MAB Part 3Water Balance

explain why the concentration of water in cells should be maintained within a narrow range for optimal function

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The Role of Water:

Water is essential for life.

Living organisms are composed of between 70 and 90% water.

Water is the solvent for all the metabolic reactions that occur in living cells.

It is the solvent in which most substances dissolve and is the transport medium for

distributing them.

Water takes part in many metabolic reactions and is formed as a product in many

others, including respiration.

Living cells work best in an ISOTONIC environment – one in which the solute

concentration is the same both inside and outside the cell.

It is critical for the proper functioning of these reactions that the amount and

concentration of water in the cell is kept constant.

Cells are very sensitive to changes in solute concentration and may lose or take in a

large amount of water by osmosis if the concentration in their external environment

changes too much.

Living organisms try to ensure the water balance is maintained in their cells and the

concentration of solutes is kept constant so that the cells can function properly.

In mammals such as humans, living cells are kept isotonic to the interstitial fluid that

bathes the cells.

Water balance in cells

Therefore it is critical for the proper functioning of metabolic reactions that the amount and concentration of water in a cell is kept constant. Most cells die when water content is changed significantly.

explain why the removal of wastes is essential for continued metabolic activity

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Metabolic wastes are the product of metabolism. They are constantly being formed

in cells as a result of metabolic processes.

If they are allowed to accumulate in cells and tissues and not removed their

concentration in the cell increases and this inhibits the reactions that produce them

i.e. slows down metabolism and poison the cells.

Metabolic wastes particularly nitrogenous wastes are the by-products of the

breakdown of proteins and nucleic acids and are toxic to cells and must be

removed quickly.

Ammonia is the nitrogenous waste product of protein metabolism, it is highly toxic

and needs to be either removed quickly or converted to a less harmful form.

Nitrogenous wastes have the ability to change pH levels in cells and interfere with

membrane transport functions and may denature proteins.

Different Animals Secrete Different Waste Products:

A. Aquatic animals, fish and invertebrates mostly excrete ammonia.

B. Terrestrial animals excrete nitrogenous waste as either urea or uric acid.

There is a correlation between the type of waste produced and the animal’s

environment.

Aquatic animals like fish and invertebrates mostly excrete ammonia. This is toxic

but can be released continuously and directly into water and quickly dispersed.

On land, animals usually need to conserve water. So by converting it into less toxic

forms, they can hold it for longer in the body and release it periodically.

The waste is either excreted as urea (e.g. humans) or uric acid (e.g. insects).

a) Urea is soluble (dissolves) and is released in urine.

Urea is toxic but 10,000 times less toxic than ammonia therefore can be

stored in a more concentrated solution so requires less water to remove

than ammonia.

It can be safely stored in the body for a limited time.

The concentration of urine varies according to the regulation of water

within an animal’s body.

Mammals excrete urea. It is also the waste product of adult amphibians,

sharks and some bony fish.

Some animals – particularly desert dwelling mammals, can produce small

amounts of highly concentrated urine.

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b) Uric acid is almost insoluble and non-toxic.

Little water is expended to remove it. This is a great survival advantage.

It is often excreted by animals as a whitish paste. Many animals get rid of their

excretory products together with the faeces from digestion and in doing so loose

very little water.

Reptiles, birds and insects secrete uric acid.

Earthworms secrete both ammonia and urea.

Tadpoles excrete ammonia but as adult frogs they excrete urea.

c.) Ammonia

Very toxic and must be removed immediately either by diffusion or in very dilute

urine.

Excretory product of most aquatic animals, including many fish and tadpoles.

Ammonia is highly soluble in water and rapidly diffuses across the cell

membrane. However it needs large quantities of water to be constantly and safely

removed.

identify the role of the kidney in the excretory system of fish and mammals

The Role of the Kidney

The primary role of the Kidneys is osmoregulation. The kidney is an organ of

excretion of both fish and mammals. It plays a central role in homeostasis,

forming and excreting urine while regulating water and salt concentration of the

blood.

Excretion of all nitrogenous wastes mainly in the form of urine (humans).

Excretory System in Fish:

The role of the kidney in fish is dependent on the environment of the fish.

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In fish, excretion of nitrogenous waste products i.e. ammonia as NH , occurs

across the gills.

The kidneys adjust the levels of water and mineral ions in the fish’s body in order

to maintain a constant concentration of internal fluid for the cells.

