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9.2 Maintaining a balance: 1. Temperature range

Background: All organisms are adapted to a particular environment with its characteristictemperature range. The temperature range allows the organism's enzymes to control its

metabolism by operating at their optimum efficiency within this range.

Some organisms are adapted to live at high temperatures (80 - 100oC) and these are calledthermophiles. At the other end of the scale, there are organisms that are adapted to extremely

cold temperatures (0-4oC), termed psychrophiles. Most mammals and microbes are adapted

to a temperature range 30 - 45oC, averaging around 37

oC. The optimum temperature for

plants is around 25oC.

identify the role of enzymes in metabolism, describe their chemical composition and use

a simple model to describe their specificity on substrates

y Enzymes are biological catalysts. This means that they lower the energy required to

start a chemical reaction within a cell but do not get used up by that reaction. Everyreaction and process within a cell (metabolism) is controlled by a specific enzyme.

y Enzymes are globular proteins whose shapes are specialised so that other chemicals(substrates) can form a temporary bond with them. There are two models used to

show how an enzyme work:

y One model used to illustrate the action of an enzyme is the lock-key model. This is

where only one small part of the enzyme molecule can form a complex with thesubstrate. This part of the molecule is called the active site. Only a specific

substrate(s) can bond in that site and this makes the enzyme specific to that substrate.

y The induced fit model, a more recent modification on the lock-key model, proposes

that the active site slightly changes its shape to accommodate the substrate perfectly.



identify the pH as a way of describing the acidity of a substance

y pH is a scale related to the concentration of hydrogen ions in a solution.

y A pH value of 0 - 6 indicates an acid solution, where 0 is more acidic than 6, e.g.

lemon juice has a pH value of 2, hydrochloric acid has a pH value of 1.

y A pH value of 7 indicates a neutral solution, e.g. water.

y A pH of 8 - 14 indicates a basic solution, where 14 is far more basic than 8, e.g.sodium hydroxide (drain cleaner) has a pH of 14, sodium bicarbonate has a pH of 8.

identify data sources, plan, choose , equipment or resources and perform a first-hand

investigation to test the effect of:

o increased temperature

o change in pH

o change in substrate concentration

on the activity of named enzyme(s)

y For this investigation, you need data that will assist you to determine appropriateways in which each aspect may be researched. Enzymes that could be used include

salivary amylase, trypsin and rennin.

Rennin is an enzyme found in the stomachs of young mammals that are still being fed onmilk. The rennin 'curdles' or sets the protein in the milk separating it into curds (solids) and

whey (liquid).

y Plan your investigation using the procedure provided below.

y When choosing resources, you should be able to buy rennin as a junket tablet from

supermarkets.

Procedures to investigate the activity of an enzyme

A. To demonstrate the effect of increased temperature:

1. Make a rennin solution by dissolving a junket tablet in distilled water.

2. Add the same amount of rennin solution to a number of test tubes of milk, eg 7 test

tubes.

3. Place test tubes in different water baths at temperature ranges such as 0oC, 10

oC,

20oC, 30

oC, 40

oC, 50

oC and 60

oC. Make sure each water bath is kept at the

temperature it has been allocated.

4. Time the interval between adding the rennin and curdling of the milk for eachtemperature.

5. Note that the variables kept constant in each test tube are the junket solution, the pH

of the solution, the type of milk and the quantity of milk in each test tube.6. Comment on which temperature is the most effective in curdling the milk. Could adifferent temperature be better?



B. To demonstrate the effect of change in pH:

1. Make a rennin solution the same as was done in A and add pH solution to each withknown concentrations of pH solutions from for example pH 3, pH 4, pH 5, pH 6, pH 7

and pH 8.

2. Add the same amount of rennin solution with the varying pH to six test tubes of milk.

3. Place in a water bath kept at a constant temperature of 37oC.4. Time the interval between adding the rennin and curdling of the milk in each test tube.

5. Note that the variables kept constant in each test tube are the junket solution, the type

of milk, the temperature of 37oC, and the quantity of milk in each test tube.

6. Comment on which pH is the most effective in curdling the milk.

C. To demonstrate the effect of change in substrate concentration:

1. Make different concentrations of the substrate by diluting the milk using different

amounts of powdered milk to get different concentrations.

2. Add the same amount of rennin solution to each test tube of milk.3. Place in a water bath kept at a constant temperature of 37

oC.

4. Time the interval between adding the rennin and curdling of the milk.5. Note that the variables kept constant in each test tube are the type of milk, the

temperature of 37oC, and the quantity of milk in each test tube.

6. Should smaller increments of milk concentrations have been used?

y Perform the investigation by using the procedures above and carrying them out,recognising where and when modifications are needed and analysing the effect of any

adjustments that you make.

explain why the maintenance of a constant internal environment is important for

optimal metabolic efficiency

y Enzymes control all the metabolic processes in the body.

y Enzymes work optimally in an environment where their optimum temperature and pH

conditions are met. At temperatures and pH values other than the optimum, the

enzymes fail to work as efficiently as they should or not at all.

describe homeostasis as the process by which organisms maintain a relatively stable

internal environment

y 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 kept as

stable as possible.

explain that homeostasis consists of two stages:

o detecting changes from the stable state

o counteracting changes from the stable state

Background



For a state of homeostasis to exist, the body must have some way of detecting stimuli thatindicate a change in the body's internal or external environment.

y 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.

