urine would increase.

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(D) The volumes of both sweat and urine would decrease.

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This question is asking us about two different excretions from the body, sweat and urine, excreted by the skin and kidneys, respectively.

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Both of these organs belong to the excretory system, which is responsible for removing excess or harmful waste products from the body.

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Here we can see a sweat gland in a section of skin in the diagram.

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Sweat is primarily made up of excess water that the body can get rid of in addition to other wastes, including minerals, ions, and urea.

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When sweat is produced, it can actually help to cool the body due to a phenomenon called evaporative cooling.

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This occurs as the water that is excreted as sweat absorbs heat from the body and evaporates from the skin.

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On a hot day, the body may overheat, so it produces sweat to try and cool the body down.

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This results in an increase in sweat volume.

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Here we can see a diagram of the kidneys, which produce urine after filtering different wastes from the blood.

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This urine is stored in the bladder until it is expelled by urination.

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On a hot day, we’ve just learned that sweat production increases.

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Because of this, the overall amount of water available in the body decreases.

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Because there’s a lower amount of water available, less water will be excreted in the urine in order to conserve water for the body.

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So the volume of urine will decrease.

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Getting back to our question, on a hot day, the option that correctly identifies what would happen to volumes of sweat and urine is given by answer choice (B).

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The volume of sweat would increase, and the volume of urine would decrease.