This document provides information about excretion in humans and plants. It discusses that plants release carbon dioxide and oxygen through stomata as waste, while the lungs, kidneys, and skin are human excretory organs. It then focuses on the structure and function of the human kidney and nephron, including ultrafiltration in the glomerulus, selective reabsorption in the proximal convoluted tubule, and the role of ADH in water regulation. Urine is the final waste product containing water, urea, and salts.

1. IGCSE BIOLOGY
SECTION 2 LESSON 6

2. Content
Section 2
Structures
and
functions
in living
organisms
a) Levels of organisation
b) Cell structure
c) Biological molecules
d) Movement of substances
into and out of cells
e) Nutrition
f) Respiration
g) Gas exchange
h) Transport
i) Excretion
j) Coordination and response

3. Content
Lesson 6
i) Excretion
i) Excretion
Flowering plants
2.67 understand the origin of carbon dioxide and oxygen as waste
products of metabolism and their loss from the stomata of a leaf
Humans
2.68 recall that the lungs, kidneys and skin are organs of excretion
2.69 understand how the kidney carries out its roles of excretion
and osmoregulation
2.70 describe the structure of the urinary system, including the
kidneys, ureters, bladder and urethra
2.71 describe the structure of a nephron, to include Bowman’s
capsule and glomerulus, convoluted tubules, loop of Henlé and
collecting duct
2.72 describe ultrafiltration in the Bowman’s capsule and the
composition of the glomerular filtrate
2.73 understand that water is reabsorbed into the blood from the
collecting duct
2.74 understand that selective reabsorption of glucose occurs at
the proximal convoluted tubule
2.75 describe the role of ADH in regulating the water content of
the blood
2.76 understand that urine contains water, urea and salts.

4. Content
Lesson 6
i) Excretion
i) Excretion
Flowering plants
2.67 understand the origin of carbon dioxide and oxygen as waste
products of metabolism and their loss from the stomata of a leaf
Humans
2.68 recall that the lungs, kidneys and skin are organs of excretion
2.69 understand how the kidney carries out its roles of excretion
and osmoregulation
2.70 describe the structure of the urinary system, including the
kidneys, ureters, bladder and urethra
2.71 describe the structure of a nephron, to include Bowman’s
capsule and glomerulus, convoluted tubules, loop of Henlé and
collecting duct
2.72 describe ultrafiltration in the Bowman’s capsule and the
composition of the glomerular filtrate
2.73 understand that water is reabsorbed into the blood from the
collecting duct
2.74 understand that selective reabsorption of glucose occurs at
the proximal convoluted tubule
2.75 describe the role of ADH in regulating the water content of
the blood
2.76 understand that urine contains water, urea and salts.

5. Waste products in plants

6. Waste products in plants
1. Carbon dioxide

7. Waste products in plants
1. Carbon dioxide
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + energy

8. Waste products in plants
1. Carbon dioxide
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + energy

9. Waste products in plants
1. Carbon dioxide
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + energy
2. Oxygen

10. Waste products in plants
1. Carbon dioxide
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + energy
2. Oxygen
6CO2 + 6H2O + energy  C6H12O6 + 6O2
carbon dioxide + water + energy  Glucose + oxygen

11. Waste products in plants
1. Carbon dioxide
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + energy
2. Oxygen
6CO2 + 6H2O + energy  C6H12O6 + 6O2
carbon dioxide + water + energy  Glucose + oxygen

12. Waste products in plants
1. Carbon dioxide
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + energy
2. Oxygen
6CO2 + 6H2O + energy  C6H12O6 + 6O2
carbon dioxide + water + energy  Glucose + oxygen
From respiration
From photosynthesis

13. Stomata and excretion
Cross section through a leaf
Lower epidermis – note the presence here
of stomata (tiny pores surrounded by
guard cells).
Inter-cellular air
spaces

14. Stomata and excretion
Cross section through a leaf
CO2 O2
Both gases
diffuse out
through the
stomata

15. Content
Lesson 6
i) Excretion
i) Excretion
Flowering plants
2.67 understand the origin of carbon dioxide and oxygen as waste
products of metabolism and their loss from the stomata of a leaf
Humans
2.68 recall that the lungs, kidneys and skin are organs of excretion
2.69 understand how the kidney carries out its roles of excretion
and osmoregulation
2.70 describe the structure of the urinary system, including the
kidneys, ureters, bladder and urethra
2.71 describe the structure of a nephron, to include Bowman’s
capsule and glomerulus, convoluted tubules, loop of Henlé and
collecting duct
2.72 describe ultrafiltration in the Bowman’s capsule and the
composition of the glomerular filtrate
2.73 understand that water is reabsorbed into the blood from the
collecting duct
2.74 understand that selective reabsorption of glucose occurs at
the proximal convoluted tubule
2.75 describe the role of ADH in regulating the water content of
the blood
2.76 understand that urine contains water, urea and salts.

