Bio5.Maintaining a Balance

keep it simple science TM

www.keepitsimplescience.com.auHSC Biology Topic 1copyright © 2005-2007 keep it simple science

Baulkham Hills High School SL#802445

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What is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. THE FUNCTION OF ENZYMES & HOMEOSTASIS

2. TEMPERATURE REGULATION IN ORGANISMS3. INTERNAL TRANSPORT SYSTEMS IN ORGANISMS

4. EXCRETION & WATER BALANCE

but first, an introduction...Living Things are Made of CellsAll living things are composed of microscopic unitscalled cells. You learned in a previous topic aboutthe structure of a cell and the functions of theorganelles.

Each cell is “alive” in its own right, and capable of allthe life functions:-

• growth • reproduction• movement • assimilation• response to changes in its environment

Metabolism is ChemistryControlled by Enzymes

What goes on inside a living cell is mainly a matterof chemical reactions... new molecules are built,others are torn apart. Special reactions release theenergy needed to make all this chemistry happen.

In this topic you will learn about the importance ofEnzymes... the special molecules that control thechemistry of each cell.

HomeostasisThe enzymes that control all the chemical reactionsin every living cell are very sensitive to thetemperature and the pH (acidity) of thesurroundings. It is vital that the “internalenvironment” of any organism is kept as constant aspossible so that the enzymes and the chemistry ofeach cell keep operating normally.

The process of “keeping everything the same” is calledhomeostasis, and is one of the most important andvital processes in every organism. In this topic you willstudy some of the basic mechanisms of homeostasis,and how certain body systems are involved byabsorbing, transporting, regulating and excreting thevital chemicals of life.

As well as the homeostatic processes in mammalsand some other animals, you will study someregulatory processes in plants.

HSC Biology Topic 1

MAINTAINING A BALANCE

NNeerrvvoouuss SSyysstteemmRegulates bodytemperature

CCiirrccuullaattoorryy SSyysstteemmtransports gases,nutrients & wastes

RReessppiirraattoorryy SSyysstteemmGas exchange

EExxccrreettoorryy SSyysstteemmRegulates waterbalance and excretesmetabolic wastes

GENERALIZED DIAGRAM OF A LIVING CELL

“Membrane” on theoutside contains thecell , and controls

what goes in or out

Organelles

Cytoplasmjelly-like liquid fills

the cell




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CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorizing the OUTLINE of a topic helps them learn and remember the concepts andimportant facts. As you proceed through the topic, come back to this page regularly to see how each bit fits thewhole. At the end of the notes you will find a blank version of this “Mind Map” to practise on.

Functions &characteristics

of Enzymes

Shape &specificity of

Enzymes

Concept ofNegative Feedback

Effects of Temp, pH& substrate conc. on

enzyme activity

Receptor, Control Centre

EffectorsHypothalamus

& EffectorOrgans

Processessesof heating &

cooling

Temperaturerange of life

Ectotherms

Endotherms

Plants

Substancescarried in

blood.Where from,

where to?

Artificialblood? Blood products

Oxygensaturation

Water Balancein Aust. insects

& mammals

Dialysis & HRTExcretion

Filtration & ReabsorptionHomeostasis

ADH & Aldosterone

Enantiostasis

Coping with salt

Importance ofwater &

Water Balance

Transpirationin XylemTranslocation

in Phloem

Blood & Blood Vessels

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BBAALLAANNCCEE

Enzymes &

Homeostasis

Excretion&

WaterBalance

Internal TransportSystems

TemperatureRegulation

in Organisms

Temperatureregulation in...

How the gasesare carried

Importance ofHaemoglobin

Transport in Plants

Water conservation inAust. Plants

Kidney & NephronStructure & Function




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Metabolism is ChemistryEverything that happens inside a living thing is really amatter of cell chemistry... “metabolism”. For example...

• In order to move, protein fibres inside muscle cells mustbe made to slide past each other. This is achieved bychemical reactions occurring along the muscle fibres.

• For your body to grow, cells must divide and add moremembranes, cytoplasm and organelles to increase the cellsize. This involves the chemical construction of new DNAmolecules, new phospholipids for membranes and so on.

• All these chemical reactions require energy. Energy isdelivered by the ATP molecule, itself the product of aseries of chemical reactions in the mitochondria... cellularrespiration.

All of these reactions, and more, add up to “metabolism”:the sum total of all the thousands of chemical reactionsgoing on constantly in all the billions of cells in your body.

EnzymesEvery one of these reactions requires a catalyst... achemical which speeds the reaction up and makes ithappen, without being changed in the process.

In living cells there is a catalyst for every reaction type.Biological catalysts are called enzymes, and:

• are protein molecules (made of folded chains of amino acids)

• have a particular 3-dimensional shape, which fits the“substrate” molecule(s) of the reaction

• are highly “substrate-specific”. This means that eachenzyme will only catalyse one particular reaction, and noother.

• will only work effectively in a relatively narrow range oftemperature and pH (acidity).

The Importance of ShapeMany of the properties of enzymes are related to theirprecise 3-dimensional shape.

The shape of the enzyme fits the “substrate” molecule(s) asclosely as a key fits a lock.

This is why enzymes are “substrate-specific”... only oneparticular enzyme can fit each substrate molecule. Eachchemical reaction requires a different enzyme.

Changes in temperature and pH (acidity) can cause theshape of the enzyme to change. If it changes its shape evenslightly, it might not fit the substrate properly any more, sothe reaction cannot run as quickly and efficiently. This iswhy enzymes are found to work best at particular“optimum” temperature and pH values.

1. THE FUNCTION OF ENZYMES & HOMEOSTASIS

Enzyme

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Shape changes slightlyat different pH or temp.

Substrate...

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The pH ScaleThe acidity or alkalinity of any solution or environment ismeasured on a numerical scale known as “pH”.

On the pH scale, anything which is neutral (neither acid noralkaline) has a pH = 7.

The inside environment of a cell, and most parts of anorganism’s body, is always very close to pH 7... i.e. neutral.An exception is in the digestive system where conditions areusually quite strongly acidic in the stomach (approx. pH 2).

Enzyme Activity GraphsYou will have carried out experimental work to measure the“activity” of an enzyme under different conditions oftemperature, pH and the concentration of the substratechemical.

You may have measured the rate of a chemical reactionbeing catalysed by an enzyme, such as:• the rate of milk clotting by rennin (junket tablets)• the rate of digestion of some starch by amylase• the rate of decomposition of hydrogen peroxide by

“catalase” enzyme.

A common way to measure the rate of a reaction is tomeasure the time taken for a reaction to reach completion...the shorter the time taken, the faster the reaction. This whythe reciprocal of time taken (1/time) is used as the measureof rate of reaction.

The Effect of TemperatureWhen enzyme activity is measured over a range oftemperatures, the results produce a graph as below.

Optimum TemperatureNot all enzymes will “peak” at the same temperature, orhave exactly the same shape graph. In mammals, mostenzymes will peak at around the animal’s normal bodytemperature, and often work only within a narrow range oftemperatures.

An enzyme from a plant may show a much broader graph,indicating that it will work, at least partly, at a wider rangeof temperatures.

An enzyme from a thermophilic bacteria from a hotvolcanic spring will show a totally different “peak”temperature, indicating that its metabolism will performmost efficiently at temperatures that would kill otherorganisms.

The graph of reaction rate (or “enzyme activity”) againsttemperature is usually not symmetrical. It tends to risegradually at temperatures below the optimum, but oftenfalls more steeply at temperatures above optimum, becausethe denaturation of the enzyme can lead to a rapid declinein activity.

7766 88554433 111199 1100

Neutralincreasingacidity

increasingalkalinity

Explanation: As temperature rises the rate increases becausethe molecules move faster and are more likely to collide andreact. All chemical reactions show this response.

