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9.2 Maintaining a Balance
Contextual Outline
Multicellular organisms have specialised organ systems that are adapted for the uptake and transport of essential nutrients
from the environment, the utilisation or production of energy and the removal of waste products arising from cellular
activities.
The basis of healthy body-functioning in all organisms is the health of their cells. The physical and chemical factors of
the environment surrounding these cells must remain within narrow limits for cells to survive. These narrow limits need
to be maintained and any deviation from these limits must be quickly corrected. A breakdown in the maintenance of this
balance causes problems for the organism.
The nervous and endocrine systems in animals and the hormone system in plants bring about the coordinated functioning
of these organ systems. They are able to monitor and provide the feedback necessary to maintain a constant internal
environment. Enzyme action is a prime example of the need for this balance. Enzymes control all of the chemical
reactions that constitute the body’s metabolism. As enzymes normally function only within a narrow temperature range,
even small rises in body temperature can result in failure of many of the reactions of metabolism that are essential to life.
This module increases students understanding of the applications and uses of biology, implications for society and the
environment and current issues, research and developments in biology.
9.2 – Maintaining a Balance:
1. Most organisms are active within a limited temperature range:

Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to
describe their specificity in substrates:
–
Metabolism is the sum total of all chemical reactions occurring within a living organism. The only reason you
grow, heal etc is because of this.
–
Without enzymes, metabolism would occur at a rate too slow to support life
–
It is divided into two parts:

Anabolic: are reactions that involve the building up of larger organic compounds from simple molecules, e.g.
large polysaccharide molecule such as starch being made from monosaccharide units such as glucose (product
of photosynthesis).

Catabolic: are reactions that involve the breaking down of complex organic compounds to simple ones, eg
digestion of food, large food molecules such as proteins are broken down into small amino acids, which can be
used for other uses. (they create enzyme for other use by the body – which is integral in metabolic efficiency)
–
All the above, i.e. every metabolic reaction in your body is carried out by enzymes; they are organic protein
catalysts (chemical substance that speed reactions without taking part in it).
–
In the following diagram, the arrow signifies the occurrence of a chemical reaction and as it embodies the enzyme,
the enzyme is seen to be a biological catalyst which facilitates the reaction
–
Chemical composition of enzymes:

An enzyme is a protein

Recall: proteins are made of polypeptides which in turn are made of grouped amino acids.

Recall: a molecule is a chemical compound made out of two or more atoms

The substrate can only incur reaction

The amount of amino acids which constitute an enzyme is not numerically restricted; it can be up to 10,000
amino acids which formulate an enzyme

All enzymes are made of protein as well as other elements that are known as co-enzymes/co-factors which help
specific enzymes function, such as carbon, hydrogen, oxygen and nitrogen.

Enzymes are globular proteins, meaning the polypeptide chains (ie amino acids) are folded into a 3-dimensional
globular shape.

This shape is what effectively gives each enzyme its function, and parts of it are called active sites. The
molecule on which an enzyme acts on is called the substrate.

The enzyme provides the active site which the substrate binds upon, and initiates the enzyme/substrate complex
in order to produce the final product

The fundamental idea that an enzyme catalyses a reaction but is not directly involved within the chemical
reaction, means that it remains unchanged through the entire occurrence of the reaction. This ultimately means
that a used enzyme can be subsequently used in further chemical reactions, sustaining its role as a biological
catalyst that catalyses chemical reactions.
–
Specificity of enzymes:

Enzymes are highly specific in their action; this means that each enzyme acts on one substrate only, this is
because the shape of the active site of the enzyme matches the shape of the substrate material.

The products are the substances that the substrate(s) become. One substrate can be split, or two substrates can be
joined.
–
Models to explain specificity:

There are two current hypothesis:

The Lock and Key Model: This suggests that an enzyme can only react with a substrate which is reciprocal to
its shape and can bind to the enzyme at the active site and initiate reaction. The substrate fits perfectly into the
active site like a ‘key’ fits into a ‘lock’. It assumes that the enzyme had a rigid and unchanging shape, and is
therefore exclusive to the one substrate which can accordingly match this rigid and unchanging shape .

The Induced Fit Model: states that the binding of the substrate to the enzyme ‘induces’ a temporary change in
shape of the enzyme. The new shape of the enzyme better accommodates the shape of the substrate and a
reaction occurs. With accordance to this temporarily ‘induced’ shape, the enzyme returns to its regular state
after catalysing the reactions, and is therefore subject to catalysing further chemical reactions

Identify the pH as a way of describing the acidity of a substance:
–
pH is a way of describing the acidity or the alkalinity of a substance
–
it’s a measure of the concentration of hydrogen ions per litre of solution, so the more acidic a substance is, the
more hydrogen ions, the LOWER the pH.
–
–
The pH scale is from 0 to 14: a pH of 7 is neutral (pure water); above 7 is alkaline and below 7 is acidic.

3-6 slightly acidic

0-2 strongly acidic

7-11 slightly basic/alkaline

12-14 strongly basic/alkaline
Example of pH levels:

pH of 0 – 1 = Hydrochloric Acid (HCl)

pH of 3 = Lemon juice

pH of 5 = Banana

pH of 7 = Water

pH of 9 = Baking soda

pH of 10 = toothpaste

pH of 12-13 = Bleach

The stomach has a pH of 2-3 due to the
production of Hydrochloric Acid (HCl)

As seen in the graph to the right, the
optimum pH for Pepsin – an enzyme found
within the stomach is around 2.7 = which is
consistent with the stomach’s pH range of 23 due to the production of Hydrochloric
Acid (HCl)

Identical notion with Trypsin - the pH of the small intestine is 6-7. With accordance to the graph, we can
see that the graph has the optimum pH for Trypsin – an enzyme found in the small intestine at 6.8

pH of our blood needs to be finely controlled at 7.35 pH

If it’s low, acidosis ensues which has effects which could lead to headaches, weakness and even death
if it reaches around 7.10 pH – this is a small discrepancy from 7.35 pH, reiterating that the pH of the
blood needs to be finely controlled

If high – alkalosis ensues, whereby muscular weakness occurs, cramps due to disturbed function of
skeletal muscles

Identify data sources, plan, choose equipment or resources and perform a first-hand investigation to test the
effect of increased temperature, change in pH and change in substrate concentrations on the activity of enzymes:
–
Aim: To investigate the effect of a variety of factors (such as temperature, pH (acidity/alkalinity), substrate
concentrations) on the effect on enzyme activity.
–
Equipment:

Potato pieces/living tissue (i.e. cow liver pieces) (both contain the enzyme catalyse)

Catalyse is a enzyme that breaks poisonous hydrogen peroxide into harmless water and oxygen gas

20 test-tubes

Hydrogen peroxide (H2O2)

Acid: H2SO4, Base: NaOH

Source of heat (i.e. hot plate)

pH probe

Thermometer
–
Safety:

Hydrogen peroxide is an extremely poisonous substance, it must not be ingested, and teacher supervision is
needed.

