Osmoregulation and Excretion

Question 1

What is homeostasis?

Answer 1

Homeostasis – maintaining a healthy internal environment

» eg thermoregulation: maintaining body temperature by balancing heat loss and gain

Question 2

What, other than homeostasis, do animals need to regulate?

Answer 2

Animals also need to regulate chemical composition of body fluids by balancing uptake and loss of chemicals and fluids

Question 3

What is Osmoregulation?

Answer 3

Active control of the movement of solutes between internal fluids and external environment
» Balances uptake and loss of water and solutes

Question 4

What is Osmosis

Answer 4

Cell membrane is permeable to water molecules (aquaporins), but generally impermeable to charged ions (require channels or pumps)

Question 5

What is Osmolarity?

Answer 5

Osmolarity = solute concentration
» Lower osmolarity = hypoosmostic (hypotonic)
» Higher osmolarity = hyperosmotic (hypertonic)
» Same osmolarity = isoosmotic (isotonic)

Question 6

How does osmolarity work?

Answer 6

Water moves from hypoosmotic side to hyperosmotic side until both sides have same osmolarity (isoosmotic)
» Osmolarity of human blood = 300 mOsm/L
» Osmolarity of seawater = 1,000 mOsm/L

Question 7

What are the two strategies of Osmoregulation?

Answer 7

» Osmoconformer → isoosmotic w/ environment

» Osmoregulator → control internal osmolarity independent of external environment

Question 8

Are marine invertebrates osmoconformers or osmoregulators?

Answer 8

Most marine inverts are osmoconformers
» Don’t need to control water movement
» Still need to control specific ion concentration
• eg Mg+ in seawater is 50 mM, but Mg+ in haemolymph of lobster is 9 mM

Question 9

Are marine vertebrates osmoconformers or osmoregulators?

Answer 9

Many marine vertebrates (and some inverts) are osmoregulators
» Big challenge -ocean is a strongly dehydrating environment
» Drink lots of seawater, then specifically eliminate salts through gills and kidneys

Question 10

What does mOsm stand for?

Answer 10

Milli-osmolarity

Question 11

Are fresh water animals osmoconformers or osmoregulators?

Answer 11

• Freshwater (≈0.05% salt) has very low osmolarity (≈1 mOsm/L) compared to blood (≈300 mOsm/L)
• All freshwater animals are osmoregulators
  » Must avoid excess gain of water (by osmosis) and loss of solutes (by diffusion)
  » Drink almost no water, excrete lots of it (in dilute urine)
  » Actively take up salts across gills and from diet

Question 12

Draw the Fresh vs. saltwater regulators diagram

Answer 12

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Question 13

What is the difference between Anadromous species and Catadromous species?

Answer 13

Some animals migrate between fresh and salt water habitats
» Anadromous: live in sea, spawn in fresh (eg salmon)
» Catadromous: live in fresh, spawn in sea (eg eels)

Question 14

What is a major osmoregulatory problem for land animals and what adaptions are key to their survival?

Answer 14

• Dehydration
• Adaptations are key
  » Physical adaptations, eg. impermeable outer layer to avoid water loss (waxy layers, shell, dead skin cells)
  » Behavioural adaptations (eg nocturnal)

Question 15

How do animals maintain their water balance?

Answer 15

» Drinking
» Eating moist food
» Producing water through
cellular respiration

Question 16

What is dessication?

Answer 16

Dessication (extreme dehydration) is lethal for most animals

» eg, humans: up to 12%; camels: up to 25%

Question 17

What do some animals do to avoid dessication when they don’t have access to water?

Answer 17

Some can go into inactive state and survive (“anhydrobiosis”)
» eg, tardigrade: up to 98%

Question 18

Albatross live on the ocean, drink seawater, how do they survive without fresh water?

Answer 18

• Specialised glands excrete salt

» Counter-current exchange

Question 19

What is excretion?

Answer 19

• Metabolic processes produce waste, which cannot be used by the organism (not poo, just stuff in our blood after we have digested the food that we have to filtre out), eg.
  » Cellular respiration produces CO2 and H2O
  » Biosynthesis and catabolism produces nitrogen compounds

Question 20

What is the general process of excretion and why do we need it?

Answer 20

• Most metabolic wastes are dissolved in water → excretion tightly linked to osmoregulation
• Need to eliminate that waste, lest it accumulates in tissues
• Most metabolic wastes are dissolved in water → excretion tightly linked to osmoregulation

Question 21

What does the amount and type of Nitrogenous wastes excreted depend on?

Answer 21

The animal’s evolutionary history, their habitat and especially how much water is availability

Question 22

What are the three types of nitrogenous waste?

Answer 22

Ammonia, Urea and Uric acid

Question 23

What animals produce ammonia?

