Microsoft word - biology 9.2 - maintaining a balance.doc
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
Metabolism refers to all the chemical reactions occurring in organisms
Enzymes are biological catalysts which increase the rate of chemical reactions
Without enzymes, metabolism would be too slow to support life
Most enzymes are made up of protein
Proteins are composed of long chains of amino acids joined together by
These long chains are called polypeptide chains
Proteins consist of one or more polypeptide chains
In enzymes, the polypeptide chain is folded into a 3-dimensional globular
Part of the enzyme is called the active site. This part attaches to the substrate
The substrate are the molecules the enzymes acts upon
Enzymes are highly specific in their action; this means that each enzyme acts
This is because the shape of the active site of the enzyme matches the shape of
The molecules the enzyme act upon are called the substrate
The substrate molecules bind to the active site and a chemical reaction occurs
The products are the substances that the substrate(s) become. One substrate
can be split, or two substrates can be joined
The Lock and Key Model suggests that the substrate fits exactly into the
active site of the enzyme like a key fits into a lock. It assumes that the enzyme
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.
• Identify the pH as a way of describing the acidity of a substance:
– The substance that makes a solution acidic is hydrogen ions
– pH is a measure of the acidity or the alkalinity of a substance
– pH is a measure of the concentration of hydrogen ions per litre of solution
– The pH scale is from 0 to 14: a pH of 7 is neutral (pure water); above 7 is alkaline
• Explain why the maintenance of a constant internal environment is
important for optimal metabolic efficiency:
– Enzymes are essential for proper metabolic function in an organism
– However, enzyme efficiency is affected greatly by certain factors
– Enzymes work best within a limited range
– Therefore, a constant and stable internal environment is needed so that enzymes
will always be working at an optimum rate, and thus metabolism will be a
• Describe homeostasis as the process by which organisms maintain a
relatively stable internal environment:
– Homeostasis is the process by which the body maintains a stable internal
– Multicellular organisms regulate their internal environment in order to remain
– The internal environment of cells are kept within certain limits by the
– These systems monitor all the activities of cells, their requirements and the wastes
• Explain that homeostasis consists of two stages
Detecting changes from the stable state;
Counteracting changes from the stable state:
The body needs to maintain a ‘stable state’ in order to function properly
Changes, or deviations, from the stable state are caused by the external and
Any change, or information, that provokes a response is called a STIMULUS
RECEPTORS detect stimuli; organisms then react to the change
There are two types of receptors within the body:
These receptors, usually in the skin, detect changes
These receptors detect changes from the body’s
Examples of external stimuli: light, day length, sound, temperature, odours
Examples of internal stimuli: levels of CO2, oxygen levels, water, wastes, etc.
Receptors can range from a patch of sensitive cells, to complex organs like the
After receptors detect changes, organisms can then react to the change
When a change affects the organism’s normal/stable state, the response is
This type of response will counteract the change to ensure the stable state is
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
• Outline the role of the nervous system in detecting and responding to
– The nervous system works to regulate and maintain an animal’s internal
environment and respond to the external environment
– The nervous system is made up of two parts:
Central Nervous System: This part acts as the CONTROL CENTRE for all of
the body’s responses. It coordinates all the responses. It is made up of the
brain and the spinal cord. It receives information, interprets it and initiates a
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 nervous system works with another system called the endocrine system
– This system produces hormones in response to certain stimuli
• Identify the broad range over which life is found compared with the narrow
– Ambient temperature
is the temperature of the environment
– The range of temperatures over which life is found is broad compared to the
– Organisms on Earth life in environments with ambient temperatures ranging from
less than 0ºC (eg bacteria in snow) to more than 100ºC (eg bacteria in boiling hot
– However, individual organisms cannot survive this entire range of temperatures
– Eg, 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:
– ECTOTHERMS are organisms that have a limited ability to control their body
temperature. 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 are organisms whose metabolism generates enough heat to
maintain an internal temperature independent of the ambient temperature.