y An appropriate response occurs that counteracts the changes and thus maintains thestable environment, for example, shivering to generate heat in muscles.

outline the role of the nervous system in detecting and responding to environmental

changes

y The nervous system consists of the central nervous system (CNS) and the peripheral

nervous system (PNS). The CNS consists of the brain and spinal cord and the PNS

consists of the sensory nerves and the effector nerves. When the environmental

temperature begins to exceed a comfortable level for the body, temperature sensors in

the skin detect the temperature change and a sensory neuron conducts a nervousimpulse to the hypothalamus found in the brain. Nerve impulses pass this information

from the receptors to effector neurons then onto effectors, such as blood vessels,sweat glands, endocrine glands and muscles.

gather, process and analyse information from secondary sources and use available

evidence to develop a model of a feedback mechanism

Background

The body has some effective mechanisms to alter body temperature. To reduce temperature,

heat can be expelled by sweating or radiation of heat from the skin. To increase heat, the

body can respond by shivering or by contracting the skin. These responses can be activated

by heat receptors. If a mechanism is activated, it will operate until receptors indicate that the

optimum temperature has been reached.

If receptors in the skin detect heat, they relay information via the nerves to the hypothalamus,

which also contains receptors sensitive to the heat of passing blood. This triggers the

sympathetic nervous system to dilate skin capillaries and activate sweat glands. When

receptors in the skin detect a low temperature, a negative feedback mechanism is activated to

stop the original action. If skin temperature is still low, the hypothalamus may activatethyroid hormones to increase metabolic rate, activate the sympathetic nervous system to shut

down skin capillaries and sweat glands and activate food metabolism in the liver to produceheat. In this way, the body can maintain a stable body temperature.

y Gather samples of feedback mechanisms from biology texts, from scientific journalsor from the Internet. Often, analogies, such as the operation of a thermostat in a

refrigerator or an air conditioning system, are used.

y Process the samples to identify the common elements of each system. Evaluate the

validity of your sources by checking the reputation of the sources and by looking to

see how consistently the information compares.

y Analyse and use the information to design a creative model to represent a feedback

mechanism. The model might be a physical model, e.g. may be based on a see-saw

action, or it might be a conceptual model, based on an analogy.



identify the broad range of temperatures over which life is found compared with the

narrow limits for individual species

y Life, in some form, can be found at extremes ranging from - 40 oC to +120oC.

However, the great majority of living organisms are found in the - 2oC to +40

oC range

and for each individual species the range is even narrower. Below 0oC, cells risk ice

crystals forming in them and above 45oC, proteins within cells may denature.

analyse information from secondary sources to describe adaptations and responses that

have occurred in Australian organisms to assist temperature regulation

Background

Endotherms derive most of their body heat from cell metabolism. Mammals and birds are

endothermic animals. Australian endotherms include: the kangaroos and the platypus

(temperate regions); the rabbit-eared bandicoot (desert dweller); and the alpine pygmy

possum (alpine dweller)

Ectotherms derive most of their body heat from their surroundings. All invertebrates and fish,reptiles and amphibians are ectothermic. Australian ectotherms include the blue-tongued

lizard, the green tree frog and barramundi.Some sites to get you started are:

A land of lizards University of Texas, Austin, Texas, USA

Alpine Pygmy possum University of Michigan, Museum of Zoology, Ann Arbor,

Michigan, USA

Crocodilian Biology Crocodile Specialist Group Website, IUCN (The World Conservation

Union), Species Survival Commission

y You can analyse the information by designing a table like the one below. Describe

adaptations or responses of the organisms that assist temperature regulation.

Australian

organism

Endotherm

or ectotherm

Adaptation or response to

temperature regulation

compare responses of named Australian ectothermic and endothermic organisms to

changes in the ambient temperature and explain how these responses assist temperature

regulation

Endotherms

y In hot conditions, the red kangaroo licks the inside of its paws, where skin is thinner,

and blood supply is closer to surface, so that heat can be easily dumped to the outside.

Evaporation from saliva promotes the loss of heat from the blood.

y The large ears of the rabbit-eared bandicoot provide a large surface area to pass

excess heat when it is burrowing during the heat of day and when it is active at dusk.



Ectotherms

y Magnetic termites ( Amitermes meridionalis) pack the walls of their mounds withinsulating wood pulp and align their mounds north-south to maximize exposure to the

sun in the mornings and evenings when the air is cooler and to minimize exposure

during heat of day.

y Bogong moths are able to avoid their bodies freezing by supercooling their tissues.This process involves reducing the temperature of body fluids below their usual point

of freezing and as a result, ice crystals do not form and destroy the cells.

y Insects in alpine areas, as a rule, tend to be smaller, darker and use basking behaviours

to absorb what heat is available.

y Antarctic ice fish produce antifreeze (glycoproteins) that prevent ice formation.

identify some responses of plants to temperature change

y Plants can be damaged at temperature extremes when enzyme structures are altered or

membranes change their properties. As many important enzymes that are involved in photosynthesis and respiration are embedded in plant membranes, extremes of

temperature can be a major problem.y In cold conditions, extracellular ice formation causes dehydration. Some plants can

tolerate freezing temperatures as low as - 50oC by altering their solute concentrations

and through the lack of ice-nucleating sites in cells to prevent intracellular freezing.

y In hot desert conditions, plants have to develop a compromise between access to gasesfor photosynthesis and access to gases for respiration by keeping their stomates open

and cooling by evaporation. This risks dehydration of the plant.

