Biology 3A – wastes and water balance

Organisms need nutrients

Nutrients provide

• Energy for cellular and body activity eg movement, growth, active transport, etc

• Matter for building cell components and body structures eg cell membranes, enzymes, muscle, bone, etc

• Essential compounds eg cofactors, minerals, vitamins, for healthy functioning

Organisms produce wastes

The wastes produced depend on diet:Carbohydrates are broken down into carbon

dioxide and waterFats are broken down into carbon dioxide and

waterProteins are broken down into carbohydrates

and ammoniaThe greater the amount of protein in the diet,

the more ammonia produced

Wastes depend on lifestyle

Herbivores eat plant material and produce small amounts of nitrogenous wastes

Carnivores eat meat and produce large amounts of nitrogenous wastes

Nitrogenous wastes

These come from the breakdown of

In deamination the amine group is removed

The carbohydrate is then used for energy or stored

The amine group turns into ammonia which can be excreted or turned into urea or uric acid

Carbohydrate

Amine group

Terminology

• Toxicity – how poisonous a substance is

The greater the toxicity, the faster wastes must be removed

Solubility – how easily substance dissolves

The greater the solubility, the more water is needed for removal

Comparing nitrogenous wastesAmmonia Uric acid Urea

Toxicity

Solubility

Water use

Energy use

Advantages

Disadvantages

Examples

Comparing nitrogenous wastesAmmonia Uric acid Urea

Toxicity High Low MediumSolubility High Low Medium

Water use High Low MediumEnergy use Low High MediumAdvantages Less energy

neededLess water needed, less toxic than ammonia

Easier to remove from placenta, less toxic than ammonia

Disadvantages Very toxic, needs removal quickly, large water use

High energy use, can’t be used with a placenta

Moderate energy use, moderate water loss

Examples fish Birds & reptiles Mammals

Sharks

Removing wastes

Aquatic organisms excrete wastes from gills and kidneys into the water surrounding them. Most waste is lost from the gills

Land organisms excrete wastes from respiratory surfaces (lungs) and kidneys.

Most waste is lost from the kidneys

The kidneycortex

capsule

medulla

Renal artery

Renal vein

pelvis

ureter

The nephron

Functions of nephron

• Filtration sieving or separation by passing through small pores

• Reabsorption retrieval or taking substances back from the nephron into the blood, so essential substances are not lost

• Secretion throwing away or placing substances from the blood into the nephron to get rid of wastes

How the nephron works

Differences between nephrons

Freshwater animals

• Freshwater organisms must cope with a hypotonic (less salty) environment

• Water constantly enters and salts leave• Freshwater organisms must constantly

remove excess water and actively bring in salts

• The nitrogenous waste is ammonia• Most of the nitrogenous wastes leave from

the gills

Dealing with freshwater• In freshwater fish filtration occurs at the

glomerulus

• Essential ingredients are reclaimed by the tubules

• The loop is reduced so little water is reabsorbed

• There is very little secretion

• The urine is dilute and copious

Saltwater organisms

• Marine organisms cope with a hypertonic (more salty) environment

• Osmoconformers eg jellyfish, sharks solve the problem by maintaining body fluids at the same concentration as seawater, by increasing salts (jellyfish) or other substances eg urea in sharks

• Osmoregulators eg bony fish, lose water continuously and gain salt

• The nitrogenous waste is ammonia

Dealing with salt water

• Because there is no reason to pump out large amounts of filtrate at the glomerulus, many bony fishes have small glomeruli and some have no glomeruli at all

• As they reduce filtration and reabsorption, marine bony fishes rely more on for eliminating excess or waste solutes

Osmotic challengesDescribe the osmotic challenge faced by each creature and describe how they solve the problems faced

Osmotic challenges 2

Marine invertebrates are osmoconformers – they maintain their body salt levels at the same concentration as their surroundings

Sharks are osmoconformers – they maintain high concentrations of urea so their osmotic pressure is the same as their surroundings

Freshwater fish have a higher salt concentration than their surroundingsThis means they constantly gain water and lose saltsThey maintain balance by ingesting salts, not drinking and producing large amounts of dilute urine

Saltwater fish have a lower salt concentration than their surroundingsThis means they constantly lose water and gain saltsThey maintain balance by secreting salts from gills and kidneys, constantly drinking and producing small amounts of concentrated urine

Osmoregulators Osmoconformers

Terrestrial organisms• The major problem is water availability

• Organisms can gain water by eating, drinking or metabolism (eg respiration, fat metabolism)

• Organisms can lose water by urine, faeces, respiratory surfaces (eg panting) and body surfaces (eg sweating)

Reptiles and birds

• Reptiles and birds excrete uric acid

• Uric acid is quite insoluble and so can be excreted using very little water

• This is useful in egg layers because it takes up very little space in the eggs

Adaptations in egg-layers

• Bird and reptile glomeruli are quite small, some reptiles have no glomeruli at all.

• Those with glomeruli filter just enough fluid to wash the uric acid, secreted by the tubules, into the cloaca. Most of this moisture is reabsorbed in the cloaca.

• Most reptiles don’t drink water. The water content of its diet plus the water produced by respiration is usually sufficient.

• Most birds drink a small amount fresh water. Marine birds often drink salt water and secrete salt from glands above the beak

Mammals

• All mammals excrete urea

• Urea requires much more water to be excreted than uric acid but less than ammonia

• Mammals produce large amounts of nephric filtrate but are able to reabsorb most of this in the tubules.

• The efficiency of reabsorption is related to the size of the medulla or length of loop

Adaptations in mammals

• Kangaroo rats can produce a urine 17 times more concentrated that its blood so it doesn’t drink water – getting water from its diet

• Camels can metabolise fat stored in their hump to produce water, so they don’t need to drink for days