– EXTENSION (Not really needed but anyway…)
Poikilotherms are animals whose body temperatures are always changing.
True poikilotherms have temperatures that are the same as the environment.
An example is jellyfish. Poikilothermy is often assumed to be the same as
ectothermy; however, this is incorrect. Some ectotherms, like snakes, can
regulate their temperatures using behaviour to maintain a stable temperature.
Homeotherms are animals with stable body temperatures. Most endotherms
The poikilotherm/homeotherm classification system was based on the stability
of the body temperature of the organism. This system is now redundant.
The ectotherm/endotherm system uses the organism’s source of body heat as a
way of classification. This system is accepted today.
Migration: Animals can move to avoid temperature changes. Many birds that
spend spring and summer in Australia migrate before the temperature
Hibernation: To survive cold conditions, many animals hibernate; that is they
remain in a sheltered spot, their metabolism slows and the body temperature
drops. Aestivation is the ‘hibernation’ of organisms in heat conditions.
Bogong moths migrate to spend the summer months in caves in the Australian
Shelter: Animals seek shelter to avoid extreme conditions. They can dig
burrows or seek shelter in caves or crevices. They can shelter to avoid high
temperatures or avoid low temperatures. An example is the central netted
Nocturnal Activity: Brown snakes can change into nocturnal animals when the
temperature becomes very hot. Many desert animals sleep in burrows during
Controlling Exposure: Animals can reduce the amount of their body they
expose to the sun, to reduce the amount of heat absorbed.
– STRUCTURAL AND PHYSIOLOGICAL ADAPTATIONS:
Endotherms have more structural & physiological adaptations for temperature
control than ectotherms. Most ectotherm adaptations are behavioural
Insulation: Fur in mammals and feathers in birds maintain a layer of trapped
air as insulation. This air reduces heat exchange with the environment.
Contracting the muscles of the hairs or feathers makes it lift up, increasing the
amount of air that can be trapped. Some mammals grow a thick coat in winter
and lose it in summer. Animals in cold conditions have a permanent layer of
Metabolic Activity: In cold conditions, metabolic activity increases, as this
produces heat; shivering and muscle activity increase heat. In hot conditions,
Control of blood flow: Controlling the flow of blood to extremities can be
used to reduce heat loss with the environment
Counter-current exchange: Used by endotherms in cold conditions. Blood
vessels from extremities and those going to extremities are placed next to each
other and they pick up heat from each other.
Evaporation: Endotherms can keep cool by controlling the rate of water
evaporation. Dogs pant, birds flutter a throat membrane and humans sweat.
Kangaroos can lick their arms to cool themselves.
• Identify some responses of plants to temperature change:
– Plants respond to change by altering their growth rate.
– In extreme heat or cold, plants can die, but leave behind dormant seeds.
– Plants may die above the ground, but leave bulbs, roots, rhizomes or tubers to
survive underground. These then sprout when favourable conditions return
– Vernalisation: this means that some plants need exposure to cold conditions
– Seed dispersal is also stimulated sometimes by fire
– Reflective leaf surfaces can also keep a plant cool
– The orientation of the leaves of a plant can also reduce water loss
• Identify data sources, plan, choose equipment or resources and perform a
first-hand investigation to test the effect of:
change in pH
change in substrate concentrations on the activity of the named
– However, enzyme efficiency is affected greatly by certain factors
Sensitivity to temperature relates to the protein structure of enzymes
As temperature increases, enzyme activity increases, up to the optimum
This is because the enzyme and substrate molecules are moving faster
(more kinetic energy) and therefore more collisions between enzyme and
At high temperatures, the shape of the enzyme changes, and some of the
enzymes can no longer accommodate the substrate. Activity decreases.