9.2 Maintaining a balance: 2. A watery medium

Background:

Blood is the transport medium of mammals. It maintains the internal environment of all

organs as it supplies material to every cell in the body and removes the unwanted substances

that cannot be allowed to accumulate in cells. From the Preliminary course, recall that blood

consists of 55% plasma, a straw-coloured liquid of which 90% is water. The other

components of the blood are red and white blood cells and platelets.

Red blood cells are unique in that they do not contain a nucleus and have a biconcave shape.They are much smaller than white blood cells and more numerous. They contain the protein

haemoglobin, a complex protein molecule consisting of four polypeptides, each containing aniron atom. The iron atom has an affinity for oxygen molecules. When haemoglobin is

combined with an oxygen molecule, it is called oxyhaemoglobin.

Plants carry dissolved mineral nutrients in the xylem vessels and carry food (mostly glucose)in phloem tubes.



identify the form(s) in which each of the following is carried in mammalian blood:

o carbon dioxide

o oxygen

o water

o salts

o lipids

o nitrogenous waste o other products of digestion

y Most carbon dioxide enters the red blood cells and is combined with water to form

bicarbonate ions (HCO3-). Some is attached to haemoglobin molecules in red blood

cells and a small percentage is transported in plasma as dissolved CO2.

y Oxygen attaches itself to haemoglobin in the red blood cells, becoming a complex

called oxyhaemoglobin (HbO2).

y Liquid water is the solvent making up 90% of the plasma.

y Salts are carried as dissolved ions in the plasma.

y Lipids are carried with phospholipids and cholesterol in a protein coated packagecalled a chylomicron.

y The nitrogenous wastes (urea, uric acid and creatinine) are dissolved in blood plasma.

y Other products of digestion, such as sugars, amino acids and various vitamins, aretransported in the plasma.

perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide

on the pH of water

y Perform your investigation, making sure you take readings of the initial pH of the

distilled water.

Basic procedure

Using a data logger with a pH probe, take readings of the change in pH of 100 mL of distilled

water as exhaled air is bubbled through it over a two-minute period.

This experiment can also be performed using universal indicator paper and an indicator

colour chart to estimate the pH at various stages of the experiment.

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 scaleddiagrams of each

y To perform this investigation, you need to go through the steps for using a lightmicroscope that you learned in the Preliminary course. Revise how to focus themicroscope using low power (LP) first and then going to high power (HP).

y To gather information to estimate the size of blood cells, you will have to learn an

appropriate technique for estimating. If your school has a grid slide, put it on the stage

of the microscope and focus the microscope on low power. If you don't have a grid

slide, use a plastic ruler so you can see the millimetre lines under the microscope.

y Note what size each grid is and when you focus the slide, count the number of grids

across the diameter of the field of view. If there is part of one grid, estimate what



fraction it is. If the grids are one millimetre apart, you might estimate that thediameter of the LP field of view is 1.5 mm, which is 1500 m.

y When you go from LP to HP, you see less in the field of view. The diameters of thelow and high power fields are inversely proportional to their magnification. If your LP

magnifies 100X and the HP magnifies 400X, you will see one quarter of the field that

you saw in HP than you saw in LP, so if you saw twenty cells across the diameter

under LP, you would see approximately five of the same cells under HP.y Once you have focused on some red blood cells under LP, estimate the size using the

above method, then turn to HP and see if you agree with the first estimate. Draw

several cells and draw a scale bar.

y Once you have drawn a few red blood cells, browse over the field looking for some

white blood cells. Look for larger cells with clearly defined and stained nuclei and

draw several. Draw a scale bar to indicate the size of the cells.

Red blood cells in a blood vessel Department of Biomedical Engineering and

Computational Science (BECS) Centre of Excellence in Computational Complex

Systems Research, Helsinki, Finland

Blood cells Wadsworth Center, New York State Department of Health

explain the adaptive advantage of haemoglobin

y Oxygen is not very soluble in water and so cannot be carried efficiently dissolved in

the blood plasma. Most of the oxygen is carried by haemoglobin in the red blood

cells. Thus, the presence of haemoglobin in red blood cells in blood increases the

blood's capacity to carry oxygen. Organisms with blood (containing haemoglobin) are

able to deliver oxygen to cells more efficiently than other organisms with blood that

has no haemoglobin. The net effect is that these organisms are more effective

operators in a given environment than their competitors.

y At high altitudes, blood is not able to absorb as much oxygen as at sea level. The

human body adapts to what is effectively oxygen deprivation by initially increasing

heart rate, breathing rate, then the number of red blood cells (more haemoglobin),

then density of capillaries.

analyse information from secondary sources to identify the products extracted from

donated blood and discuss the uses of these products

Background

When blood is donated, it can be used almost immediately as whole blood or it can be

separated into its components. Whole blood is given to patients where major functions of the

blood, such as oxygen carrying capacity, are impaired, or where more than 20% of blood has been lost and there is a decrease in blood pressure.

A good source of information on the components of blood is the Australian Red Cross, Blood

Bank Service web site:

Different Donation Types Australia



Uses of blood can be found at Science clarified , USA 2007. Scroll down to Separation of blood components.

(These website were last accessed 2 June 2009).

y Analyse the information so that it fits under the headings P roducts of blood and Use

of the product .

