Download Maintaining a Balance by Arthur Huang

1. Most organisms are active in a limited temperature range
Identify the role of enzymes in metabolism, describe their chemical composition and use a simple
model to describe their specificity on substances
Metabolism refers to all the chemical reactions occurring within an organism.
Enzymes are protein molecules within cells that act as biological catalysts. Enzymes speed up
chemical reactions and enable reactions to occur at lower temperatures within the body (increasing
the efficiency of metabolic processes). They aren’t consumed in the process and can be reused.
Enzymes are globular proteins (shaped like a sphere). They are composed of one or more
polypeptides (long chains of amino acids) that are folded into a 3D structure.
The molecule on which an enzyme acts upon is called a substrate. Enzymes are substrate specific,
meaning that one enzyme can only work on one type of substrate. This can be illustrated through
the lock and key model:
The enzyme fits together with its substrate molecule at a precise place of the much larger enzyme
molecule, called the active site. The active site is shaped specifically to work on only one substrate.
Identify the pH as a way of describing the acidity of a substance
pH is a scale related to the concentration of hydrogen ions in a solution. It is therefore a measure of
the acidity of a substance (0 – most acidic; 14 – most basic)
Explain why the maintenance of a constant internal environment is important for optimal
metabolic efficiency
Enzymes, which control all the metabolic processes of a body, work best in an environment where
their optimum temperature and pH conditions are met. At other temperatures and pH values,
enzymes fail to work at optimum efficiency. By keeping a constant internal environment, enzymes
work effectively and metabolic efficiency is maintained.
Describe homeostasis as the process by which organisms maintain a relatively stable internal
environment
Homeostasis is the process by which an organism maintains a constant internal environment,
despite fluctuations that may arise in its external surroundings. It involves an enormous amount of
co-ordination and control – involving both the nervous system and endocrine system (hormones)
Explain that homeostasis consists of two stages: detecting changes from the stable state,
counteracting changes from the stable state
Homeostasis is brought about in two stages:
1. Detecting change - sensory cells or receptors detect change in the temperature/chemical
composition within the body. This change in the environment is called a stimulus.
2. Counteracting change - effector organs (e.g. muscles/glands) then work to reverse the
change. A response that successfully reverses the change will return the body to
homeostasis – its relatively constant state
Overall, homeostasis ensures that variables in the internal environment of an organism are
maintained within a narrow range.
Outline the role of the nervous system in detecting and responding to environmental changes
The nervous system provides rapid coordination of internal organ systems, detecting and
responding to environmental changes. It consists of the central nervous system (brain, spinal chord)
and peripheral nerves.
The function of the nervous system takes place in three steps:
1. Detects information via receptors
2. Transmits information to a control centre This is done by generating nerve impulses which
travel along sensory neurones to the CNS
3. Information is processed by the CNS, generating a response through the generation of nerve
impulses sent along motor neurones to stimulate effector organs (muscles/glands)
Summary: receptors that detect change transmit messages that are processed within the central
nervous system and messages are then conveyed to effector organs.
Identify the broad range of temperatures over which life is found compared with the narrow limits
for individual species
There is a diverse range of species living on Earth, existing across temperatures ranging from under
0oC to over 100oC. However, no single organism can remain active and thriving under the full range
of the temperatures on Earth; in fact, most organisms can only function in a relatively narrow
temperature range.
Compare responses of named Australian ectothermic and endothermic organisms to changes in
the ambient temperature and explain how these responses assist temperature regulation
Ambient temperature refers to the external or environmental temperature.