Freshwater Fish

Fish (bony) living in freshwater are hypertonic to their surroundings.

Hypertonic – they maintain a higher concentration of solutes in their body than the

concentration of water outside.

Water therefore tends to diffuse into their bodies and so the fish need to continuously

get rid of the excess water.

Their kidneys produce copious amounts of very dilute urine in an almost

continuous stream in order to achieve this.

As the fresh water has a lower concentration of ions than the fish do they actively

reabsorb salts to prevent this loss.

Saltwater Fish

Bony salt water fish have the opposite problem.

Their internal body fluids are less concentrated (more dilute) than the surrounding

water. To avoid loss of water from their body they drink saltwater continuously,

They absorb the water and salts.

The water is retained and the salts are actively excreted, some via the gills and

some via the kidneys.

Saltwater bony fish excrete very little urine.

Marine cartilaginous fish (sharks and rays) have their tissues isotonic with the

seawater so that there is no net movement of water in or out. In this way they avoid

the osmoregulation problems of bony fish.

Osmoregulation in freshwater and saltwater fish.

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explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes in some organisms

Diffusion and osmosis are both examples of passive transport, relying on the

random movement of molecules. Diffusion is too slow for the normal functioning

of the body and does not select for useful solutes.

Osmosis only deals with the movement of water and thus would only allow water

to move out of the body not nitrogenous waste.

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distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney

Diffusion and osmosis are passive forms of transport that do not require the

expenditure of energy.

Diffusion and osmosis involve the movement of substances with the concentration

gradient – that is from where there are many particles to where there are few.

Movement of substances against a concentration gradient requires energy. This is

called active transport.

In the kidneys both forms of transport are use in the regulation of the body fluid

composition.

Passive transport occurs in filtration and the osmosis of water back into the blood.

Active transport occurs in the secretion of substances into the nephron, the active

transport of nutrients back into the blood and the selective reabsorption of salts

required by the body.

explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid composition

Main Function: the kidneys of mammals regulate the internal water and salt

concentrations in the body and excrete urea, the nitrogenous waste produced by

mammals.

Deamination:

Proteins are made up of amino acids. They are made used and broken down by

cell metabolism. However the body cannot store excess amino acids so any excess

becomes nitrogenous waste to be removed.

Deamination: This is the process by which excess amino acids are broken down in

the liver. This process involves removing the part containing nitrogen (the amino

group, -NH ) to form urea.

The remainder is converted to carbohydrate which may be stored (as glycogen) or

used immediately.

Urea is transported by the blood to the kidneys and excreted as urine.

The kidneys make urine. It is an organ of filtration, reabsorption and secretion.

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Kidney Structure

The kidneys are a pair of bean shaped organs found on either side of the abdomen.

Kidneys produce urine.

The main components of the mammalian urinary system can be seen in diagram 3

below. It is composed of two kidneys, two ureters, a bladder and the urethra.

Urine leaves the kidneys via the ureters and is stored in a muscular bag, the

bladder. The bladder expands as it fills with urine.

At a certain point this expansion stimulated nerve endings in the bladder which

send a message to the brain. The brain sends a message to the sphincter muscles

surrounding the base of the bladder which relaxes so urine can pass through the

urethra out of the body.

The mammalian urinary system

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The Internal Structure of the Kidney

Renal Artery: supplies the kidney with oxygenated blood. This blood also carries

the urea with it to the kidneys.

Renal vein: drains the blood from the kidneys and empties it into the inferior vena

cava.

Each kidney is made up of about one million small filtering units called

nephrons.

It is in these structures that urine is produced.

Each nephron is a convoluted tubule measuring up to 4.5 cm in length.

The nephrons are surrounded by a dense network of capillaries.

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Nephron is the basic structural and functional unit of the kidney.

Its chief function is to regulate the concentration of water and soluble substances

like sodium salts by filtering the blood, reabsorbing what is needed and excreting

the rest as urine.

A nephron eliminates wastes from the body, regulates blood volume and blood

pressure, controls levels of electrolytes and metabolites, and regulates blood pH.

Its functions are vital to life and are regulated by the endocrine system by

hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. In

humans, a normal kidney contains 800,000 to 1.5 million nephrons.

