Lecture 20: Excretion & Osmoregulation Flashcards
What are the 4 excretory/osmoregulatory structures?
- Protonephridia
- Metanephridia
- Malpighian tubules
- vertebrate nephron
define osmoregulation
The process by which animals control solute concentration and balance water gain and loss
This process is what allows animals to maintain an internal environment that differs from the external environment (in terms of chemical concentrations)
Why does the movement of solutes between the internal and external environment affect the movement of water?
Water spontaneously (passively) moves from areas of LOW [solute] –> HIGH [solute] by OSMOSIS
therefore, solvent movement will be followed by water movement
define osmoconformer and give an example
Osmoconformers are organisms that are ISO-OSMOTIC, meaning they have the same overall solute concentration as their surrounding environments.
Example: Cnidarians
What osmoregulatory problems do marine bony fish face? How do they overcome this challenge?
Marine fish LOSE water to the environment by OSMOSIS because they are HYPO-osmotic compared to the surrounding ocean water (they have lower salinity inside than the ocean)
a concentration gradient must be maintained because they lose water to their environment
ocean water and the food they consume have a high salt concentration, ions diffuse in through gills too and they must drink the salt water so they are taking in a LOT of salt
SOLUTIONS:
to maintain an internal ion concentration that is LOWER than the seawater…
- active transport of ions out through gills
- EXCRETION –> produce concentrated urine to remove ions with minimal water loss (small amount of urine too)
What osmoregulatory problems do freshwater bony fish face? How do they overcome these challenges?
Freshwater fish are HYPERosmotic in comparison to their environment (they have a higher [salt] than the water) so they have too much water diffusing in and too many ions diffusing out of gills
SOLUTIONS:
- active transport IN from the environment through the gills to replace lost ions
- EXCRETION: large amounts of diluted urine to get rid of nitrogenous waste and excess water
- they don’t drink water
T or F: osmotic refers to the overall solute differences between cells and their environments
TRUE
Define Osmoregulator - give examples of both kinds
Osmoregulators are organisms that are either:
HYPERosmotic: meaning they maintain a higher solute concentration than their surrounding environment
ex. fresh water fish
or
HYPOosmotic: meaning they maintain a lower solute concentration than their surrounding environment
ex. marine fish
Define Osmoregulator - give examples of both kinds
Osmoregulators are organisms that are either:
HYPERosmotic: meaning they maintain a higher solute concentration than their surrounding environment
ex. fresh water fish
or
HYPOosmotic: meaning they maintain a lower solute concentration than their surrounding environment
ex. marine fish
What is an advantage and a disadvantage of being an osmoconformer?
Advantage: lower energy requirements because they don’t have to invest any energy in maintaining a concentration balance
Disadvantage: internal solute concentration fluctuates with the external environment which can make them very vulnerable to changes in the environment
What is an advantage and a disadvantage of being an osmoconformer?
Advantage: lower energy requirements because they don’t have to invest any energy in maintaining a concentration balance
Disadvantage: internal solute concentration fluctuates with the external environment which can make them very vulnerable to changes in the environment
T or F: most marine invertebrates are osmoconformers. why/why not?
TRUE because most marine invertebrates live in stable conditions in shallow or deep waters with little changes in salinity
What challenges do intertidal species face as osmoconformers?
must deal with extreme DAILY changes in salinity and moisture conditions
tide in: organisms under water, temperature cooler, salinity lower
tide out: organisms exposed to air or shallow tide pools, temperature increases, salinity increases
What challenges do intertidal species face as osmoconformers?
must deal with extreme DAILY changes in salinity and moisture conditions
tide in: organisms under water, temperature cooler, salinity lower
tide out: organisms exposed to air or shallow tide pools, temperature increases, salinity increases
T or F: Osmoregulators live in ALL terrestrial and aquatic environments
TRUE! pretty much everything else that isn’t an aquatic invertebrate is an osmoregulator
T or F: Osmoregulators live in ALL terrestrial and aquatic environments
TRUE! pretty much everything else that isn’t an aquatic invertebrate is an osmoregulator
Advantage and disadvantage of being an osmoregulator
Advantage: they can maintain an ideal chemical environment to support cell function and are not as vulnerable to environmental changes
Disadvantage: requires significant energy to maintain a different internal environment
Advantage and disadvantage of being an osmoregulator
Advantage: they can maintain an ideal chemical environment to support cell function and are not as vulnerable to environmental changes
Disadvantage: requires significant energy to maintain a different internal environment because they must constantly adjust the levels of both ions and water in their bodies using ACTIVE transport
Where does most of the water loss occur in marine fish?