Ectotherms are organisms that rely on external sources of heat
Endotherms are organisms that rely on internal sources, such as metabolic activity, for heat
Australian Red Kangaroo (endotherm)
Cold conditions
Physiological:
o Increased metabolic rate to create more
body heat
Behavioural:
o Basking in the sun
Hot conditions
Physiological:
o Decreased metabolic rate
Behavioural:
o Panting and sweating (releasing heat)
o Licking forelimbs to increase heat loss by
evaporation
Structural:
o Exposed areas of skin on forelegs to
increase evaporative cooling of blood
Australian Diamond Python (ectotherm)
Cold conditions
Physiological:
o Shivers to create more heat within body
Structural:
o Dark colour to absorb heat
Behavioural:
o Basks in sun
o Hibernation in winter
o Migration to warmer areas
Hot conditions
Behavioural:
o Nocturnal – hunts a night and burrows
during the day to avoid higher daytime
temperatures
Identify some responses of plants to temperature change
On land, where temperature fluctuations are greater than in water, plant responses can include:
 The ability to orientate leaves vertically to reduce SA exposed to the sun (therefore reducing
heat exposure and supporting convective cooling)
 The ability to drop their leaves if temperatures become too cold
 Budding as the temperature and length of day increases in spring
 Closing stomates in response to high temperatures to reduce water loss
Gather, process and analyse information from secondary sources and use available evidence to
develop a model of a feedback mechanism:
 Homeostasis involves the detection of the change in the environment and the response to
that change
 The mechanism that brings about this change is called feedback
 In feedback systems, the response alters the stimulus
 In living organisms, the feedback system has 3 main parts:
- Receptors: A type of sensor that constantly monitors the internal environment
- Control Centre: Receives info from the receptors and determines the response
- Effector: Restores the set value. Keeps environments stable.
 An example of a feedback system would be the control of body temperature
 The receptors send their information to the control centre. The temperature control centre
in mammals is the hypothalamus. The hypothalamus responds by initiating responses to
increase or decrease temperature, until it goes back to the set value (which is 37ºC)
 Temperature control responses:
Analyse information from secondary sources to describe adaptations and responses that have
occurred in Australian organisms to assist temperature regulation
Adaptations
Behavioural: The main behavioural adaptation in
animals is they alter the position of the body or
decrease the amount of exposure of SA to
sunlight. They may seek shade or shelter in
burrows if the temperature exceeds their
tolerance level.
Structural: Structural adaptations that assist
with temperature control include insulation such
as fur, hair, feathers etc.
Physiological: Physiological adaptations focus on
the inner body functions. Metabolic activity is
important for the survival of individuals, but this
also generates. Thus, the rate of this activity has
be altered according to temperature variations
Examples
 Frill-necked lizards bask in the sun until
they reach an adequate core
temperature then they retreat into the
shade
 The bilby is nocturnal (inactive at day,
active at night) so that it doesn’t
generate additional metabolic body heat
during the heat of the day.
 The Australian fur seal has blubber – a
form of insulation to reduce heat loss
 The common wombat slows its
metabolism down to a third of its normal
rate during hot days when it shelters in
its burrow
 The bilby has an extensive network of
capillaries throughout the ear which aid
the release of heat to the surroundings
(due to large SA)
2. Plants and animals transport dissolved nutrients and gases in a fluid medium
Identify the form(s) in which each of the following is carried in mammalian blood: carbon dioxide,
oxygen, water, salts, lipids, nitrogenous waste and other products of digestion
Oxygen – when blood in the lungs comes into contact with oxygen that has entered the body by
diffusion, haemoglobin (in the red blood cells) bind with the oxygen and form a compound called
oxyhaemoglobin. This compound gives the bright red colour to blood.
Carbon dioxide – when CO2 enters the blood, 70% of it is transported in the form of hydrogen
carbonate ions – formed in red blood cells but carried in the plasma. The remaining CO2 is either
dissolved in plasma (7%) or is combined with haemoglobin (23%)
Water is carried as blood plasma, which is 90% water.
Salts – carried in blood as ions dissolved in plasma.
Lipids – a small proportion of lipids (fatty acids and glycerol) are soluble and enter the bloodstream
directly, but most need to be packaged into small droplets, which pass into the lymphatic system
and then into the bloodstream.
Nitrogenous wastes – these include ammonia, urea and uric acid which are all carried dissolved in
blood plasma
Other products of digestion (glucose, amino acids) – glucose and amino acids are water soluble and
are transported in the bloodstream dissolved in plasma
Explain the adaptive advantage of haemoglobin
Haemoglobin is a complex molecule within red blood cells which enable them to carry oxygen.
