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 on substrates.
Role
Enzymes are organic catalysts. A catalyst is a general term for any substance that speeds up or
brings about a chemical change, without itself being used up.
They also enable chemical reactions to occur at lower temperatures, meaning body temperatures
don’t have to be so high.
Enzymes control all the chemical processes of living systems. Enzymes are produced within living
cells.
Chemical Composition
Enzymes are proteins. They are made up of amino acids that are linked and then folded to produce
a 3-D structure. The folded shape is related to enzyme specificity.
There are large numbers of metabolic processes occurring in living organisms. Most would not occur
at an efficient rate without enzymes. An efficient metabolic rate is essential for life processes to
continue.
A Model for Specificity
Specificity means that only one compound (or very few) can react with a particular enzyme.
Each enzyme catalyses a distinct chemical reaction.
Lock and Key Model
A lock and key model for enzyme specificity shows that a certain enzyme can only react with a
certain substrate because of the shape of its active site which correlates to the shape of the
substrate. Neither chemical will change to fit the other.
Induced-Fit Model
The shape of the active site and the substrate molecules will both modify slightly, so the enzyme can
react with more substrates. These enzymes have a lower specificity.
Identify the pH as a way of describing the acidity of a substance.
The pH is a way of describing the acidity of a substance. A pH of 7 is neutral, which means it is
neither acidic nor alkaline. High acidity is shown by a lower pH.
Enzymes have an optimum pH for activity, for example digestive enzymes in the stomach work best
under conditions below pH 6. Changing pH reduces an enzyme’s activity.
Explain why the maintenance of a constant internal environment is important for optimal
metabolic efficiency.
Enzymes control all metabolic processes in the body.
Enzymes work optimally in an environment where their optimum temperature and pH conditions
are met. At temperatures and pH values other than the optimum, the enzymes fail to work
efficiently and kept as stable as possible.
If internal temperatures were to rise too much, enzymes would denature (breakdown).
If internal temperatures drop, enzymes cannot function.
Describe Homeostasis as the process by which organisms maintain a relatively stable internal
environment.
Homeostasis is the process by which the internal environment is kept within normal limits,
regardless of the external environmental conditions. This includes conditions, such as temperature,
pH, gas levels, water and salt concentrations. This allows the enzyme’s optimal conditions to be met
and the body to work efficiently and be kept as stable as possible.
Explain that Homeostasis consists of two stages:
Detecting changes from the stable state
Counteracting changes from the stable state
For a state of homeostasis to exist, the body must have some way of detecting stimuli that indicate a
change in the body’s internal or external environment.
A receptor detects a change in some variable in the organism’s internal environment, for example,
sensory neurons in the skin pick up a decrease or increase in temperature of air surrounding the
body.
An appropriate response occurs that counteracts the changes and thus maintains the stable
environment, for example, shivering to generate heat in muscles.
Outline the role of the nervous system in detecting and responding to environmental changes.
The nervous system sends messages to the brain & back to the sensory organs.
Brain –> Processing information
Nerves –> Sending information
Sense Organs –> Detecting information
The advantages of the nervous system are:
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Speed
its specificity on effectors (sensory organs)
Identify the broad range of temperatures over which life is found compared with the narrow limits
for individual species.
Identify some responses of plants to temperature change
Leaf Fall
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Plants reduce their surface area exposed to heat by dropping their leaves.
This also reduces the amount of water that is lost through transpiration.
Radiation
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Some plants living in very exposed areas, such as sand dunes, reduce the amount of heat
absorbed by having shiny leaves that reflect solar radiation.
Heat-Shock Proteins
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These are proteins produced by plants that are under stress from very high temperatures.
These molecules are thought to stop enzymes denaturing, so normal cell reactions can
continue.
Transpiration
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The movement of water up the plant from the roots to the leaves via the transpiration
system serves to cool the plant during hot conditions.
The evaporation of the water from the stomata of the leaves also serve to cool the plant.
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Die back
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In harsh conditions the shoots and leaves of a plant may die, but left in the soil are bulbs,
roots or rhizoids that will begin to grow again when favourable conditions return.