However, beyond a certain “peak” temperature, the enzyme’sintricate shape begins to be distorted. The substrate no longerfits the active site so well, and the reaction slows. If thetemperature was lowered again, the enzyme shape, andreaction rate could be restored.

If the temperature reaches an extreme level, the distortion ofthe enzyme’s shape may result in total shut-down of thereaction. The enzyme may be permanently distorted out ofshape, and its activity cannot be restored. We say the enzymehas been “denatured”.

Temperature

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0 20 40 60 80 100

Temperature (ooC)

Reac

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MammalEnzyme

PlantEnzyme

Thermophilicbacteria enzyme

ExperimentalPoints

HSC Biology Topic 1copyright © 2005-2007 keep it simple science


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The Effect of pHWhen the temperature is kept constant and the enzymetested at various pH levels, the results will produce a graphas shown.

Generally, all intra-cellular enzymes (i.e. those from withina cell) will show peak activity at a pH close to neutrality...their optimum pH is close to 7.

The digestive enzyme “pepsin” from the stomach shows anoptimum pH about 2 or 3, allowing it to work best in theacidic environment.

The shape of the pH graph is usually symmetrical on eitherside of the “peak”... optimum pH.

The explanation for the shape is as follows:

• at the optimum pH the enzyme’s 3-D shape is ideal forattracting the substrate, so reaction rate is maximum

• at any pH higher or lower than optimum, the enzyme’sshape begins to distort, and reaction rate declines as the substrate no longer fits so perfectly.

• at extremes of pH, the enzyme can be irreversiblydenatured and shows no activity at all.

The Effect of Substrate ConcentrationGenerally in any chemical reaction occurring in solution therate of the reaction increases if the concentration of thereacting chemical(s) is increased. The explanation is simplythat if the molecules are more concentrated, then itbecomes more likely that they will collide and react witheach other.

When an enzyme is involved, the situation is a little morecomplicated:

Initially the rate of the reaction increases as the substrateconcentration goes up, just as it does with any reaction.

Soon though, the graph begins to flatten out and level offbecause the enzyme molecules are “saturated” withsubstrate and cannot work any faster.

If, at this point, you were to add more enzyme then thereaction rate would once again go up. It would level offagain as the enzyme molecules were once again swampedand saturated with the substrate.

www.keepitsimplescience.com.au


2 3 4 5 6 77 8 9 10 11 12

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Enz

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Activ

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Substrate Concentration

Reac

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Rate

Reac

tion

Rate

Substrate Concentration

1 2 3 4 5 6 77 8 9 10 11 12

ppHH

Intra-cellular enzyme

Pepsin.(Stomachenzyme)

Extra enzymeadded



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HomeostasisSince...

• an organism’s metabolism is largely a matter of chemical reactions, and

• each reaction is catalysed by an enzyme, and • each enzyme is quite sensitive to temperature and pH

... it follows that the interior environment of the organism’sbody and cells must be maintained at stable levels oftemperature and pH close to the optimum for the enzymes.The process of maintaining a stable, internal environmentis called “Homeostasis”.

As well as regulation of temperature and pH, homeostasisinvolves the regulation of many other factors such as:• water and salt balance in body fluids• blood sugar levels• oxygen and carbon dioxide levels.

Feedback MechanismsThe mechanism of Homeostasis involves “feedback”... asituation where the result of some action feeds back intothe system to cause the next change to the system.

In a “Positive Feedback” system any change re-reinforcesitself by causing more change in the same direction.

For example, a fire growing bigger...

Homeostasis always involves “Negative Feedback”. This iswhen any change in a system causes a shift in the oppositedirection.

For example, a thermostat control of an oven:

The result is that the temperature of the oven remains fairlystable. It oscillates up and down a little, but always staysclose to the temperature the oven was set at.

The key parts of a feedback system are:

• a receptor, to measure and monitor the conditions• a control centre, which “decides” how to respond, and• effectors, which carry out the commands of the control

centre and make the necessary adjustments to the system.

In animals, it is the Nervous System which is largelyresponsible for carrying out the receptor and control centrefunctions necessary for many aspects of homeostasis.

In mammals, which maintain fairly constant bodytemperatures, it is the Hypothalamus at the base of thebrain which monitors blood temperature and sends outcommand messages for negative feedback, rather like theoven thermostat system.



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out of control, orshrink away to

nothing

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Negative Feedback causes a system to maintain stability.

TemperatureSensor

(detector)

Turn heaterOFF

Turn heaterON

If temperatureis too high

If temperatureis too low

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Cerebrum Hypothalamus

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PituitaryGland




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Worksheet 1Part A Fill in the blanks. Check your answers at the back.

The sum total of all the chemical reactions in an organism’sbody is called a)....................................................... Eachreaction requires a catalyst, which is a chemical whichb)............................................. the reaction, without beingc)........................................... itself.

Biological catalysts are called d).....................................These have the following properties:• They are molecules of e)......................................, which arepolymers of f)................... ...................• Each one has its own unique g)........................., whichperfectly fits the molecule(s) of the reaction. Thesemolecules are referred to as the h)..................................• Because each enzyme only fits its own particularh)............................., they are said to be h)................................i)...............................................• Enzymes will only work effectively in a narrow range ofj)............................................. and k)........................ This isbecause their l).................................. changes so that they nolonger fit their substrate.

The pH scale is a numerical measurement of m)......................and n)...................................... Things that are neutral have apH= o)............. Acids have pH values p).................... 7, whilealkalis (bases) have pH q).......................... The pH insideliving cells, and in most parts of an organism’s body is aboutr)..........., but an exception is the s)............................... which isquite strongly t).....................................

Part B Enzyme Graphs1. Sketch the shape of a graph of Enzyme Activity againstTemperature.

2. Explain the shape of the graph;a) at temperatures below the “optimum”

b) at temperatures above the optimum.

3. Sketch a graph of Enzyme activity against pH.

4. Explain why the graph shows a “peak” of optimumactivity at a certain pH.

5. Why does activity decline at pH values higher or lowerthan the optimum?

6. Sketch a graph of enzyme activity against substrateconcentration.

7. Explain a) why the graph rises

b) why the graph levels off

Part C Fill in the blanksHomeostasis is the process of keeping an organism’sinternal environment a)......................................... The factorsthat need to be maintained include b)..................................and c)................... as well as d)............................. and saltbalance, e)...................... .............................. levels and oxygenand carbon dioxide levels.

Homeostasis involves f)..................................... feedback.The 3 parts of any feedback system are theg)........................................, which measures or monitorsconditions, the h)........................................ which decideshow to respond and issues commands, and thei)........................................... which carry out the commands.

In animals generally it is the j)..........................................system which is largely responsible for monitoring andcontrol. In mammals, homeostasis of body temperature iscontrolled by the k).............................................. at the base ofthe l).................................................




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Temperature Control in MammalsIn a healthy human the internal “core” temperature of thebody is about 37oC and is maintained within about 0.5oC atall times. If the body temperature goes up, or down, bymore than about 4oC, this is a life-threatening situation.

Control of body temperature is achieved as shown in thisschematic diagram:

Main Parts of the SystemReceptor and Control Centre is the Hypothalamus at thebase of the brain. Special cells constantly monitor thetemperature of blood flowing by. If blood temperaturevaries by even a fraction of a degree, nerve messages aresent to the effectors.The Effectors include blood vessels, sweat glands,endocrine (hormone) glands, muscles and body hairs.

BODY TEMPERATURETOO HIGH

BODY TEMPERATURETOO LOW

COOLING MECHANISMSBlood vessels dilate

Sweat glands activatedHair lowered

Metabolic rate reduced

WARMING MECHANISMSBlood vessels constrictedMuscles begin “shivering”

Hairs erected (goose bumps)Metabolic rate increased

BODY TEMPERATURE REDUCESBLOOD COOLS

BODY TEMPERATURE INCREASESBLOOD WARMS

Ner

ve C

omm

and

to E

ffec

tors

Nerve Com

mand

to Effectors

HYPOTHALAMUSmonitors bloodtemperature

How the Effectors Make a Difference

Blood VesselsDilation (widening) of veins,arteries and capillaries near theskin allows more blood to flowout near the skin surface.This allows more body heat toescape from the skin, thuscooling the body.