Adaptive advantages
 It increases the oxygen-carrying capacity in blood (relative to plasma) Haemoglobin
contains four haem units – giving one molecule the ability to bond with four oxygen
molecules. Thus, far more oxygen can be carried in blood cells by haemoglobin than would
be carried dissolved in plasma
 Its ability to bind oxygen increases once the first oxygen molecule binds with it. The
binding of each oxygen molecule changes the shape of the haemoglobin – making it easier
for each subsequent oxygen molecule to bind to it. This means that it can bind with a
maximum amount of oxygen in the lungs (high oxygen concentrations)
 Its capacity to release oxygen increases when CO2 is present. It is important for
haemoglobin to release the oxygen from the blood in tissues where the oxygen
concentration is low so that oxygen is delivered to the cells that need it. Metabolising cells
release CO2 which (indirectly) causes more oxygen to be released from haemoglobin.
Compare the structure of arteries, capillaries and veins in relation to their function
The function of arteries and veins is to carry blood over relatively long distances, from one organ to
another, whereas capillaries form branching networks to carry blood over relatively short distances
within organisms.
Arteries carry blood away from the heart
Veins return blood to the heart
Capillaries bring the blood into close contact with
tissues, allowing for the exchange of gases,
nutrients and wastes.
Arteries
Structure
o Walls of arteries are
relatively thick (compared
to veins)
o Walls of arteries have a
large proportion of elastic
fibres
o No valves
Function related to structure
o The walls are thick to suit
blood pumping out of the
heart in regular bursts of
high pressure
o Elastic fibres allow the
arteries to expand and
accommodate for the
increases in blood volume
with each heartbeat
o No valves – pressure of
heartbeat ensures one way
flow
Veins
o
o
o
Few elastic fibres
Thinner wall than arteries
Valves
o
o
o
Capillaries
o
o
Very thin walls
Vast network
o
o
Few elastic fibres as no
stretch or recoil necessary
Thinner wall due to blood
flowing through is at a lower
pressure than blood through
arteries
Valves ensure one way flow
of blood
Wall is only one-cell thick to
allow efficient diffusion of
nutrient/wastes and
efficient gas exchange
Vast network allows a large
surface area of exchange
with cells
Describe the main changes in the chemical composition of the blood as it moves around the body
and identify tissues in which these changes occur
 An increase in oxygen and a decrease in carbon dioxide concentrations are evident in the
blood that has passed through the lungs; whilst a decrease in oxygen and an increase in
carbon dioxide is evident in blood that has passed through any organ other than the lungs
(i.e. in any organ where cellular respiration has occurred)
 An increase in digestive end products (e.g. glucose, fatty acids) is evident in blood that has
passed through the small intestine (which absorbs digested food). These products then
travel through the bloodstream to the liver
 A decrease in digestive end products, and an increase in nitrogenous wastes (e.g. ammonia,
urea) is evident once blood has passed through the liver
 A decrease in nitrogenous wastes is evident in blood that has passed through the kidneys,
since they filter nitrogenous wastes out the blood and excrete them
Outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is
essential
Oxygen is necessary for respiration, a process by which cells release energy from glucose. Energy is
needed for the growth, repair of tissues, movement, excretion and reproduction. Without oxygen,
this chemical energy stored in glucose and other food molecules cannot be released; thus preventing
the metabolic processes within cells.
Carbon dioxide is produced in cells as a waste product of cellular respiration. It must be removed
from cells to prevent a change in the pH, as carbon dioxide reacts with water in the body to form
carbonic acid. A build-up of carbon acid is toxic, as it lowers pH of cells – reducing the efficiency of
enzymes and affecting the overall homeostatic balance within an organism. Therefore, the removal
of carbon dioxide is essential for the normal functioning of cells.
Describe current theories about processes responsible for the movement of materials through
plants in xylem and phloem tissue
Xylem
 Transpiration is the loss of water from plant leaves. Transpiration stream is the movement
of water in the xylem vessels up the plant, from the roots to the leaves
 The processes involved in the transpiration stream can be explained by the transpiration
(evaporation) - tension- cohesion mechanism.
 Transpiration: water is evaporated from the leaves through the stomates, pulling water
from cells and xylem tissue
 Cohesion: water molecules stick together and have the ability to instantaneously
transfer pressure and tension
 Tension: As water is evaporated from the leaves, it causes tension in the water column
within the xylem. Due to the cohesion of the water molecules, water moves up the
xylem like a wire being pulled up, and replaces the water lost
 Adhesion: when the pull stops, water sticks to the side of the xylem vessel and does not
fall down
Phloem
 In the phloem, sugars and small amounts of other nutrients are transported by
translocation from sugar sources in the plant to sugar ‘sinks’
 The current theory explaining translocation uses the pressure-flow mechanism and is called
the ‘source to sink’ model.