However, if the temperature cools down, activity will start again
At VERY high temperatures, the enzyme is denatured; i.e. the chemical
bonds holding the protein molecule together are broken and the shape is
permanently changed. The enzyme is destroyed, can no longer
accommodate the substrate, and will remain inactive even if the
Enzymes work best at an optimum pH
This is usually within a very narrow range
Extremes of acidity or alkalinity can affect the bonds holding the 3D
An increase in substrate concentration will increase the reaction until all
enzyme active sites are occupied. Then the reactions will proceed at a
• Gather, process and analyse information from secondary sources and use
available evidence to develop a model of a feedback mechanism:
involves the detection of the change in the environment and the
– The mechanism
that brings about this change is called FEEDBACK
– In feedback systems, the response alters the stimulus
– In living organisms, the feedback system has 3 main parts:
Receptors: A type of sensor that constantly monitors the internal environment
Control Centre: Receives info from the receptors and determines the response
Effector: Restores the set value. Keeps environments stable.
– An example of a feedback system would be the control of body temperature
– There are two types of temperature receptors in the body:
These receptors detect changes in the skin temperature,
These receptors monitor the temperature of the blood
– These receptors send their information to the control centre
– The temperature control centre in mammals is the hypothalamus
– The hypothalamus responds by initiating responses to increase or decrease
temperature, until it goes back to the set value (which is 37ºC)
Blood vessels constrict; less blood flow,
• Analyse information from secondary sources to describe adaptations and
responses that have occurred in Australian organisms to assist in
How It Assists Temperature
2. Plants and animals transport dissolved nutrients and gases in a fluid
• Identify the forms in which each of the following is carried in mammalian
– The mammalian circulatory system has four main functions:
TRANSPORT: The major function of the circulatory system is to transport
BLOOD CLOTTING: This complex mechanism repairs damage to blood
vessels and seals wounds to prevent loss of blood
DEFENCE AGAINST DISEASE: White blood cells help to fight infection in
the body. Antibodies provide immunity against further attack
TEMPERATURE REGULATOIN: The flow of blood distributes heat around
the body. Control of the amount of blood passing close to the skin helps
PLASMA: This make up 55% of the volume of the blood. It is sticky, straw-
coloured and slightly salty. It is made up of 90% water. Other substances
salts (as ions)
plasma proteins (including antibodies, clotting factors, lipid transporters)
products of digestion (sugars, amino acids, hormones, etc)
waste products (carbon dioxide, urea)
♦ Shape is bi-concave discs, thinner at centre than at edges
♦ Contains the pigment haemoglobin
♦ Their function is to transport respiratory gases; mainly oxygen
♦ They have no nuclei; they only live for 3 months. After this they are
♦ 5-6 million in every millilitre of blood.
♦ They are produced in the bone marrow
♦ Shape is irregular; can change shape
♦ Their function is to defend against disease
♦ The two main types of leucocytes are phagocytes
♦ PHAGOCYTES surround and ingest foreign bodies, bacteria and dead
cells and collect around areas of infection or injury
♦ LYMPHOCYTES act only on specific foreign material. They make
antibodies which help the body’s defence against disease.
♦ They are much less common than red blood cells
♦ Only 4 – 12 thousand per mL of blood
♦ They have nuclei, unlike red blood cells
♦ They are produced in the lymph nodes and glands.
♦ Their function is to make the blood clot
Lymph is blood without red blood cells, platelets and large plasma
Interstitial fluid is the fluid that runs in between your body cells.
– Transporting Substances In The Blood:
It is produced as a waste product of respiration in body cells. After
Be converted into carbonic acid which is then changed into hydrogen
carbonate ions. This change from carbon dioxide to carbonate ions
happens on the red blood cells. Then they are just transported in the
plasma (only 70% of the carbon dioxide)
Carbon + Water Carbonic Hydrogen + Hydrogen
Binds 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 is needed in the body for respiration. It is brought in across the
It binds with haemoglobin in red blood cells, forming oxyhaemoglobin.