Constriction (narrowing) ofblood vessels causes lessblood to flow near skin.Less heat flows out to skinto be lost. Body heat isretained more.

MusclesNerve signals can cause the skeletalmuscles to begin “shivering”. This extra

muscle activity generates more heatto warm the body.

Sweat GlandsWhen activated, the sweat glands secrete perspiration.The water evaporates from the skin, carrying away bodyheat... this has a powerful cooling effect.

Body HairsEach hair on your body has a tiny muscleat its base which can cause the hair tostand up erect and give you “goosebumps”. This traps a layer of still airagainst the skin and helps insulate andprevent heat loss.

If the hair follicle muscle is relaxed thehair lies flat and allows more heat loss.

Hormonesare chemicals which controlvarious body functions, includingthe rate of metabolism and heatproduction.The hormone thyroxine(produced by the thyroid gland inthe neck) does exactly that and isunder the control of thehypothalamus, via anotherhormone from the pituitarygland.

2. TEMPERATURE REGULATION IN ORGANISMS



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The Temperature Range of LifeHomeostatic control of body temperature allows anorganism to maintain its cells at a temperature close to theoptimum for its enzymes. This allows metabolism to runefficiently, despite changes in the surrounding temperatureof the environment.

However, homeostasis has its limits, and no organism canremain active and thriving under the full range oftemperatures of the biosphere of the Earth. Differentorganisms have adapted to survive in extreme coldenvironments, or in extremely hot conditions, but neverboth extremes.

Extreme HeatThere are thermophilic bacteria (members of the Archaea)which live and thrive in volcanic hot springs attemperatures up to 120oC.

In terrestrial environments such as hot deserts, thetemperature can often reach 40oC and sometimes as highas 60oC. Many plants and animals are adapted to survivethese extremes, but few remain active in this heat.Generally in deserts the animals seek shelter and becomeinactive, while plants shut down their metabolism andmerely survive.

Extreme ColdOnce again, there are many organisms which can surviveextreme cold, but few that remain active. Certain types ofalgae and photosynthetic bacteria are found to live withinthe snow and ice near the poles and are still metabolicallyactive at temperatures as low as -10oC. Below this, the cellsbecome inactive, but survive and re-activate when it warmsup again.

Generally however, plants and animals cannot tolerate theirbody temperature going below 0oC, since ice crystals formingin cell cytoplasm can destroy membranes and kill cells. Also,the chemical reactions of metabolism run so slowly at lowtemperature, that life functions are not possible.

Of course, many animals do live and survive in the coldbecause they can produce their own body heat (mammalsand birds) and are equipped with body insulation andhomeostatic mechanisms to maintain their coretemperature despite the cold environment. Perhaps theworld champions in this regard are the Emperor Penguinswhich maintain core body temperatures around +33oCthroughout the Antarctic winter in air temperatures as lowas -50oC... an amazing difference of over 80oC!

Cold Water EnvironmentsEven when ice forms on the surface, water environmentsrarely fall below +4oC, and are remarkably stable intemperature. Life-forms do not need to cope with change,although they may need serious insulation to stay warm. Itis the terrestrial environment that is more of a challenge.

Temperature Control in EctothermsEctotherms are the “cold-blooded” animals, such asreptiles, amphibians, insects, fish and worms. “Cold-blooded” is a misleading term and is best avoided, sincethese animals are NOT always cold, but rather they rely onthe outside environment for their body heat... they do notgenerate heat internally like a mammal or bird.

Ectotherms have a variety of adaptations, many of thembehavioural, to regulate their body temperature and keep itwithin the range in which they can be active; generallybetween 10-30oC.

For example, the Blue-Tongue Lizard will lie in a sunnyspot with its body flattened and turned side-on to the Sunon a cool morning. This way it absorbs heat more quicklyto get its body temperature high enough to become active.

As the day becomes hotter, the lizard will turn facing theSun to absorb less heat, and seek shade to avoid over-heating.

In prolonged periods of cold weather, such as winter in theAustralian Alps, ectotherms cannot be active because theenvironment cannot supply them with the body heat theyneed. Animals such as the Copperhead Snake and theCorroboree Frog seek shelter underground and becomedormant throughout the winter.

In a process similar to the hibernation of bears, the animal’sheartbeat and breathing slow down, their metabolismalmost stops and their body temperature chills to only justabove freezing. As long as they are more than about 50centimetres underground, the ground will not freeze eventhough buried in snow for several months. If they haven’tburrowed deeply enough they will freeze to death!



Ectotherms seek, or avoidthe heat of the Sun

Reptiles sun-bakewhen too cool...

... and seek shelterwhen too hot



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Temperature Control in EndothermsEndotherms are the animals which produce their owninternal body heat and maintain a relatively constant bodytemperature... the birds and mammals.

All endotherms rely heavily on having bodily insulation...fur, feathers or blubber (fat). Humans are endotherms too,but we rely mostly on our technology to provide heaters,air-con, jackets, wetsuits, gloves, etc, to protect our fragilebodies from extreme temperatures. What do otherendothermic animals in the wild do?

Firstly, they have all the responses for homeostasisdescribed earlier... dilation or constriction of blood vessels,shivering and sweating etc. As well as these, they may haveextra adaptations to help regulate their temperature.

In hot environments such as the Australian deserts, manymammals such as the Red Kangaroo or the Bilby, havemany adaptations to help them cool their bodies:

• large ears, with good blood supply, increases the surface area for heat loss

• like the reptiles, they seek shade in the heat of the day• panting evaporates water from the mouth and throat, andcools the oral membranes which have a rich blood supply.

• they may lick their forearms. The evaporation of salivacools their body in the same way as sweating.

(Note: many desert animals lack sweat glands because theycannot afford the water loss of perspiration.)

In the cold, endotherms go for thick fur coats (Wallaroo)or layers of fat (Australian Fur Seal) to limit the loss ofbody heat.

Penguins, such as the Fairy Penguins along Australia’ssouthern coast, have a special “blood shunt” in their legs.In warm conditions the shunt is closed and blood flowsnormally to the feet. Since the feet are about the only partof their body not well insulated, in cold water they couldlose a lot of body heat.

So in cold water the flow of blood from body toward thefeet is “shunted” via a special vein with a valve in it, backinto the body. The feet receive virtually no blood, soconserving body heat.

Responses of Plants to Temperature ChangePlants cannot respond to temperature change by movingaway or hiding. To cope with temperature extremes theymust have structural or physiological adaptations.

To cope with seasonal cold weather, many plants (especiallyin the northern hemisphere) are deciduous... they shed theirleaves and basically shut down their metabolism for thewinter, rather like an animal hibernating. Their leavescannot be protected from freezing, so the strategy is to losethe vulnerable parts, survive until next spring, and grownew leaves then.

Coping with heat is another story. If there is plenty ofwater available, such as in a tropical jungle, then the plantscool themselves by allowing maximum evaporative cooling.The leaves open their stomates and allow transpiration tooccur. The evaporation has a cooling effect, in the sameway that sweating cools an animal.

When it is hot and DRY as well, they have a problem.Desert plants tend to have very small leaves and thick,“stocky” shaped stems. This reduces the surface area beinghit by heat radiation from the Sun, and helps prevent over-heating. The cacti plant group have taken the strategy to thelimit... their leaves are spines, and stems are “fat” androunded. They are also light coloured to reflect a lot of theradiant heat away.