 The sugars from the leaves (source) are loaded into the phloem by active transport,
causing the osmotic pressure to shift (due to the difference in sugar/water
concentrations) and thus water follows in by osmosis.
 The opposite occurs at the sugar ‘sink’. Sugar and materials are removed from the
phloem by active transport, reducing osmotic pressure in the phloem (due to higher
water concentration), and water moves out by osmosis.
 These two processes produce a difference in hydrostatic pressure in the phloem, causing
the sap (sugar solution) to move from source to sink. Pressure flow, therefore drives the
sugars in the phloem from photosynthetic/storage sites to other parts of the plant
Analyse information from secondary sources to identify current technologies that allow
measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and
explain the conditions under which these technologies are used
Current technologies that allow measurement of oxygen saturation and carbon dioxide
concentrations in blood are:
 Pulse oximeters
 Arterial blood gas (ABG) analysis
Pulse oximeters
Pulse oximeters are used to measure the amount of oxygen in the patient’s blood. A clip with a
sensor is placed on the finger or earlobe and the sensor is connected to a monitor that shows the
pulse rate and oxygen saturation level. Two wavelengths of light: red and infra-red pass through the
finger from the light source to the photo detector. The amount of light absorbed by the
haemoglobin (and consequently the amount of light reaching the detector) depends on its degree of
saturation with oxygen.
Note that most oximeters don’t measure carbon-dioxide levels (it is only as recently as 2005 that
some oximeters with a carbon dioxide sensor were developed)
Conditions under which it is used:
 When a non-invasive technique is required
 When rapid, continuous monitoring of arterial blood is needed
 Examples: during anaesthesia, during recovery phase or in intensive care units during
mechanical ventilation. Oximeters are useful in such situations as it can quickly detect
problems with oxygenation.
Arterial blood gas (ABG) analysis
Arterial blood gas analysis is a more invasive technique of analysis, and involves removing blood
from an artery (usually in the arm) and performing a blood test using a sensor which translates the
chemical properties of the blood into an electrical signal that can be measured. It reveals far more
detail about the levels of chemicals in the blood, including partial pressure of oxygen and carbon
dioxid, the pH and level of bicarbonate ions.
Conditions under which it is used
 Invasive, and there could be delay between sampling and availability of results
 When more detailed information about oxygen, carbon dioxide and pH levels are required
 Examples: provides vital information for critically ill patients who are on ventilators or
respiratory therapy, studies of lung diseases, or in severe cases of breathing disturbance.
Analyse information from secondary sources to identify the products extracted from donated
blood and discuss the uses of these products
 Red blood cells – they help increase the amount of oxygen that can be carried to
the body’s tissues (by increasing haemoglobin levels) while not increasing blood
volume. They are given to people with anaemia (whose bone marrow doesn’t
make enough red blood cells), those who have kidney failure or acute blood loss.
 Platelets – essential for blood clotting. They are given to people who have
cancer of the blood or lymph. Patients undergoing cancer therapy do not make
enough platelets and are also given platelets from donated blood
 Plasma – contains blood clotting factors. It us used to treat people with clotting
disorders such as haemophilia. It can also be used to adjust the osmotic pressure
of blood and to pull fluids out of the tissues.
 White blood cells - infection fighting component of the blood. White blood cells
are only used occasionally to treat life-threatening situations when the cell count
is very low or the white blood cells are not functioning properly (in most cases,
antibiotics is used rather than white blood cell transfusions)
 Whole blood – only used when absolutely needed, for example when a person
has lost more than 20% blood volume
Analyse and present information from secondary sources to report on progress in the production
of artificial blood and use available evidence to propose reasons why such research is needed
Artificial blood or blood substitutes are designed to carry oxygen and carbon dioxide. They are not
involved in clotting, coagulation and immune defence.