Orientation of Leaves
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Vertical orientation of some leaves has the advantage of reducing the amount of leaf
surface area in contact with sun rays, e.g. Eucalyptus leaves hang vertically.
Seed Dispersal
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Some Australian natives require extremely high temperatures, such as those produced by a
fire, to germinate their seeds.
Plant seeds from species such as Banksia ericifolia are only able to open their seed coats
when they are exposed to fire.
Vernalisation
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This is when plants must be exposed to cold conditions to produce flowers and therefore
reproduce. Plants in alpine regions use vernalisation to reproduce when conditions are more
favourable at the end of winter.
The presence of cold conditions will stimulate flowers to grow, and when spring approaches
they are almost mature.
A model of a feedback mechanism
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Controlling Temperature
Skin
Receptor: Hot and cold thermo-receptors (nerves) in skin
Brain- Hypothalamus
Effector (muscles, sweat glands)
Perform a first-hand investigation to demonstrate the effect of dissolved Co₂ on water
Aim: to demonstrate and observe the effect of Carbon dioxide on water
Materials:
- distilled water
- test tube
- straw
- universal indicator
Method:
1.
Distilled water was added to the test-tube. A dropper-full of universal indicator was added and
shaken slightly to mix well. (The pH of this solution was 7.0 when matched to the chart and was
green)
2.
The straw was placed into the solution and we blew through it and observed the changes (the
pH had changed to 5.9 and was yellow)
Discussion:
We can assume that it is the Carbon dioxide in our breath that causes the increase in acidity, but we
must perform a test to ensure the reliability of this hypothesis
Part 2.
Aim: to qualify the results obtained in part 1
Materials:
- distilled water
- two test tubes
- straw
- limewater
- Hydrochloric acid
- Calcium carbonate crystals
- delivery tube
- rubber cork
Method:
1.
We set up one test-tube according to diagram 1 (making sure the limewater was not shaken
otherwise it would have combined with the precipitate and its cloudiness would have made the
results hard to observe)
2.
The straw was blown into, and the limewater changed from clear to cloudy indicating the
presence of Carbon dioxide in exhaled breath
3.
The other test-tubes were set up according to diagram 2 (once again we made sure the
limewater being used was clear)
4.
The reaction between the HCl and CaCO3 produced CO2 and changes in the limewater were
observed
Results: This verified Part 1’s hypothesis, thus demonstrating that CO2 increases the acidity of water
(lowering the pH from 7 to 5.9). Thus we are able to deduce that CO2 released during respiration
must be removed from the body as it will lower the pH of blood, which causes an imbalance in
homeostasis and therefore inhibits the action of enzymes.
Perform a First-hand investigation to gather information to estimate the size of red and white
blood cells.
Aim: to estimate the size of red and white blood cells
Materials:
- light microscope
- small ruler
- prepared slide of blood
Safety precaution: Always carry the microscope with one hand on the base to make sure it does not
drop as it is heavy and could shatter. By using a prepared slide it eliminates the risk of a biohazard
Method:
1.
The microscope was set up
2.
The small ruler was placed on the stage and was focused on using low power objective
3.
The scale on the ruler was used to calculate the field of view
4.
The prepared slide of blood was placed on the microscope and focused on using of low power
objective. The objective was changed to high power
5.
The established field of view was used to calculate the dimensions of the red and white blood
cells.
Results:
Red blood cell diameter = 7.5 ųm
White blood cell diameter = 16 ųm
Plants and animals transport dissolved nutrients and gases in a fluid medium
Explain the adaptive advantage of Haemoglobin.
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Haemoglobin readily associates with oxygen & increases the ability of blood to carry O₂,
compared with dissolving in plasma.
Haemoglobin readily loses O₂ in tissues with low oxygen levels.
When O₂ associates with one Haem unit, it promotes the other Haem units to take up O₂.
Generally, a molecule of haemoglobin is fully saturated or is not at all.
At altitude with lower pressure of O₂ (e.g. 3000m has 66% less O₂ than sea level),
haemoglobin is still relatively saturated in 0₂.
Outline the need for oxygen in living cells and explain why the removal of carbon dioxide is
essential.
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Living cells need a continued supply of oxygen to carry out respiration, to produce energy
and carbon dioxide.
