Physiology 6: Waste Flashcards
What generates nitrogenous waste?
Breakdown of proteins and nucleic acids
- In digestive system
- For energy / conversion to fats / carbs
- Amino group (NH2) is removed
Why do we need to get rid of nitrogenous waste?
amino groups react with water to form ammonia
- Ammonia is highly toxic
- Ammonia raised pH of bodliy fluids
= inhibits key enzymes
How do organisms get rid of nitrogenous waste? (3 ways)
- Immediately, as ammonia: easy to do in aquatic environments
- Convert to urea
- Convert to uric acid
Describe why some organisms get rid of nitrogenous waste as ammonia
Doesn’t require energy to get rid of
Small molecule → rapid diffusion in aquatic environments
Highly soluble in water (need a high vol to get rid of effectively)
Which organisms excrete ammonia?
most bony fishes, aquatic life stages of amphibians, aquatic invertebrates
Describe urea (5)
- Urea produced in the liver
- Produced from Ammonia and Co2
- 1000x less toxic than ammonia
- Less soluble than ammonia, so requires less water to get rid of it
- Requires energy to make
which organisms excrete urea?
mammals, most amphibians, cartilaginous fish
How do elasmobranchs use urea to their advantage?
- They’re osmoconformers
- They use urea to maintain bodily fluids:
When urea (non toxic) stored in tissue, increases osmolarity of body fluids
= Elasmobranchs use this to make them isosmotic to salt water around them
Describe uric acid
- Larger molecule, semi-solid
- Insoluble (compared to urea and ammonia)
- Even less toxic than urea (can be stored for a long time and doesn’t affect pH)
- Excretes as a semi-solid → conserves water
- Requires 3x the amount of energy to make as urea
Which organisms excrete uric acid?
birds, reptiles, insects and some amphibians
Why is uric acids storing capabilities useful for some organisms?
Storing capabilities make it useful in egg development:
Egg is closed = unable to gain more water
Uric acid can build up inside without being toxic
Even urea would build up to toxic conc.s
Give some examples of how habitat is important in excreting nitrogenous waste
Terrestrial tortoises excrete uric acid (dry environ so limits water loss)
But, aquatic turtles excrete urea and ammonia (access to lots of water)
African lungfish can switch:
in mud during dry season excretes urea
in water during rainy season excretes ammonia
What is the nephrida
Excretory organ in annelid worms, molluscs, platyhelminthes
Describe how the nephrida functions
Nephrostome (ciliated funnel end) pumps water, ions & nitrogenous waste into highly vascularised tube (surrounded by capillaries)
Water reabsorbed from tube
Waste exits body through nephridiopore
What are malpighian tubes?
Excretory organ in insects
Tubules blind ended and open up into gut