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7.3.4Unit 6: Practical Skills in Biology II

Urea as a Waste Product — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 4 parts Lesson 31 of 48 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 4Formation of Urea

1
The body cannot store excess amino acids, so liver cells remove the amino group from them in a process called deamination.
2
Deamination produces ammonia and a keto acid, which can be respired, converted to glucose, or stored as glycogen or fat.
3
Ammonia is toxic and very soluble, so the liver converts it to the much less toxic urea in the ornithine cycle.
4
The overall change can be summarised as 2NH₃ + CO₂ → CO(NH₂)₂ + H₂O.
5
Urea is carried in the blood plasma to the kidneys, where it is filtered out and excreted in urine.

Part 2 of 4Ultrafiltration

High pressure
  • High pressure The afferent arteriole is wider than the efferent, so blood pressure in the glomerulus is high.
Forcing out
  • Forcing out Pressure forces water and small solutes out of the capillaries into the Bowman's capsule.
Retained
  • Retained Blood cells and large plasma proteins stay in the blood because they are too big to pass the basement membrane.
Filtrate
  • Filtrate Glomerular filtrate contains water, glucose, amino acids, urea and ions, but no protein or cells.

Part 3 of 4Adaptations for Filtration

Adaptations for Filtration
Capillary endothelium
  • Capillary endothelium Gaps between the cells allow fluid to pass out of the glomerular capillaries.
Basement membrane
  • Basement membrane A mesh of proteins and carbohydrates that acts as the filter and stops large proteins escaping.
Epithelium of Bowman's capsule
  • Epithelium of Bowman's capsule Cells have gaps between them so filtrate can pass into the capsule space.
Large surface area
  • Large surface area Many capillaries in each glomerulus provide a big area for filtration.
In filtrateNot in filtrate
Water, urea, glucose, amino acids, ionsRed blood cells, platelets, plasma proteins

Part 4 of 4Exam Checklist & Tips

7.3.4 – Key Points for the Exam

  • Deamination Removal of the amino group from an amino acid, producing ammonia and a keto acid.
  • Ornithine cycle The liver pathway that converts ammonia and carbon dioxide into urea.
  • Ultrafiltration Filtration of small molecules from blood in the glomerulus under high pressure.
  • Glomerular filtrate The fluid that enters the Bowman's capsule.
  • Basement membrane The mesh layer that stops large proteins entering the filtrate.

Common Mistakes

  • Saying the kidney makes urea; it is made in the liver.
  • Stating that proteins and blood cells are filtered into the capsule.
  • Describing ultrafiltration as selective, when it filters by size only.
  • Confusing deamination with transamination or digestion of protein.

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