Because Carbon dioxide readily dissolves in water, it lowers the pH of the blood. Carbon
dioxide needs to be removed as quickly as possible, because this lowering of pH affects
homeostasis and can denature enzymes.
Current theories about processes responsible for the movement of materials through plants
in xylem and phloem tissue
Xylem
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Ongoing research has conclusively shown that water moves upwards by the transpirationtension-cohesion mechanism.
Transpiration pull is the energy provided by the sun when water moves evaporates from the
surface of the plant.
Tension is the negative pressure, or pull, from above.
Cohesion is the attraction of molecules to each other. As one moves up, it pulls others below
it.
In addition, adhesion between water molecules & the side of the xylem walls results in
capillarity observed in the way water ‘climbs’ up narrow tubes.
Large trees move hundreds of litres of water in the transpiration system.
Since this uses no energy from the plant, it is a passive process (energy comes from the sun).
Xylem vessels are not living, and are strengthened with lignin.
The movement of water (and dissolved ions) is upwards only.
The only way that plants can control the transpiration stream is by opening or closing
stomata in times of water stress. Plants still need to open stomata for part of the day for gas
exchange, to facilitate photosynthesis.
Phloem
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Transport in phloem is called translocation.
This transports sucrose, amino acids and glucose.
Translocation requires energy, and is driven by the osmotic pressure gradient.
Phloem is actively loaded with sugar at the source, against the osmotic gradient.
Water follows sugar into phloem
Phloem is actively unloaded at sink against osmotic gradient.
Water follows sugar out of phloem.
This mechanism is called pressure flow.
Analyse information from secondary sources to identify current technologies that allow
measurement of oxygen saturation and carbon dioxide saturation in blood, and describe and
explain the conditions under which these technologies are used.
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Arterial Blood Gas (ABG) Analysis
Analysis takes blood samples from an artery, and the sample is tested for the concentration
of oxygen and carbon dioxide, and for pH.
This procedure is invasive, and delays can occur between sampling and result processing.
The information obtained is vital for critically ill patients, in determining their situation, as
many illnesses present with similar symptoms.
Pulse Oximetry
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This uses two wavelengths of light to measure the absorption of light as it passes through a
patient’s finger. The amount of light absorbed by haemoglobin is dependent on how
saturated it is with oxygen.
Mathematical calculations work out the proportion of oxygenated haemoglobin present.
This is useful as it is non-invasive, and allows for the constant monitoring of arterial blood.
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 treat people with Anaemia, as red blood cells increase the amount of oxygen that can be
carried to body tissues, and consequently increase the amount of iron.
Given to people whose bone marrow doesn’t make enough RBCs.
Used for treatment of trauma patients and surgery patients, e.g. Open Heart Surgery.
White Blood Cells
Infection fighting components of blood
Used to treat life-threatening illnesses or infections when the white blood cell count is low.
Plasma
Contains blood clotting factors and immunoglobins.
Used for treatment of patients with clotting disorders such as haemophilia.
Used to adjust the osmotic pressure of blood, to pull fluids out of tissues
Platelets
Essential for blood clotting.
Platelets are given to patients suffering from leukaemia or lymphoma, who do not produce enough
platelets.
Analyse information from secondary sources to identify to report on progress in the production of
artificial blood and use available evidence to propose reasons why such research is needed.
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Perflurochemicals
Synthetic, inert materials.
Can dissolve 50 times more oxygen than plasma.
Free of biological materials, so are infection risk free.
More research is needed, as perflurochemicals need to combine with other substances in
order to mix in the blood.
Haemoglobin based oxygen carriers
Made from sterilised haemoglobin, extracted from red blood cells.
Haemoglobin is not contained in a membrane, therefore does not need to be cross checked
before being given to a patient- it is essentially a universal blood type.
It can be stored for long periods of time, and does not need to be stored at a certain
temperature.
Haemoglobin that has been removed from cells breaks down easily, and can be toxic. This
then needs to be modified so it is not dangerous.
Reasons for Shortage and Advantages of Artificial Blood
There is a shortage of donor blood, especially in developing countries, and in times of emergency,
e.g. terrorist attacks or tsunamis.
