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Maintaining A Balance
Most organisms are active in a limited temperature range
Enzymes:
 Biological catalysts. A specific enzyme controls every reaction and process
within a cell. Enzymes control all the chemical processes of living systems.
 Enzymes are proteins made up of amino acids that are linked and then folded
to produce a three-dimensional protein structure. Most metabolic processes
would not occur at an efficient rate without enzymes.
 One model used to illustrate the action of an enzyme is the lock-and-key
model.
o Enzymes are unique to one substrate
o The enzyme combines with the substrate to form an enzymesubstrate molecule. This somehow alters the substrate so that a
chemical reaction can occur.
o The substrate is then altered and no longer ‘fits’ the enzyme – the
enzyme is released.
- Effect of temperature on enzymes: each has an optimum temperature for activity.
High temperatures can denature enzymes.
- Effect of pH on enzymes: each has an optimum pH (acidity level) for activity.
Changing the pH from the optimum reduces the enzyme’s activity.
- Effect of substrate concentration on enzymes: substrate concentration means the
amount of compound present that the enzymes catalyses. Beyond certain substrate
concentrations, the rate of reaction is limited by the amount of enzyme.
pH as a way of describing the acidity of a substance:
 A measure of the concentration of hydrogen ions that are released by acids,
therefore a way of describing the acidity of a substance.
 A pH value of 0-6 indicates an acid solution, a pH value of 8 – 14 indicates a
basic (alkaline) solution. A pH of 7 indicates a neutral solution.
Procedures to investigate the activity of an enzyme:
 Aim: to demonstrate the effect of increased temperature on the enzyme,
rennin
 Method: make a rennin solution by dissolving a junket tablet in distilled
water. Add the same amount of rennin solution to a number of test tubes of
milk. Place test tubes in different water baths with different temperature
ranges (0-60), making sure each water bath is kept at its allocated
temperature. Time the interval between adding the rennin and curdling of
the milk for each temperature.
 Results: The optimum temperature for curdling milk is 30-40 degrees.
Anything above that optimum temperature will denature the rennin,
preventing it from curdling the milk. Anything below the optimum
temperature won’t work as effectively.
Maintenance of an optimal internal environment:
 Enzymes control all the metabolic processes in the body.
 Despite the internal and external changes occurring in the body, organisms
need to maintain a constant internal environment for optimal metabolic
efficiency.
 Enzymes work optimally in an environment where their optimum
temperature and pH conditions are met. At temperatures and pH values
other than the optimum, the enzymes fail to work as they should or not at all.
 The maintenance of an optimal internal environment is important for optimal
enzyme efficiency.
Homeostasis:
 The process by which organisms maintain their internal environment
regardless of the external environmental conditions. Through homeostasis,
organisms maintain an internal equilibrium by adjusting their physiological
processes. Homeostasis ensures that the organism operates at maximum
performance. To maintain homeostasis, this involves:
 A receptor: constantly monitors the internal environment, which may reflect
the external environment
 A control centre: monitors the information passed on from the receptor
 An effector: carries the message from the control centre.
 Hypothalamus: the control centre for maintaining homeostasis.
Homeostasis as a two-stage process:
 Coordination in animals is controlled by two systems; the nervous system and
the endocrine system
 A feedback mechanism is self-regulating, which maintains balance or
homeostasis. For a state of homeostasis to exist, the body must have some
way of detecting stimuli that indicate a change in the body’s internal or
external environment.
- Stage 1 - Detecting changes from the stable state:
 A receptor detects a change in some variable in the organism’s internal
environment.

If our body temperature rises, the temperature rise in the blood
stimulates the brain’s anterior hypothalamus.
 Alternatively, when a mammal is exposed to cold, skin receptors increase
their activity, sending nerve impulses to the posterior hypothalamus.
- Stage 2 - Counteracting changes from the stable state:
 An appropriate response occurs that counteracts the changes and thus
maintains the stable environment.