Some blood products

Red blood cells (RBCs)

R BCs help patients who need to be able to carry more oxygen. R BCs may also be used to

help replace cells lost following significant bleeding.

Platelet concentrate

Platelets are essential for the coagulation of blood and are used to treat bleeding caused by

conditions or diseases where the platelets are not functioning properly.

Fresh frozen plasma (FFP)

FFP is used mainly to provide blood components that coagulate the blood. FFP contains allcoagulation factors in normal amounts and is free of red cells, white blood cells and platelets.

It is used for patients who require immediate clotting effects, such as those undergoingwarfarin therapy (blood thinning) or when massive transfusions have taken place.

Cryoprecipitate anti-haemophilic factor

Cryoprecipitate AHF is a concentrate of clotting proteins and is used for the treatment of von

Willebrand disease (similar to haemophilia), replacement of the clotting proteins, fibrinogen,

Factor XIII and Factor VIII when no other option is successful.

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.

The Internet is more likely to carry information about current technologies than reference

books. Here is a place to begin.

Pulse oximetry Nuffield Department of Anaesthetists, University of Oxford, UK (This sitelast accessed 12 June 2008)

Assess the reliability by comparing with information from different sources. Informationfrom an organisation, like the World Federation of Societies of Anaesthesiologists, is likelyto be more reliable than information from an individual who is not affiliated to any

organisation.

y Analyse the information to make a generalisation about current technologies being

used. You will also need to describe and explain the conditions under which the

different technologies are used. The information from the Internet will come from

different countries. Some countries may be ahead of other countries so making



generalisations will avoid the problem of some information contradicting other information. However, you will need to keep in mind the above point about reliability.

Monitoring oxygen and carbon dioxide concentration

One method used by hospitals to monitor blood oxygen and carbon dioxide levels in patient's

blood is to use a pulse oximeter. A small clip with a sensor is attached to the person's finger,earlobe or toe. A cable connects the sensor to the pulse oximeter machine. The colour of the

blood changes according to the amount of oxygen that is dissolved in the blood. Blood that is

high in oxygen is bright red while blood low in oxygen is a darker colour. The sensor emits a

light signal that passes through the skin. The sensor measures the amount of light absorbed as

it passes through the tissue and blood, and transmits the information to the pulse oximeter. A

reading is given in a percentage form.

Pulse oximetry is used to monitor the level of oxygen in a person's blood during heavy

sedation or anesthesia. This device is also used when a person is on a ventilator, artificial

breathing machine, during stress testing, in sleep laboratories, when checking the body'sresponse to different medications or to monitor a person with asthma or who is having trouble

breathing.

Another method of analysing blood gases is with arterial blood gas (ABG) analysis machines.These can measure the amount of oxygen and carbon dioxide in a sample of blood by

monitoring the rate of diffusion of these gases through artificial membranes which are permeable to these gases. When moving through a membrane, oxygen in the blood produces

an electrical current while carbon dioxide changes the pH of the solution.

analyse and present information from secondary sources to report on progress in the

production of artificial blood and use available evidence to propose reasons why such

research is needed

Background

Blood transfusions have been the subject of medical research for centuries. In the early

1900s, successful transfusions were carried out as an understanding of blood components

were understood. Up until the HIV crisis in the 1980s, there was little interest in artificial

blood as there did not seem a great need. With the transmission of the virus during

transfusions, there was nothing to replace donor blood, so artificial blood became a priorityfor research. Sensitive screening tests have now been developed for potential infective

organisms, such as HIV and hepatitis, making donor blood much safer. There are nowavailable safe and effective blood substitutes for certain applications, although they are still

not ready for widespread use. Better blood substitutes are still needed. There is a continuing

shortage of donor blood to help the victims of emergencies, civil and international conflictsand natural disasters. Furthermore, there is no guarantee that something similar to the HIVcrisis will not occur in the future.

An Internet search on artificial blood will provide links, which include the history, current

research and uses of artificial blood substitutes in blood transfusions. Some sites you could

start with are:

Artificial blood Royal Society of Chemistry 2011



Perflurochemicals Wikipedia

y Analyse the information you have gathered to identify examples of theinterconnectedness of ideas concerning artificial blood. In your analysis, consider the

two types of artificial blood, one based on chemically modified haemoglobin and the

other based on perfluoroorganic compounds.

y You could present the information as a speech to fellow students.y Use the available evidence to propose reasons why research on artificial blood is

needed.

Why research on artificial blood is needed

Some advantages of artificial blood could include the following:

y Pasteurisation could be used to remove all pathogens.

y There would be no need for cross-matching and typing as the artificial blood contains

no blood-group antigens. This saves time and allows on-the-spot transfusion.

y Artificial blood can be stored for more than one year, compared with about one month

for donor blood using standard methods.

compare the structure of arteries, capillaries and veins in relation to their function

y Arteries carry blood away from the heart under high pressure and so must have astructure that can withstand the pressure. They have thick, but elastic walls, made up

of three tissue layers: endothelium as a lining, smooth muscle to contract the vessel

and connective tissue to allow for expansion. Arteries do not pump blood.

Veins carry blood back toward the heart. They carry the same quantity of blood as the

arteries but not at the same high pressures. Veins have the same three layers as the

arteries: endothelium, smooth muscle and connective tissue. However, the layers are

not as thick. The veins also contain valves that prevent the backflow of blood.