Donated blood can only be stored for short periods of time, whereas artificial blood can be stored
almost indefinitely.
Artificial blood can be sterilised, eliminating the chance of transferring infection and disease, such
as HIV/AIDS.
Artificial blood is useful for patients whose religious beliefs don’t allow for blood transfusions.
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.
Substrate concentration needs to be maintained to ensure enzyme efficiency.
If the concentration becomes too dilute, there are insufficient interactions between enzyme and
substrate.
If the substrate becomes too concentrated, dehydration occurs, there is insufficient water to carry
out metabolism and waste concentration becomes higher. This leads to a change in pH, which
affects enzymes.
Explain why the removal of wastes is essential for continued metabolic activity.
Reactions stop happening if metabolic wastes build up.
Build up of CO₂ increases pH.
Waste products can be directly toxic, e.g. Urea in high concentrations.
Identify the role of the kidney in the excretory system of mammals and fish.
What problems do fish have with water?
Fresh Water Fish
Continually being diluted with water (too much H₂O in tissues)
Have to reduce water in, and increase water out. (Dilute urine)
Marine Fish
Continually being dehydrated as water leaves via osmosis.
Have to increase water in, and reduce water out. (Concentrated urine)
What problems do terrestrials have with water?
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Dehydration- has to reduce water loss and increase water intake (Drinking)
Role of the Kidney
Remove nitrogenous wastes
Balance water and salts
Explain why the processes of diffusion and osmosis are inadequate in removing dissolved
nitrogenous wastes in some organisms.
Diffusion and osmosis are both examples of passive transport, relying on random movements of
molecules.
Diffusion is too slow for the normal functioning of the body and does not select for useful solutes.
Osmosis only deals with the movement of water and thus would only allow water to move out of
the body, not the nitrogenous wastes.
Distinguish between active and passive transport and relate these to processes occurring in the
mammalian kidney.
Active Transport
Active transport involves an expenditure of energy on the part of the organism, usually because the
substance is moving against the concentration gradient, i.e. when a salt moves to an area of high salt
concentration from an area of low salt concentration.
Passive Transport
Passive transport involves no expenditure of energy as the materials follow the natural
concentration gradient, i.e. movement from an area of high concentration to an area of low
concentration.
Both diffusion and osmosis are examples of passive transport.
Processes in the Kidney
In the kidney, both active and passive transport occurs.
Passive transport occurs when water returns to the capillary via osmosis, after filtration.
Active transport occurs when ions in the blood are transported to cells in the nephron tubule. Some
poisons and drugs are removed in this way.
Explain how the processes of filtration and reabsorption in the mammalian nephron regulate body
fluid composition.
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Filtration of the blood occurs in the Bowman’s capsule where high blood pressure in the
glomerulus forces all small molecules out of the blood into the capsule.
Water, urea, ions (Na, K, Cl, Ca, and HCO), glucose, amino acids and vitamins are all small
enough to be moved into the glomerular filtrate.
Blood cells and proteins are too large to be removed. This filtering process is non-selective
and therefore many valuable components of the blood must be recovered by reabsorption.
Reabsorption takes place selectively at various points along the proximal tubule, loop of
Henle and distal tubules.
All glucose molecules, amino acids and most vitamins are recovered, although the kidneys
do not regulate their concentrations.
The reabsorption of the ions Na, K, Cl, Ca and HCO occurs at different rates depending on
feedback from the body. In some cases, active transport is required.
Water is reabsorbed in all parts of the tubule except the ascending loop of Henle.
The amount of water reabsorbed depends on feedback from the hypothalamus.
If no water were to be reabsorbed, the mammal would soon dehydrate, losing water at a
rate of around 7.5 L per hour.
The chemical composition of the body fluids is precisely regulated by the control of solute
reabsorption from the glomerular filtrate.
Outline the roles of the hormones Aldosterone and ADH (anti-diuretic hormone), in the regulation
of water and salt levels in the blood.
Aldosterone
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This is a steroid hormone secreted by the adrenal gland.
Its function is to regulate the transfer of sodium and potassium ions into the kidney.