The sclerophyll plants of Australia (gum trees for example)also have small narrow leaves to reduce heat absorptionfrom the Sun. Their other “trick” is to allow the leaves todroop downward. This allows them to catch light forphotosynthesis in the cooler mornings when the Sun is low,but avoid absorbing heat when the Sun is overhead in theheat of midday.



In the desert, big ears are cool!

Spikes for leaves= lower surface

area

Pale colourreflects

radiationLow surfacearea stem

Narrow,droopinggum tree

leaves




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Worksheet 2Fill in the blanksCheck your answers at the back.

Temperature regulation in mammals iscontrolled by the a).............................................at the base of the brain. If body temperature istoo high it sends commands to theb)................................ organs to cool the body.Cooling mechanisms include c)............................of blood vessels to allow d)...................(more/less) blood to flow near skin. Also, thee)............................... glands may be activated,allowing f)............................... to flow. As itg).............................. from the skin, it carriesheat away. Metabolic rate may be reduced, toreduce heat production. This is achieved byh)............................. which are controlchemicals. An example is Thyroxine, producedby the i)................................... gland.

If the body is too cool, then the hypothalamuscommands various warming mechanisms.Blood vessels can be j)...........................................to reduce blood flow to k)............................Body hairs are l).............................. to trap alayer of still air, which acts tom).............................. better. Nerve commandsto muscles can cause them ton)........................................ which produces extraheat. The metabolic rate can be raised byhormones too.

Animals which rely on the environment tosupply their body heat are calledo)........................................... Examples arep)........................................., amphibians, fish etc.In terrestrial environments they often seek oravoid the heat of the q)................ in order toregulate temperature. An Australian example isthe r)...................................., which oftens)................................ in the morning to warmup, and t)..................................................... whentoo hot. In cold winters, ectotherms cannot getany heat from the environment and many, suchas the u).................................................... surviveby v)............................................................ for thewinter.

Animals which can regulate their bodytemperature are called w)......................................Examples are the x)................................ andy)........................................ They use all thehomeostasis techniques above, and rely onbody insulation with fur, z)........................... oraa)................................... as well.

In extreme environments endotherms mayhave extra adaptations as well. In Australiandeserts many animals have large ab)....................to radiate heat away. They don’t have sweatglands because they can’t afford toac).............................................................................but may lick their ad)............................... or pantto achieve some evaporative cooling.

In cold environments, thick fur or blubbergives ae)......................................................toretain body heat. The penguins have a specialadaptation in the blood vessels to their legs. Incold water, the blood flow to the feet isaf).............................................................................so that less heat is lost through the uninsulatedfeet.

Plants also have many adaptations to cope withtemperature extremes. In cold climates manyplants are ag)............................................. whichmeans they ah)....................................................in winter.

In hot climates with plenty of water, plantsopen their ai).....................................................allowing evaporation to cool them. In dryclimates, plants cannot afford the water loss, sothey have other ways to stay cool withoutlosing water. For example, cacti haveaj).......................-shaped leaves to reduce thesurface area absorbing heat from directsunlight. They are often ak)...........................-coloured to reflect heat radiation.

The Australian al)........................................plants mostly have am).....................................(shape) leaves to reduce surface area, andoften allow the leaves toan)................................................. (orientation) toavoid the Sun’s heat at midday.

WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES




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Internal Transport in MammalsAs is the case with most animals, mammals rely mainly ontheir Circulatory System for internal transport ofsubstances... their blood, heart and blood vessels; veins,arteries and capillaries. A basic knowledge of how thesystem operates was covered in Preliminary Topic 2.

Blood and Blood VesselsYou will have examined blood under a microscope andseen something like this:

You should be able to sketch diagrams of blood cells, andhave an idea of their sizes.

Red Blood Cellscontain the red pigment haemoglobin, which carriesoxygen. This is covered in more detail later.

White Blood Cellscome in a huge variety of types, but all are involved withdefence against disease. This is covered in a later topic.

Arteriescarry blood from the heart out to the body tissues. Thewalls of an artery are relatively thick and muscular towithstand the high pressure in the blood when the heartpumps.

Artery walls are very elastic, and when a pulse of highpressure blood passes through, they expand outwards andthen contract again, helping to push the blood along. Thisrhythmic expanding and contracting is what you can feel asyour “pulse” wherever an artery is close to the skin, such asin your wrist or throat.

Veinscarry blood back from the body tissues to the heart. Theblood here is under lower pressure and the walls of a veinare relatively thin. With little pressure to push bloodforward, it is the contraction of the surrounding muscleswhich helps push the blood along.

Veins may contain valves to prevent back-flow of the blood.

Capillariesare the tiny blood vessels which form a network throughoutthe tissues so that every living cell is close to the bloodsupply. The walls of a capillary are only 1 cell thick, sodiffusion of substances from blood to cells (or cells toblood) is easily achieved.

The inside of a capillary is so small that red blood cellsoften travel through it in single file.

3. INTERNAL TRANSPORT SYSTEMS IN ORGANISMS

Sketch of Blood Cells

RReeddCCeellllss

Shaped like adonut with the

hole closedover

nonucleus

WWhhiittee CCeellllmuch larger than

red cells

large, irregularnucleus.

Ratio: about 600 redcells to 1 white cell

ARTERYCross-SSection

VEINCross-SSection

Connective Tissue

Layers ofmuscle

blood blood

Side view of VEINshowing a valve.

Blood can flow one way,but not back the other.

bloodflow

Wall just 1 cell thick foreasy diffusion

CAPILLARY Cross-SSection

RED BLOOD CELLSLLiigghhtt mmiiccrroossccooppee vviieeww

Size = 7 μμm

EElleeccttrroonnmmiiccrroossccooppee

vviieeww



Changes to the Blood as it CirculatesAs the blood circulates around the body its chemicalcomposition undergoes a number of changes...

Nutrients & Nitrogenous WastesAs the blood flows through capillaries surrounding thedigestive system it picks up increased quantities of sugars,amino acids, salts, water, vitamins, etc that have beenabsorbed from the gut. (However, lipids are first absorbedinto the lymphatic “drains” and enter the blood much later)

This blood from the gut is collected in a vein which takes itdirectly to the liver. Here some of the nutrients may beabsorbed from the blood for storage or chemicalprocessing (e.g. glucose is extracted from the blood andpolymerized to form glycogen and stored in the liver). Alsoin the liver, large amounts of the nitrogenous waste urea isadded to the blood to be carried away and later excreted.

Later, as blood flows through capillaries in body tissuessuch as muscle or bone, nutrients are absorbed from theblood into the cells which need energy (glucose) and newchemical building blocks (amino acids, lipids).

Sooner or later, every bit of blood flows through thekidneys which extract the nitrogenous wastes and excesssalts and water for excretion as urine.



13

Substances Carried in the Blood

Oxygen O2is carried in the red blood cells by haemoglobin.

Carbon Dioxide CO2is partly carried by the haemoglobin in red blood cells, butmost of it is carried in the blood plasma, in the form ofbicarbonate ions (HCO3

-)

Wateris carried as the liquid solvent of blood plasma.

Salts & Products of Digestionsuch as sugars and amino acids, are generally water solubleand are carried dissolved in the blood plasma.

Lipids (Fats)absorbed from the digestive system are “packaged” in aprotein coat which makes the fat molecule miscible inwater. This means that, while not fully dissolved, themolecules can be dispersed in water and carried withoutjoining together into droplets of fat and separating fromthe water.

In this form they are carried dispersed in the blood plasma.

Nitrogenous Wastessuch as urea, are water soluble and carried dissolved in theblood plasma.

You will have carried out an experiment to see the effectof dissolved CO2 on the pH of water.

You might have chemically produced some CO2 andbubbled it through water. Using a pH meter, or perhapsUniversal Indicator, you will have measured any changein the pH of the water.