Water is the solvent of plasma
It makes up 60% of the volume of blood
These are transported by dissolving in the plasma
E.G. sodium, potassium, magnesium, etc
Digested lipids are changed into triglycerides
(this happens in the lining of
Triglycerides, together with phospholipids and cholesterol, are wrapped in
a coat of protein to form a package called a chylomicron.
These are released into the lymph and eventually pass into the veins
Wastes such as ammonia are changed in urea
Urea is transported dissolved in the plasma
Includes amino acids, sugars, glycerol and vitamins
They are mainly water soluble and transported in the plasma
• Explain the adaptive advantage of haemoglobin:
Globule-shaped protein containing four polypeptide sub-units
4 polypeptide chains:
2 identical alpha chains
2 identical beta chains
Each polypeptide encloses an IRON-containing structure, called the HAEM
The haem groups combine with the oxygen.
– Oxygen fuses with haemoglobin where the concentration of oxygen in the blood
– It makes an unstable compound – oxyhaemoglobin
– One haemoglobin molecule can carry four molecules of oxygen
– Where oxygen is needed, the oxygen bond easily breaks and the oxygen is used.
Mammalian cells need a lot of energy and therefore must have a continual
Oxygen is not very soluble in water
Blood is a WATERY liquid; 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. Now 100 ml of blood can carry 20 ml of oxygen.
Dissolved only ----> 0.2 ml O2 / 100 ml blood
Haemoglobin ----> 20 ml O2 / 100 ml blood
This ability of blood to carry large quantities of oxygen gives mammals a
It allows mammals to be active, as well as grow large.
• Compare the structure of arteries, capillaries and veins in relation to their
Carry blood away from heart (high blood pressure)
The pressure created by the heart’s pumping creates great stress in the arteries
This is why the arteries are thick walled, elastic and muscular
The arteries are not motionless; they have muscle fibres in them which can
This contracting maintains the pressure on the blood, so that the blood travels
in spurts towards the body tissues (the contracting and relaxing also creates
The muscle fibres of the arteries also maintain the rate of the flow of blood.
Arteries usually carry oxygenated blood
Arteries lead to arterioles (small arteries).
Capillaries are an extension of the inner layers of the arteries and veins
They join arterioles and venules (small veins)
Capillaries are only one cell thick, and are so narrow, that only one red blood
Capillaries surround all tissue cells
Thus, they provide a very large surface area over which exchange of materials
The capillaries join to form venules, which join to form veins
Veins are not under a lot of stress - blood pressure is low
This is why they have thinner walls than arteries, less muscle and a wider
Since there are no thick muscular walls to keep the blood pulsing along, the
veins have a series of valves which prevent the blood from back-flowing on its
The veins also run through muscles, such as your leg muscles, and as you use
these muscles, they press on the veins, pushing blood through the veins.
• Describe the main changes in the composition of the blood as it moves
around the body and identify tissues in which these changes occur:
Blood flows from heart to lungs and then back to the heart
Blood is under lower pressure than in the systemic circuit
However, the rate of blood flow is faster
Very little body fluid is formed
The blood, having just returned from the body, contains high CO2 levels and
In the lungs, blood loses CO2 collects oxygen
Blood flows from the heart to the body (except the lungs) and returns back to
Blood is under high pressure due to contractions of the left ventricle of the
Blood pressure forces some fluid out of blood to become body fluid
In the tissues:
Blood gives up oxygen and other ions and nutrients
Waste products, eg urea, CO2, enter the blood
Blood loses urea and has the composition of water and salt balanced
Blood collects the products of digestion
Levels of glucose, lipids, and amino acids rise
Regulates the level of glucose in blood
Excess glucose is converted to glycogen and is stored
Converts excess amino acids to urea
• Outline the need for oxygen in living cells and explain why the removal of
carbon dioxide from cells is essential:
– All living cells need oxygen for respiration.