 After detecting the rise in body temperature, the hypothalamus then
stimulates heat loss by  blood circulation through the skin,  sweating
and  metabolic activity, thus lowering the body’s temperature.
 After detecting a drop in temperature, activity in the posterior
hypothalamus detects the nervous system to activate mechanisms to
conserve heat.
A model of a feedback system:
 The body has some effective mechanisms to alter body temperature.
 To reduce temperature, heat can be expelled through sweating or the
radiation of heat from the skin. To increase heat, the body can respond by
shivering or by contracting the skin. These responses can be activated by heat
receptors.
 If receptors in the skin detect heat, they relay information via the nerves to
the hypothalamus, which also contains receptors sensitive to the heat of
passing blood. This triggers the nervous system to activate sweat glands.
 When receptors in the skin detect a low temperature, a negative feedback
mechanism is activated to stop the original action.
Feedback system model: thermostat
 Controls temperature to a set level in a room.
 Has a device to measure
temperature
(hypothalamus). If the
temperature is too low, then
a heating process will be
initiated. Eventually, the
device will detect that the
temperature is at the
appropriate level and then
will send a message to the heater to cease operations.
 This is a negative feedback mechanism. This occurs when an appropriate
response has occurred and the increase in some factor has been sensed,
resulting in the termination of a further response.
The role of the nervous system:
 Provides rapid coordination of internal organ systems, and detects and
responds to environmental changes.
 The nervous system consists of the central nervous system (CNS) - the brain,
spinal cord and peripheral nerves.

Special endings on the sensory nerves detect stimuli such as heat, pressure or
chemical conditions. These receptors relay messages that are processed
within the CNS and then messages are conveyed to effector organs or
muscles that bring about the responses.
Temperature ranges:
 Organisms live in environments with ambient temperatures ranging from less
than 0 to 100 degrees. Ambient temperatures are the external or
environmental temperature.
 Individual organisms cannot survive this wide range of temperatures, e.g.
mammals can only generally survive temperatures of about 0-45 degrees and
can only be normally active in a range of body temperatures between 30-45
degrees.
Ectotherms and endotherms:
 Ectotherms: animals whose temperature is determined by an external
environment. Desert lizards respond to changes in temperature by burrowing
during the warmer parts of the day and increasing body temperature by
basking in the sun.
 Endotherms: animals that regulate their internal body heat regardless of the
external environment. Red kangaroos respond to changes in temperature by
sheltering during the heat of the day and licking the inside of their paws to
increase heat loss by evaporation of water.
Responses to changes in ambient temperature:
 Adaptations are structural, functional or behavioural characteristics that help
an organism to survive in certain environments.
Behavioural
Migration: animals move to avoid
temperature change (birds)
Nocturnal: allows animals to escape the
daily heat and become active during the
cooler night (brown snake)
Hibernation: to survive cold conditions,
many animals hibernate during cooler
periods of the year (bears)
Structural and Physiological
Insulation: fur, feather, fat layers and/or
blubber. Reduces heat exchange with the
environment.
Evaporation: endotherms keep cool by
controlling the rate of water loss
(kangaroos)
Metabolic activity:
- cold:  activity, heat produced through
shivering
- heat:  sweating, cooling the body
Responses of plants to temperature change:
 Plants need certain temperatures for growth and the germination of seeds.
 Responses of plants to temperature change includes:
o Reduced surface area, reducing heat absorption and supporting
convective cooling
o The dropping of leaves in the result of cooler temperatures
o Closing stomates in response to high temperatures to reduce water
loss
Plants and animals transport dissolved nutrients and gases in a fluid medium
The forms in which substances are carried in mammalian blood:
 Mammalian blood consists of cells and cell-like bodies that are carried about
in a watery fluid called plasma.