You would have found that the pH went down...i.e. the water became more acidic.

Explanation and Chemistry:Carbon dioxide reacts with water to form carbonic acid

CO2 + H2O H2CO3

Carbonic acid is a weak acid which partly ionizes

H2CO3 H+ + HCO3-

Hydrogen ionmakes water more acidic Bicarbonate ion.

This is how CO2 is carriedin blood

CHANGES IN NUTRIENTS, WATER & WASTESAS THE BLOOD CIRCULATES

Heart

WWaasstteessinto

blood

Liver

Gut

Arte

ries

Body tissues

Vein

s

NNuuttrriieennttss fromblood to cells

DigestedNNuuttrriieennttss

into blood

Some NNuuttrriieennttssto storage

WWaasstteess and excess water,salts excreted in urine

Lungs

Kidneys



14

Respiratory Gases O2 & CO2As blood passes through capillaries in body tissues, oxygenis released from the haemoglobin molecules and diffusesalong the concentration gradient into the body cells.

There is always a concentration gradient favouring thisbecause the cells are constantly using up oxygen for cellularrespiration.

Revision

Meanwhile, the concentration of carbon dioxide is highbecause of its constant production by cellular respiration,so it diffuses from the cells into the blood.

When the blood gets to the lungs the opposite occurs.Inside the alveoli (air sacs of the lungs) the air has a veryhigh concentration of oxygen and is very low in CO2.Therefore, oxygen diffuses into the blood, while carbondioxide diffuses from the blood into the air.

This gas exchange and transport is essential for deliveringoxygen to every cell for cellular respiration...

... but why must CO2 be removed?

The Need to Remove Carbon DioxideAs already discussed, carbon dioxide doesn’t just dissolve inwater, it reacts to form a weak acid.

It’s the hydrogen ions that create problems. Hydrogen ionsare acids and can lower the pH of cell cytoplasm.

At the concentrations produced by a typical cell, the hydrogenions could easily lower the pH of the cytoplasm by 0.5 pHunit or more. Remember that enzymes are very sensitive topH changes and quickly change shape and lose their catalyticactivity. This would be disastrous for cell metabolism.

To avoid this problem, CO2 is carried away by the blood asrapidly as it is produced in the cells.

The Importance of HaemoglobinBlood is red because of the many red cells, and red cells arered because they are packed with the red-coloured, iron-containing protein haemoglobin.

In the lungs, where the oxygen concentration is very high,some oxygen dissolves in the moisture lining the alveoli thendiffuses into the blood flowing in the surrounding capillaries.

Oxygen is not very soluble in water, however, and if that’s allthere was to the story, then our blood could never carry enoughoxygen to supply our cells with what they need. Haemoglobinmolecules have a great attraction for oxygen molecules andquickly pick up 4 O2 molecules each. Because of this, ourblood can carry thousands of times more oxygen than wouldbe possible by simply dissolving oxygen in the blood plasma.

When the blood gets to the body tissues with its load ofoxygen, something very “clever” happens...

The high concentration of dissolved CO2 lowers the pH ofthe blood slightly. This causes the haemoglobin proteins tochange shape slightly and release the oxygen molecules.

HbO22 Hb + O22

The oxygen diffuses into the cells, and the freed haemoglobinmolecules can pick up some of the CO2 molecules and carrythem back to the lungs.

Of course, this isn’t really “clever” in any sense of intelligenceamong haemoglobin molecules. It is the result of NaturalSelection and Evolution... it gave a huge survival advantage tosome primitive ancestor millions of years ago, so all mammals(and many others) have inherited this quite amazing substance.



C6H12O6 + 6O2 6CO2 + 6H2O + ATP

Glucose and Oxygendelivered to cells by the

blood stream

Chemical wastes

the importantproduct.

ATP is the energysupplier in cells

OO2

OO2

CCOO2

CCOO2

CO2 + H2O H2CO3 H+ + HCO3-

carbonic acid hydrogen

ionbicarbonate

ion

Hb + O22 HbO22

abbreviation forHaemoglobin “Oxyhaemoglobin”

Oxygen

Air Blood

OxygenBlood Cells

Carbon dioxide

Blood Air

Carbon dioxideCells Blood

Heart

Arte

ries

Body tissues

Vein

s

Lungs

CHANGES IN OXYGEN AND CARBON DIOXIDE

AS THE BLOOD CIRCULATES




15

Oxygen Saturation & Its MeasurementThe concentration of O2 and CO2 in the blood is of greatinterest to doctors monitoring a patient, or an athlete intraining, or even to a pilot or mountain-climber at high altitude.

The most important measurement is “percentage oxygensaturation” (%SpO2). A reading of 100 would mean that100% of all haemoglobin in an artery is totally saturatedwith oxygen. Readings between 95-100% indicate goodhealth, fitness and adequate oxygen supplies.

Lower readings (e.g. 80%) could indicate:• respiratory or circulatory problems in a patient• lack of fitness, or excessive exertion in an athlete• need for supplementary oxygen for a pilot or climber.

In years gone by, %SpO2 was measured by taking bloodsamples and carrying out complex chemical testing. Withmodern technology, however, the readings are doneinstantly and non-invasively by a small, portable instrumentclipped onto the end of the finger or ear lobe.

The “Oximeter” works by sending red light and infra-redbeams through the flesh. The amount of each lightabsorbed by the haemoglobin gives a direct measurementof %SpO2, because haemoglobin carrying oxygen, orwithout, or with carbon dioxide, all absorb these lightbeams differently.

Products of Blood DonationThe Australian Red Cross Blood Service collects about amillion blood donations per year. Most of this blood isused for people who need regular treatment with bloodproducts for conditions such as leukemia.

Only a very small amount is kept as whole blood foremergency transfusions. Most donated blood is separatedinto about 20 different fractions or products, so eachdonation can treat many different patients.

The main blood products are:

Red Cell Concentrate which contains about twice asmany red cells as normal, is used to boost the oxygen-carrying capacity of patients with anaemia or after bloodloss.

Platelet Concentrate is given to patients who need extrablood-clotting capability, such as leukemia sufferers, orfollowing severe blood loss.

White Cell Concentrate is given to patients needing aboost to their immune system, perhaps following a severeinfection.

Plasma is the liquid part of the blood and is often given inemergency to boost the volume of blood following severeblood loss.

Cryoprecipitate is a fraction collected from plasma andcontains blood-clotting factors. It is used to treat severehaemorrhaging.

Factor VIII and Monofix are extracts from plasma used totreat people who have haemophilia... an inherited, incurabledisorder in which the blood will not clot properly. Theseblood products allow patients to lead a relatively normallife.

Finger-cclamp Oximeter measures %SpO22

Light source sends redlight and infra-red

Receiver measuresabsorption of lightby haemoglobin

Why Is It Needed?

• Fresh blood cannot be storedfor long, and many parts of theworld lack the necessary storagefacilities.

• Many blood products can set offimmune-responses in long-termpatients, even after correct blood-typing. (Similar to “rejection” of atransplanted organ)

• Donated blood can carrydiseases, such as hepatitis or HIV.

Perfluorocarbon-Based SubstitutesAnother area of research aims todevelop a truly artificial bloodsubstitute. The most promising basechemicals are the “perfluorocarbon”compounds.

These can carry up to 5 times moreoxygen than blood can, can be storedindefinitely at room temperature.They can be made totally sterile anddisease free.

At least 5 different products are beingtested and trialled (USA), but noneare yet approved for medical use.

Haemoglobin-BBased Oxygen Carriersare one of the areas of current research.

Haemoglobin extracted from animal bloodcan be purified and treated so that it isdisease-free and cannot cause any allergicor “rejection” responses in patients.

The products can be stored for years atroom temperature, and is highly effectiveat carrying oxygen and releasing it into thetissues.

Currently undergoing clinical trials, but notyet approved for medical use.