– As a result of respiration, carbon dioxide is produced
– When carbon dioxide dissolves in water, it makes carbonic acid.
– This means that if a lot of carbon dioxide is produced, the body cells (and the
– As studied before, enzymes can only function within a specific pH range
– So an increase in carbon dioxide will result in a lowering of pH, which will affect
• Describe current theories about processes responsible for the movement of
materials through plants in xylem and phloem tissue:
Transport of water is passive and depends on transpiration
and the physical
Transpiration: Evaporation of water from the leaf cells through the
stomates initiates the pull of the TRANSPIRATON STREAM. Water is
then drawn up the xylem tubes to replace this loss
Cohesion: Water molecules tend to bind together, forming a continuous
column in the xylem, which replaces any loss
Adhesion: Water molecules stick to the sides of the xylem tubes (cellulose
The movement of water through narrow tubes is called CAPILLARITY
It is caused by the two forces of COHESION and ADHESION
Movement of organic molecules, eg sugars, amino acids and hormones, in the
Materials are transported both up and down the stem. Materials are distributed
especially to the growing points
and reproductive structures
Flow of materials in the phloem is an active process that requires energy
It is thought to occur by a mechanism called the source-path-sink system and
is driven by a gradient generated osmotically
Theory 1: The source-path-sink system
Sugars and other mineral nutrients are ‘loaded’ into phloem sieve tubes of
♦ SYMPLASTIC LOADING: Sugars and nutrients move in the
cytoplasm from the mesophyll cells to the sieve elements through
plasmodesmata. (NOTE: Plasmodesmata have not been found in all
♦ APOPLASTIC LOADING: Sugar and nutrients move along the cell
walls to the sieve tube. Then they cross the cell membrane by active
As sugars enter the phloem the concentration of phloem sap increases and
the. This causes the entry of water by osmosis from the surrounding cells.
This resulting pressure causes water and dissolved solutes to flow towards
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
Theory 2: Sugars are moved through the phloem by CYTOPLASMIC
STREAMING and ACTIVE DIFFUSION within the sieve tubes.
• Analyse information from secondary sources to identify current
technologies that allow measurement of oxygen saturation and carbon
dioxide concentrations in blood and describe the conditions under which
How it Works
The Conditions It Is Used
the concentration) of O2 and • Helps for diagnosing as well as
• Measures saturation of oxygen • Helpful for monitoring patients
• Measures levels of bicarbonate • Eg, a patient in a coma can have
• Analyse information from secondary sources to identify the products
extracted from donated blood and the uses of these products:
– Whole blood is rarely given to patients
– Usually only certain products of blood are given.
– 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
– PLATELETS: Used to make the blood clot; is given to people with cancer of the
blood (leukaemia or lymphoma). Patients undergoing chemotherapy, whose blood
does not make enough platelets, are given this.
– 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. Very rarely
given, but are used when cell count is very low
– IMMUNOGLOBINS: Also called gamma globulins, immune serum, or antibodies,
these are also infection fighting parts of the blood plasma. Given to people who
have difficulty fighting infections, eg AIDS sufferers.
• 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:
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.
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).
– Some proposed replacements for blood:
o Free of biological materials, therefore no risk of infections
o BUT - must be combined with other materials to mix in with the
Haemoglobin Based Oxygen Carriers (HBOCs):
o Made from haemoglobin extracted from red blood cells
o Haemoglobin is not contained in membrane - cross matching unnecessary
o BUT - haemoglobin tends to oxidise to a different form, break down, and
o Made of 4% glucose solution in a fluid with equal salinity to blood
o Only used to restore blood pressure after accidents.
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
– Water is the solvent of all metabolic reactions in living cells, and sometimes
directly takes part in it (eg. Respiration)
: Concentration of solutes outside the cell is the same as inside the cell.
: Concentration of solutes is greater outside the cell than inside.
: Concentration of solutes is greater inside the cell than out. Water
– Living cells work best in an isotonic environment.