 Carbon Dioxide: mostly carried in solution in plasma as bicarbonate ions
 Oxygen: carried as an oxygen-haemoglobin combination in red blood cells
 Water: carried as blood plasma, which is 90% water
 Salts: carried as dissolved ions in the plasma
 Lipids: mostly transported in the blood as phospholipids and cholesterol that
are associated with plasma proteins
 Nitrogenous wastes: mostly carried as urea, with a small amount of
ammonia and uric acid
 Other products of digestion: carried as substances such as amino acids or
glucose and are dissolved or suspended in the plasma.
Estimating the size of red and white blood cells:
 Red blood cells contain no nucleus, while white blood cells are larger and
contain and large, lobular nucleus
 Red blood cells are about 7 microns in diameter and are disc-shaped
 White blood cells are about 10 microns in diameter and are more spherical
and contain an obvious nucleus.
Haemoglobin:
 Globule-shaped protein containing four polypeptide sub-units, enabling red
blood cells to carry oxygen.
 One haemoglobin molecule can carry four molecules of oxygen, increasing
the rate and efficiency of oxygen intake and transport in the molecule.
Adaptive advantage of haemoglobin:
 The presence of haemoglobin increases the oxygen carrying capacity of blood
by 100 times, giving mammals a considerable survival advantage.
 The structure of the haemoglobin molecule is also an advantage as it’s the
type of molecule that can combine with oxygen loosely at the respiratory
surfaces and then release the oxygen freely in capillaries.
Technologies to measure oxygen saturation and carbon dioxide concentrations in
blood:
 ABG (arterial blood gas) analysis measures the amounts of oxygen and
carbon dioxide in the blood. This analysis evaluates how effectively the lungs
are delivering oxygen and how well the lungs are getting rid of carbon
dioxide.
 A blood gas analyser measures the partial pressure of oxygen and carbon
dioxide, the oxygen content, oxygen saturation, bicarbonate content and
blood pH. Oxygen saturation compares the amount of oxygen actually
combined with haemoglobin to the total amount of oxygen the haemoglobin
is capable of combining with. Arterial blood is collected for this analysis.
 A pulse oximeter can be used for monitoring oxygen saturation. It is a device
attached to the finger and uses the absorption of light to measure oxygen
saturation. It has the advantage of being non-invasive and can provide
continuous monitoring for patients undergoing anaesthesia or mechanical
ventilation.
 The conditions under which blood gas studies are used are to assess
respiratory disease and other conditions that may affect the lungs, as well as
to manage patient receiving oxygen therapy, mechanical ventilation or
anaesthesia.
The structure and function of arteries, capillaries and veins
Arteries
Veins
Capillaries
- Thick, muscular walls
- Thin walled
- Thin walled, often only
- No valves present
- Valves are present to
one cell thick
- Carry blood away from
prevent back-flow of
- Carry blood between
the heart
blood
arteries and veins
- Carry oxygenated blood
- Carry blood back to the
(except for the pulmonary heart
artery)
- Carry deoxygenated
- Blood is arteries is
blood (except for the
pumped under high
pulmonary vein)
pressure
- Blood is under low
pressure; movement is
assisted by body muscles
Chemical composition of blood in the body:
-Blood flow through the heart:
 Pulmonary system: Deoxygenated blood from the body enters the right
atrium, is squeezed into the right ventricle and then pumped into the lungs.
Carbon dioxide is decreased and oxygen levels increased.
 Systemic system: Oxygenated blood from the lungs enters the left atrium, is
squeezed into the left ventricle and then pumped to the body tissues through
the aorta. Deoxygenated blood then returns to the heart via the vena cava.
-Changes in the chemical composition of blood:
Chemical composition of the blood as it Tissues in which these changes occur
moves around the body
Blood receives oxygen and carbon
Lung tissue
dioxide is released
Blood receives carbon dioxide and
General body tissues, such as skin tissues
oxygen is released
Water diffuses into blood
Stomach tissue
Digested foods diffuse into the blood and Small intestinal tissue
go straight to the liver
Glucose is added or removed
Liver tissue
Water, salts and vitamins are absorbed
Large intestinal tissue
in the large intestine and pass into the
blood
Urea, excess water and salts are
Kidney tissue
removed from the blood to be excreted
Hormones are secreted directly into the
Endocrine tissue
blood stream
Products extracted from donated blood and their uses:
 Red blood cells are used to increase the amount of oxygen that can be
carried to the body’s tissues. They are given to people who have anaemia.