Hot plate can reach temperatures well over 200-400 degrees, it must be put in a rigid and safe position – placed
in the middle of the table to avoid subjecting the table to direct student contact which can ensue heat injury

–
Gloves and glasses must be worn, in case of accidental test-tube damage.
Method:

3 separate tests were carried out in test tubes with potatoes placed in them; pH, temperature, substrate
concentration.

Evidence for enzyme activity came from the sound of 'fizzing effect', the louder the more activity is presumed.

This is further determined by the 'formation of bubbles', where bubbles that are in greater in height show greater
activity – i.e. a greater rate of reaction of the enzyme/substrate complex
–
Result:
–
pH:

Each enzymes work best at its optimum pH, which is usually within a very narrow range, for example enzymes
in the stomach can work at 1-2 pH , whilst enzymes as catalase work at 7 pH.

Extremes of acidity or alkalinity can affect the bonds holding the 3D globular shape of the enzyme. Thus losing
activity and distorting the enzyme

Enzymes work best at an optimum pH and if this range is exceeded dramatically, the enzyme will become
denatured and the rate of reaction will eventually stop – i.e. the enzyme substrate/complex will continue to
decrease beyond the optimum pH, eventually till its denatured and the enzyme cannot sustain its role as a
biological catalyst that increases the rate of chemical reactions
–
Temperature:

As temperature increases, MOST enzyme activity increases, up to the optimum temperature (a particular
temperature, approx. 40°C, an enzyme is most active). This is because the enzyme and substrate molecules
move faster as (more kinetic energy) and therefore more collisions between enzyme and substrate occur.

At very high temperatures beyond the optimum pH, the activity of the enzyme falls rapidly, because the heat
energy breaks the polypeptide bonds that cause the protein to fold, so destroying the active site in an irreversible
process, called denaturation.

When the enzyme is denatured, the shape of the enzyme is permanently changed and it cannot perform to
function as a biological catalyst that increases the rate of chemical reactions
–
Substrate concentration:

An increase in substrate concentration will increase the reaction until all enzyme active sites are occupied this is
known as saturation point, thus reaction proceeds at maximum rate (VMax or Maximum velocity). A further
increase in substrate, cannot increase the rate because there are no active sites of enzymes available which the
substrate can bind onto as a reactant

This is because once all the active sites of the enzymes are occupied the rate of reaction ceases to increase but
will proceed at the maximum rate.

A low amount of substrate concentration still catalyses the reaction, but not all the enzymes were active so it
wasn’t at the maximum amount yet

Explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency:
–
Example of a road trip – going from Penrith to the Blue Mountains – two disparate climates (hot and cold), yet
body maintains body temperature of 37°C
–
There is a fundamental point where the enzyme activity lessens (beyond or below optimum temperature, pH and
substrate concentration) and when it denatures (much above this level)
–
Optimum metabolic efficiency refers to the chemical reaction occurring at optimum speed to support metabolic
efficiency, and therefore life
–
Metabolism is severely affected by enzymes, and hence the functioning of an organism. Efficient metabolic
function is dependent upon the optimum operation of Enzymes. Enzymes work best within a limited range of
environmental conditions, but their efficiency is affected greatly by certain factors which include temperature, pH
and substrate concentration.

All enzymes have a specific temperature in which they function best (optimum temperature). If the
temperature is low, enzymes are “sluggish”, and reactions occur at a slow rate. When the temperature
increases, reaction rates increase until the enzyme is at its optimum temperature. If the temperature
continually increases, reactions rates dramatically decrease. This increase in temperature causes the peptide
bonds to break, which in turn makes the active site inactive, effectively destroying the enzyme – i.e.
denaturing the enzyme in a permanent, irreversible process where it can no longer function (active site is
destroyed and therefore substrate has nothing to bind onto)

All enzymes have an optimum pH. This means that if an enzyme carries a pH level of 6 it needs to be in an
environment which has a pH of around 6. Changing the pH slightly will change the enzyme activity, while
changing the pH dramatically will cause irreversible changes in the enzyme.

Substrate concentration also affects metabolic activity. If we increase the substrate concentration the
enzyme activity increases to a certain point until all active sites are being occupied by a substrate. So how
does the substrate concentration stay at a level which enables the enzyme to continually function at the
optimum level? Enzymes are continually reacting with substrates to produce a product, these products are
then metabolised by another enzyme. A process called feedback regulates enzyme activity, a key factor in
metabolic efficiency. Feedback also controls temperature and pH.
–
Hence a constant and stable internal environment is needed so that enzymes will always be working at an optimum
rate, and thus metabolism will be at optimum efficiency, if these factors do not remain relatively stable then the
rate of enzyme-catalysed reactions decrease, this rate could affect an entire metabolic pathway
–
Therefore, this reiterates the biological principle that without enzymes and their optimum operation therein,
metabolism would be too slow to support life

Describe homeostasis as the process by which organisms maintain a relatively stable internal environment:
–
Homeostasis is the process by which organisms maintain a relatively stable (constant) or almost constant, internal
environment despite external changes in the environment
–
No matter what is happening on the external environment, the human body is capable of maintaining a constant
internal environment. For example our blood sugar remains fairly constant, (90mg/100mL) body temperature (37
degrees Celsius) and pH of the blood (7.38 – 7.42). This constant internal environment is known as homeostasis.
Homeostasis is the constant internal composition of a cell or an organism and the mechanisms that maintain it. In
simple terms homeostasis is the steady state of an organism. Homeostasis does not merely occur on its own.
Certain stimuli that cause an imbalance will in effect illicit a response, in turn returning the organism to its steady
state.

OTHER FACTS

The idea of homeostasis was introduced by Claude Bernard in 1859, he did not call the process
homeostasis

–
Term homeostasis was first created by Walter Cannon (1929)
Homeostasis falls into 2 categories, depending if it is ectothermic (doesn't produce own heat) or endothermic
(produce own heat). An organism may be a conformer or a regulator.

Regulators try to maintain (regulate) the parameter at a constant level over possibly wide environmental
variations. (ectothermic)


Conformers allow the environment to determine the parameter. (endothermic)
Explain that homeostasis consists of two stages
–
–
Detecting changes from the stable state;
–
Counteracting changes from the stable state:
Homeostasis in endotherms is carried out in 2 steps, this mechanism is known as feedback:

Detecting change.

Counteracting the change.
–
Detecting Changes:

Any change that provokes a response is a stimulus.

Receptors detect stimuli.

Examples of external stimuli: light, day length, sound, temperature, odours.