16. http://www.bbc.co.uk/science/humanbody/body/factfiles/organs_anatomy.shtml
Organs of excretion

17. http://www.bbc.co.uk/science/humanbody/body/factfiles/organs_anatomy.shtml
Organs of excretion
The lungs excrete
carbon dioxide
from respiration
and also water
vapour.

18. http://www.bbc.co.uk/science/humanbody/body/factfiles/organs_anatomy.shtml
Organs of excretion
The kidneys
excrete urea,
water and other
metabolic waste

19. http://www.bbc.co.uk/science/humanbody/body/factfiles/organs_anatomy.shtml
Organs of excretion
The skin secretes
sweat, maintaining
levels of salt, and
controlling body
temperature

20. Kidneys
The kidneys regulate
the amount of water
and ions in the blood
and remove all UREA

21. What is urea?
In the liver, excess
proteins are broken
down into amino acids.
These amino acids are
further broken down to
form toxic ammonia,
which is immediately
converted to urea and
carried to the kidneys
in the bloodstream.

22. Kidneys
The kidneys are
involved in the process
of
OSMOREGULATION
- This is the control of
water concentration in
the blood and body
fluids.

23. Kidneys
The kidneys are
involved in the process
of
OSMOREGULATION
- This is the control of
water concentration in
the blood and body
fluids.
The water levels in the
blood are controlled by
ADH, a hormone
secreted by the pituitary
gland in the brain

24. Kidneys
The NEPHRON is the basic
structural unit of the
kidney.

25. Kidneys
The NEPHRON is the basic
structural unit of the
kidney. Each kidney normally
contains between 800,000
and 1.5 million nephrons.

26. Kidneys
The NEPHRON is the basic
structural unit of the
kidney. Each kidney normally
contains between 800,000
and 1.5 million nephrons.
The nephrons are often
referred to as the kidney
tubules.

27. Kidneys
In the nephron nearly
everything is squeezed out
of the blood.

28. Kidneys
In the nephron nearly
everything is squeezed out
of the blood. The
substances we need to keep
are reabsorbed back into
the blood.

29. Kidneys
In the nephron nearly
everything is squeezed out
of the blood. The
substances we need to keep
are reabsorbed back into
the blood. Unwanted
substances are released as
urine.

30. Kidneys
In the nephron nearly
everything is squeezed out
of the blood. The
substances we need to keep
are reabsorbed back into
the blood. Unwanted
substances are released as
urine.

31. The Kidney Nephron

32. The Kidney Nephron
GLOMERULUS
– a coiled
capillary.

33. The Kidney Nephron
GLOMERULUS
– a coiled
capillary.
BOWMAN’S
CAPSULE – a
cup-shaped
structure
where ultra-
filtration
occurs

34. The Kidney Nephron
ULTRAFILTRATION occurs in Bowman’s Capsule. Lots of
water plus all the smaller molecules are squeezed out of
the blood, under high pressure, into the tubules. Only red
blood cells and larger proteins are left in the capillary.

35. The Kidney Nephron
GLOMERULUS
– a coiled
capillary.
BOWMAN’S
CAPSULE – a
cup-shaped
structure
where ultra-
filtration
occurs
PROXIMAL CONVOLUTED TUBULE
– selective reabsorption occurs here
back into the blood.

36. The Kidney Nephron
Glucose, amino acids, vitamins and
water diffuse into the cells
surrounding the PCT, and are then
actively transported into
surrounding blood capillaries.

37. The Kidney Nephron
GLOMERULUS
– a coiled
capillary.
BOWMAN’S
CAPSULE – a
cup-shaped
structure
where ultra-
filtration
occurs
PROXIMAL CONVOLUTED TUBULE
– selective reabsorption occurs here
back into the blood.
LOOP OF HENLE –
(descending and
ascending) .