In the mammalian kidney:

1. Water re-absorption is a passive process.

2. Re-absorption of sodium salts is an active process

3. Glucose and amino acids are actively re-absorbed

4. Many drugs are selectively secreted by the kidney.

A nephron

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The starting point of a nephron is a Bowman’s capsule which is a small cup shaped

structure situated in the cortex. This leads into a narrow convoluted tubule that makes

a loop (the loop of Henle) in the medulla back up to the cortex and then joins with a

collecting duct. The collecting duct transports urine to the pelvis of the kidney which

leads to the ureter.

The Formation of Urine:

The kidneys continuously process a large volume of blood to form a small volume of urine.

This involves three processes: filtration, reabsorption and secretion.

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Filtration:

Blood is brought to the kidney by the renal artery. This divides into smaller

vessels which form a network of capillaries called a glamorous outside the

Bowman’s capsule.

The pressure is very high in the glomerulus and this causes some fluid to be

forced out through the walls of the blood vessels into the Bowman’s capsule. This

liquid consists of urea, glucose, amino acids, some hormones, vitamins, salts and

water (no plasma proteins or blood cells). Small soluble molecules pass through

by a process of passive filtration. This liquid is known as glomerular filtrate.

Filtration is a non- selective process. The filtrate contains some substances that

the body can re-use and some that are wastes.

They are all forced into the first part of the nephron tubules – the proximal

tubule.

Along the length of the tubule the composition of the filtrate is adjusted carefully

until it contains only unwanted substances. It is then called urine.

Filtration in the Bowman’s capsule:

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Reabsorption:

Surrounding each nephron is a large capillary network.

As the filtrate travels down the capsule the materials that the body can reuse are

reabsorbed into the blood.

These materials include glucose, amino acids, some vitamins, minerals,

bicarbonate and water.

It occurs in the proximal and distal parts of the tubule and the Loop of Henle.

In the proximal tubule about 80% of water is reabsorbed by osmosis.

All the glucose, amino acids and vitamins pass from the filtrate into the capillaries

by a combination of diffusion and active transport.

Most salts are reabsorbed by a combination of active transport and diffusion.

Reabsorption is an active process that requires energy.

Secretion:

Secretion is a selective process whereby the body actively transports substances

from the blood into the nephron.

This occurs in both the proximal and distal parts of the tubule.

Regulation of Body Fluid Composition

The nephron is a regulatory unit – it selectively reabsorbs materials required to

maintain homeostasis.

The readjustments occur as substances are moved in either direction – reabsorption

back into the blood or secretion back into the nephron.

The reabsorption of ions ( Na , Cl , K and HNO ) occurs at different rates depending

on feedback from the body.

This regulation helps to maintain the constant composition of the blood and interstitial

fluid.

In the proximal tubule – most of the bicarbonate ions are reabsorbed and there

may be some secretion of hydrogen ions.

This helps to maintain a constant pH of the blood and body fluids.

Drugs such as aspirin and penicillin and poisons identified by the liver are actively

secreted into the tubule.

Nutrients such as glucose and amino acids are actively transported from the tubule

back to the blood. (reabsorbed)

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Regulation of salts also occurs. Sodium salts Na are actively transported back into

the blood (reabsorbed). Chlorine ions Cl-1 follow passively. As the salt moves out,

water by osmosis passes back into the blood. Potassium ions are also reabsorbed

here.

In the Loop of Henle – in the descending part, the walls are permeable to water but

not to salt.

Water passes across by osmosis.

In the ascending part the walls are permeable to salt not to water.

Salt passes out passively across a thin walled section and then actively across a thick

walled section. The salt passing out makes the interstitial fluid of the medulla area of

the kidney quite concentrated. (This hypertonic medulla helps remove water by

osmosis from the descending part and collecting duct).

In the distal tubule – selective reabsorption and secretion again occur to adjust pH of

the blood and level of salts particularly sodium and potassium.

The walls of the collecting ducts are permeable to water but not to salt. Water passes

out by osmosis and the final filtrate or urine is formed. (due to high salt concentration

in the medulla)

gather, process and analyse information from secondary sources to compare the process of renal dialysis with the function of the kidney

Analyse the information by determining the outcomes of the dialysis process and

show whether the kidney is more efficient at osmoregulation and excretion than the

dialysis machine.

Research and complete the following table:

Dialysis Machine Kidney

e.g. Artificial Tubing Nephron

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perform a first-hand investigation of the structure of a mammalian kidney by dissection, use of a model or visual resource and identify the regions involved in the excretion of waste products

outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in the regulation of water and salt levels in blood

Aldosterone is a steroid hormone secreted by the adrenal gland.