Capillaries have walls that are only one endothelium cell thick, as they have to allow

diffusion of materials through their wall to reach the cells found in the tissues in

which the capillary is located.

describe the main changes in the chemical composition of the blood as it moves around

the body and identify tissues in which these changes occur

y The blood circulates through two systems in the body: the pulmonary system and the

systemic system.

y In the pulmonary system, blood flows from the heart to the lungs and then back to the

heart. Blood travels in the pulmonary artery from the right ventricle to the lungs

where carbon dioxide is released into the alveoli of the lungs. This is then ultimatelyreleased out of the body. Oxygen is picked up from the alveoli and diffused into thered blood cells to then be taken back to the heart. So via the pulmonary system,

carbon dioxide is decreased and oxygen levels increased.

y In the systemic system, blood flows from the heart to the rest of the body, except the

lungs, and then returns. The left ventricle pumps oxygenated blood to the rest of the

body, and as this blood circulates in capillaries, oxygen is delivered to the cells and

carbon dioxide is picked up. Other waste products, such as urea, are also picked up

from the liver and transported in the blood to the kidneys. Blood flowing to the small



intestines collects the products of digestion and transports them to the liver. Glucoseis circulated in the blood stream to all cells in the body for respiration. Deoxygenated

blood returns to the heart via the inferior and superior vena cava.

outline the need for oxygen in living cells and explain why removal of carbon dioxide

from cells is essential

y Cells require oxygen in the process of respiration: Glucose + oxygen carbon

dioxide + water + energy (in the form of ATP)

y 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 inwater. At normal levels, (after excess removal of carbon dioxide) the carbon dioxide -

bicarbonate ion (HCO3-) equilibrium is an important mechanism for buffering the

blood to maintain a constant pH.

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

y Talk to your teacher to help you decide which are the best plants to use for this

activity. O btain the plants by students bringing them from home or if necessary obtainthem from a nursery.

y Choose appropriate equipment, which should include sharp instruments so you cando a clean cut, without tearing the plant material. The instruments you choose will

depend on their availability at school.y Perform the investigation by doing transverse and longitudinal cuts on stems of the

chosen plants. One way of doing this is to embed the plant in material like a carrot or

potato or if available in wax.

y Put the cut pieces in water, then mount them on a slide.

You may choose to stain thematerial. If so, decide what is an appropriate stain. Cover the slide with a cover slip.

y Gather first-hand data by drawing the samples, while looking under the LP

magnification of your microscope. It is better to draw just a few cells and do them as

accurately as possible than draw many cells that don't show clearly the differences

between xylem and phloem vessels.

describe current theories about processes responsible for the movement of materials

through plants in xylem and phloem tissue

Background

From your Preliminary course, you should recall that the transport system in plants involves phloem and xylem. Xylem transports water and mineral ions upward only, from roots toward

leaves. Phloem transports organic materials, in particular sugars, up and down to where thematerial is needed or for storage.

y Xylem: The transpiration-cohesion-tension mechanism is currently the theory that

accounts for the ascent of xylem sap. This sap is mainly pulled by transpiration rather

than pushed by root pressure. Cohesion is the ³sticking´ together of water molecules

so that they form a continuous stream of molecules extending from the leaves down to



the roots. Water molecules also adhere to the cellulose molecules in the walls of thexylem. As water molecules are removed by transpiration in the leaf, the next molecule

moves upwards to take its place, pulling the stream of molecules continuously along.This is passive transport.

y Phloem: The pressure-flow mechanism (or Source to Sink) is a model for phloem

transport now widely accepted.

The model has the following steps.Step 1: Sugar is loaded into the phloem tube from the sugar source, e.g. the leaf

(active transport)

Step 2: Water enters by osmosis due to a high solute concentration in the phloem tube.

Water pressure is now raised at this end of the tube.

Step 3: At the sugar sink, where sugar is taken to be used or stored, it leaves the

phloem tube.Water follows the sugar, leaving by osmosis and thus the water pressure

in the tube drops.

The building up of pressure at the source end, and the reduction of pressure at the sink end,

causes water to flow from source to sink. As sugar is dissolved in the water, it flows at thesame rate as the water. Sieve tubes between phloem cells allow the movement of the phloem

sap to continue relatively unimpeded.

9.2 Maintaining a balance: 3. Gases, water and waste products

Background information:

Plants and animals carry out the normal functions for living on a daily basis. To do this, they

require gases such as oxygen for respiration and, in plants, carbon dioxide for photosynthesis.

These metabolic reactions are chemical reactions that accumulate wastes. If these wastes

aren't disposed of, they could kill the organism.

perform a first-hand investigation of the structure of a mammalian kidney by

dissection, use of a model or visual resource and identify the regions involved in the

excretion of waste products

y Use the diagram below as a visual resource to identify the regions of the kidney, or

use the models provided on these Internet sites.