 Platelets are essential for blood clotting. Platelets are given to people who
have cancer of the blood or lymph such as leukemia.
 Plasma is the liquid portion of the blood and is used to treat people with
clotting disorders such as haemophilia. It is also used to adjust the osmotic
pressure of blood and to pull fluids out of tissues.
 White blood cells are an infection-fighting component of the blood. Are only
used occasionally to treat life-threatening infections when the cell count is
very low or the white blood cells are not working properly.
The importance of research into the production of artificial blood:
 Up until the HIV crisis in the 1980s, there was little interest in artificial blood,
as there did not seem like a great need.
 Artificial blood is currently only designed to increase plasma volume and
carry oxygen (and carbon dioxide).
 No substitutes have yet been developed that can replace other function –
coagulation and immune defence.
- Two types of oxygen-carrying artificial blood have been produced:
 Perflurochemicals are synthetic materials that can be dissolved about fifty
times more oxygen than blood plasma. They are cheap to produce and,
because they are synthetic, there is no risk of the material being infected by
disease.
 More research is needed because perflurochemicals must combine with
other substances in order to mix in the blood stream. Research has included
mixing them with lipids and more recently, lecithin
 Haemoglobin-based oxygen carriers are made from haemoglobin extracted
from red blood cells. They are not contained in a membrane and therefore do
not require blood typing and cross matching of blood. More research is
needed because haemoglobin must be modified before it can be used.
 Current blood substitutes do not have the enzymes that prevent
haemoglobin from oxidizing. Once haemoglobin is oxidized, it cannot carry
oxygen.
- Some advantages of artificial blood include:
 Pasteurisation could be used to remove all pathogens
 No need for cross matching and blood typing
 Storage benefits – artificial blood can be stored for more than one year,
compared with donor blood only lasting for one month
Oxygen and carbon dioxide in cells:
- The need for oxygen:
 Cells require oxygen in the process of respiration: glucose + oxygen  carbon
dioxide + water + energy (in the form of ATP)
 A constant supply of oxygen to cells and tissues is essential. If oxygen is not
available, the cell dies.
- Why the removal of carbon dioxide is essential:
 Carbon dioxide is a waste product and must be removed to maintain the
normal pH balance of the blood.
 By removing excess carbon dioxide, it prevents a build up of carbonic acid,
which causes the lowering of the
pH, and therefore increasing
breathing rate and depth.
The movement of materials through
plants in xylem and phloem tissue:
 Xylem tissue transports water in
plants. Phloem tissue transports
sugars.
- Processes responsible for the
movement of materials in xylem
 The current mechanism, which transports materials in xylem, is the
transpiration-cohesion-tension mechanism, which accounts for the ascent of
xylem sap.
 The transpiration-cohesion-tension mechanism is passive transport.

The mechanism is summarized as three processes:
o Cohesion: water molecules stick together within a continuous
network of liquid columns, which have the ability to instantaneously
transfer pressure or tension.
o Transpiration: water is evaporated through the stomates and is
replaced by water from cells and xylem tissue.
o Tension: water moves up the xylem like a wire being pulled up, due to
cohesion. This helps resist the formation of bubbles within the
stream.
- Processes responsible for the movement of materials in phloem:
 Movement of materials in phloem moves both up and down the stem.
 The pressure-flow mechanism (Source to Sink) is the model for phloem
transport.
 In this mechanism, sieve elements accumulate solutes such as sugars from
the leaves (source), which is a process that requires metabolic energy.