Examples of internal stimuli: levels of CO2, oxygen levels, water, wastes.

–
Receptors can range from a patch of sensitive cells, to complex organs like the eyes and ears of mammals.
Counteracting Changes:

After receptors detect changes, organisms are therefore able to react to the change to maintain a relatively stable
(constant) internal environment i.e. homeostasis.

This type of response will counteract the change to ensure the stable state is maintained, relative to the idea of
homeostasis – the process of maintaining a relatively stable internal environment despite external changes


Effectors bring about responses to stimuli.

Effectors can either be muscles or glands:

Muscles bring about change by movement

Glands bring about change by secreting chemical substances
Gather, process and analyse information from secondary sources and use available evidence to develop a model of
a feedback mechanism:
–
The mechanism that brings about homeostatic change is called FEEDBACK
–
Homeostasis does not maintain the exact set point, but homeostasis is maintained as long as there is only a narrow
range of fluctuation (increase and decrease) of the variable around the set point. If the fluctuation is large (this is
the most common in humans), and exceeds the normal range, a negative feedback mechanism comes into
operation in response to this change; it is termed negative because it counteracts (negates) the change, thus
returning the body to within the normal range.
–
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 carbon dioxide levels (an increase in it):

Outline the role of the nervous system in detecting and responding to environmental changes:
–
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate
the actions of an animal and transmit signals between different parts of its body.
–
The nervous system works to regulate and maintain an animal’s internal environment and respond to the external
environment, i.e. maintain homeostasis.
–
The nervous system is made up of two parts:

Central Nervous System: This acts as a CONTROL CENTRE for all the body’s responses and it coordinates
all these responses, it consists of the brain (specifically hypothalamus) and the spinal chord where it receives
information, interprets it and initiates a response.

Peripheral Nervous System: This is a branching system of nerves that connects receptors and effectors. This
system transmits messages from the central nervous system and back. It acts as a communication channel.

The stimulus response pathway occurs as follows

Special endings on sensory nerves located in the PNS, such as heat sensors detect stimuli such as changes in
heat, pressure or chemical conditions

Receptors relay messages that are processed within the CNS

A response is formulated and the messages are relayed to effector organs or muscles that bring about the
response (initiate the response)

Identify the broad range over which life is found compared with the narrow limits for individual species:
–
Ambient temperature literally means the temperature of the environment; room temperature implies a
temperature inside a temperature-controlled building (the building has specific parts which affect the ambient
temp).
–
Organisms on Earth life in environments with ambient temperatures ranging from less than 0ºC (such as arctic
animals) to more than 100ºC (such bacteria found in boiling undersea volcano vents).
–
However, individual organisms cannot survive this entire range of temperatures for example mammals can only
survive temperatures from about 0 - 45ºC.
–
This means that life is found in a very wide range of temperatures, but individual species can only be found in a
narrow temperature range.

Compare responses of named Australian ectothermic and endothermic organisms to changes in the ambient
temperature and explain how these responses assist in temperature regulation:

Analyse information from secondary sources to describe adaptations and responses that have occurred in
Australian organisms to assist temperature regulation:
–
Ectotherms (cold blooded): are organisms that have a limited ability to control their body temperature (due to
their cellular activities generate little heat). Their body temperatures rise and fall with ambient temperature
changes.

–
Most organisms are ectotherms; examples are plants, all invertebrates, fish, amphibians and reptiles.
Endotherms (warm blooded): are organisms whose metabolism generates enough heat to maintain an internal
temperature independent of the ambient temperature.

–
Examples are birds and mammals.
Ectothermic response; Central netted dragon (Ctenophorus nuchalis):

Increase in temperature (i.e. hotter):

Stays in sheltered areas to avoid extreme heat. They can dig burrows or seek shelter in caves or crevices. This
reduces the effect of heat on their body.

It can change into nocturnal animal when the temperature becomes very hot. Many desert animals sleep in
burrows during the day and are active at night, to escape the heat.

Decrease in temperature (i.e. colder):

It will change its body position, to expose more of its body surface area to sun's rays, increasing core body
temperature.

–
They will seek areas of higher heat rays, such as on top of ledges instead of burrows.
Endothermic response; Red Kangaroo (Macropus rufus):

Increase in temperature (ie hotter):

It licks its arms to cool itself. The evaporation of the saliva cools its skin by convection.


It becomes less active, activity generates heat as many reactions are exothermic (release heat).
Decrease in temperature (ie colder):

Insulation: they have a thick fur layer, and contract their muscles controlling and shiver to generate heat.

They seek group warming, where they are exposed to less cold air.

Identify some responses of plants to temperature change:
–
Since plants cannot move from environment to environment, they respond to temperature by various changes:
–
Increase in temperature (i.e. hotter):

Leaf orientation: Some plants can change the orientation of their leaves in relation to the sun at different times,
for example their leaves hang down vertically, to reduce exposure, thus controlling temperature.

Growth rates: They alter their growth rate for example; some Eucalyptus trees grow more in spring than in
winter, hence using less water which can be use for cooling itself.
–
Decrease in temperature (i.e. colder):

Deciduous trees (trees that shed their leaves for a part of every year) lose their leaves in winter (leaf fall) and
undergo a period of dormancy, which allows them to survive not only the extremely low temperatures, but also
water shortages and lower availability of sunlight.

Plants may die above the ground, but leave bulbs, roots, rhizomes or tubers to survive underground. These then
sprout when favourable conditions return.
2. Plants and animals transport dissolved nutrients and gases in a fluid medium:

Perform a first-hand investigation using the light microscope and prepared slides to gather information to estimate
the size of red and white blood cells and draw scaled diagrams of each:
–
Aim: To estimate the size of red blood cells and white blood cells seen with a light microscope.
–
Equipment:

Light microscope

Prepared slides of human blood

1mm sized Mini-grid plastic paper

Pencil and drawing paper
–
Safety:

Slides can have sharp or unseen flint pieces of glass, gloves and glasses should be worn.

Use commercially prepared microscope slides of blood and not fresh blood, to eliminate the risk of contracting
blood-borne disease.
–
Method:

The microscope on normal view ie 1X, has a limited field of view of 16mm.

Hence set your microscope with the millimetre-squared graph paper first. Then 'click' the 1X objective lense,
this will show you what the 'normal' eye of 16mm can see.

Then click the 10X objective, this will magnify the 10mm by a factor of 10. Hence now youll see a maximum
field of view of 1.6mm, and its sub-ten components. (also note 1mm= 1000µm)

Now using the 40X objective, this now makes the initial 16mm diameter four times less then the 10X, so the
diameter is approximately 0.4mm. Hence this diameter is 0.4mm, or 400µm

Now, putting a slide of a prepared blood, at 40X objective, estimate how many blood cells there exists in that
'field of view', approximately 50 red blood cells exist, hence the size of 1 RBC is 400 µm divided by 50
(400/50), which is 8 µm.