The need for research in the development of artificial blood is as follows:
 It can be stored for long periods and time and is easily transported
 It does not need to be cross-matched for different blood types (i.e. it is universally accepted
by all blood groups)
 Can be produced at large quantities at low cost (meaning it can be readily available in large
supplies, solving the problem of a shortage of blood donors)
 It is completely safe (has no toxic effects, is free of disease and does not trigger an immune
response)
Proposed replacements for blood include:
Perfluorocarbons (PFC)
 Biologically inert materials
 Relatively inexpensive to make
 Can be made without biological materials, eliminating possibility of spreading an infectious
disease via blood transfusion
 However, it is not soluble in water, meaning that they need to be combined with other
materials (emulsifiers) to mix with blood
 Also, it can carry much less oxygen than haemoglobin-base d products, meaning that a lot of
PFC must be used
Haemoglobin-based products
 Unlike whole blood, haemoglobin products do not have the problem of blood typing
 Raw haemoglobin cannot be used because it breaks down into smaller, toxic compounds
within body. There are also problems with the stability of haemoglobin in solution
 Modifications, such as cross-linking molecules or using recombinant DNA technology are
currently undergoing trial phases for eventual commercial use.
3.
Plants and animals regulate the concentration of gases, water and waste products of
metabolism in cells and in interstitial fluid
Explain why the concentration of water in cells should be maintained within a narrow range for
optimal function
Water makes up 70-90% of living things and is essential for life. It is the solvent for all metabolic
reactions in living cells.
Chemical reactions in cells can proceed only if the reactants are dissolved in water. Water and solute
concentration in cells and fluids in living organs therefore must be maintained at a relatively
constant level, within a narrow range so that these cellular reactions can take place
The movement of water into and out of cells depends directly on the concentration of solutions both
inside and outside of cells.
 If too much water moved into cells, they could burst (e.g. in animal cells which have no cell
wall). If too much water has moved out, the cell contents could shrink, and the cytoplasm
would become too concentrated for normal cell functioning
Thus, to ensure the proper functioning of living cells, the concentration of water must be kept
constant.
Explain why the removal of wastes is essential for continued metabolic activity
If metabolic wastes were left to accumulate within the body, it would alter the conditions in the
internal environment – inhibiting enzyme functioning and preventing cells from undergoing normal
metabolic activity
 The build-up of nitrogenous wastes such as ammonia would cause an increase in the pH of
cells; the build-up of carbon dioxide in the body would react with water in cells and become
carbonic acid, which would lower the pH of the internal environment. These changes in pH
would prevent optimal enzyme functioning
 Accumulation of wastes that do not alter pH may cause other problems such as increased
solute concentration interfering with reaction rates and an osmotic imbalance affecting
membrane functioning
Therefore, metabolic wastes need to be removed in order to maintain homeostasis within an
organism.
Identify the role of the kidney in the excretory system of fish and mammals
In mammals and fish, the kidney has a dual role of excreting nitrogenous wastes and maintaining
water and salt concentrations (osmoregulation).
Fish do not excrete nitrogenous wastes through their kidneys; they use their gills.
Marine Fish: Their kidneys conserve water, excrete salts and nitrogenous wastes. These fish are in a
hypertonic environment (concentration of solutes is greater outside the organism)
Freshwater Fish: Their kidneys conserve salt, excrete excess water and nitrogenous wastes (by
producing large amounts of dilute urine). These fish are in a hypotonic environment (concentration
of solutes is higher inside the organism
Mammals: Their kidneys conserve water and salts when required, excrete excess water and salts
and excrete nitrogenous wastes. The mammalian kidney can adjust the reabsorption of nitrogenous
wastes, water and salts – varying the concentration of urine produced.
The kidney ensures that both the concentration of blood and interstitial fluid are constant.
Explain why the processes of diffusion and osmosis are inadequate in removing dissolved
nitrogenous wastes in some organisms
Osmosis is a selective form of diffusion in which the cell membrane acts as a selectively permeable
barrier that allows the passage of water but not larger molecules.
Diffusion and osmosis are both types of passive transport that require no energy input but are slow
(relying on differences in the concentration gradient). They slow down as the concentration gradient
becomes smaller and stop once the concentration gradient reaches equilibrium.