Video of kidney dissected Broward Community College Ft. Lauderdale, Florida,USA

y Before starting, consider safe working practices. Carry out a risk assessment by listing

any potential dangers involved in this procedure and then say how you will avoid

these dangers.y If a mammalian kidney, such as a sheep's kidney, is available, perform a dissection of

it.



y Identify the parts of the kidney using the diagram above as a guide.

explain why the concentration of water in cells should be maintained within a narrow

range for optimal function

y Water is the solvent for metabolic reactions in living cells. Many molecules and allions important for the life of the cell are carried in an aqueous solution and these

diffuse to reaction sites through the water in the cell.

y Metabolic reactions within the cell can occur only in solution where water is the

solvent. It is critical for proper functioning of these reactions that the amount andconcentration of water in the cell be kept constant. Most cells die when the water

content is changed significantly.

explain why the removal of wastes is essential for continued metabolic activity

y Metabolic wastes, particularly nitrogenous wastes that are the by-products of the

breakdown of proteins and nucleic acids, are toxic to cells and must therefore be

removed quickly. Nitrogenous wastes have the ability to change the pH of cells and

interfere with membrane transport functions and may denature enzymes.

y Metabolic wastes are the product of metabolic reactions. If they are not removed their

concentration in the cell increases. This inhibits the reactions that produce them,

interfering with normal metabolic activity.

use available evidence to explain the relationship between the conservation of water and

the production and excretion of concentrated nitrogenous wastes in a range of

Australian insects and terrestrial mammals

Background

The following provides general information for the waste products, ammonia, urea and uric

acid.

Ammonia is very toxic and must be removed immediately, either by diffusion or in very

dilute urine. It is the waste product of most aquatic animals, including many fish andtadpoles. Ammonia is the immediate product of break down of amino acids ² no energy is



required to make it. It is highly soluble in water and diffuses rapidly across the cellmembrane. However, it needs large quantities of water to be constantly and safely removed.

Ammonia does not diffuse quickly in air.

Urea is toxic, but 10 000 times less toxic than ammonia, so it can be safely stored in the body

for a limited time. It is the waste product of mammals, and some other terrestrial animals, but

also of adult amphibians, sharks and some bony fish. It is made from amino acids but requiresmore steps and energy to make than does ammonia. It is highly soluble in water, but being

less toxic than ammonia, it can be stored in a more concentrated solution and so requires less

water to remove than ammonia. It is a source of water loss for these species.

Uric acid is less toxic than ammonia or urea, so can be safely stored in or on the body for

extended periods of time. It is the waste product of terrestrial animals such as birds, many

reptiles, insects and land snails. It is a more complex molecule than urea so it requires even

more energy to produce. It is thousands of times less soluble than ammonia or urea and has

low toxicity, which means that little water is expended to remove it. This is a great advantage

for survival.

Organism Terrestrial

or aquatic

Waste

product(s)

Explanation

spinifex

hopping

mouse of Central

Australia

terrestrial urea in a

concentrated

form

The animal lives in a

very arid environment.

It drinks very littlewater and excretes

urea in a concentratedform, so that water can

be conserved.

Euro,wallaroo

( M acropusrobustus)

terrestrial concentratedurine

Euros have a veryefficient excretory

system that recyclesnitrogen and urea to

make a veryconcentrated urine.

This allows them to

survive in very arid

environments

Insects terrestrial uric acid Insects are covered

with a cuticleimpervious to water.

They conserve water by producing a dry

paste of uric acid.



y There is a fine balance between the use of water to remove nitrogenous wastes andconservation of water in the body. Australian terrestrial mammals that live in

predominantly arid areas, such as the Bilby ( M acrotus lagotus), must produce veryconcentrated urine and tolerate high levels of urea in their systems. Some insects

excrete ammonia as a vapour across the body surface rather than as a solution of

urine, an adaptation for conserving water. More commonly, uric acid is produced,

which is a dry urate waste requiring no water to remove and with low toxicity so thatit can be kept in the body for long periods of time. Find out how a range of Australian

insects and terrestrial mammals excrete nitrogenous wastes.

y Use available evidence to examine cause and effect relationships such as the lack of

water and the production of water-efficient waste removal and use this to write an

explanation of the relationship between the conservation of water and the production

and excretion of concentrated nitrogenous wastes in a range of Australian insects and

terrestrial mammals.

Here are some starting points.

Euro University of Michigan, USA

Mulgara The Australian Arid Lands Botanic Garden, Port Augusta, South AustraliaKowari Animal Info, Maryland, USA (These websites last accessed 22 December

2005.)

analyse information from secondary sources to compare and explain the differences inurine concentration of terrestrial mammals, marine fish and freshwater fish

Some summary information is provided in the box below.

Excretory system of different animals Estrella Mountain Community College, Avondale,

Arizona, USA

y Present the information through use of an information organising device, such as the

table below.

Type of

organism

Excretory product

and concentration

Environmental

reason

terrestrial

mammal

marine fish

freshwater fish

y Analyse the information by making generalisations about urine concentration of

terrestrial mammals, marine fish and freshwater fish.



Summary:

Differences in urine concentration of terrestrial mammals, marine fish and freshwater

fish

Terrestrial mammals

Terrestrial mammals must work to find water and they are surrounded by air into which water

quickly evaporates. Water conservation is of prime concern and these animals cannot excrete

large quantities of water for the removal of metabolic waste.

Marine fish

The loss of water to the external environment is a problem that all marine fish must deal with.

The marine environment in which the fish lives is hyperosmotic to the internal environment,

i.e. there is a higher salt concentration in the water than inside the cells. This results in an

osmotic gradient in which water is lost from the fish to the environment while ions are gained by diffusion. Ions are excreted by specialised glands.