Now for white blood cells since there are so few of them, it is NOT possible to count the number of white cells
across the diameter, and even much more difficult to estimate how many would fit across the diameter. Hence
there size is estimated by proportion in comparison to that of RBC.
– Result:

Red blood cells (Erythrocytes):

Size: 6-9 µm

Shape: Bi-concave (concave on both side) discs

Function: Transport of oxygen.

They have no nuclei; they only live for 3 months. After this they are destroyed in the liver
or spleen.

5-6 million in every millilitre of blood.

They are produced in the bone marrow


White blood cells (Leucocytes):

Size: 12-15 µm

Shape: Irregular shape; can change shape

Function: To defend against disease

Only 4-12 thousand per millilitre of blood

They have nuclei, unlike red blood cells

They are produced in the lymph glands.
Identify the forms in which each of the following is carried in mammalian blood:
–
–
Carbon Dioxide
–
Oxygen
–
Water
–
Salts
–
Lipids
–
Nitrogenous wastes
–
Other products of digestion
Carbon dioxide:

It is produced as a waste product of respiration in body cells. As its concentration is higher in the cell than in the
blood its diffuses in the blood:

70% of the carbon dioxide is converted into carbonic acid then changed into hydrogen carbonate ions. This
change from carbon dioxide to carbonate ions happens on the red blood cells. The ions are transported in the
plasma, NOT dissolved in it.
Carbon + Water
Dioxide
CO2
–
+
Carbonic
Acid
H2O
H2CO3
Hydrogen +
Ions
Hydrogen
Carbonate Ions
H+ + HCO-

Bind to haemoglobin in erythrocytes forming carbaminohaemoglobin (only 23% of the carbon dioxide).

Be dissolved directly in the plasma (only 7% of the carbon dioxide).
Oxygen:

Oxygen is needed in the body for respiration. It is brought in across the respiratory surfaces of the lungs.

It binds with haemoglobin in red blood cells, forming oxyhaemoglobin.
–
Water:

Water is the solvent of plasma; it makes up the bulk of blood volume.

It makes up 60% of the volume of blood.
–
Salts:

These are transported directly dissolved in the plasma as ions (ie NaCl as Na+ and Cl-), these are known as
electrolytes.
–
Lipids and other products of digestion:

The aim of digestion is to break large molecules down to a size small enough for absorption through the
intestine wall and into the bloodstream, so that they can be transported to cells in the body where they are
required.

Lipids are any of a group of organic compounds (i.e. containing carbon), including the fats, oils, waxes, sterols,
and triglycerides that are insoluble in water, are oily to the touch, and together with carbohydrates and proteins
constitute the principal structural material of living cells.

Digested lipids are changed into triglycerides (this happens in the lining of the small intestine).

Lipids are then transported as chylomicrons (these are clusters of triglycerides, phospholipids and
cholesterol), wrapped in a coat of protein.

–
These are released into the lymph and eventually pass into the veins
Other products:

Nitrogenous wastes:

Wastes such as ammonia are changed in urea


Urea is transported dissolved in the plasma
Minute minerals:

Includes amino acids, sugars and vitamins

They are mainly water soluble and transported in the plasma.

Explain the adaptive advantage of haemoglobin:
–
Haemoglobin is a protein made up of four polypeptide chains (called globins) and each is bonded to a haem
(iron-containing) group which can attach to an O molecule, forming oxyhaemoglobin.
–
For every haemoglobin, 4 oxygen molecules can attach. There about 250 million molecules of haemoglobin in
each red blood cell, hence the very high oxygen carrying capacity.
–
If blood carried oxygen without haemoglobin, the oxygen would have to be dissolved directly into the plasma
(into water). But oxygen is not very soluble in water therefore, if oxygen was carried only by being dissolved in
blood plasma, 100 ml of water would only be able to carry 0.2 ml of oxygen.
–
The presence of haemoglobin increases the oxygen carrying capacity of blood by 100 times

Dissolved only

Haemoglobin
–
0.2 ml O2/ 100 ml blood
20 ml O2/ 100 ml blood
The adaptive advantage:

It increases the oxygen carrying capacity of blood (proven above). Mammalian cells need a lot of energy and
therefore must have a continual supply of OXYGEN for RESPIRATION (making ATP – a form of chemical
energy); this ability of blood to carry large quantities of oxygen gives mammals a considerable survival
advantage. The extra energy allows mammals to be active, as well as grow large.

It has the ability to bind oxygen at an increasing rate once the first oxygen molecule binds to it. The bonding of
each oxygen molecule causes the haemoglobin to change slightly in shape, making it easier for every subsequent
oxygen molecule to bind to it. This increases the rate and efficiency of oxygen uptake. As a result, a very small
increase in the oxygen concentration in the lungs can result in a large increase in the oxygen saturation in the
blood.

It has the capacity to release oxygen at an increasing rate when carbon dioxide is present. Metabolising cells
release carbon dioxide, which combines to form acidic carbonic acid, and this lower pH, thus increases chances
to affect enzymes, and toxicoses cells (acid is corrosive).

It can undergo the Bohr effect, which at lower pH (due to increasing CO2) levels can release oxygen to tissue
areas that in need of it, expressing its adaptive advantage.

Outline the need for oxygen in living cells and explain why the removal of carbon dioxide from cells is essential:
–
Cells require oxygen in the process of respiration:

–
Glucose + oxygen
carbon dioxide + water + energy (in the form of ATP).
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. Carbonic acid forms when carbon dioxide dissolves in water. At
normal levels, the carbon dioxide; bicarbonate ion (HCO 3-) equilibrium is an important mechanism for buffering
the blood to maintain a constant pH, if greater amounts of carbon dioxide are produced the body cells (blood and
lymph) will become acidic due to the formation of carbonic acid, enzymes can only function within a specific pH
range, therefore an increase in carbon dioxide will result in lowering the pH which will affect the overall
metabolism of the body.

Perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water:
–
Aim: To model the effect of carbon dioxide on the pH of water.
–
Equipment:

25ml of Distilled water in 100mL beaker

Universal indictor (its an indicator that changes colour depending on the pH of a solution)

pH probe attached to data logger
–
Safety:

Gloves and glasses should be worn, in case of glass breaking.

The water can become corrosive due to increasing pH, it should NOT be ingested after use, dispose in an
organic waste container.

–
Straws should NOT be used by more then one student, to minimise contracting diseases.
Method:

In a beaker, pour water till the 25mL grade mark, then put 3 drops of universal indicator, this should now
change into greenish colour.

Then put the pH probe, and check the pH is about 7.