When sodium levels are low, Aldosterone is released into the blood, causing more sodium to
pass from the nephron to the blood. Water then flows from the nephron to the blood via
osmosis. This results in the homeostatic balance of blood pressure.
Anti-diuretic hormone (ADH or vasopressin)
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Controls water reabsorption in the nephron. When fluid levels drop, the hypothalamus
causes the pituitary gland to release more ADH. This increases the permeability of the
collecting ducts to water, allowing more water to be absorbed from the urine into the blood.
The resulting urine is more concentrated.
When there is too much fluid in the blood, sensors in the heart cause the hypothalamus to
reduce the production of ADH in the pituitary, decreasing the amount of water reabsorbed
in the kidney. This results in a lower blood volume and larger quantities of more dilute urine.
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.
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Enantiostasis is the maintenance of normal metabolic and physiological functioning, in the
absence of homeostasis, in an organism experiencing variations in its environment.
All organisms that live in estuaries experience dramatic changes in salt concentration over a
short time span, as tides fluctuate and fresh water mixes with salt water. Organisms that
need to withstand great fluctuations in salinity are said to be euryhaline.
Allowing the body’s osmotic pressure to vary with the environment is one strategy to
withstand changes in salt concentration. Organisms that do this, and don’t maintain
homeostasis, are said to be osmoconformers.
Most marine invertebrates are osmoconformers, whilst marine mammals and fish are
osmoregulators- maintaining homeostasis.
As salt concentration in an osmoconformer changes, body functions and enzyme activity are
affected. For normal functioning to be maintained, another body function must be changed
in a way that compensates for the enzymic change.
An example of enantiostasis is when a change in salt concentration in body fluids, which
reduces enzymic efficiency, is compensated for by a change in pH, which increases the
efficiency of the same enzyme.
Describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss.
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Adaptations of Australian xerophytes (plants adapted to dry conditions) include:
Hard leathery, needle-shaped leaves with reduced surface areas such as in Hakea sericea
(needlebush) and coastal tea trees.
The Use of phyllodes for photosynthesis rather than leaves that would lose water by
transpiration, as in many acacias.
Some salt bushes, e.g. Atriplex, change the reflectiveness of their leaves during leaf
development so that they have highly reflective leaves during summer.
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Eucalypts avoid high radiation in the middle of the day by hanging their leaves vertically to
present less surface area to sun.
Heat loss is greater for small leaves or highly dissected leaves than it is for larger leaves and
many Acacias have fronds of bi-pinnate leaves.
Waxy cuticle prevents evaporation in many Eucalypts.
An investigation to observe the structure of the mammalian kidney, and identify the regions
involved in the excretion of waste products.
Aim:
To identify parts of a mammalian kidney.
Method:
1.
Place the kidney on the dissecting tray.
2.
Use a scalpel to cut a median longitudinal section of the kidney. Do not cut the tubes, and
leave the two halves of the kidney attached to them.
3.
Draw the internal structure of the kidney and label the structures.
Diagram:
Conclusion:
The parts are correctly identified.
Compare the process of renal dialysis with the function of the kidney.
Function of the Kidney
1. Kidneys act as a filter to remove the correct amount of fluids and wastes from our body,
they keep a correct balance of salts and acids in the body, and they produce hormones.
2. Each day, the kidneys filter 200 litres of blood, and remove about 2 litres of waste products
and unnecessary water.
3. Blood enters the kidney through the Renal Artery; blood is then cleaned in the kidney as it
passes through tiny filters called nephrons.
4. Each kidney contains about a million nephrons, and each nephron contains a glomerulus
(filtering apparatus) with a semi-permeable membrane.
5. Clean blood returns to the body via the Renal Vein; wastes and water that are removed by
the kidney pass through the Ureter to the bladder, where it is stored as urine.
Renal Dialysis
There are two main types of renal dialysis- Haemodialysis and Peritoneal Dialysis.
Haemodialysis
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This treatments involves circulation a patient’s blood outside their body, through an ECC
(dialysis circuit). Two needs are inserted into the patient’s vein, and are attached to the ECC.
