Excretion in Humans (Cambridge (CIE) IGCSE Biology)
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Define the term excretion.
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Define the term excretion.
Excretion is the removal from the body of the waste products of metabolism, and any substances present in excess, e.g. excess salts
Which waste products of metabolism are excreted by the lungs?
The metabolic waste products excreted by the lungs are water and carbon dioxide, both produced during respiration.
True or False?
The kidneys excrete urea, excess water and carbon dioxide.
False.
The kidneys excrete urea, excess water and ions.
Carbon dioxide is excreted via the lungs.
What are the structures labelled A-D in the diagram?
Structures A-D are:
A = kidney
B = ureter
C = bladder
D = urethra
What is the role of the bladder in the urinary system?
The role of the bladder is to store urine that is produced by the kidneys.
True or False?
The ureter carries urine from the bladder to the exterior of the body.
False.
The urethra carries urine from the bladder to the exterior of the body. The ureters are a pair of tubes that connect the kidneys to the bladder
What are the kidney regions indicated by labels X and Y? (Extended Tier Only)
The kidney regions are:
X = medulla
Y = cortex
Define the term nephron. (Extended Tier Only)
Nephrons are tiny tubes found in the kidney. Each kidney contains many nephrons, the role of which is to produce urine.
True or False?
The Bowman's capsule of each nephron surrounds a glomerulus. (Extended Tier Only)
True.
The Bowman's capsule directly surround the glomerulus, a ball of blood vessels from which the blood filters into the nephron.
Where in the kidney nephron does filtration occur? (Extended Tier Only)
Filtration, or ultrafiltration occurs between the glomerulus and the Bowman's capsule.
Name the substances that are forced out of the capillaries during filtration. (Extended Tier Only)
Substances that are forced out of the capillaries during ultrafiltration are:
Glucose
Water
Urea
Salts
These molecules form the glomerular filtrate.
True or False?
All of the substances filtered by the glomerulus are reabsorbed into the blood further along the nephron. (Extended Tier Only)
False.
Substances that are reabsorbed further along the nephron include:
all of the glucose
some of the ions
most of the water
Urea and excess substances are not reabsorbed.
Which components of the kidney filtrate are normally found in urine? (Extended Tier Only)
Components of the kidney filtrate are normally found in urine are:
urea
excess water
excess ions
How does the liver enable assimilation of amino acids? (Extended Tier Only)
The liver enables assimilation of amino acids by building them into new proteins which can then be used by the body.
How is urea formed? (Extended Tier Only)
Urea is formed from excess amino acids.
This involves the following:
the nitrogen-containing part of amino acids is removed
the removed chemicals are converted into ammonia and then into urea
True or False?
Urea is produced in the kidneys. (Extended Tier Only)
False.
Urea is produced in the liver.
The kidneys filter the urea, causing it to be excreted.
Define the term deamination. (Extended Tier Only)
Deamination is the removal of the nitrogen-containing part of amino acids to form urea.
Why does urea need to be excreted? (Extended Tier Only)
Urea needs to be excreted because it is toxic at high concentrations.