Exhale air into the straw that is dipped into the solution, for about 3 minutes.
–
Result:

After about 30 seconds, the colour of the solution began to change into pale yellow, and the pH on the data
logger started decreasing.

This is because carbon dioxide forms a weak acid; carbonic acid (H2CO3) so the water becomes more acidic.
Carbonic acid in water dissociates to form hydrogen carbonate ions (HCO 3-), and some carbonate ions (CO32-).

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:
Technology
How it Works
The Conditions It Is Used
Pulse oximeter
Measures O2 levels ONLY.
Used in many conditions; this is because it is
Device like a peg sits on the finger and
painless, easy to apply and quick to give results,
measures the transmission of light through
example:
tissues ie measures the amount of oxygen in

arterial blood.
anaesthesia.
There is a large difference between red light

absorbed by haemoglobin compared to
oxyhaemoglobin, hence this can be analysed
gas (ABG)

analysis
Measures

pressure
(or
the
concentration) of O2 and CO2 in the

Used when there are signs of dangerously low
oxygen or high carbon dioxide levels.

Helpful
for
monitoring
patients
under
blood
anaesthesia, in intensive care, in accident or
Measures saturation of oxygen (which is
emergency facilities and for premature babies.
the amount of oxygen combined to
haemoglobin
compared
to
the
maximum)

Can be used as a general check-up procedure to
analyse O2 levels
Measures O2 and CO2 levels.

Monitor premature babies that are in neo-natal
wards.
to give a reading.
Arterial blood
During surgeries, to monitor patients under
Measures levels of bicarbonate and pH
(to show CO2 levels)
This analysis evaluates how effectively the
lungs are delivering oxygen and removing
carbon dioxide.

Helps for diagnosing as well as monitoring
patients eg a patient in a coma can have their
blood gases regularly monitored.

Compare the structure of arteries, capillaries and veins in relation to their function:
Arteries
Veins
Structure
Thick walled, elastic, muscular
Thinner walls then arteries, elastic, less
muscle , wider diameter (larger lumen)
Direction of blood: flow /
pressure
Carry blood away from heart, pressure
created by hearts pumping puts stress on
arteries, blood pressure is high
Contain muscle fibres which contract and
relax, rate is maintained as blood travels in
spurts towards body tissues
Oxygenated blood taken away from heart
(oxygenated blood is with oxygen. They are
found in the pulmonary vein and systemic
artery)
Carry blood to heart, as there is no stress on
veins the blood pressure is low
Diagram
Blood movement and
rate
Carries
–
Contain no muscle, rely on valves and when
large muscle contract they help push the blood
flow through the veins
Deoxygenated blood taken to the heart
(deoxygenated blood is with little oxygen.
They are found in the pulomary artery and
systemic vein)
Capillaries:

Capillaries are an extension of the inner layers of the arteries and veins (Artery  arterioles  capillary 
venules  veins).

Capillaries are only one cell thick, and are so narrow, that only one red blood cell can pass at a time.

Capillaries surround all tissue cells, thus they provide a very large surface area over which exchange of
materials between blood and body cells can occur.

Describe the main changes in the composition of the blood as it moves around the body and identify tissues in
which these changes occur:
–
Pulmonary circuit (From Body to HEART to the Lungs):

Blood enters the right atrium of the heart via the vena cava (major vein):

The blood is deoxygenated, and high in carbon dioxide.

It is also low in glucose and other nutrients; high in urea, other nitrogenous wastes and various poisons.

As the heart beats, the right ventricle pumps the blood through the pulmonary artery, to the lungs:

Here the blood gains oxygen through exchange with alveoli in the lungs (ie air sacs), and loses its carbon
dioxide. pulmonary

–
The blood then enters the left atrium via the vein.
Systemic circuit (From Lungs to HEART to the Body):

The left ventricle pumps oxygenated blood to the body through the aorta.

In the body, various changes occur to the blood.

The blood loses oxygen and gains carbon dioxide in all body cells, as respiration occurs.

In the Liver:

Levels of glucose are regulated: excess glucose is changed to glycogen, or glycogen stores are changed to
glucose (if needed).

Excess amino acids are changed to ammonia, and then to urea.

Poisons are also reduced, as the liver changes them to less toxic forms.

In the Intestines:

Levels of nutrients from digestion increase.

Glucose, amino acids, ions, lipids and other substances from food enter the blood.



In the Kidneys:

Salt and water levels are regulated.

All urea is removed, toxins are excreted into the urine.
The changed blood, again highly deoxygenated, from the body then flows back to the pulmonary circuit.
Analyse information from secondary sources to identify the products extracted from donated blood and discuss the
uses of these products:
–
Red blood cells:

Used to increase the amount of oxygen that can be carried to the body’s tissues; given to anaemic patients, or
people whose bone marrow do not make enough red blood cells
–
Plasma:

This liquid portion of the blood, is given to people with clotting disorders (such as haemophilia), and also used
to adjust the osmotic pressure of the blood (to pull fluids out of tissues).
–
White blood cells:


Infection fighting component of the blood.
Analyse and present information from secondary sources to report progress in the production of artificial blood and
use available evidence to propose reasons why such research is needed:
– The problems of using real blood:

Shortage of real blood

It has to be ‘cross-matched’. This is because, if you receive the wrong type of blood, it can be fatal. This is a
great disadvantage in emergency situations.

It has to be free of infectious agents. Only blood that is free of bacteria and infectious agents (such as HIV) can
be used. Testing the blood is costly. This limits its applicability, and again reiterates the shortage of blood

It has a short shelf-life. Because red blood cells only survive for 3 months, the blood has a short life span (blood
can only survive for 3-4 weeks).
– Proposed replacement; Perflurochemicals (perflurocarbons):


Synthetic and inert, are completely sterile

Cheap to produce, compared to using real blood.

Can dissolve 5 times more oxygen than blood.

Free of biological materials, therefore no risk of infections

BUT; must be combined with other materials to mix in with the bloodstream (eg lecithin).
Choose equipment or resources to perform a first-hand investigation to gather first-hand data to draw transverse
and longitudinal sections of phloem and xylem tissue:
–
Aim: To draw the transverse (top view) and longitudinal section (side view) of plant tissue (ie xylem and phloem).
–
Equipment:

A stick of celery

Red food colouring

Water in a 100mL beaker

Razor blade

Light microscope
–
Safety:

The razor blade is extremely sharp, gloves should be worn in case of accidental flicking of blade onto skin.

Glasses should be worn in case of glass breaking.
–
Method:

In the 100mL beaker filled with water, put 3-5 drops of red food colouring into the solution. It should change to
dilute red colour.

Place the celery stick into the beaker, and leave it over night, so the coloured water can seep into the plant
sections to rise through xylem vessels, hence staining them strongly. Some water also travelled down the
phloem vessels.