Function: Its function is to regulate the transfer of sodium and potassium

ions in the kidney.

When sodium levels are low, aldosterone is released into the blood causing

more sodium ions to pass from the nephron to the blood.

Water then flows from the nephron into the blood by osmosis. This results

in the homeostatic balance of blood pressure.

If there is an increase in blood volume and pressure (resulting from high

salt concentrations, which causes water retention), the out put of

aldosterone is reduced. Less salt and water is reabsorbed by the nephron

tubules and increased amounts of water and salts are lost in the urine.

Antidiuretic hormone (ADH or vasopressin) controls water reabsorption in the

nephron. Made in the hypothalamus.

When levels of fluid in the blood drop, the hypothalamus causes the

pituitary gland to release ADH.

ADH increases the permeability of the collecting ducts and distal

tubules allowing more water to be reabsorbed from the urine into the

blood.

The resulting urine is more concentrated.

When there is too much fluid in the blood, sensors in the heart cause

the hypothalamus to reduce the production of ADH in the pituitary,

decreasing the amount of water reabsorbed in the kidney.

This results in a lower blood volume and larger quantities of more

dilute urine.

https://www.youtube.com/watch?v=e-oe9mr3bTg

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The role of the Antidiuretic Hormone

ADH and the water balance of the body

The amount of water in the blood must be kept more or less the same all the time to

avoid cell damage as a result of osmosis.

There has to be a balance between the amount of water gained (from your diet though

drinks and food and the water produced by cellular respiration) and the amount of

water lost by the body (in sweating, evaporation, faeces and urine).

This is achieved by the action of the hormone ADH (anti-diuretic hormone).

Perhaps you have not drunk anything for a while or you have been sweating a lot. Part

of the brain, the hypothalamus, detects that there is not enough water in the blood.

The hypothalamus sends a message to the pituitary gland which releases ADH. This

travels in the blood to your kidneys and affects the tubules so more water is

reabsorbed into your blood. As a result you make a smaller volume of more

concentrated urine. The level of water in your blood increases until it is back to

normal.

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Sometimes the level of water in your blood goes up because, for example, it is cold

and you have not been losing any water through sweating or because you have had a

lot to drink. The hypothalamus detects the change and sends a message to the

pituitary. The release of ADH into the blood is slowed down or even stopped. Without

ADH the kidneys will not save as much water and you produce large volumes of

dilute urine. The level of water in the blood falls back to the normal level.

This is an example of negative feedback. As the level of water in the blood falls,

negative feedback ensures that the amount of ADH rises. As the level of water in the

blood rises negative feedback ensures that the amount of ADH falls.

present information to outline the general use of hormone replacement therapy in people who cannot secrete aldosterone

Research this dot point. The following information is a good place to start.Present the information as a discussion, with clearly identified issues and or

points provided for or against the use of the therapy. Here is a key word to get

you started in your web search:

Addison’s disease: Nation Institute of Diabetes and Digestive and Kidney

Diseases, USA

Background:

Hypoaldosteronism is a condition where people fail to secrete aldosterone.

Addison’s disease is the name of a disease with these symptoms which

include high urine output with a resulting low blood volume. Eventually

as blood pressure falls, this can result in heart failure. A replacement

hormone, Fludrocortisone is used to treat this condition.

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define enantiostasis as the maintenance of metabolic and physiological functions in response to variations in the environment and discuss its importance to estuarine organisms in maintaining appropriate salt concentrations

Enantiostasis: is the maintenance of metabolic and physiological functions in

the absence of homeostasis, in an organism experiencing variations in its

environment.

For organisms living in an estuary this ability is tested as they all experience

large changes in salt concentration in their environment over a short period of

time, with tidal movement and mixing of fresh and salt water.

Estuary – an estuary is formed when a river meets the sea. In this environment

fresh water draining form the land mixes with saline water from the sea. On

the flood tide the sea invades the estuary. On the ebb tide the fresh water

invades, the water is shallower, and areas of land such as mudflats may be

exposed.

Organisms living in an estuary that must tolerate wide fluctuations of salinity

are said to be euryhaline.

One strategy to withstand such changes in salt concentration is to allow the

body’s osmotic pressure to vary with that of the environment. Organisms

that do this therefore do not maintain homeostasis and are said to be

osmoconformers.