– Any change in the concentration of solutes will result in a change in the levels of
– This is why the concentration of water must be kept constant: To ensure the
• Explain why the removal of wastes is essential for continued metabolic
– As a result of metabolism, many waste products are formed (eg CO2)
– If these were allowed to accumulate, they would slow down metabolism and kill
– This is why they need to quickly be removed, or converted into a less toxic form.
– When proteins and amino acids are broken down (in a process called
deamination), a nitrogenous waste called ammonia, is produced
– Ammonia is highly toxic and must be removed or changed to a less toxic form
• Identify the role of the kidney in the excretory system of fish and mammals:
– This is the regulation of salt and water levels in the body
– Fish do not excrete nitrogenous wastes through the kidneys; they use their gills
– Their urine contains mainly excess water and salts
– Mammals’ urine contains urea as well as water and salts
– The kidneys ensure that the concentration of blood and interstitial fluid is constant
• Distinguish between active and passive transport and relate these to
processes occurring in the mammalian kidney:
– Active transport uses energy to transport substances across a membrane it would
normally not be able to cross due to a diffusion gradient or its own properties
– Passive transport is the movement of substances across a membrane without
– A kidney is made up of around a million nephrons.
– A nephron is made up of a Bowman’s capsule, connected to a proximal tubule,
leading to the loop of Henle, which connects to the distal tubule. This all connects
to the collecting duct which leads to the bladder.
– The nephrons are densely surrounded by capillaries
– Three processes occur in the nephrons (kidneys):
Filtration: Within the Bowman’s capsule is the glomerulus, a dense clump of
capillaries. The blood pressure here is so high that fluid and substance from
the blood are forced into the Bowman’s capsule, and form a fluid called the
. It contains:
Substances the body can reuse: Glucose, water, amino acids, etc
Wastes: Urea and poisons.
Reabsorption: The substances the body can reuse are reabsorbed into the
capillaries surrounding the nephron. Eg, vitamins and hormones. This is active
transport and requires energy. Some other substances passively re-enter the
blood. Eg, water and salts. This occurs in the proximal and distal tubules and
Secretion: This is the process where the body actively transports substances
from the blood into the nephron. This is active transport.
• Explain how the processes of filtration and reabsorption in the mammalian
nephron regulate body fluid composition:
– The nephron is a regulatory unit; it absorbs or secretes substances in order to
– This regulation maintains the constant composition of body fluids.
Bicarbonate ions are reabsorbed into the blood, hydrogen ions are secreted out.
Drugs, such as aspirin, penicillin and poisons are secreted out of the blood
Regulation of salts occurs here. Sodium ions are actively reabsorbed and
chlorine ions follow passively. Potassium ions are also reabsorbed
– The Loop of Henle: It has a descending limb and an ascending limb
In the descending limb, it is permeable to water, not salt.
Water passes out of the nephron by osmosis
In the ascending limb, the walls are permeable to salt, but not water
Salt passively passes out in the bottom, thin-walled section, but is actively
passed out in the top, thick-walled section.
Selective reabsorption of sodium ions and potassium ions occurs here again,
to regulate the pH of the blood, and the concentration of salts.
This is the end of the nephron, and connects to the ureters.
The walls are permeable to water only, and water is transported out
• Outline the role of the hormones, aldosterone and ADH (anti-diuretic
hormone) in the regulation of water and salt levels in blood:
Also called vasopressin
Controls the reabsorption of water by adjusting the permeability of the
collecting ducts and the distal tubules.
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 increased, collecting ducts and distal
tubules less permeable, less water absorbed, concentration returns to stable
ADH does not control the levels of salt in the blood. It only controls the
of salt through water retention.
Produced and released by the adrenal glands, which sit above the kidneys
Controls the amount of salt in the blood by regulating the reabsorption of salt
High blood volume and blood pressure due to water diffusing in.
Levels of aldosterone decreased.