Freshwater fish

The freshwater environment is hypo-osmotic to the internal environment of fish, i.e. there is a

lower salt concentration in the water than inside the cells. This results in an osmotic gradientin which water is gained by the fish from the environment without drinking and salts are lost

by diffusion. Ions are absorbed in the gut and by active uptake across the gills.

identify the role of the kidney in the excretory system of fish and mammals

y The kidney is an organ of the excretory system of both fish and mammals. It plays a

central role in homeostasis, forming and excreting urine while regulating water and

salt concentration in the blood. It maintains the precise balance between waste

disposal and the animal's needs for water and salt.

y The role of the kidney in fish is dependant on the environment of the fish.

o In marine (salt water) environments, the kidneys excrete small quantities of

isotonic (same concentration as sea water) urine. This helps conserve water

and excrete the excess salt they gain from their hyperosmotic environment.

o In freshwater fish, the kidneys work continuously to excrete copious quantitiesof dilute urine, which also has a very low salt concentration. This helps to

remove excess water gained from the hypo-osmotic environment.

explain why the processes of diffusion and osmosis are inadequate in removing

dissolved nitrogenous wastes

y 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

y 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 involves no expenditure of energy as the materialsfollow 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.

y In the mammalian kidney, both active and passive transport processes occur.

o Passive transport: Once filtration has occurred in Bowman's capsule, water

returns via the interstitial fluid from the tubule to the capillary in the process

of osmosis. This occurs along the length of the tubule.

o Active transport: Depending on their concentration, the ions in the blood (Na+,

K +, Cl

-, H

+and HCO3) can be transported to cells in the nephron tubule and

then secreted by the cells into the tubule. Some poisons and certain drugs areeliminated from the body in this manner.

explain how the processes of filtration and reabsorption in the mammalian nephron

regulate body fluid composition

y Filtration of the blood occurs in Bowman's capsule where high blood pressure in theglomerulus forces all small molecules out of the blood into the capsule. Water, urea,

ions (Na+, K

+, Cl

-, Ca

2+, HCO3

-), 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.

y Reabsorption takes place selectively at various points along the proximal tubule, loop

of Henle and distal tubule.

y 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

-

, Ca2+ and HCO3- occurs at different rates depending on feedback from the body. In

some cases, active transport is required. Water is reabsorbed in all parts of the tubule

except the ascending loop of Henle. The amount of water reabsorbed depends on

feedback from the hypothalamus. If no water were reabsorbed human would soon

dehydrate, losing water at a rate of around 7.5 L per hour.

y The chemical composition of the body fluids is precisely regulated by the control of

solute reabsorption from the glomerular filtrate.

gather, process and analyse information from secondary sources to compare the process

of renal dialysis with the function of the kidney

y Gather information on renal dialysis using books and digital technology, including

the Internet.

y Process the information by comparing the dialysis machine with the kidney and

matching the parts of the dialysis machine to the structure of the kidney. You could

use a table like the one following.



Dialysis machine Kidney

artificial tubing Nephron

dialysing solution

distal tubule

y Analyse the information by determining the outcomes of the dialysis process and

showing whether the kidney is more efficient at osmoregulation and excretion thanthe dialysis machine.

Information from Davita.com .

Summary: Comparison of the process of renal dialysis with the function of the kidney

Dialysis means separation in Greek, and, like the nephrons of the kidney, the dialysismachine separates molecules from the blood removing some and returning others. The

patient's blood is pumped from an artery through tubes made of selectively permeable

membrane. The artificial tubing allows only water and small solute molecules to pass through

it into a dialysing solution that surrounds the tube. This dialysing solution is similar to the

interstitial fluid found around nephrons. As the blood circulates through the dialysis tubing,

urea and excess salts diffuse out of it instead of leaving by pressure filtration, as in the

nephron. Those substances needed by the body, such as bicarbonate ions (HCO3-) diffuse

from the dialysing solution into the blood (reabsorption). The machine continually discards

used dialysing solution as wastes build up in it.

Two healthy kidneys filter the blood volume about once every half-hour. Dialysis is a much

slower and less efficient process than the natural processes found in a healthy kidney but it isa lifesaver for those people with damaged kidneys.

outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone), in the

regulation of water and salt levels in blood

y Aldosterone is a steroid hormone secreted by the adrenal gland. Its function is to

regulate the transfer of sodium and potassium ions in the kidney. When sodium levelsare low, aldosterone is released into the blood causing more sodium to pass from the

nephron to the blood. Water then flows from the nephron into the blood by osmosis.

This results in the homeostatic balance of blood pressure.

y Antidiuretic hormone (ADH or vasopressin) controls water reabsorption in the

nephron. When levels of fluid in the blood drop, the hypothalamus causes the

pituitary to release 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.



present information to outline the general use of hormone replacement therapy in

people who cannot secrete aldosterone

Background

Hypoaldosteronism is a condition where people fail to secrete aldosterone. Addison's disease

is the name of a disease with these symptoms which include high urine output with aresulting low blood volume. Eventually, as blood pressure falls, this can result in heart

failure. A replacement hormone, fludrocortisone (Florinef), is used to treat this condition but

a careful monitoring must be maintained to avoid fluid retention and high blood pressure.

Here is an Internet site to get you started in your search.