Answer 23

Most aquatic animals including most bony fish

Question 24

What animals produce Urea?

Answer 24

Mammals, most amphibians, sharks and some bony fish

Question 25

What animals produce Uric acid?

Answer 25

Birds and many other reptiles, insects, land snails.

Question 26

What are the pro's and con's of Ammonia?

Answer 26

Pro's: - Small molecule, readily lost by diffusion across membranes Con's: - Toxic even at low concentration - Requires lots of water to excrete (≠ land animals)

Question 27

What are the pro's and con's of Urea?

Answer 27

Pro's - 100,000× less toxic than NH3 - Less water required for excretion than NH3 - Can be stored Con's - Energetically expensive to produce - Still requires some water (≠ desert, flying)

Question 28

What are the pro's and con's of Uric Acid?

Answer 28

Pro's - Even less toxic than urea - Excreted as a semi-solid paste, almost no water required Con's - Energetically very expensive to produce

Question 29

From lowest to highest, rank the toxicity, size, Amount of water needed to excrete and energy needed to produce for ammonia, urea and uric acid.

Answer 29

Toxicity: Uric Acid -> Urea - > Ammonia Size of Molecule: Ammonia -> Urea -> Uric Acid Amount of water needed to excrete: Uric Acid -> Urea -> Ammonia Energy needed to produce: Ammonia -> Urea -> Uric acid

Question 30

What are the different functions of the Excretory system?

Answer 30

- Filtration - Reabsorption - Secretion - Excretion

Question 31

Draw the stylised version of the excretory system

Answer 31

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Question 32

What happens in Filtration?

Answer 32

- The Excretory tubule collects a filtrate from the blood. - Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule.

Question 33

What happens in Reabsorption?

Answer 33

The transport epithelium reclaims valuable substances from the filtrate and returns them the body fluid.

Question 34

What happens in Secretion?

Answer 34

Other substances such as toxins and excess ions, are extracted from the body fluids and added to the contents of the excretory tubule.

Question 35

What happens in Excretion?

Answer 35

The altered filtrate (Urine) leaves the system and the body.

Question 36

How is a flatworms excretory system different to humans?

Answer 36

- Flatworms (Planaria) lack a coelom (body cavity) and have a system of protonephridia (Networks of dead end tubules connected to external opening) - Filtrate collected and emptied into surrounding environment

Question 37

What is a protonephridia excretory system?

Answer 37

Where there are networks of dead-end tubules connected to external opening to release the waste instead of one main excretory exit.

Question 38

How is a Earthworms excretory system different to humans?

Answer 38

- They have Metanephridia excretory organs (Each segment of an earthworm has this system) - Also osmoregulation » Nitrogenous waste excreted » Valuable solutes reabsorbed » Lots of water in environment (damp soil), so urine is dilute

Question 39

What do Metanephridia excretory organs do?

Answer 39

Collect fluid directly from the coelom and release into surrounding environment

Question 40

What kind of excretory system do insects have?

Answer 40

- Insects and terrestrial arthropods have Malpighian tubules » Remove nitrogenous wastes » Osmoregulation - Dead-end tips immersed into haemolymph open into digestive tract - Nitrogenous waste (mostly insoluble uric acid) excreted with faeces - Conserves lots of water

Question 41

How does excretion in Vertebrates work

Answer 41

- Specialised organ: Kidneys - Both excretion and osmoregulation - Network of tubules, counter-current exchange - Nitrogenous wastes excreted as urea - Collecting duct carries hyperosmotic urine → bladder » Except in birds, which have no bladder (weight saving) and produce uric acid

Question 42

What is so special about the kidneys?

Answer 42

≈10 cm long, on left and right side of body - Filter 1,000 - 2,000 L blood per day - Produce 180 L of urine per day - We excrete ≈1.5 L of urine per day, so kidneys reabsorb ≈99% of water!

Question 43

What are Kidney stones?

Answer 43

» Calcium salts accumulate and form a mass | » Caused intake of foods rich in oxalate (beets, nuts, spinach, rhubarb, chocolate)

Question 44

What is Renal failure?

Answer 44

» Nephrons are damaged (by infection, tumors, shock, toxic compounds etc) and cannot perform regulatory and excretory function » Requires dialysis • Removes waste and excess water from blood

Question 45

What is a Nephron?

Answer 45

Each of the functional units in the kidney, consisting of a glomerulus and its associated tubule, through which the glomerular filtrate passes before emerging as urine.

Question 46

What are soe unique adaptions in animals in their excretory sstems?

Answer 46

- Desert animals have very particularly long loop of Henle → maximise water reabsorption - Vertebrates that live in water have very short loop of Henle

Question 47

Draw the Nephron Organisation Diagram

Answer 47

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