Companion cells also accumulate solutes and deluver them to sieve
elements. At these sites, the sugar concentration is high and this causes the
entry of water by osmosis from surrounding cells and xylem. The resulting
pressure causes water and dissolved solutes to flow along under the force of
turgor pressure to the places where sugar is being removed (sink).
 The building up of pressure at the source end, and the reduction of pressure
at the sink end, causes water to flow from source to sink. As sugar is
dissolved in the water, it flows at the same rate as the water. Sieve tubes
between phloem cells allow the movement of phloem sap.

Longitudinal sections show relatively long, narrow cells in both phloem and
xylem. Transverse sections show the relatively thick cell walls of xylem tubes
and the perforated sieve plates in phloem cells.
Plants and animals regulate the concentration of gases, water and waste products
of metabolism in cells and in interstitial fluid
The concentration of water in cells:
 Water is the solvent for metabolic reactions in living cells. Many molecules
and all ions important for the life of the cell are carried in an aqueous
solution and these diffuse to reaction sites through the water in the cell.
 Metabolic reactions within the cell can occur only in solution where water is
the solvent. It is critical for proper functioning of these reactions that the
amount and concentration of water in the cell be kept constant.
 Most cells die when the water content is changed significantly.
The removal of wastes:
 Metabolic wastes, particularly nitrogenous wastes, are toxic to cells and must
therefore be removed quickly. Nitrogenous wastes have the ability to change
the pH of cells, interfere with membrane transport functions and may
denature enzymes.
 The excretory system is concerned with the removal of metabolic waste
products from the body. In humans, the organ systems for excretion are the
kidneys, the lungs and the skin.
 The excretory system is also responsible for maintaining a constant blood
composition and therefore maintaining a constant internal environment in
cells.
The role of the kidney in the excretory system:
 The kidney is an organ of the excretory system of both fish and mammals. It
has a dual role of excreting nitrogenous wastes and maintaining the water
balance in mammals and fish. It is an organ of filtration, reabsorption and
secretion.
 In mammals, it plays a central role in homeostasis, forming and excreting
urine while regulating water and salt concentration in the blood. It maintains
the precise balance between waste disposal and the animal’s needs for water
and salt.

The role of the kidney in fish is dependent on their environment:
o In marine (saltwater) environments, the kidneys excrete small
quantities of isotonic urine, helping to converse water and excrete
salt they gain from their environment.
o In freshwater environments, the kidneys work continuously to excrete
copious quantities of dilute urine with very low salt concentration.
This helps to remove excess water gained from their environment.
The processes of diffusion and osmosis:
 Diffusion: the movement of molecules from an area of low concentration to
an area of high concentration divided by a concentration gradient.
 Osmosis: movement of water from an area of high water concentration (low
solute concentration) to an area of low water concentration (high solute
concentration) across a semi permeable membrane.
 The processes of diffusion and osmosis are inadequate in removing dissolved
nitrogenous wastes because diffusion is too slow and non-selective of solutes
and osmosis would mean that waste would stay in the body and water would
leave it. These problems are resolved by having a kidney that dumps
everything ‘outside’ the body and selectively reabsorbs the still-useful
materials.
Active and passive transport in the mammalian kidney:
 Active transport involves an expenditure of energy. Passive transport involves
no expenditure of energy.
 In the mammalian kidney, both active and passive transport processes occur.
 Passive transport: once filtration has occurred in the Bowman’s capsule,
water returns via the interstitial fluid from the tubule to the capillary in the
process of osmosis. This occurs along the length of the tubule.
 Active transport: depending on their concentration, the ions in the blood can
be transported to cells in the nephron tubule and then secreted by the cells
into the tubule. Some poisons and certain drugs are eliminated from the
body in this manner.
The processes of filtration and reabsorption in the mammalian nephron:
 Filtration of all the blood occurs in the Bowman’s capsule where high blood
pressure in the glomerulus forces all small molecules out of the blood into
the capsule. The structure of the glomerulus means that it acts as an ultrafilter.