mostly across the gills (ventilation surface) because it is only a few cell layers thick so diffusion is easy
some lost across skin, but there are mechanisms to minimize this loss
Where does most of the water loss occur in marine fish?
mostly across the gills (ventilation surface) because it is only a few cell layers thick so diffusion is easy
some lost across skin, but there are mechanisms to minimize this loss
Define diadromous fish and give an example. Explain their osmotic challenges
Diadromous fish spend part of their life in fresh water and part of their life in salt water
Ex. sockeye salmon
their osmoregulatory apparatus undergoes physiological and anatomical rearrangement
Define diadromous fish and give an example. Explain their osmotic challenges
Diadromous fish spend part of their life in fresh water and part of their life in salt water
Ex. sockeye salmon
their osmoregulatory apparatus undergoes physiological and anatomical rearrangement
In terms of osmoregulation, the terrestrial environment is most like: A) marine B) freshwater C) neither Why?
MARINE!
because on land, water is lost by evaporation; in saltwater, water is lost by osmosis
either way, water is lost, just by a different mechanism
What are the osmotic challenges for land animals?
WATER LOSS is the main osmotic challenge faced by animals on land and it can be lost through:
- evaporation from skin (sweat) and respiratory surfaces
- digestion (some water is reclaimed during feces formation)
- excretion (production of urine)
What are some adaptations land animals (including: insects, vertebrates, desert animals) have developed in order to overcome the osmotic challenges they face?
to reduce water loss…
INSECTS: have an exoskeleton with a waxy cuticle that prevents water loss from evaporation
VERTEBRATES: have layers of dead skin cells
DESERT ANIMALS: have specialized adaptations that vary, but most are only active at night
2 ways land animals obtain water?
drinking and eating moist foods
it is a byproduct of cellular respiration
Define excretion
the process by which nitrogenous wastes are removed from the body (typically in water)
Define nitrogenous wastes
N. wastes are formed during digestion of proteins and DNA/RNA because these molecules contain more nitrogen than most organisms need
T or F: excess nitrogen can become toxic
TRUE
What are the 3 forms of nitrogenous waste?
- Ammonia
- Urea
- Uric acid
What is the toxicity, water solubility, and energetic cost of AMMONIA?
Toxicity: High even at low concentrations
Solubility: soluble
Energetic cost: low
What is the toxicity, water solubility, and energetic cost of UREA?
Toxicity: low
Solubility: soluble
Energetic cost: High
What is the toxicity, water solubility, and energetic cost of URIC ACID?
Toxicity: low
Solubility: not soluble (it is a semi-solid paste)
Energetic cost: VERY high
Which vertebrate excretes nitrogenous waste in the form of AMMONIA? why?
Fish (freshwater or marine) because they live in an aquatic environment and ammonia is very soluble
T or F: Ammonia toxic and to be excreted it must be heavily diluted in water?
TRUE
How do animals that excrete ammonia do so?
Fish diffuse ammonia out gills and some marine fish produce small amounts of urea.
Amphibian tadpoles excrete ammonia
Cnidarians and platyhelminthes diffuse ammonia directly across body surface
Which 4 animals excrete nitrogenous waste as ammonia?
Most fish
Immature amphibians
cnidarians
platyhelminthes
AQUATIC ANIMALS*
Advantages and disadvantages of excreting nitrogen waste as ammonia?
Advantages:
- requires less energy to produce than urea or uric acid
Disadvantages:
- it is highly toxic even at low concentrations so it has to be diluted in a LOT of water
- therefore, it is only practical for aquatic animals
Which two animals excrete nitrogen waste as urea in the form of urine?