The Dialysis circuit consists of dialysis tubing (blood vessels and veins), dialyser (artificial
kidney) and a dialysis machine that monitors the flow of blood in and out of the patient, and
administers dialysate as required.
Dialysate is a chemical that draws out impurities and wastes in the blood.
The two components of the dialyser are the blood compartment and the dialysate
compartment, and there is a semi-permeable membrane in between these.
The semi permeable membrane allows particles of a certain size to diffuse across the
membrane into the dialysate compartment, where they are removed from the ‘blood
stream.’
At the same time, chemicals and electrolytes in the dialysate diffuse across the membrane
into the blood compartment.
This purified, chemically and hormonally balanced blood is then returned to the body.
Treatment is required three times a week, for three to four hours per treatment.
The use of hormone replacement therapy in people who cannot secrete aldosterone
Hypoaldosteronism
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Hypoaldosteronism is a condition where people fail to secrete aldosterone, and therefore
cannot maintain water and salt balances.
Addison’s disease is the name of a disease with these symptoms, which include high urine
output with a resulting low blood volume.
Eventually, as blood pressure falls, heart failure results.
A replacement hormone, fludrocortisone (Florinef), is used to treat this condition but careful
monitoring must be maintained to avoid fluid retention and high blood pressure.
Compare the urine concentration of terrestrial mammals, marine fish and freshwater fish
Terrestrial mammals
Excretory product and concentration: Urea or uretic acid. Concentration of urine caries as part of
the regulation of water within an animal’s body. Excretory of urine is a periodic process; urine is
stored in the bladder before excretion.
Environmental reason: On land, animals need to conserve water. By converting ammonia to less
toxic forms, they can hold it longer in the body and excrete it periodically so less water is at loss.
Marine fish
Excretory product and concentration: Small amount of concentrated urine. Some ammonia Is
excreted through the gills.
Environmental reason: Marine fish’s internal fluid is less concentrated than the surrounding water.
To avoid water loss from their body, marine fish keep drinking saltwater. They absorb the water and
salts. The water is retained and the salts actively secreted.
Freshwater fish
Excretory product and concentration: Large amount of dilute urine
Environmental reason: They have a higher concentration of solutes in their body than the
concentration of water outside. Water therefore tends to diffuse into the body and so fish need to
continually get rid of the excess.
Processes used by different plants for salt regulation in saline environments.
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Halophytes are plants adapted to living in salty environments. They are able to tolerate
higher levels than other organisms, or have special mechanisms to control their levels of
salt.
In Australia, the chenopod or goosefoot family is a good example. It includes the saltbushes
(genus Atriplex) which have special salt excretion glands in their leaves. Chenopods are the
dominant species in salt-marsh communities throughout Australia.
Mangroves grow in conditions of varying salinity as the tide comes and goes, flooding them
regularly with saltwater. Some mangroves such as the grey mangrove excrete salt from
special glands in their leaves. Others accumulate salt in their leaves and then shed to leaves
to dispose of it.
The relationship between the conservation of water and the production and excretion of
concentrated nitrogenous wastes
Spinifex hopping mouse of Central Australia
Waste products: Urea in a concentrated form
Reason: The animal lives in a very arid environment. It drinks very little water and excretes urea in a
concentrated form, so that water can be conserved.
Euro, wallaroo (Macropus robustus)
Waste products: Concentrated urine
Reason: Euros have a very efficient excretory system that recycles nitrogen and urea to make very
concentrated urine. This allows them to survive in very arid environments.
Insects
Waste Products: Uric acid
Reason: Insects are covered with a cuticle impervious to water. They conserve water by producing a
dry paste of uric acid.
Structures in plants that assist in the conservation of water
Aim:
Observe structures in plant that assist in the conservation of water
Method:
Carefully paint a small square of clear nail varnish onto both the upper and under surface of a leaf.
When the varnish dries, use a scalpel to remove the square.
Observe under a microscope, noting the small dots. These are the locations of the stomata.
Observations:
There was a larger number of stomata on the under surface of the leaf, and only a few on the upper
surface. This is to reduce the amount of water lost to transpiration, by hiding the majority of
stomata from the sun.
Conclusion:
The location of stomata on the leaf is important to controlling water loss within a plant.