FLOWERING PLANTS (2.67)
2.67 – Understand the origin of carbon dioxide and oxygen as waste products of
metabolism and their loss from the stomata of a leaf.
– Carbon dioxide and oxygen are waste products of metabolism.
• Carbon dioxide is a waste product of respiration.
• Oxygen is a waste product of photosynthesis.
– Carbon dioxide and oxygen are lost through the stomata of a leaf.
HUMANS (2.68 – 2.76)
2.68 – Recall that the lungs, kidneys and skin are organs of excretion.
– The lungs, kidneys and skin are organs of excretion.
• The lungs excrete carbon dioxide.
• The kidneys excrete excess water, urea and salts.
• The skin excretes water and salts.
2.69 – Understand how the kidney carries out its roles of excretion and osmoregulation.
– Excretion: The removal of waste products from the body.
• Amino acids contain nitrogen which is toxic to the body.
• The liver converts the nitrogen to urea.
• The kidneys filter urea from the bloodstream and dissolve it in water to create urine.
• Urine moves through the ureter into the bladder and is excreted through the urethra.
– Osmoregulation: Maintaining the optimum salt and water levels in the blood.
• ADH (anti-diuretic hormone) is released from the pituitary gland.
• ADH makes the collecting duct more permeable.
• Different amounts of ADH is released depending on the water levels in the blood
(see 2.75).
2.70 – Describe the structure of the urinary system, including the kidneys, ureters,
bladder and urethra.
– Kidneys remove waste products from the blood.
– The ureter is a long tube that carries urine from the kidney to the bladder.
– The bladder is a hollow elastic sac that stores urine.
– The urethra transports urine out of the body.
2.71 – Describe the structure of a nephron, to include Bowman’s capsule and
glomerulus, convoluted tubules, loop of Henlé and collecting duct.
– Nephron: Microscopic tubular filtration units found in the kidney.
• Blood enters the glomerulus in the Bowman’s capsule. Blood is filtered to create
a filtrate of water, glucose, salts and urea [glomerular filtrate].
• The filtrate travels through the proximal convoluted tubule where glucose is
selectively reabsorbed into the blood.
• The filtrate travels through the Loop of Henlé where water and sodium chloride is
reabsorbed into the blood.
• The filtrate travels through the distal convoluted tubule and into the collecting duct
where water is reabsorbed depending on its permeability caused by ADH.
• The remaining substances (urea and water) in the filtrate travel down the ureter into
the bladder and are excreted via the urethra.
2.72 – Describe ultrafiltration in the Bowman’s capsule and the composition of the
glomerular filtrate.
– Ultrafiltration: The separation of different-sized molecules by pressure.
• Pressure in the glomerulus is high, which forces the smaller components of the
blood into the Bowman’s capsule.
• Substances filtered into the Bowman’s capsule form the glomerular filtrate: water,
salt, urea, glucose.
• Large molecules such as proteins cannot be filtered in.
2.73 – Understand that water is reabsorbed into the blood from the collecting duct.
– Water is reabsorbed into the blood from the collecting duct.
2.74 – Understand that selective reabsorption of glucose occurs at the proximal
convoluted tubule.
– Selective reabsorption: The reabsorption of specific substances in specific amounts.
– 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.
– ADH regulates water content in the blood.
– Abnormal water contents are detected by the hypothalamus in the brain. It sends a
signal to the pituitary gland, causing it to produce more or stop producing ADH.
Water
Content ADH Permeability of
Collecting Duct
Water
Reabsorbed Urine
Too High Less Less Less Large in amount and diluted (pale yellow).
Too Low More More More Small in amount and concentrated (very yellow).
2.76 – Understand that urine contains water, urea and salts.
– Urine contains water, urea and salts.