Kidneys: filtration and selective reabsorption
| English | 中文 | Pinyin |
|---|---|---|
| filtration/fɪlˈtreɪʃn/ | 过滤 | guò lǜ |
| selective reabsorption/sɪˈlektɪv riːbˈsɔːpʃn/ | 选择性重吸收 | xuǎn zé xìng zhòng xī shōu |
What would explain this observation?
- Useful glucose can enter filtered fluid without being lost in the final urine. Filtration 过滤 is followed by selective return of needed substances to the blood.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Water leaves the body during exhalation. Sweat carries water, ions and urea, while kidneys remove excess water, ions and urea in urine. The specification distinguishes these losses from selective control by the kidneys. If cells gain or lose too much water by osmosis, they do not function efficiently. More concentrated fluid outside causes net water loss through the partially permeable cell membrane and shrinking; more dilute fluid causes net entry and swelling.
- filtration: Separation producing filtered fluid from blood in the kidney; selective reabsorption 选择性重吸收: Return of needed substances from filtered fluid to blood.
Why can glucose occur in filtrate but not in the stated final urine?
Kidneys produce urine by filtering blood and selectively reabsorbing useful substances, including glucose, some ions and water. A substance in the initial filtrate is not automatically a waste product. The final composition depends on what is reabsorbed. Detailed nephron structure and other urinary-system anatomy are not required by this GCSE section.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Kidneys produce urine by filtering blood and selectively reabsorbing useful substances, including glucose, some ions and water. A substance in the initial filtrate is not automatically a waste product. The final composition depends on what is reabsorbed. Detailed nephron structure and other urinary-system anatomy are not required by this GCSE section.
- Use supplied tables of amounts before filtration, in filtrate and after reabsorption. Keep amount and concentration distinct: removing water can change concentration even when the amount of a substance does not rise. Trace material across a paper filtration model; do not collect urine or medical information from students.
Which two habits make the investigation or model in this case more defensible?
Use supplied tables of amounts before filtration, in filtrate and after reabsorption. Keep amount and concentration distinct: removing water can change concentration even when the amount of a substance does not rise. Trace material across a paper filtration model; do not collect urine or medical information from students.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a fictional filtered sample contains 8 units of glucose and all 8 are reabsorbed. The stated final sample contains zero glucose units. If 20 water units are filtered and 16 reabsorbed, 4 remain in the model urine. These are simple amount balances, not real kidney volumes or diagnostic measurements.
A model filters 32 water units and reabsorbs 25. Calculate units remaining. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A model filters 32 water units and reabsorbs 25. Calculate units remaining.
The result is 7 units. Known: a fictional filtered sample contains 8 units of glucose and all 8 are reabsorbed. The stated final sample contains zero glucose units. If 20 water units are filtered and 16 reabsorbed, 4 remain in the model urine. These are simple amount balances, not real kidney volumes or diagnostic measurements.
Check the conclusion and its limits
- Reabsorption moves useful material back into blood; it is not the same as producing it. Urine and initial filtrate are different. The kidneys do not make urea in this model; Higher Tier liver processing and ADH permeability control are taught separately.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Every substance in kidney filtrate is a waste product. This claim is false: Reabsorption moves useful material back into blood; it is not the same as producing it. Urine and initial filtrate are different. The kidneys do not make urea in this model; Higher Tier liver processing and ADH permeability control are taught separately.
Kidneys: filtration and selective reabsorption: Kidneys produce urine by filtering blood and selectively reabsorbing useful substances, including glucose, some ions and water. A substance in the initial filtrate is not automatically a waste product. The final composition depends on what is reabsorbed. Detailed nephron structure and other urinary-system anatomy are not required by this GCSE section.
Every substance in kidney filtrate is a waste product.
Reabsorption moves useful material back into blood; it is not the same as producing it. Urine and initial filtrate are different. The kidneys do not make urea in this model; Higher Tier liver processing and ADH permeability control are taught separately.
Separation producing filtered fluid from blood in the kidney: write the technical term.
filtration means Separation producing filtered fluid from blood in the kidney.