ARTIFICIAL BLOOD?




16

Transport Systems in PlantsIn Preliminary Topic 2 you were introduced to thetransport systems in plants...

Xylem Tubes Carry Water

Xylem tubes are dead, hollow cells, joined end-to-endforming a continuous tube from root to leaf. The xylemtubes transport water (and dissolved minerals). How dothey work to lift water from roots to leaves, against theforce of gravity?

“Transpiration” is the evaporation of water from theleaves. When the stomates are open, water can constantlyevaporate, creating a tension, or “pull” in the remainingwater in the leaves.

Water molecules are quite strongly attracted to each otherand tend to cling tightly together. This force is called“cohesion” and is the reason that water tends to formdroplets... little blobs of water that cling together.

So, when water evaporates from leaves and creates a “pull”force, each water molecule pulls on those behind it becauseof the cohesion. Each molecule pulls others upward and sothe entire column of water in a xylem tube moves upwardsto replace the water lost by transpiration. So water is pulledupwards by a combination of transpiration and cohesion.This flow is called the “transpiration stream”.

Another factor which helps the process is called“capillarity” or the “capillary effect”. This is the way thatwater can “climb up” the walls of a container forming ameniscus in a test tube, for example. This happens becausewater molecules are not only attracted to each other(“cohesion”) but also to some other substances such asglass. This attraction is called “adhesion”.

In very narrow tubes (“capillaries”) the water will climbupwards against gravity because of adhesion, and dragmore molecules along by cohesion. This happens in xylemand helps lift water upwards.

Higher Pressure

DESTINATIONLower Pressure

PHLOEMTUBES

Translocation

Sugar is removed by activetransport, requiring energy.

Water flows out due toosmosis, lowering pressure

Sugar is carried in by activetransport, requiring energy.

Water flows in due toosmosis, raising pressure

Sugar solutionflows due to

pressuredifferential

Translocation...

how it works

Hollow, dead cells, joined endto-end forming a tube

Cell wallsre-inforcedwith ringsand spirals

of lignin

PHLOEM CELLalive and filled with

cytoplasm.

Circulation ofcytoplasm carriessugars through

each cell

Sieve platebetween cells

“Companioncell”

has manymitochondria toprovide ATP tothe phloem cell

sugarsactively

transported inthe cytoplasm

of the cells

sugarsdiffuse

from onecell

into thenext

Active & Passive TransportNote that the flow of water in the xylem costs the plantnothing in energy to run the system... it is “passive”transport.

In contrast, the other transport system in plants is an“active transport” system... the plant must constantlysupply energy to make it happen.

Phloem Tubes Carry Food NutrientsWhile the xylem tubes are formed from dead cells, thephloem are living cells joined end-to-end. The ends of eachcell are perforated (“sieve plates”) so each cell is open intothe next so they form a continuous tube.

While the xylem is a one-way flow system, the phloemsystem can carry food (especially sugars) in either direction.If a lot of photosynthesis is occurring, the phloem will carrysugar to storage sites in roots or stem. If photosynthesis isnot possible for an extended time, then the phloem willcarry sugars back from the storage sites to feed the leaf cells,or supply a growing flower or fruit.




17

Worksheet 3

Part A Fill in the blanks

Blood is made up mainly of a liquid called a)..........................and many blood cells. The most numerous blood cells are theb)........................... which contain the protein c).............................responsible for carrying d).............................. gas. Most of thecarbon dioxide in blood is carried in the form ofe).................................... ions. These are made when carbondioxide reacts with f).................. forming g).......................... acid.

Most other substances carried in blood are dissolved in theh)....................................... This includes nutrients such asi).................................... and j)......................................., water andsalts, and the nitrogenous waste k).............................Lipids (fats) are first wrapped in a coating of l)............................so they can be dispersed without separating.

There are 3 types of blood vessels: the m)...................................have thick muscular walls to withstand the high n)......................of the blood being pumped from the o)..................................p)................................ have thinner walls, and have q)...................along their length to prevent blood r)............................................Capillaries have walls which are s)..........................................thickand form a network throughout the body’s t)..............................

As the blood flows around the intestines it picks upu)......................................... It then flows straight to thev)...................................., where some nutrients are removed forw).......................&............................, and wastes such asx).............................are added. These wastes are later removedfrom the blood by the y)............................ and excreted with anyexcess z)........................... & .......................... as urine.

Meanwhile, when blood flows through the capillaries of thelungs, aa)........................... gas is absorbed into the blood andab).............................. gas is released from blood into lungs.When blood flows through the body tissues, nutrients movefrom ac)............................ to ad)................................. as doesae)............................... gas, while af)..................................... gasmoves the other way.

Part B Questions 1. Write 2 chemical equations to summarize how carbondioxide reacts with water. In what form is CO2 carried inblood?

2. With reference to a chemical equation, explain why it isessential to remove carbon dioxide from body tissues.

3. With reference to a chemical equation, explain howtransfere of oxygen from blood to cells is facilitated.

Part C Fill in the blanks Check your answers at the back.

Oxygen is carried by the a)...............-coloured, b)...................-containing protein called c).........................................................It has a great affinity for oxygen molecules, and eachmolecule can absorb d).................... (number) oxygenmolecules, in which form it is called e)..............-.............................................. In the body tissues, the presenceof f)......................................... gas lowers the pH slightly,which causes haemoglobin to change shape slightly andg).......................................... the oxygen, which thenh)..................................... into the cells.

The “%SpO2” is a measure of thei)............................................. in a person’s blood. Goodhealth, fitness and adequate oxygen supply are indicated byreadings above j)..............% This can be easily measured bya k).............................................. which sends beams ofl).......................................... and .............................................through a finger or ear-lobe. Oxygen saturation is measuredaccording to how much of each type of light ism)....................................... by the blood.Most blood donated to the “Blood Bank” is separated intodifferent fractions for different uses. Some of the mainblood products are:• n)..................... Cell Concentrate, to boost O2-carryingcapacity. •White Cell Concentrate, to boosto)...............................................p).................................. Concentrate, to help blood clottingq)...................................., which is the liquid part of theblood, used in emergency to increaser).....................................................

Research is going on into developing artificial blood. This isneeded because fresh blood cannot bes)..................................... for long, and can causet)............................................................. in some patients, andthere is a danger that donated blood might carryu).....................................................Two of the areas of research for artificial blood arev)................................-Based w)................................. Carriers,made from animal blood, and completely artificialsubstitutes based on the chemicals calledx)......................................................

Part DTransport in plants is carried out by 2 separate systems. Thea)..................................... tubes carry water and dissolvedminerals from the b)............................. to c)...............................These tubes are d).............................. (dead or living) cells. Thetransport is e)......................................... (active or passive) andthe movement of water is called f).................................................Basically the process works because, as waterg)......................................... from the leaves, this “pulls” water upfrom above because water molecules are h).............................and tend to cling together.

Meanwhile, the i)..................................... vessels carry outj)................................................. (name of process) which movesk)................................................ around the plant to wherever it isneeded. The cells are l)..................................... (dead or living)and the transport is m).........................................(active/passive)requiring the plant to n)......................................................... inorder to make the process happen.

WWHHEENN CCOOMMPPLLEETTEEDD,, WWOORRKKSSHHEEEETTSS BBEECCOOMMEE SSEECCTTIIOONN

SSUUMMMMAARRIIEESS




18

The Importance of WaterLife cannot exist without water. All living cells are about75% water. The functions of water in living things include:

Water is the solvent of lifeAll the chemical reactions of metabolism take place inwater solution, and the transport of materials in cytoplasm,blood or phloem takes place mainly in water solution.

Water is involved in life chemistryWater is a reactant or product of many metabolic reactions.The reactions of photosynthesis and cellular respiration arejust two of the many examples.