Using a sharp one-sided razor blade, very thin slices were cut from across the stalk (for the transverse section)
and from the length of the stalk (for the longitudinal section).

–
Suitable slices were then prepared as wet mounts and viewed under a light microscope.
Result:

Phloem:

Xylem:

Describe current theories about processes responsible for the movement of materials through plants in xylem and
phloem tissue:
–
There are 2 types of transport tissues in plants:

Xylem: This transports water and mineral ions upwards from the roots to the leaves of a plant.

Phloem: This transports organic materials (particularly sugars) up and down the stem to other parts of the plant.
–
There exist two theories (i.e. possible explanations based on empirical evidence) into how water/nutrient moves in
each tissue respectively.

In Xylem:

The transpiration stream theory (ie cohesion-adhesion-tension theory) poses, that due to physical forces of
water (and ions) being removed from the plant stomates by passive transport (i.e. transpiration), causes a
column of water to be sucked up into the stem by the evaporative pull, also the low concentration of water at
the roots allows more water to diffuse in.

Once water has been absorbed into the roots of plants (by osmosis) along with mineral ions (by diffusion and
active transport), these substances move across the root into the xylem. A small amount of root pressure
results from the continual influx of more water and ions, hence forcing the solution already present upwards
(due to pressure build up), however this is usually not enough.

The constant loss of water, leads to a transpiration stream (which is the constant upward flow of water
through a plant), this is because of waters 2 properties, which are adhesive forces (the ability of molecules to
attach to walls), and cohesive forces (the attraction of molecules to each other), hence leading to the
capillarity (water rising up through bore of tissue) and hence the stream.

In Phloem:

The pressure flow theory (ie source-path-sink theory) states that in the plants, there are sources of nutrients,
e.g. leaf cells are the sources of sucrose. As the sucrose, amino acids and other minerals build up, the cells
actively transport the glucose sugars by active transport into the phloem tubes, this is known as loading, it
can be done by 2 ways:

Symplastic Loading: Sugars and nutrients move in the phloem from the mesophyll cells to the sieve
elements through the plasmodesmata that join adjacent cells (note: Plasmodesmata have not been found in
all plants).

Apoplastic Loading: sugar and nutrients move along the cell walls to the sieve plate. Then they cross the
cell membrane by active transport to enter the phloem tube.

As sugars enter the phloem the concentration of phloem sap increases, this causes the entry of water by
osmosis from the surrounding cells (osmotic pressure gradient is low). This resulting pressure causes water
and dissolved solutes to flow towards a SINK.

A sink is a region of the plant where sugars and other nutrients are actively begin removed from the phloem.
As sugars move out of the phloem, water flows out with them. This reduces the pressure in the sieve cells at
the sink region.

Materials are transported both up and down the stem and are distributed especially to the growing points and
reproductive structures, including developing fruits and seeds, it is driven by a gradient generated osmotically.
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 around 70-90% of living things; it is essential for life, it is the solvent of all metabolic reactions in
living cells (universal solvent), and sometimes directly takes part in it (eg. respiration). Therefore a deviation can
cause:

Isotonic: Concentration of solutes outside the cell is the same as inside the cell. No overall movement of water.

Hypertonic: Concentration of solutes is greater outside the cell than inside. Water tends to move out of the cell.

Hypotonic: Concentration of solutes is greater inside the cell than out. Water tends to move inside the cell.
–
Living cells work best in an isotonic environment where the levels of water in cells need to be kept relatively
constant, any change in the concentration of solutes will result in a change in the levels of water in cells which
usually results in death (either dehydration or cell bursting)
–
Enzymes also require specific conditions of functioning, some of which could relate to the levels of water and
solutes in cells, as an increase in water changes the concentration of acid (either dilutes it or makes it
concentrated).

Explain why the removal of wastes is essential for continued metabolic activity:
–
As a result of metabolism, many waste products are formed, for example:

In the process of deamination (process by which amino acids and proteins are broken down into ammonia),
ammonia is highly toxic and must be removed or changed to a less toxic form. It can greatly increase the pH and
make it more alkaline.

–
It carbon dioxide accumulates, it can form carbonic acid, which lowers the pH i.e. makes the pH more acidic
If these toxins are allowed to accumulate, they would slow down metabolism and kill the cells (e.g. excess toxins
is acidic thus increases pH, affection enzyme function which can lead to denaturation), this is why they need to
quickly be removed, or converted into a less toxic form.

Identify the role of the kidney in the excretory system of fish and mammals:
–
The maintenance of a constant concentration of nutrients, water and waste products in the internal environment of
organism, is crucial to its wellbeing. The concentration of these substances directly affects metabolism in cells,
and hence needs to be balanced.
–
Many wastes are excreted (process by which waste products, which have been produced as a result of metabolism,
are removed from the body). The excretory system is made up of systems and organs that carry out the removal of
metabolic wastes.
–

Carbon dioxide is excreted via the lungs (ie respiratory system).

Nitrogenous wastes are removed along with excess salts and water via the kidneys (ie urinary system).
The kidney is an organ of the excretory system of both fish and mammals. It plays a central role in homeostasis,
forming excreting urine while maintaining osmoregulatory.
–
Osmoregulation: means the physiological processes that an organism uses to maintain water balance; that is, to
compensate for water loss, avoid excess water gain, and maintain the proper osmotic concentration (osmolarity) of
the body fluids.

Distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney:

Explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid
composition:
–
Active transport: is the process of using energy to transport substances across highly concentrated membrane
from an area of low concentration, it would normally not be able to cross due to a concentration gradient (the
amount of substance in a particular area).
–
Passive transport: is the process of movement substances across a membrane from an area of higher
concentration to an area of lower concentration without energy expenditure (this is diffusion and osmosis).
–
The excretory system is a group of organs that function together remove metabolic wastes from the tissues of an
organism and expel them to the outside, a kidney is the main excretory organ responsible for removing
nitrogenous wastes from the bodies of vertebrate animals (including fish and humans).
–
The function of the kidney in excretion is to filter the blood that enters it, removing the waste in the blood
solution, for this waste to be excreted. This filtration is carried out by millions of small filtering units that are in
kidneys which are known as nephrons.

The nephron is a regulatory unit; it absorbs or secretes substances in order to maintain homeostasis, this
regulation maintains the constant composition of body fluids which is done by adjusting salts and water levels to
maintain fluid concentration, different ions also adjusted to maintain pH.
–
Urine is the final solution produced by these microscopic tubules, and passes out the kidney via ducts (ureters) and
then goes to the urine storage organ (bladder), which after a certain limit fills and the human passes this urine
through the urethra to the outside. (In vertebrates this goes to the a chamber (cloaca) instead of the urethra, which
empties to the outside)
–
Detailed structure of a nephron:

It consists of 4 parts (in order of movement) THAT are heavily surrounded by capillaries: Bowmans capsule
Proximal (i.e. first) convoluted tubule
tubule
–
the loop of Henle
Distal (i.e. second) convoluted
collecting duct which produces urine that leads to the bladder.
Function of nephrons

Three main process occur in the kidney, in the parts mentioned above, they are filtration
secretion.