 Water, urea, ions, glucose, amino acids and vitamins are all small enough to
be moved into the glomerulus filtrate. Blood cells and proteins are too large
to be removed. This filtering process is non-selective and therefore many
valuable components of the blood must be recovered by reabsorption.
 Reabsorption takes place selectively at various points along the proximal
tubule, loop of Henle and the distal tubule. All glucose molecules, amino
acids and most vitamins are recovered, although the kidneys do not regulate
their concentrations. The reabsorption of the ions occurs at different rates
depending on feedback from the body. In some cases, active transport is
required.
 Water is reabsorbed in all parts of the tubule except the ascending loop of
Henle. The amount of water reabsorbed depends on feedback from the
hypothalamus. If no water were reabsorbed, humans would soon dehydrate.
The chemical composition of the body fluids is precisely regulated by the
control of solute reabsorption from the glomerulus filtrate.
Renal dialysis compared with the function of the kidney:
 The artificial kidney does not match the complexity of a natural kidney and
has limits as a long-term substitute for the kidney. The artificial kidney
regulates the concentration of the patient’s blood by removing substances
(such as urea and other toxins) and selectively adding substances. The basic
process is called dialysis.
 The fluid used in dialysis promotes diffusion of the appropriate substances
into and out of the blood. Two healthy kidneys filter the blood volume about
once every half-hour. Dialysis is a much slower and less efficient process than
the natural processes found in a healthy kidney, but it is a lifesaver for those
people with damaged kidneys.
Aldosterone and ADH (anti-diuretic hormone):
 Aldosterone is a steroid hormone produced by the adrenal cortex of the
kidney. Its role is to maintain the balance of water and salts in the body. It
stimulates the nephrons to decrease reabsorption of potassium and increase
reabsorption of sodium into the blood, leading to an increased reabsorption
of chloride ions and water. The reabsorption of these substances causes a
rise in blood volume and blood pressure.
 ADH is a hormone produced by the hypothalamus and stored in the
posterior pituitary of the brain. ADH stimulates the nephrons to reabsorb
more water. It acts to decrease urine volume, increase urine concentration
and increase blood volume.
Hormone replacement of aldosterone:
 The replacement hormone is called fludrocortisone, used to treat people
with Addison’s disease mostly caused by the destructing or shrinking of the
adrenal cortex.
 The adrenal cortex produces two hormones, cortisol and aldosterone. If the
body cannot secrete aldosterone, water and salt balance cannot be
maintained. When this balance is upset, the volume of blood falls
dangerously low; there is a drop in blood pressure and severe dehydration.
When levels of both cortisol and aldosterone drop, many functions
throughout the body are disrupted.
Enantiostasis and salt concentrations:
 The maintenance of normal metabolic and physiological functioning, in the
absence of homeostasis, in an organism experiencing variations in its
environment. It is particularly important for organisms living in an estuarine
environment where salinity varies greatly.
 Organisms that must tolerate wide fluctuations of salinity are said to be
euryhaline.
 Marine mammals and most fish maintain homeostasis in estuarine
environments in a process called osmoregulation. They carry out a range of
activities that maintain a constant body fluid composition, despite the
changing environment. Activities such as excreting salt or concentrating urine
are essential to their survival.


Many plants and marine invertebrates are osmoconformers and so rely on
enantiostasis to survive. This means that the composition of their body fluids
varies along with the environment. Adjustments are made in their
physiology. Their enzymes keep functioning despite changes to conditions or
metabolic pathways so that their needs are met.
Both homeostasis and enantiostasis are essential to maintaining the diversity
of estuarine ecosystems.
Comparison of the urine concentration of terrestrial mammals, marine fish and
freshwater fish:
Urine concentration
Reason for the difference
Terrestrial mammal
Concentration and volume Terrestrial organisms face
varies
the issue of conserving
water and at the same
time removing
nitrogenous wastes.
Marine fish
Highly concentrated
Aquatic organisms face
the problem of osmosis.