Mammals and adult amphibians
What are the advantages and disadvantages of excreting nitrogen waste as urea?
ADV:
- it can be stored at high concentrations and transported through blood because it has low toxicity (which is good because they have less access to water)
- requires LESS WATER than ammonia so animals can survive much longer on land without having to take in as much water
DIS:
- uses more energy than ammonia
- requires more water than uric acid
Which 3 animals excrete nitrogen waste as uric acid?
Insects, land snails, and most reptiles (including birds)
Advantages and disadvantages of excreting nitrogen waste as uric acid?
ADV:
- it is non-soluble, so it reduces water loss on land and it isn’t transported out of the body as urine (with water) it comes out with feces
- stores as a harmless solid inside amniotic egg
DIS:
- it is the most energetically expensive waste type
Define excretory systems
Systems that dispose of metabolic wastes and help with osmoregulation
excretory systems can vary among invertebrate and vertebrate animals but typically include:
networks of tubules composed of tissues specialized for transport
What is the transport epithelium?
a specialized tissue lining secretory tubules of excretory systems to MAXIMIZE THE RATE OF REABSORPTION of materials from the filtrate back into the circulatory fluid
arranged in a network of tubules to maximize surface area of diffusion
What are the 4 steps of the excretory process? briefly describe each
- Filtration: circulatory fluid (hemolymph or blood) filtered into excretory tubule
- Reabsorption: useful molecules reabsorbed into the circulatory fluid
- Secretion: non-essential solutes and wastes secreted into the tubules and into the filtrate
- Excretion: processed filtrate released from body as urine
What are the 4 different excretory systems in animals? and which animals have which one?
- Protonephridia: Platyhelminthes, larval molluscs
- Metanephridia: in Annelida, most adult molluscs
- Malpighian tubules: insects and other arthropods
- Nephrons in vertebrates
Describe the structure and function of the Protonephridia excretory system. which animals have this?
this system is composed of NETWORKS OF TUBULES that terminate in FLAME BULBS
- the cells at the blind end of the tubule (flame bulbs) are ciliated and are able to draw water and solutes from interstitial fluid into the tubule network
- filtrate moves through the tubule network and leaves body as AMMONIA through openings in the body wall
this network extends throughout the animal body and is not centralized; it is the simplest of systems.
ex. flatworms (platyhelminthes)
- in free-living flatworms, this system is used primarily for osmoregulation because AMMONIA can diffuse directly across the body wall
Describe the structure and function of the Metanephridia excretory system. which animals have this? what is metanephridia?
this system collects fluids directly from the coelom (body cavity)
- each body segment has a pair of METANEPHRIDIA that is surrounded by a capillary network (only in closed circulatory systems) where the fluids can exchange with the tubules and the capillaries
METANEPHRIDIA: two exits into the external environment
- cilia beat and pull fluid into internal opening of tubules (there are no flame bulbs, the tubules are either open to the outside of the body or have an internal opening to the coelom)
- transport epithelia REABSORB most solutes and return them to the blood and secrete wastes into the tubules
- urine is released out through pores opening to external environment
- filtrate concentrates more as solute transferred from blood to excretory tubules
ex. Annelids
Describe the structure and function of the Malpighian tubules excretory system. which animals have this?
A system used for excretion and osmoregulation.
In this system, there is no filtration step.
- waste products are secreted directly from hemolymph into blind ended tubular extensions into the gut–> URIC ACID is the waste product that is excreted with feces
- water ions and useful molecules are reabsorbed into the hemolymph by osmosis across the lining of the rectum
- all things secreted into the malpighian tubules are moved into the gut and excreted with feces
ex. Insects and other arthropods
What are the major differences between the invertebrate excretory systems?
Protonephridia:
- excretory tubules open only at one end to external environment
- concentrated filtrate that enters tubules, not a body fluid
Metanephridia:
- tubules open at both ends
- coelomic fluid enters tubules
- reabsorption of useful molecules into capillaries
Malpighian tubules:
- closed end immersed in hemolymph
- tubules open into gut – uric acid mixed in with feces
- rectum wall reabsorbs water