Most marine invertebrates are osmoconformers.

In contrast most marine mammals and fish are osmoregulators,

maintaining homeostasis regardless of the osmotic pressure of the

environment.

As the salt concentration of body fluids in an osmoconformer changes,

various functions are affected, such as enzyme activity. For normal

functioning to be maintained another body function must be changes in a

way that compensates for the change in enzyme activity.

One example of enantiostasis is when a change in salt concentration in body

fluid which reduces the efficiency of an enzyme, is compensated for by a

change in pH, which increases the efficiency of the same enzyme.

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Salmon, trout and eels that move from sea to rivers must have adaptations

to deal with salt and water problems experienced in freshwater and marine

environments. Eels for example have special cells in their gills that can act

as salt absorbers and salt secretors.

analyse information from secondary sources to compare and explain the differences in urine concentration of terrestrial mammals, marine fish and freshwater fish

Freshwater Fish:

Osmotic Problem: They are hypotonic to their environment. Water will

tend to diffuse INTO their bodies. Salts will diffuse out.

Role of Kidney: Removes excess water. Produces large amounts of

dilute urine. Kidneys also reabsorb salts. They also rarely drink water.

Urine: Large amount but dilute.

Marine Fish:

Osmotic Problem: Hypertonic to environment. Water diffuses out.

High salt levels present in the water

Role of Kidney: Continually drinks water. Kidneys reabsorb water,

while excreting salts. Small amounts of concentrated urine. Sale is

also excreted across gills.

Urine: Small, concentrated amount.

Terrestrial Mammals:

Osmotic Problem: Water needs to be conserved.

Role of Kidney: Regulates concentration of blood, while at the

same time excretes urea and conserves water.

Urine: Concentration changes with the availability of water, as well

as temperature and water loss through sweat. Water levels in blood

rise, urine amount rises, and concentration decreases and vice versa.

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describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss

use available evidence to explain the relationship between the conservation of water and the production and excretion of concentrated nitrogenous wastes in a range of Australian insects and terrestrial mammals

Aquatic Animals and Fish: These organisms directly release ammonia into

the environment. This uses a lot of water, but they have no need to

conserve it. Ammonia is very water soluble and is excreted through the gills.

Terrestrial Animals: Releasing ammonia would be unfeasible due to lack of

water. Instead, land-dwellers change ammonia into less toxic forms and

release it periodically. Mammals change it into UREA and release it as urine.

Birds: Birds change ammonia into URIC ACID, a whitish paste which uses

hardly any water. This is lighter than using urea, and helps in flight.

process and analyse information from secondary sources and use available evidence to discuss processes used by different plants for salt regulation in saline environments

Maintaining Salt Concentrations in Plants

Most plants cannot tolerate high salt concentrations in the root zone as it leads to

water stress. The salt accumulates in its leaves and is toxic. Enzymes are inhibited

by Na+ ions.

Halophytes are plants adapted to living in salty environments. They are able to

tolerate higher levels of salt than any other plants or they have special

mechanisms to control their levels of salt.

Three different mechanisms are salt exclusion, salt excretion and salt

accumulation.

1. Salt excluders – prevent the entry of salt into their root systems by filtration.

This is a passive process that does not use energy and relies on the

transpiration stream. It can be very successful. Example: The grey mangrove

Avicenna marina can exclude 95% of their salt via the filtration system in its

roots and lower stems.

Other mangroves that rely on this system are the red mangrove Rhizophora

stylosa and the orange mangrove Bruguiera gymnorrhiza.

red mangrove Rhizophora stylosa

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2. Salt excretors – have special salt glands usually in their leaves. Salt is

concentrated there and then actively secreted from the plant.

The salt can often be seen and tasted as salt crystals on the leaves. Rain washes

the salt off.

Examples: The grey mangrove Avicenna marina and river mangrove Aegiceras

corniculatum have salt glands as do salt bushes (genus Atriplex). Sporobolus

viriginicus has salt glands on its leaves (salt marsh plant)

Atriplex is a genus of the salt bush family that produces a covering of bladder-

like hairs into which salt is excreted at extraordinary high concentrations.

Atriplex

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3. Salt accumulators – these concentrate or accumulate salt in a part of the

plant usually the bark or older leaves, which is then shed.