Filtration:
reabsorption

When highly oxygenated, unfiltered blood enters the kidney through the renal artery it goes to the nephrons,
upon reaching it splits into a spherical network of blood capillaries called glomerulus that are in a Bowman's
capsule, the blood pressure here is so high that fluid and substance from the blood are forced into the
Bowman’s capsule, and forms a fluid called the glomerular filtrate.

Blood cells and proteins are retained in the blood, while large volumes of water pass through contained
dissolved substances such as: water, amino acids, glucose, salts (ions), nitrogenous wastes and other toxic
molecules.

This process is known as filtration, it separates based on SIZE of molecules, since proteins and RBC are
larger then other molecules they cannot pass the Bowmans capsule. Therefore:

Substances that the body needs will require reabsorption, so they are not lost with urine.

Additional wastes that were in the bloodstream, and managed to escape the higher pressure of the Bowmans
capsule need to be added to this 'urine' mixture.

Hence this is not the final fluid excretion.

Reabsorption:

Depending on the feedback of the body, varying amounts of solutes are reabsorbed from the solution, for
example water, amino acids, glucose, salts (Na+, K+, Cl-, Ca2+, Mg2+, HCO3-).

This occurs in the proximal, loop of Henle and distal tubules.

In the proximal tube:

All organic nutrients (amino acids and glucose) are reabsorbed, aswell as some ions such as (Na +, K+, Cl-,
Ca2+, Mg2+, HCO3-).

In the loop of Henle:

After the initial reabsorption from the distil tube, you'll have a liquid that is primarily urine, whether its
concentrated or not, is dependent in the loop of Henle.

The loop of Henle has 2 limbs, a descending then ascending, where the descending is permeable to water
ONLY, and the descending is permeable to salt ONLY.

Secretion:

This is the last process and leads to the formation of urine. It occurs in the distil and collecting tubule.

The liquid present in the tubule, are then added with metabolic wastes (such as urea, ammonia, hydrogen ions,
durgs: pencillin, morphine) etc that are brought by active transport to the distil tubule.

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 (ie they do not require energy), this is too slow for
the normal functioning, because the movement of molecules relies on differences in the concentration gradient
between two solutions (it moves from high conc. to low conc.)
–
Also this process greatly slows down once the difference in concentration gradient becomes smaller, and stops
once the concentrations are at equilibrium.
–
Further problems with:

Diffusion:

Toxins such as drugs can accumulate in the body, and can only be removed if they are in water, hence they
would ONLY move if there was a higher concentration of toxins in the blood then the urine itself. And this
would stop if the concentrations equalise.

Osmosis:

Too much water is lost in urine: If there is a high concentration of urine, water will continually be drawn from
the body to even out the conc. gradient. However, excretion of dilute urine means the loss of large amount of
water from body, a loss to great for terrestrial animals.

Osmosis only deals with the movement of water and thus would only allow water to move out of the body,
not the nitrogenous wastes.

Perform a first-hand investigation of the structure of a mammalian kidney by dissection, use a model or visual
resource and identify the regions of the mammalian kidney involved in the excretion of waste products:
–
Aim: To identify the regions of the mammalian kidney, notably the ones involved in the excretion of waste
products.
–
Equipment:

One commercially packed cow (mammalian) kidney

One sharp medical cutting scalpel

Dissecting tray

Clean 'laying' paper

Latex gloves

Tissue forceps (they are things that help pull skin)

Disinfecting agent
–
Safety:

Gloves and protective face masks are crucial, incase of a diseased kidney, or the possible contracting of a
disease between touching.

Gloves are also crucial in handling of sharp object, incase of accidental damage.

Disinfecting agent was used on the tray, and the paper, incase of airborne particles that may be ingested and
cause allergies or disease.

–
Material was carefully disposed, to inhibit the build up of bacteria and other organisms.
Method:

Carefully layer brush the tray with agent, and paper, and place them together.

Place the kidney facing sideways, and carefully cut sideways to obtain a 'longitudinal' cut (ie sideway cut), using
forceps to open the skin.
–
Result:

The kidney is made up of 3 sections, the pelvis, the medulla and the cortex, the obvious observable sections
where located, and an imaginary "large" nephron was placed, to observe where the 3 mains process (ie
filteration


Contains the glomeruli. It is very dark red due to the capillaries

It is involved in the filtration of blood.
Medulla:

Contains the nephron tubules, as can be observed by the striped appearance of the medulla

It is involved in the reabsorption and secretion of substances
Pelvis:


secretion) occur.
Cortex:


reabsorption
It is where all the collecting ducts connect to, ie the collecting of urine.
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, they have to undergo renal dialysis
to regulate their blood.
–
Renal dialysis is an artificial process in which waste in the blood are removed by diffusion across a partially
permeable membrane of solution known as dialysis fluid. It is a solution of salts, glucose, dissolved gases and
other substances (it has an equivalent composition to interstitial fluid), wastes (particular urea and excess salts),
diffuse out of the blood into the dialysis fluid. The clean blood is then returned.
–
The process:

The blood is extracted from the body from a artery (as it has come from the heart with oxygen, and going to
body to pass its waste and regulate levels etc., but it can’t as kidney has failed hence blood from artery is used)
and passed into a dialyser, which is a medical unit which is a bundle of hollow fibres made of partially
permeable membrane to help units suffering from artery failure.

The dialyser is in a solution of dialysing fluid, which has similar concentrations of substances as blood.

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 wastes diffuse into the solution, and it is constantly replaced

The anti-clotting agent, heparin, is also added to prevent clotting.

The blood is then returned to the body via a vein.
Comparison of dialysis and normal kidney function:
Kidneys
-
Continuous process; very efficient
Renal Dialysis
-
Slow process; occurs a few times a week for
patients
-
Active and passive transport is used throughout
-
Only passive transport is used
-
Useful substances are not reabsorbed as they
the nephron
-
Useful substances are reabsorbed actively by
the kidney
-
Uses a series of membranes (nephrons) which
are selectively permeable.

-
Also uses membranes (but artificial) which are
selectively permeable.
Outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in the regulation of water and salt
levels in blood:
–
diffuse into blood from dialysing fluid
Recall:

Dehydration is defined as an excessive loss of body fluid.

