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Flashcards in Waste Deck (32)
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How is nitrogenous waste generated?

Breakdown of proteins and nucleic acids. Amino group (NH2) is removed. Occurs in:
the digestive system
For energy or conversion to fats/carbohydrates –


Why does nitrogenous waste need o be removed from the body?

Because it forms a toxic ammonia, which raises the pH of body fluids and inhibits key enzymes


In what form is the nitrogenous waste excreted by most aquatic animals?

As ammonia


In what form is the nitrogenous waste excreted by mammals, amphibians and sharks?

As urea


In what form is the nitrogenous waste excreted by reptiles and birds?

As uric acid


What are the benefits of excreting ammonia?

Doesn't require energy, is a small molecule, so very rapid diffusion.


What is necessary for excteritian via ammonia?

Lots of water, as is very toxic and can only be tolerated at very low concentration


Where is urea produced?

In the liver, from ammonia and carbon dioxide


Why can't terrestrial animals excrete ammonia?

Because has to be stored in the body at low concentrations in large volumes of water, which most terrestrial animals don't have access to


What are the benefits of urea?

1000x less toxic than ammonia, can be transported in the circulatory system and stored safely at high concentration, Much less water is lost.


What are the costs of extortion by urea?

Requires energy


What is the benefits of exerting uric acid?

Relatively non toxic and insoluble in water, therefore can be excreted as a semisolid, paste with little water loss. Useful if developement takes place inside an egg


What are the costs of uric acid?

Even more energetically expensive than urea


How does habitat influence ammonia excretion in frogs?

Tadpoles excrete ammonia, but adults excrete urea


How do protozoa excrete waste?

Via a contractile vesicle


How so annelids, molluscs and Platyhelminthes etc excrete waste?

Via nephridia, a tubule open to the exterior, collecting tubules throughout the body lead to this


How do Insects excrete waste?

Malpighian tubules, spread throughout the body in the haemolymph and open into the insects hindgut for excretion


How do vertebrates excrete waste?

Via the kidneys. Consists of highly organised tubules that are closely associated with a network of capillaries


Why do insects excrete uric acid?

Have relatively high SA:V ratio, which means high rate of water loss, so uric acid excretion conserves water


What are the mechanisms of excretion in the Malpighian tubules?

Salts and nitrogenous waste actively transported into gut lumen, water follows by osmosis. Reabsorption occurs the rectum, H20, ions and valuable organic molecules pumped back into heamolymph. Water follows by osmosis
Uric acid is excreted as nearly dry matter in faeces


What happens during filtration in the kidneys?

Fluids in the blood are collected


What happens during reabsorption?

Selective transport of needed substances back to
tissue fluid/blood


What happens in the renal cortex?



What role of the renal medulla?

Regulate salt and water concentration in the blood


What is a nephron?

Consists of a single long table and a ball of capillaries called the glomerulus, Which is where the bowman capsule is effective


When does filtration occur?

As blood pressure forces fluid from the blood in the glomerulus into the lumen of the bowman's capsule. This is non selective filtration - all small molecules will pass through


Where does fluid travel after being filtered in the bowman's capsule?

To the proximal table, where water and salts are reabsorbed


What happens in the loop of hence?

Has a descending and ascending limb. In the descending limb, water leaves the filtrate which increases its osmolarity. In the ascending limb, salt leaves the filtrate, which decreases the osmolarity.


What does this reabsorption process mean for excretion?

Can produce hyper osmotic urine, where there is a much higher solute concentration than the body fluids


What is the counter current multiplier system?

Tubule fluid in descending limb flows in opposite direction from ascending limb, which means there is a steep osmotic gradient. Loops increase solute potential of surrounding tissue fluid setting up a concentration gradient