38. The Kidney Nephron
Adjustments are made to the urine
concentration if necessary, with
water and salts being transferred
according to the needs of the body

39. The Kidney Nephron
Adjustments are made to the urine
concentration if necessary, with
water and salts being transferred
according to the needs of the body
Permeable
to water

40. The Kidney Nephron
Adjustments are made to the urine
concentration if necessary, with
water and salts being transferred
according to the needs of the body
impermeable
to water

41. The Kidney Nephron
GLOMERULUS
– a coiled
capillary.
BOWMAN’S
CAPSULE – a
cup-shaped
structure
where ultra-
filtration
occurs
PROXIMAL CONVOLUTED TUBULE
– selective reabsorption occurs here
back into the blood.
LOOP OF HENLE –
(descending and
ascending) .
DISTAL
CONVOLUTED
TUBULE – final
adjustments to the
urine.

42. The Kidney Nephron
In the DCT, the final concentration
of the urine depends upon the
amount of anti-diuretic hormone
(ADH). If ADH is present then the
DCT becomes permeable to water,
and more water is reabsorbed back
into the blood

43. The Kidney Nephron
GLOMERULUS
– a coiled
capillary.
BOWMAN’S
CAPSULE – a
cup-shaped
structure
where ultra-
filtration
occurs
PROXIMAL CONVOLUTED TUBULE
– selective reabsorption occurs here
back into the blood.
LOOP OF HENLE –
(descending and
ascending) .
DISTAL
CONVOLUTED
TUBULE – final
adjustments to the
urine.
COLLECTING DUCT –
takes urine to the
ureter and on to the
bladder

44. The Kidney Nephron
The collecting duct is also under
the influence of ADH, and further
water / salt re-adjustments will
take place here.

45. The Kidney Nephron
The collecting duct is also under
the influence of ADH, and further
water / salt re-adjustments will
take place here.
Excess water, ions and all the urea now pass to the bladder
in the form of urine and are eventually released from the
body.

46. ADH and the control of water content

47. ADH and the control of water content
Anti-diuretic hormone
(ADH) is a hormone
released from the
pituitary gland in the
brain. It controls the
amount of water
reabsorbed by the
kidneys and directly
affects the
permeability of the
kidney tubules to water

48. ADH and the control of water content
Blood
water
level TOO
HIGH
Detected
by
Pituitary
Gland
Less ADH
released
into the
blood
Less water
reabsorbed
into the
blood
Large
volume of
dilute
urine
Normal
blood
water
level

49. ADH and the control of water content
Blood
water
level TOO
HIGH
Detected
by
Pituitary
Gland
Less ADH
released
into the
blood
Less water
reabsorbed
into the
blood
Large
volume of
dilute
urine
Normal
blood
water
level
Blood
water
level TOO
LOW
Small volume
of
concentrated
urine
More water
reabsorbed
into the
blood
More ADH
released
into the
blood
Detected
by
Pituitary
Gland

50. Composition of blood plasma and
urine
Blood plasma % Urine %
Water 90 – 93 95
Urea 0.03 2
Uric acid 0.003 0.05
Ammonia 0.0001 0.05
Sodium 0.3 0.6
Potassium 0.02 0.15
Chloride 0.37 0.6
Phosphate 0.003 0.12
In a healthy person, all glucose will be reabsorbed back into the
blood. If glucose is found in the blood then this is indicative of
diabetes, a metabolic disease.

51. Content
Lesson 6
i) Excretion
i) Excretion
Flowering plants
2.67 understand the origin of carbon dioxide and oxygen as waste
products of metabolism and their loss from the stomata of a leaf
Humans
2.68 recall that the lungs, kidneys and skin are organs of excretion
2.69 understand how the kidney carries out its roles of excretion
and osmoregulation
2.70 describe the structure of the urinary system, including the
kidneys, ureters, bladder and urethra
2.71 describe the structure of a nephron, to include Bowman’s
capsule and glomerulus, convoluted tubules, loop of Henlé and
collecting duct
2.72 describe ultrafiltration in the Bowman’s capsule and the
composition of the glomerular filtrate
2.73 understand that water is reabsorbed into the blood from the
collecting duct
2.74 understand that selective reabsorption of glucose occurs at
the proximal convoluted tubule
2.75 describe the role of ADH in regulating the water content of
the blood
2.76 understand that urine contains water, urea and salts.

52. End of Section 2 Lesson 6
In this lesson we have covered:
Excretion