Blood volume is the volume of blood (both red blood cells and plasma) in a person's circulatory system. Blood
volume is determined by the amount of water and sodium ingested, excreted by the kidneys into the urine.
–
A hormone is a chemical released by one or more cells that affects cells in other parts of the organism. It is
essentially a chemical messenger that transports a signal from one cell to another, only a small amount of hormone
is required to alter cell metabolism. All multicellular organisms produce hormones however animals usually
produce hormones which are often transported in the blood.
–
The kidneys maintain constant conditions within the body by excreting wastes such as urea and by regulating the
amounts of water and salts that are reabsorbed. This aspect of homeostasis is mainly due to the actions of two
hormones: aldosterone and antidiuretic hormone (ADH):
–
ADH (Anti-Diuretic Hormone):

Also called vasopressin, anti-diuretic hormone literally means (anti-'water losing'), diuretic are heavily used in
pro-bodybuilding shows to lose water.

It controls the reabsorption of water, this is done by adjusting the permeability of the collecting ducts and the
distal tubules.

Hence a release of it (ie increase levels), increases (sucks) water out from the tubules, hence the urine
becomes more concentrated (as less water is present).

It is made in the hypothalamus in the brain, but stored in the pituitary gland.

Receptors in the hypothalamus monitor the concentration of the blood:

High Salt Concentration: ADH levels increased, collecting ducts and distal tubules become more permeable to
water, more water reabsorbed, concentration returns to normal. (Concentrated urine)

Low Salt Concentration: ADH levels reduced, collecting ducts and distal tubules less permeable to water, less
water absorbed, concentration returns to stable state. (Dilute urine)

ADH does not control the levels of salt in the blood. It only controls the concentration of salt through water
retention.
–
Aldosterone:

Is a hormone that increases the reabsorption of sodium and the release (secretion) of potassium in the kidneys.
Hence a release of it (ie increase levels), causes more salts to be sucked out of the tubules.

Aldosterone is produced by the outer-section of the adrenal cortex in the adrenal gland, (which sits above the
kidney) and acts on the distal tubules and collecting ducts of the kidney.

When there is a lack of absorption of salts (ex. NaCl, NH 3, K+ etc) , a signal goes to the hypothalamus which
triggers the secretion of aldosterone.

High Salt Concentration: Aldosterone levels decreased, less salt reabsorbed, hence less water diffusing into
body cells.

Low Salt Concentration: Aldosterone levels increased, more salt reabsorbed, more water diffusing into body
cells.

Present information to outline the general use of hormone replacement therapy in people who cannot secrete
aldosterone:
–
This is a second developed technology, where the first was renal dialysis to aid people with affected kidneys.
–
Addison’s disease is a rare endocrine disorder occurring when the adrenal glands, seated above the kidney, fail to
produce enough aldosterone. Without aldosterone, the body would not be able to reabsorb salt (specifically sodium
ions) this would cause severe dehydration and excessive potassium loss which may cause brain damage and death.
–
The artificial replacement hormone is called Fludrocortisone, a drug that decreases the amount of salt the body
excretes. It is taken either orally or intravenously, patients are also advised by their doctors to increase their salt
intake.

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:
–
Homeostasis is the process by which organisms maintain a relatively stable (constant) or almost constant, internal
environment.
–
Enantiostasis is the maintenance of metabolic and physiological functions in response to variations in the
environment.
–
The difference between the two, is the fact that homeostasis requires only a SPECIFIC internal condition for an
organism to function properly, example 37o is the required temperature for humans to function, enantiostasis is for
a VARIETY of internal condition which the function can function properly at, for example diving birds rely on
enantiostasis to function properly at extremely high and low pressure sky levels.

–
In homeostasis heat is 'acted against' by sweating etc, the pressure for birds isn't 'acted against'; it is 'adapted' to.
An estuary is where a freshwater river meets and mixes with saltwater sea, and as such the salinity levels are
always changing dramatically. This is determined by the tide of the sea:

At high tide: sea water flows into the river mouth, creating an environment with higher salt concentration, hence
this salt water has the tendency to draw water out cells by osmosis (as the organism will be in freshwater)

At low tide: sea water flows out of the river mouth, and freshwater from the estuary is abundant, hence by
diffusion organism face the challenge of water moving into their tissue.
–
Organisms living in such an environment need to have mechanisms to cope with such changes in order to survive,
this is collectively called enantiostasis.
–
Enantiostasis is carried out by 2 process (these are present in normal homestasis conditions too, but they carry out
different roles):

Osmoconformation: process by which organisms tolerate the changes in the environment, and conform, or alter
the concentration of their internal solutes to match the external environment. Their metabolism can handle it.


Osmoregulation: is the control of the levels of water and mineral salts in the blood.
Process and analyse information from secondary sources and use available evidence to discuss processes used by
different plants for salt regulation in saline environments:
–
Salt, even in small concentrations, has a damaging effect on cell metabolism.
–
Halophytes are plants that adapted and can tolerate high salt levelled environments, they are commonly found in
areas such as estuaries.
–
Grey Mangroves (Avicennia marina):

Salt Prevention: In its roots, it has a layer of cells that actively restrict the movement of salt into xylem vessels.

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.

Describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss:

Perform a first-hand investigation to gather information about structures in plants that assist in the conservation of
water:
–
Aim: To gather information from plant specimens about structures that assist in the conservation of water.
–
Equipment:

Different type of leafs that exist around the school (typical environment)

Hand lens
–
Safety:

Sun has strong UV light outside, sunscreen and hats should be worn.

Leaf can be diseased and can have splinters and can be sharp, gloves should be worn.
–
Method:

Carefully, leaves where looked at for different 'prominent' features that could inhibit water loss, these where
then cross-checked with reliable sources.
–
Result:

Banksia:

Leaves have sunken stomates: this reduces transpiration.

Hard, waxy cuticles: this reduces the amount of water loss through transpiration.

Eucalyptus trees:

Hard, waxy cuticles: this reduces the amount of water loss through transpiration.

Leaves hang vertically: reduce sun exposure.


Spinifex grass:

Have extensive root systems that can reach underground water.

Leaves are also long and thin: to reduce water loss by transpiration.

Can roll up to hide their stomata's: this reduces the amount of water loss through transpiration.
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: Hypotonic to environment. Water diffuses INTO their bodies. Salts diffuses out.

Role of Kidney: Doesn’t drink continually, Kidneys removes excess water, while reabsorbing salts.

Urine: Large, dilute amount.
–
Marine Fish:

Osmotic Problem: Hypertonic to environment. Water diffuses OUT of their bodies. Salt diffuses in.

Role of Kidney: Continually drinks water, Kidneys reabsorb water, while actively secreting salts.
(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.

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 animals:
–
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 must be removed quickly, or changed to a less toxic form.
–
The removal of ammonia would require large volumes of water, and this is not possible for animals or insects that
seek to conserve water.

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 impossible 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 (ex; kangaroos, wallabies, hopping mice and koalas). 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.