Marine fish drink large
amounts of seawater to
replace water loss.
Freshwater fish
Dilute urine
In fresh water, water will
tend to move into the
organism by osmosis.
Freshwater fish must rid
themselves of excess
water.
Processes used by different plants for salt regulation in saline environments:
 Plants in mangroves and coastal marshes live in the boundary between
saltwater and freshwater. These plants use three main processes for keeping
the growing stems and leaves mostly free of salt:
 Salt barriers – special tissues in the roots and lower stems stop salt from
entering the plant but allow water uptake.
 Secretion – some plants are able to concentrate salt and get rid of it through
special glands on the leaves (grey mangrove). The salt is then washed off by
rain.
 Salt deposits – some plants deposit salt in older tissues, which are then
discarded, e.g. the mangrove Rhizophora concentrates salt in its old leaves,
which it sheds.
The relationship between the conservation of water and the production and
excretion of concentrated nitrogenous wastes:
 Terrestrial organisms face the problem of conserving water and at the same
time removing nitrogenous wastes in a form that is concentrated but not
toxic.



Ammonia is very toxic and must be removed immediately, either by diffusion
or in very dilute urine. It is the waste product of most aquatic animals.
Including many fish and tadpoles.
Urea is toxic, but less toxic than ammonia, so it can be safely stored in the
body for a limited time. It is the waste product of mammals, and some other
terrestrial animals, but also of adult amphibians, sharks and some bony fish.
Uric acid is less toxic than ammonia or urea, so can be safely stored in or on
the body for extended periods of time. It is the waste product of terrestrial
animals such as birds, many reptiles, insects and land snails.
Spinifex hopping
mouse
Terrestrial
Urea in a
concentrated
form
Wallaroo
Terrestrial
Concentrated
urine
Insects
Terrestrial
Uric acid


Lives in a very arid
environment.
Conserves water by
excreting
concentrated urea.
Drinks very little
water.
Very efficient
excretory system
that recycles
nitrogen and urea to
make very
concentrated urine,
allowing them to
survive in very arid
environments.
Insects are covered
with a cuticle
impervious to water.
They conserve water
by producing a dry
paste of uric acid.
Mammals: excrete concentrated urine, receive water from metabolism and
excrete solid faeces.
Grasshopper: passes waste into the Malpighian tubules, which pass it back
into the intestine to pass out of the body.
Adaptations of Australian plants to minimize water loss:
 Australian terrestrial plants have a range of adaptations that assist in
minimizing water loss and at the same time allowing for gas exchange.
- Adaptations of Australian xerophytes include:
 Needle-like leaves, which reduce surface area and water loss (acacias)
 Waxy leaves, which reduce water loss as cuticles prevent evaporation but
also reflect infrared radiation from the sun, reducing heat gain (atriplex)
 Sunken stomates, which result in humid air being concentrated above the
stomate, which reduces water loss (hakeas)
 Hanging leaves, which reduces exposure to the sun (eucalypts)
 Hairy or shiny leaves, which reduce air movement and increase humidity over
stomates, reducing water loss, as well as reflecting radiation from the sun
reducing heat gain (banksias)
Structures in plants that assist in the conservation of water:
 This investigation included structures such as waxy leaf cuticle, hairy leaves,
sunken stomata, few stomates on leaves, leaves rolled forward and leaves
reduced to spikes.
 Most acacia (wattle) plants do not have true leaves but flattened, green leaf
stalks called phyllodes. These carry out photosynthesis but contain fewer
stomata than leaves so that water loss is minimized.
 Casuarinas (she-oaks) have jointed needle-like growths that are actually
green stems. The leaves are reduced to tiny, teeth-like structures along the
joints of the needles. These growths are called cladodes. They also carry out
photosynthesis with minimal water loss.
 There is a wide variety of structural adaptations such as phyllodes, cladodes,
waxy cuticles and hairy leaves that reduce transpiration and so conserve
water in plants.