Water is vital in temperature regulationWater has a very high specific heat capacity. This means itcan absorb (or lose) relatively large quantities of energywith minimal temperature change. This helps stabilize thetemperature of all living things.

Water also has a very high heat of vaporization. This meansthat when it evaporates it absorbs huge amounts of heat.This is why evaporation of perspiration from the skin hassuch a cooling effect.

Water supports and cushions cells and organsMany plants and animals rely on water for body support.Non-woody plants pump their cell vacuoles full of water tomake cells “tight” and keep stems and leaves upright.Animals such as worms rely on the hydraulic pressure ofwater in their tissues to support their body and maintain itsshape.

In vertebrate animals the water solutions in the tissueshelps to cushion organs against bumps and impacts.(eg cerebrospinal fluid around the brain)

Homeostasis of Water & SaltsIt’s not just the water that is important, but itsconcentration, and the concentration of substancesdissolved in it, such as salts.

If the concentrations are not kept at the correct levels, thenosmosis may cause problems. Cells could lose water anddehydrate, or gain too much water and be damaged.

Kidneys Also Excrete Metabolic Wastes

What Are the Metabolic Wastes?The many chemical reactions of metabolism sometimesproduce chemicals which are toxic to cells, often becausethe chemical, when dissolved in water, can change the pHand reduce enzyme activity.

Therefore, it is essential that these wastes are removed(“excreted”) as soon as possible. The major wastes are:

• Carbon dioxide, produced by cellular respiration.As covered previously, it will lower the pH (acidic).It is carried in the blood and excreted by the lungs.

• Nitrogenous wastes, (contain nitrogen) are producedmainly from the metabolism of proteins.There are 3 main compounds that can be produced:

• Ammonia in fish and aquatic invertebrates• Uric acid in birds, reptiles and insects• Urea in mammals and amphibians

Excretion & Water Balance in FishFish produce the waste ammonia which is very alkaline andtoxic. Luckily it is very soluble in water. Since they livesurrounded by water, fish simply excrete ammonia fromtheir gills by simple diffusion.

Their kidneys are used not so much for excretion, but formaintaining their water balance. Freshwater fish andsaltwater fish have opposite problems with water balance.

4. EXCRETION & WATER BALANCE

THE CONCENTRATION OF WATER &DISSOLVED SALTS MUST BE MAINTAINED

THIS IS ANOTHER EXAMPLE OF HOMEOSTASIS

IN MOST ANIMALSWATER BALANCE IS REGULATED

BY THE KIDNEYS

SALTWATER FISH

FRESHWATER FISH

Water loss from tissues by osmosis

(mainly through gills)

Tissues gain water by osmosis

(mainly through gills)

Gills excrete AAmmmmoonniiaa, Carbon Dioxide and

excess salt

Constantlydrink toreplacewater

(but getsalt, too)

Kidneys producesmall amounts

of urine to save water

Kidneys produce alot of dilute urine to

remove water from body

Do notdrink

Gills excrete AAmmmmoonniiaa & CarbonDioxide, and actively

absorb salts



19

Excretion in Terrestrial EnvironmentsThe fish can get away with production of highly toxicammonia. They can rely on constant diffusion ofammonia from the blood in their gills into the waterenvironment which surrounds them.

In terrestrial environments, waste gases can do exactly thesame; that’s how carbon dioxide is excreted... by simplediffusion from the blood to the air in the lungs. However,nitrogenous wastes are not gaseous and need to be excretedin water solution. This means that:

• nitrogenous wastes are produced not as ammonia, but the less toxic compounds urea (mammals) or uric acid(birds, reptiles, insects)

• excretion is via the kidneys, and the simple processes ofdiffusion and osmosis are not adequate to achieve this.

For simple diffusion to achieve excretion it would requirehuge amounts of water to be excreted too, and no terrestrialanimal can afford to do this, especially in a desert.

How the Kidneys Work in MammalsEach kidney contains about 1 million nephrons. Eachnephron is a complicated tangle of blood vessels and renaltubules (=small tubes), but what happens in a nephron canbe summarized in a very simple way... K.I.S.S.

Filtrationremoves some of the water and many small dissolvedmolecules (including the waste urea) from the blood into therenal tubules. This occurs because the walls of theglomerulus are “leaky” and the blood is under high pressure.

Reabsorptionthen occurs to move useful substances back into the blood.This is achieved by:•Active Transport of sugar, amino acids & salts from therenal tubules back into the blood. This requires energy tobe used to transport these chemicals across the cellmembranes, against a concentration gradient.•Osmosis then occurs, which causes water to flow from thetubules back into the blood. This is Passive Transport andcosts the body no energy.



BBlloooodd iinn

ffrroomm aarrtteerryy

BBlloooodd oouutt

ttoo vveeiinn

This blood contains urea

This blood has had wastes removed,and water balance adjusted for

Homeostasis

Glomerulusa coiled blood vessel

Bowman’s Capsulea “receiving cup” to collect

the filtrate liquid from the blood

Blood CapillaryNetwork

shown in simplified form

Renal Tubules

Urineflows tocollecting

duct

then via Ureter toBladder,

forexcretion

THE NEPHRON of the KIDNEY

Filttrrattionnoccurrs herre

Filtration is the process in which some water andmany dissolved substances (including sugar, salts &urea, BUT NOT any cells or blood proteins) leave

the blood and flow into the renal tubules.

Reabsorption is the process in which any usefulsubstances (such as sugars & amino acids) are

absorbed back into the blood. Water & salts are alsoreabsorbed, but in varying quantities... the body is

adjusting water balance for Homeostasis

Urea is not reabsorbed back into the blood.Urea and some water continue along the tubule. This liquid is URINE.Urine flows into the Ureter and is carried to the Bladder for storage.When the bladder becomes full, the urine is excreted via the Urethra.

Reabsorrpttionn occurrs herre




20

The Kidneys & HomeostasisThe kidneys are not just used for excretion. As well, the kidneys can adjust the “water balance” of the body by allowingmore, or less, urine to be produced. In this way the kidneys are a vital part of homeostasis.

Once again, the Hypothalamus is involved, but the control mechanism is by hormones... chemicals which are released intothe blood and exert a control function on some “target organ”. In this case the hormone is called “Anti-Diuretic Hormone”(ADH) and the target organ is the kidney, specifically the nephron tubules.

WATER LEVEL INBODY TOO LOW

WATER LEVEL INBODY TOO HIGH

Pituitary Gland releasesmore ADH

(Also nerve signals to braincause “thirsty” feeling so you will want to drink)

Pituitary Gland releases less ADH

(Also nerve signals to braincause feeling that you do

NOT want to drink)

BODY RETAINS MORE WATER,excretes less urine.

Urine is more concentrated

BODY PASSES MORE WATER,excretes more urine.Urine is more dilute.

Ner

ve C

omm

and

to P

ituita

ry G

land

Nerve Com

mands

HYPOTHALAMUS &

PITUITARY GLAND

ADH causes morereabsorption of waterfrom kidney tubules

Less ADH causes lessreabsorption of waterfrom kidney tubules.

Note the typical pattern of anegative feedback system

How the Hormones WorkThe hypothalamus monitors the blood flowing through itfor the “osmotic balance” of water and dissolved salt. Ifthe body is even slightly dehydrated, more ADH is releasedby the pituitary gland and circulates in the blood stream.

The effect of ADH is to alter the permeability of themembranes lining the tubules of the kidney nephrons.Increased ADH levels make the membranes morepermeable to water, so more water is reabsorbed back intothe blood. This means that less urine is produced.

If the body is over-hydrated, the production of ADH isreduced. This causes the tubules to become less permeableto water so less is reabsorbed into the blood. The result ismore urine being produced.

ADH is the hormone controlling the water levels, but thisis only part of the “osmotic balance” story... the salt levelscan be controlled too. Read on...