Problems with diffusion
 The rate of movement is too slow
 Not all wastes would be removed by diffusion. Once concentrations within blood and urine
equalised, no further wastes would be removed. Their accumulation would change pH of
cells and become toxic.
 Not all glucose and amino acids (needed by the body) would be reabsorbed
Problems with osmosis
 Too much water would be lost in urine since urine contains a large number of nitrogenous
wastes, water will be drawn in by osmosis (producing dilute urine). This loss of water cannot
be afforded by many terrestrial animals.
Distinguish between active and passive transport and relate these to processes occurring in the
mammalian kidney
Passive transport occurs spontaneously – requiring no input of energy. It involves substances
moving along the concentration gradient (from an area where there are many particles to where
there are few particles). Diffusion and osmosis are examples of passive transport
Active transport requires the input of energy as it involves substances moving against the
concentration gradient
Passive
 In a mammalian kidney, water
reabsorption is a passive process (it
follows the movement of salts)
 Some nitrogenous wastes (urea and
ammonia are moved into urine by
diffusion
Active
 Reabsorption of salts is an active
process.
 Glucose and amino acids are actively
reabsorbed
 Additional nitrogenous wastes are added
to urine through active transport
Explain how the processes of filtration and reabsorption in the mammalian nephron regulate body
fluid composition
The functional unit of the kidney is
the nephron. Each nephron has three
main parts: Bowman’s capsule, the
glomerulus and a long, thin tubule.
Filtration occurs in the glomerulus,
where blood pressure forces the
movement of small molecules from
the bloodstream into the Bowman’s
capsule (urea, glucose, amino acids,
salts and water). These form the
glomerular filtrate.
Reabsorption occurs in the tubules
(proximal, distal tubules and the Loop
of Henle). It involves both passive and
active transport – whereby solutes required by the body are moved back into the bloodstream via
the capillary network (ALL glucose and amino acids, SOME ions and water)
 Glucose and amino acid reabsorption takes mainly in the proximal tubule. At frist,
movement of glucose and amino acids is by facilitated diffusion (as the concentration is
higher in the glomerular filtrate than the bloodstream) but once the concentrations become
equal, active transport is utilised, until all glucose and amino acids are eventually reabsorbed
 Salt reabsorption occurs in the proximal, distal tubule and the loop of Henle (sodium,
chloride, potassium, calcium and hydrogen bicarbonate ions – HCO3-)
 Water is reabsorbed along the length of the tubule by the passive process of osmosis. As the
reabsorption of solutes occurs, osmotic pressure is altered and water flows out passively
together with the solutes
Note this is for understanding; not part of syllabus:
Secretion involves the selective movement of further substances from the bloodstream across the
wall of the nephron into the filtrate by the process of active transport (some drugs, hydrogen ions
and toxin molecules). It occurs in the proximal and distal tubules and is highly selective.
Excretion is where excess water and solutes are eliminated via collecting tubules in the form of urine
(passing into renal, pelvis, ureter and then bladder for storage)
Outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in the regulation
of water and salt levels in the blood
Antidiuretic hormone (ADH) or vasopressin is produced by the hypothalamus and stored by the
posterior pituitary gland. Osmoreceptor cells in the hypothalamus monitor water and salt levels in
the blood; when the water levels become too low, ADH is released – changing the water
permeability of collecting duct walls so that more water is reabsorbed into the bloodstream from
the ducts. It also increases the permeability of the duct walls to urea, which diffuse in from the
bloodstream. These two effects cause the urine concentration to increase
Aldosterone is a hormone produced by the adrenal cortex in the adrenal gland when a decrease in
the concentration of sodium ions is detected. It increases the permeability of the nephron to
sodium, causing more reabsorption sodium ions, and consequently increased reabsorption of
chloride and water (which follows by osmosis) as they follow the sodium ions. Thus there is more
salt conservation within the body causing in a rise in blood volume and pressure (and also a
reduction of the salt concentration of urine)
Both ADH and Aldosterone help the kidney carry out its homeostatic functions of osmoregulation:
 Regulation of solute concentration in blood – regulating the amount of sodium and other
ions that are reabsorbed or secreted in urine
 Regulation of blood volume – maintaining a constant fluid volume by producing either
concentrated or dilute urine.