Addison's disease National Institute of Diabetes and Digestive and Kidney Diseases, USA

y Present the information as a discussion, with clearly identified issues and or points

provided for and against the use of the therapy.

define enantiostasis as the maintenance of metabolic and physiological functions in

response to variations in the environment and discuss its importance to estuarineorganisms in maintaining appropriate salt concentrations

y Enantiostasis is the maintenance of normal metabolic and physiological functioning,

in the absence of homeostasis, in an organism experiencing variations in itsenvironment.

y All organisms living in an estuary experience large changes in salt concentration in

their environment over a relatively short time span, with the tidal movement and

mixing of fresh and salt water. Organisms that must tolerate wide fluctuations of

salinity are said to be euryhaline.

y One strategy to withstand such changes in salt concentration is to allow the body's

osmotic pressure to vary with that of the environment. Organisms that do this, and

therefore do not maintain homeostasis, are said to be osmoconformers. Most marine

invertebrates are osmoconformers. In contrast, marine mammals and most fish are

osmoregulators, maintaining homeostasis regardless of the osmotic pressure of the

environment.

y However, as the salt concentration of body fluids in an osmoconformer changes,

various body functions are affected, such as the activity of enzymes. For normal

functioning to be maintained, another body function must be changed in a way thatcompensates for the change in enzyme activity.

y One example of enantiostasis is when a change in salt concentration in the body fluid,which reduces the efficiency of an enzyme, is compensated for by a change in pH,

which increases the efficiency of the same enzyme.



process and analyse information from secondary sources and use available evidence to

discuss processes used by different plants for salt regulation in saline environments

y Process information you have gathered, from the Internet or biology books about salt

regulation of different plants in saline environments, by selecting the most relevant

information and discarding peripheral information that is not as relevant.

y Analyse the information to see if there is a pattern of processes for regulating salt. Docertain families of plants use the same or similar methods or is the environment the

plants live in more important in determining the methods of salt regulation? The two

sites below will start you on your search.

y Use the evidence from your analysis to develop a discussion of the processes used by

different named plants for salt regulation in saline environments.

Poster: Salinity American Society of Plant Biologists, USA

Description of Australia's marine environment and its status, Coastal saltmarshes:

undervalued and locally threatened Department of Environment, Water, Heritage and the

Arts, Australian Government

Summary:

Coping with salt

Most plants cannot tolerate high salt concentrations in the root zone as it leads to water stress.The salt accumulates in the leaves and is toxic. Enzymes are inhibited by Na+ ions.

Halophytes are plants that can tolerate higher levels of salt in their environment.

The grey mangrove, Avicennia marina, has special salt glands in its leaves that excrete salt.

Other mangroves exclude salts at their roots through ultrafiltration and a third mechanism is

to store salt in leaves and then drop the leaves.

Another mechanism involves the efficient control of transpiration. Some mangroves have

small leaves hanging vertically to reduce the surface presented to the sun and thus reducing

transpiration.

Salt marsh plants also have mechanisms for salt regulation. For example, Sarcocornia

quinqueflora accumulates salt in the swollen leaf bases which fall off, thus removing excess

salt and Sporobolus virginicus has salt glands on its leaves.

Another form of salt stress can occur in salt laden air such as in coastal environments. Some

coastal plants, such as the Norfolk Island pine, have a mesh of cuticle over their stomates,which prevents small water droplets from entering the leaf.

perform a first-hand investigation to gather information about structures in plants that

assist in the conservation of water

y This first-hand investigation is easily performed as an observation exercise, usinglocal specimens. Look for plants that occur in areas where water conservation is

important. As Australia is a dry continent, many of our plants have evolved to

withstand periods of drought. So, no matter what part of NSW you live in, you should

have some plants you can observe that grow nearby. Some plant species to look for

are eucalyptus, casuarinas, paper barks, cacti and other succulents, spinifex and

mulga.



y Gather information by observing and recording structures in plants that assist in theconservation of water. Many plants have adaptations to assist in the conservation of

water. Here are a few adaptations to look for:

o the location and the number of stomates

o the arrangement, shape and size of the leaves

o phyllodes or cladodes rather than leaveso presence of a thick waxy cuticle

o hairy leaves

o leaves reduced to spines

o leaves rolled inwards

o the reflective nature of the leaf surface.

Your recording could best be done using a table like the one below.

Plant Adaptation

of leaves

Adaptation

of stems

Adaptation

of roots

How this

adaptation

conserveswater

C asuarina leaves

reduced to

scales

cladodes reduces

transpiration

Eucalyptus waxyleaves;

leaves hang

vertically

reducestranspiration

C actus stems store

water

Describe adaptations of a range of terrestrial Australian plants that assist in minimising

water loss

y You will recall from the Preliminary course that the leaves of plants contain stomates

or small pores that allow the exchange of gases essential for respiration and

photosynthesis. These gases include water vapour, as well as oxygen and carbon

dioxide. If stomates are open, there will be a loss of water by transpiration and

evaporation. Plants in arid areas have to balance the need for CO2 with the need to

conserve water.y Adaptations of Australian xerophytes (plants adapted to dry conditions) include:

o hard leathery, needle-shaped leaves with reduced surface areas such as in

H akea sericea (needlebush) and coastal tea trees

o use of phyllodes for photosynthesis rather than leaves that would lose water by

transpiration, as in many acacias

o some salt bushes, e.g. Atriplex, change the reflectiveness of their leaves during

leaf development so that they have highly reflective leaves during summer



o Eucalypts avoid high radiation in the middle of the day by hanging their leavesvertically to present less surface area to sun

o heat loss is greater for small leaves or highly dissected leaves than it is for larger leaves and many Acacias have fronds of bipinnate leaves

y waxy cuticle prevents evaporation in many Eucalypts.

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