Less salt reabsorbed, less water diffusing in
Salt level decreased, blood volume and pressure decreases
Low blood volume and blood pressure due to water diffusing out.
Levels of aldosterone increased.
More salt reabsorbed, more water diffusing in
Salt levels increase, blood volume and pressure increase
• 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
– Enantiostasis is the maintenance of metabolic and physiological functions in
response to variations in the environment.
– An estuary is where a river meets the sea, and freshwater mixed with saltwater
– This can cause a wide range of salinity levels in the area
– Organisms must be able to cope with these varying conditions to survive
– Animals can move to avoid changes, but plants must have mechanisms to help
them cope with these changing environmental conditions.
– In other words, organisms in estuaries have special adaptations that allow them to
maintain their metabolic and physiological functions in a changing environment
• Describe adaptations of a range of terrestrial Australian plants that assist
– Extensive root systems reach underground water
– The ability to close stomates when temperatures rise to a certain level
– Hard leaves with a thick or waxy cuticle
– Small leaves or false, photosynthesising leaves
• Identify the regions of the mammalian kidney involved in the excretion of
– The kidney is made up of three sections, the pelvis, the medulla and the cortex
– The cortex contains the glomeruli. It is very dark red due to the capillaries
– The cortex is involved in the filtration of blood
– The medulla contains the nephron tubules, as can be observed by the striped
– This section is involved in the reabsorption and secretion of substances
– The pelvis is where all the collecting ducts connect to
– The renal artery, renal vein and ureters are all connected to the pelvis.
• 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
The blood is extracted from the body from a vein and passed into a
dialyser, which is a bundle of hollow fibres made of a partially permeable
The dialyser is in a solution of dialysing fluid, which has similar ion
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
This occurs in the body
Dialysis solution is introduced into the peritoneal (abdominal) cavity
The lining of the peritoneal cavity is a natural semi-permeable membrane
The wastes diffuse into the solution, which is replaced.
• Outline the general use of hormone replacement therapy in people who
– The adrenal gland secretes aldosterone, without which the body would not be able
to regulate salt and water concentrations, causing severe dehydration
– Fludrocortisone is an artificial hormone which can be used as a treatment for
people who cannot secrete aldosterone (due to a damaged adrenal gland;
• Analyse information from secondary sources to compare and explain the
differences in urine concentration of terrestrial mammals, marine fish and
– Freshwater Fish:
Osmotic Problem: They are hypotonic to their environment. Water will tend to
diffuse INTO their bodies. Salts will diffuse out.
Role of Kidney: Removes excess water. Produces large amounts of dilute
urine. Kidneys also reabsorb salts. They also rarely drink water.
– Marine Fish:
Osmotic Problem: Hypertonic to environment. Water diffuses out. High salt
Role of Kidney: Continually drinks water. Kidneys reabsorb water, while
excreting salts. Small amounts of concentrated urine. Sale is also excreted
– Terrestrial Mammals:
Osmotic Problem: Water needs to be conserved.
Role of Kidney: Regulates concentration of blood, while at the same time
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:
– Aquatic Animals and Fish:
These organisms directly release ammonia into the
environment. This uses a lot of water, but they have no need to conserve it.
Ammonia is very water soluble and is excreted through the gills.
– Terrestrial Animals:
Releasing ammonia would be unfeasible due to lack of water.
Instead, land-dwellers change ammonia into less toxic forms and release it
periodically. Mammals change it into UREA and release it as urine.
Birds change ammonia into URIC ACID, a whitish paste which uses hardly
any water. This is lighter than using urea, and helps in flight.
• Process and analyse information from secondary sources and use available
evidence to discuss processes used by different plants for salt regulation in
Special glands in the mangroves can actively exclude the salt
from the water, so that the water absorbed has a lower salt concentration than
Salt is accumulated in old leaves that drop off, so that the
Salt can be excreted from the underside of the leaves of the
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