Aldosterone brings about conservation of salts (and consequently water) in the body; ADH
brings about water conservation in the body
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 despite variations in the
environment.
Living organisms employ one of two strategies in Enantiostasis:
 Osmoregulators are organisms that avoid changes in their internal environment and have
the ability to keep the solutes at an optimal level (i.e. ‘regulating’ solute concentrations
within the body) regardless of differing external environment. They cannot tolerate a range
of salt concentrations within their body fluids/cells.
 Osmoconformers are organisms that tolerate the changes in environment by altering the
concentration of their internal solutes to match the external environment (“conforming” to
that of the environment)
Estuarine organisms
An estuary is where a river meets the sea, and freshwater mixes with saltwater. Enantiostasis is
important for organisms living in estuarine environment where salinity varies greatly.
Factors such as tide and rainfall greatly alter the levels of salts in the water. At high tide, sea water
flows into the river mouth, creating a higher salt concentration (higher osmotic pressure); at low
tide, sea water flows out and fresh water flows in.
In order for estuarine organisms to survive, adjustments are made in their physiology, such as to
keep enzymes functioning despite changes in the salt concentrations in the external environment.
Generally, Osmoregulators have body fluids similar to that of the marine environment, so when
exposed to water, their mechanisms try to maintain the higher osmotic pressure within the body.
Osmoconformers generally use small organic molecules to vary solute concentration of cells to
match that of the surroundings
 Osmoregulators:
- In salt water, salmon can drink continuously and eliminate salts through their gills;
whereas, in fresh water they stop drinking, absorb salt through gills and excrete very
dilute urine like freshwater fish
- Mussels in rock pools close their valves when the tide is out to keep salt concentrations
inside the body the same as the seawater
 Osmoconformers:
- Eels have special cells in their gills that can act as salt absorbers and salt excretors
- Sharks use trimethylamine oxide to regulate osmotic pressure in cells to equal that of
the environment
Describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss
Mechanisms that minimise water
loss:
Examples
Reducing the internal temperature
Eucalyptus trees and banksias have coarse, leathery leaves
with a thick cuticle to reduce evaporation (from the epidermal
cells) which would occur with thinner leaf cuticles.
Australian she-oaks have cladodes, which are green needlelike structures that are modified stems. Tiny brown scale
leaves occur at regular intervals along the cladodes, a feature
to reduce the SA of leaves and their exposure to the sun – thus
minimising water loss.
The coastal banksia has epidermal hairs, which trap a moist
layer of air – resulting in a smaller difference between
concentration of water in the leaf tissue and water vapour in
the layer of air trapped by the hairs.
The desert plant parakeelya has fleshy stems and leaves which
swell up and retain moisture when it becomes available, so
that during dry periods, it can survive by using up this
moisture.
Reducing exposure of leaves to the
sun
Reducing difference in water
concentration between plant and
outside air
Features related to water storage
Gather, process and analyse information from secondary sources to compare the process of renal
dialysis with the function of the kidney
People with dysfunctional kidneys are not able to remove wastes such as urea and other toxins.
They have to undergo renal dialysis to regulate their blood.
The process (haemodialysis):
- The blood is extracted from the body from a vein (invasive) and passed into a dialyser,
which is a bundle of hollow fibres made of a semi permeable membrane.
- The dialyser is in a solution of dialysing fluid, which has similar concentrations of
substances as blood. The fluid flows in the opposite direction to the blood to maximise
diffusion rate.
- The dialyser only allows wastes to pass through, and not blood cells and proteins. In this
way it is similar to the filtrations stage of the nephron.
- The dialysing fluid must constantly be replaced so that the concentration gradient of
wastes is maintained away from the blood
- The blood is then returned to the body.
