10. Excretion
#97 Structure of the kidney, the nephron
Excretion is the removal from organisms of toxic
materials, the waste products of metabolism
and substances in excess of requirements (carbon
dioxide, urea, salts…).
Common misconceptions
Remember that faeces is not an example of excretion – it
is mainly undigested material that has passed through the
gut, but which has not been made in the body. The only
excretory materials in it are bile pigments.
The relative position of the ureters, bladder and urethra in the body
Examiner’s tip
Make sure you can label the diagram showing the relative positions of the
kidneys, ureters, bladder and urethra. The spellings of
the ureter and urethra are really important.
, Structure of a kidney
The kidney has 3 main parts:
the cortex,
medulla, and pelvis. Leading
form the pelvis is a tube, called
the ureter. The ureter carries
urine that the kidney has made to
the bladder.
Kidneys are made up of
thousands of tiny tubules,
or nephrons. Each nephron
begins in the cortex, loops down
into the medulla, back into the cortex, and then goes down again through
the medulla to the pelvis. In the pelvis, the nephrons join up with the ureter.
Sample question and answer
Figure on the right shows the human urinary system
a) Name parts X,Y and Z. [3 marks]
b) Name the blood vessel that carries blood from the
aorta to the kidneys. [1 mark]
c) Suggest two differences between the composition
of the blood flowing to the kidneys and the blood
flowing away from the kidneys. [2 marks]
Student’s answer
a) X ureta Y Bladder Z vagina
b) renal artery
c)1. Blood going to the kidneys contains more urea.
2. Blood going to the kidney contains oxygen.
Examiner’s comments
The spelling of X (ureter) must be accurate because this name is so similar
to urethra.
Part Z is the urethra, not the vagina (the vagina is attached to the uterus,
not the bladder).
In part (c) the second answer given does not make a comparison. If the
candidate had stated ‘blood going to the kidney contains more oxygen’, this
would have gained the mark.
#97 Structure of the kidney, the nephron
Excretion is the removal from organisms of toxic
materials, the waste products of metabolism
and substances in excess of requirements (carbon
dioxide, urea, salts…).
Common misconceptions
Remember that faeces is not an example of excretion – it
is mainly undigested material that has passed through the
gut, but which has not been made in the body. The only
excretory materials in it are bile pigments.
The relative position of the ureters, bladder and urethra in the body
Examiner’s tip
Make sure you can label the diagram showing the relative positions of the
kidneys, ureters, bladder and urethra. The spellings of
the ureter and urethra are really important.
, Structure of a kidney
The kidney has 3 main parts:
the cortex,
medulla, and pelvis. Leading
form the pelvis is a tube, called
the ureter. The ureter carries
urine that the kidney has made to
the bladder.
Kidneys are made up of
thousands of tiny tubules,
or nephrons. Each nephron
begins in the cortex, loops down
into the medulla, back into the cortex, and then goes down again through
the medulla to the pelvis. In the pelvis, the nephrons join up with the ureter.
Sample question and answer
Figure on the right shows the human urinary system
a) Name parts X,Y and Z. [3 marks]
b) Name the blood vessel that carries blood from the
aorta to the kidneys. [1 mark]
c) Suggest two differences between the composition
of the blood flowing to the kidneys and the blood
flowing away from the kidneys. [2 marks]
Student’s answer
a) X ureta Y Bladder Z vagina
b) renal artery
c)1. Blood going to the kidneys contains more urea.
2. Blood going to the kidney contains oxygen.
Examiner’s comments
The spelling of X (ureter) must be accurate because this name is so similar
to urethra.
Part Z is the urethra, not the vagina (the vagina is attached to the uterus,
not the bladder).
In part (c) the second answer given does not make a comparison. If the
candidate had stated ‘blood going to the kidney contains more oxygen’, this
would have gained the mark.
