Kidneys: filtration and selective reabsorption
הוצג| English | משמעות |
|---|---|
| filtration/fɪlˈtreɪʃn/ | סינון |
| selective reabsorption/sɪˈlektɪv riːbˈsɔːpʃn/ | ספיגה חוזרת נבחרתית |
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.
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?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Glucose is filtered out of the blood and then selectively reabsorbed back into the blood, so the stated final urine contains none. Filtration makes no oxygen, and many filtered substances are too useful to excrete.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
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.
In the lab: 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?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- 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.
Your turn: A model filters 32 water units and reabsorbs 25. Calculate units remaining.
A model filters 32 water units and reabsorbs 25. Calculate units remaining.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 7 units. Known: 32 water units filtered; 25 reabsorbed. Remaining = 32 - 25 = 7 units. The balance is a simple subtraction in this model.
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.
Not true: Every substance in kidney filtrate is a waste product. Filtrate contains useful substances - glucose, ions, water - alongside waste. Selective reabsorption returns the useful fraction to the blood; only the unwanted remainder becomes urine.
- Water leaves the body during exhalation.
- Kidneys produce urine by filtering blood and selectively reabsorbing useful substances, including glucose, some ions and water.
- Watch for: reabsorption moves useful material back into blood; it is not the same as producing it.
Filtrate contains useful substances - glucose, ions, water - alongside waste.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Filtrate contains useful substances - glucose, ions, water - alongside waste. Selective reabsorption returns the useful fraction to the blood; only the unwanted remainder becomes urine.
Separation producing filtered fluid from blood in the kidney: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
filtration means Separation producing filtered fluid from blood in the kidney.