Example: The milky mangrove Exoecaria agallocha sheds old leaves full

of salt. The succulent samphire plant Sarcocornia quinqueflora, found on

salt marshes accumulates salts in swollen leaf bases which then drop from

the plant, thus removing excess salt. Another form of salt stress occurs can

occur in salt laden air such as in coastal environments. Some coastal

plants such as Norfolk Island pine have a mesh of cuticle over their

stomates, which prevent small water droplets from entering the leaf.

Describe adaptations of a range of Australian plants that assist in minimizing water

loss.

Leaves of plants contain stomates or small pores that allow the exchange of gases

essential for respiration and photosynthesis. These gases include water vapour as well

as oxygen and carbon dioxide. If stomates are open there will be a loss of water by

transpiration and evaporation. Plants in arid areas have to balance the need for CO2

with the need to conserve water.

Xerophytes – are plants adapted to arid or dry condition.

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Many Australian terrestrial plants show a variety of adaptations to conserve water and

minimize water loss.

Water storage – storage of water in soft fibrous trunks such as in the bottle tree

(Brachychiton rupestris) and the boab tree (Adamsonia gregorii). Succulent plants

such as the noonflowers or pigfaces (e.g. Karella – Carpobrotus rossii and rounded

noonflower Disphyma crassifolia store water in fleshy leaves and stems.

The boab tree (Adamsonia gregorii)

Gouty stem tree, Adansonia Gregorii, 58 feet circumference, near a creek south-east of Stokes

Range, Victoria River

Extensive root systems – for water collection. The ability to collect as much water as

possible is exemplified by an extensive rot system. These include deep tap root

systems to reach deep underground water and wide shallow roots to soak up surface

moisture.

Desert plants are often widely spaced because of root competition below ground.

Example: The Mulga (Acacia aneura) – its branches are also arranges so that any rain

falling is channeled directly to the roots.

Structural Adaptations: these include features that help minimize water loss from

transpiration.

Leaves with a waxy cuticle e.g. leaves of eucalypts and mangroves.

Small leaves with a reduced surface area, for example the needle like leaves of the

Hakea plants or the replacement of leaves with photosynthetic stems such as in she-

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oaks (Casuarina and Allocasuarina) or flattened leaf stem called phyllodes of some

Wattle (Acacia Species)

Phyllodes

Wattle Acacia

Reflective leaf surfaces: these may be pale, shiny, hairy or crystalline. Some salt

bushes change the reflectiveness of their leaves during leaf development so that they

have highly reflective leaves during the summer.

Hairy leaves that reduce airflow across the leaf surface thus reducing evaporation:

often underside of the leaves or growing buds are covered in hairs.

Water Loss Adaptations –

Example 1: Ptilotus species (hairy leaves and flowers) Example 2 – A liverwort Riccia

crystallina (a reflective crystalline surface)

Example 1 - Ptilotus Joey

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Example 2 - A liverwort Riccia crystallina (a reflective crystalline surface)

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Stomates sunken into pits or grooves and / or reduced number of stomates for

example Hakea and Eucalyptus leaves.

Thick bark as in Mulga or extra thickening of cell walls to prevent wilting; many

Australian xerophytes have leaves that do not wilt.

Rolled up leaves to minimize water loss for example in the porcupine grass ans

spinifex Triodia. (Leaves rolled inwards)

Physiological Adaptations: alter a plants metabolic activities

Leaves hanging vertically that change their orientation during the day to ensure that

only the edges not the full surface of the leaves are exposed to the sun. This reduces

both heat absorption and water loss.

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Eucalypts – leaves hang vertically

Closing stomates during the hottest part of the day. This is usually associated with

plants such as succulents that open their stomates at night to take in carbon dioxide.

Dormancy periods when leaves or all above ground parts die off during hot dry

conditions. Mallee eucalypts for example die back and regenerate when favourable

conditions return from swollen underground lignotubers.

Mallee eucalypt showing lignotuber

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Tough hard seeds that can survive long dry periods as well as accelerated life cycles

may be shown by plants in response to a short wet season in arid environments.

Example: Sturt’s desert pea (Clianthus formosus), germinate grow flower and

produce many seeds within six to eight weeks of heavy rains.

Tolerance to drying out or dessication. Example: the leaves of the resurrection plant

can be dry and shriveled for four to five months then become green and swollen again

after heavy rain.

perform a first-hand investigation to gather information about structures in plants that assist in the conservation of water

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