Overall process
Functioning
Active/passive
transport
Kidney functioning
Natural process which filters our
blood-removing metabolic wastes
so that they may be excreted via
urination
Pair of kidneys filter wastes,
regulates pH, blood volume, water
and salt balance (osmoregulation)|
Both active and passive transport is
used in moving wastes from the
blood
Maintaining the
concentration
gradient
Active transport occurs, so the
concentration gradient is not as
important in ensuring the removal
of wastes
Speed at which
blood is filtered
Much faster than renal dialysis
(active transport involved, millions
of nephrons increase SA)
Hormonal control/Negative
feedback mechanisms regulate the
process naturally
Effective, efficient removal of
wastes, excess fluids/salts
Non-invasive
Regulation
process
Outcome
Renal Dialysis
Artificial process which removes
metabolic wastes that have accumulated
in the blood
Haemodialysis – blood passes through
tubules surrounded by dialysing fluid for
filtering
Relies on passive transport only – wastes
diffuse across artificial, selectively
permeable membrane of the dialysis
tubes
Waste concentration is higher in the blood
than in the dialysis tube so diffusion
occurs. The dialysis fluid is constantly
replaced to maintain the concentration
gradient
Slower as it relies on diffusion only and
the tubules do not provide as much SA as
nephrons do
Process is artificially controlled by a
computer linked to scissors
Less effective removal – only removes
wastes; doesn’t regulate ions in blood.
Takes longer
Invasive and carries risks
Present information to outline the general use of hormone replacement therapy in people who
cannot secrete aldosterone.
 Aldosterone increases the amount of salt (and consequently water) reabsorbed from kidney
tubules
 A lack of aldosterone may be the result of: damage to the adrenal glands due to accident,
surgery or disease or damage to the pituitary gland that controls the adrenal gland
 Without aldosterone, the body would not be able to reabsorb salt (specifically sodium ions)
and this would cause severe dehydration, and excessive potassium. Many functions are
disrupted as a result of this aldosterone drop and can lead to death.
Hormone replacement therapy involves restoring the balance of the hormones at levels that are
normal for the body, by giving the patients genetically engineered hormones such as fludrocortisone
to replace the hormones that they no longer produce naturally
Administered properly, it can do the job of aldosterone and enable patients to manage symptoms
such as fluid retention and high blood pressure, removing dangers of heart failure - allowing them to
lead normal lives
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 actively secreting
salts. Produces small amounts of concentrated urine. Salt 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.
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
Animals face the challenge of achieving a fine balance between the use of water to remove
nitrogenous wastes and conservation of water in the body
Ammonia is the direct result of amino acid breakdown (deamination) and is a waste product of all
organisms. It is very water soluble, but very toxic, and in its soluble form, requires large amounts of
water for its excretion.
Urea is toxic, but much less toxic than ammonia and it can be safely stored within the body for a
limited time and expelled with the removal of less water
Uric acid is less soluble than ammonia or urea and has low toxicity, meaning that little water is
expended to remove it.
Terrestrial Animals Releasing ammonia would be impossible due to lack of water. Instead, landdwellers change ammonia into less toxic forms and release it periodically.
Mammals change it into urea and release it as urine. (e.g. Kangaroos,
wallabies, hopping mice, koalas, etc.) Australian animals release very
concentrated urine, and are able to tolerate high levels of urea in their bodies.
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.
Insects
Insects also change ammonia to uric acid (e.g. Acacia psyllids).
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.
Process and analyse information form secondary sources and use available evidence to discuss
processes used by different plants for salt regulation in saline environments
 Halophytes are plants that have adapted to saline environments.
 They are commonly found in estuaries.
Grey Mangroves:
 Salt Exclusion: Special glands in the mangroves can actively exclude the salt from the water,
so that the water absorbed has a lower salt concentration than the water in the
environment.
 Salt Accumulation: Salt is accumulated in old leaves that drop off, so that the salt is out of
the plant’s system
 Salt Excretion: Salt can be excreted from the underside of the leaves of the mangrove
plants; salt crystals form under the leaves.
Saltbushes:
Salt Accumulation: This plant stores its excess salt in swollen leaf bases, which drop off, ridding the
plant of salt.
Perform a first-hand investigation to gather information about structures in plants that assist in
the conservation of water
 Saltbush:
- The saltbush has waxy leaves that reflect heat and light
 Eucalyptus:
- Waxy, hard leaves: Reduces water loss by reducing the rate of transpiration from the
leave surface.
- The leaves hang vertically, and this reduces the water loss, conserving water.
 Banksia:
- Leaves have sunken stomates – this reduces transpiration.
 Wattle:
- Leaves are small and hairy – the small size means less evaporation of water, and the
hairy leaves reduce the transpiration by trapping water.