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1.11Biology 01. Structure And Function

Describe the structure of the human excretory (renal) system and… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 11 of 12 1 quiz

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Lesson summary

1.11 The human excretory (renal) system and the function of the kidneys — CHECKPOINT - Lower Secondary Science 0893 notes: Describe excretion, the substances humans excrete, and the structure and function of the excretory system.Excretion — getting rid of waste materials that hav…

  • Carbon dioxide
  • Excess water
  • Faeces — waste from the digestive system is not excretion because it was never part of the body
  • Urea — a poisonous waste substance made in liver cells
  • Proteins in food are broken down to smaller molecules in the digestive system
  • The small molecules go into the blood and are carried to the liver

Section 1 of 8What excretion means

Excretion
  • Excretion getting rid of waste materials that have been made in the body's cells or that the body has too much of.
  • It applies only to substances that have truly been inside the body.
Faeces
  • Faeces waste from the digestive system is not excretion because it was never part of the body.

Section 2 of 8Substances humans excrete

Carbon dioxide
  • Carbon dioxide made by body cells in respiration and excreted from the lungs when we breathe out.
Urea
  • Urea a poisonous waste substance made in liver cells.
Excess water
  • Excess water water the body does not need, lost mainly in urine.

Section 3 of 8How urea is made

1
Proteins in food are broken down to smaller molecules in the digestive system.
2
The small molecules go into the blood and are carried to the liver.
3
If there is more protein than the body needs, the liver changes the extra into urea.
4
The urea is carried away from the liver in the blood.
5
The kidneys remove the urea from the blood.

Section 4 of 8Parts of the excretory (renal) system

PartFunction
KidneysFilter the blood and remove urea and excess water
Renal arteryBrings blood to the kidneys
Renal veinTakes blood away from the kidneys
UretersCarry urine from the kidneys to the bladder
BladderStores urine for a while
UrethraCarries urine out of the body

Section 5 of 8What the kidneys do

Filtering
  • Filtering the kidneys filter the blood as it flows through them.
  • They remove all the urea from the blood.
  • They remove excess water from the blood.
Urine
  • Urine the solution of urea dissolved in excess water.

Section 6 of 8Path of urine

1
Urine is made in each kidney.
2
It flows down a ureter.
3
It is stored in the bladder.
4
It leaves the body through the urethra.

Section 7 of 8Key terms

TermMeaning
ExcretionRemoval of waste substances made by the body's cells.
UreaPoisonous waste substance made in the liver from excess protein.
UrineSolution of urea and excess water made by the kidneys.
KidneyOrgan that filters the blood and makes urine.
RenalWord meaning to do with the kidneys.
UreterTube that carries urine from a kidney to the bladder.
UrethraTube that carries urine from the bladder to the outside.

Section 8 of 8Exam technique

1
Getting rid of faeces is excretion — faeces were never part of the body, so egestion is not excretion.
2
Urea and urine are the same thing — urea is the waste substance and urine is the solution of urea in water.
3
The ureter and urethra are the same tube — the ureter links kidney to bladder and the urethra links bladder to the outside.
4
Humans excrete only urine — carbon dioxide and water are excreted from the lungs as well.

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