Excretion Flashcards
What are the main needs of terrestrial animals?
Need to obtain water
Need to avoid desiccation
Body surfaces are never totally impermeable thus will suffer continuous water loss
What is a terrestrial animal’s total input?
Food and drinks
What is a terrestrial animal’s total output?
Lungs and skin
Urine and faeces
Salt glands
What is a terrestrial animal’s obligatory output?
Lungs and skin
What is a terrestrial animal’s regulatory output?
Urine, faeces, and salt glands
What is the terrestrial animal’s primary regulatory organ?
Kidneys
How do terrestrial animals gain water?
Drinking
Uptake via body surfaces
Water available in food
Metabolic water production
Respiration equation
C6H12O6 + 6O2 → 6CO2 + 6H2O
What does ammonotelic mean?
An organism that excretes nitrogenous waste in the form of ammonia
What does ureotelic mean?
An organism that excretes nitrogen in the form of urea
What does uricotelic mean?
An organism that excretes nitrogen as uric acid or its salts
Describe the properties of ammonia
Cheap, soluble, toxic
Excreted by diffusion in water
Takes 0.5L of water to excrete 1g of nitrogen
Describe the properties of urea
Expensive, less soluble, less toxic
Takes energy to make
Takes 0.05L of water to excrete 1g of nitrogen
Describe the properties of uric acid
Very expensive, not soluble, can be stored
Takes lots of energy to make
Takes 0.001L of water to excrete 1g of nitrogen
What is the main factor that determines the nature of nitrogen excretion?
Water availability
How do terrestrial birds excrete nitrogen?
90% is as uric acid
How do ducks excrete nitrogen?
50% as uric acid and 30% as ammonia
How do tadpoles excrete nitrogen?
As ammonia
How do frogs excrete nitrogen?
As urea
How do annelids produce and excrete urine?
Coelomic fluid enters the metanephridium through a nephrostome
The tubule cells of the metanephridium alter the composition of the coelomic fluid
This produces a dilute urine that is excreted through the nephridopore
How do insects produce and excrete urine?
Uric acid, Na+ and K+ are transported into the Malpighian tubules and water follows
Na+ and K+ are actively transported from the hindgut and rectum back to the coelomic fluid and water follows
Uric acid precipitates in the rectum and is secreted
What are the main functions of the kidneys?
Ion balance Osmotic balance Blood pressure maintenance pH balance Excretion Hormone production
How much does a kidney weigh?
1% of body weight
How much glomerular filtrate does the kidney see a day?
200L
How much urine does the kidney produce per day?
1-2L
What is the blood pressure in the glomerulus?
5kPa
How much water and Na+ and glucose is reabsorbed in the proximal tubule?
75% water
Most Na+
All glucose
What are the 3 stages of urine formation?
Filtration
Absorption
Secretion
What is the purpose of the loops of Henle?
Allows urine to be more concentrated than blood
The ability to concentrate urine is related to the length of the loops of Henle
Describe how the loops of Henle work
NaCl is transported- inside fluid is more dilute and outside is more concentrated
Water moves out via osmosis through water-permeable walls
Urea diffuses out where the walls are permeable to it
This raises the osmotic concentration outside the tubule
This causes water to move out
NaCl is drawn out by its concentration gradient