Control of Salt Levels by AldosteroneSitting on top of the kidneys are the “Adrenal Glands”which produce a variety of steroid hormones controlling anumber of body functions. One of the adrenal hormonesis Aldosterone which controls reabsorption of salt fromthe nephron tubules.

If salt levels are too low, special cells in the adrenal glandsdetect this and increase the production of aldosterone intothe bloodstream. This causes the cells lining the nephrontubules to actively transport more sodium ions back intothe blood. Chloride ions follow the sodium, and so moresalt is reabsorbed.

If salt levels are too high, the adrenal glands produce lessaldosterone so less salt is reabsorbed, and the excess saltwill be excreted in the urine.

Between ADH and aldosterone the body maintains aconstant “osmotic balance” of water and dissolved salt...Homeostasis.




21

Addison’s Disease & HRTAddison’s Disease occurs when a person’s adrenal glandsdo not produce enough aldosterone, even when their saltlevels are too low. Their nephrons constantly fail toreabsorb salt and so the “osmotic balance” of the body ischronically out of order.

This leads to a variety of problems and malfunctionsthroughout the body involving the heart, intestines andliver, and may cause psychological disorders as well.

This is a disease that can be sucessfuly treated by“Hormone Replacement Therapy” (HRT).

A person with Addison’s Disease can be treated withappropriate doses of steroid hormones (usually cortisone)and although they cannot be totally cured, they can lead anormal, symptom-free life on HRT.

Renal DialysisIf a person’s kidneys cease functioning properly he/she canno longer remove toxic wastes such as urea from the blood,nor maintain homeostasis of “water balance”. In the caseof complete kidney failure, this condition is fatal withinabout 3 days without treatment.

Over the past 40 years or so, many people have beensuccessfully treated by receiving a kidney transplant.However, they may have to wait months or years to find asuitable organ donor. In the meanwhile, they need to betreated by Renal Dialysis... the use of medical technologyto remove wastes from the blood artificially. In effect, arenal dialysis machine is an “artificial kidney”.

The simplified diagram explains how this works.

The dialysis fluid contains water, salts, sugars, minerals etcexactly as in healthy blood plasma. Since there is noconcentration gradient for these chemicals they do notdiffuse in or out of the blood. However, the wastes such asurea are in higher concentration in the blood, and so theydiffuse from the blood into the dialysis liquid, which is laterdisposed of.

Kidneys

Ureters

BladderUrethra

GENERAL STRUCTURE OF THE URINARY SYSTEM

Kidney Structure & NephronsYou may have dissected a kidney in your laboratory work inclass. You should be able to relate the gross structure of thekidney and urinary system to the structure and functioning ofthe nephrons. This is summarized by these diagrams.

Renal CortexDark red in colour dueto the many blood

capillaries of the nephrons

Artery &Vein

MedullaLighter in colour... lessblood vessels.Here many collectingducts carry urine to theureterUreter

carries urine tobladder

DISSECTED KIDNEY

Patient’s bloodfrom an artery

Pump

Blood flows through “dialysis tube” with semi-permeable membrane walls

FLUIDIN

OUT

DDiiaallyyssiissfflluuiidd fflloowwssppaasstt tthhee

ttuubbeessccaarrrryyiinngg tthhee

bblloooodd

Bloodreturns topatient’svein

Position of an AAddrreennaall GGllaanndd(not usually present in schoolspecimens)

Comparison of Renal Dialysis with Natural Kidney Function

Similarities•Both processes remove urea and other wastes from the blood.•Both rely on movement of dissolved substances through semi-permeable membranes.

Differences• Kidney function involves the 2 steps of filtration and

reabsorption; dialysis involves only 1 step of diffusionof wastes from blood.

• In a kidney, movement across membranes is achieved by both active transport and by passive osmosis and diffusion; dialysis involves only passive diffusion.

wastes such as urea diffuse

out of theblood



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Water Balance in Australian AnimalsThe different conditions of each environment dictate whatan animal must do to to achieve homeostasis of its “waterbalance”. In each environment there are different problemsto be overcome, and the animal’s body organs mustrespond appropriately. Exactly how homeostasis isachieved will be reflected in the urine the animal produces.

Comparison of Urine Production in Different Environments

Marine Fish (revise page 18)• problem: constant loss of water by osmosis.• urine: small amount, to conserve water.

Urine does not contain wastes, since ammoniais excreted from the gills.

Freshwater Fish (revise page 18)• problem: constant gain of water by osmosis.• urine: large volume, to remove water.

Urine does not contain wastes, since ammoniais excreted from the gills.

Terrestrial Mammal• problem: must excrete wastes in urine, but cannot

afford to lose too much water, especially in dryAustralian ecosystems.

• urine: generally small volume, to conserve water.Urine is relatively highly concentrated in wastessuch as urea.

Water Conservation & Excretion in InsectsAll insects are small, and most are adapted for flight. Thismeans they cannot afford to carry large amounts of waterin their bodies just for the purpose of excreting urine.Their excretory system must be able to remove nitrogenouswastes, while losing only a minimum of water.

Firstly, their nitrogenous wastes are processed chemicallyinto the form of uric acid, which has a low solubility inwater. This means that, when their urine is separated fromthe blood (filtration) and then concentrated byreabsorption of water, the uric acid precipitates as a solid.

After further reabsorption of water, the insect’s urine is asemi-solid paste, which is passed into the rectum andexcreted with their solid digestive wastes.

Water Conservation & Excretion in Australian Mammals

Many Australian environments are desert or semi-arid andwater conservation is vital for survival. Some adaptationsfor temperature control, while conserving water, werecovered earlier in this topic (see page 10).

Many Australian mammals have excretory systems that alsocontribute to water conservation, while managing toefficiently remove their nitrogenous waste, urea.

The desert-living Red Kangaroo, the Spinifex HoppingMouse, and even the Koala (which rarely drinks) all havethe ability to produce very small amounts of highlyconcentrated urine.

They achieve this by:• having longer tubules in their kidney nephrons, whichallows for more reabsorption of water back into the blood,thus less urine is produced.• the cells lining the tubules are able to actively transporturea from blood into the urine. So, not only is urea notreabsorbed from the “filtrate” liquid, but is actively“pumped” from the blood.

The result is less water and more urea in their urine.

EnantiostasisEnantiostasis is a special case of homeostasis. It refers tothe maintenence of metabolic and physiological functions,(i.e. homeostasis) despite significant variations in thesurrounding environment.

An important example is an estuary, where river meets sea.Organisms are able to maintain their water and salt balance,despite wild fluctuations in the water and saltconcentrations around them, every time the tides change.

Some of the ways they cope with this are:

• burrowing into the mud, where the salt concentrations aremore stable (e.g. crabs, yabbies)

• closing their shell, to avoid extreme conditions theycannot cope with. (e.g. oysters)

• switching their excretory systems from water conserverswhen salty, to water excreters when fresh. (e.g. fish)



MOUTH

MMAALLPPIIGGHHIIAANN TTUUBBEESS extend throughinsect’s body, collecting and

concentrating urine.Urine is emptied into the gut for

excretion.

ANUS

Intestine

The Malpighian Tubes arethe insect equivalent ofkidneys

Photo by Diana



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Water Conservation in Australian PlantsThe characteristics of Australia’s sclerophyll plants weredealt with in the Preliminary Course topic “Evolution ofAustralian Biota”.

In summary, the sclerophyll plants include the gum trees,banksias and acacias (wattles) and all show numerousadaptations to conserve water in our arid climate, such as:

• small, narrow, drooping leaves with thick, waxy cuticles

• In dry times, gum trees shed many of their leaves so thatthere are less surfaces for evaporation. In some species,such as the River Red Gum, entire branches are sacrificedby cutting off their water supply so that they die. (This iswhy gum trees are dangerous... whole dead branches oftenfall off onto cars, homes or campsites.)

• Species such as Spinifex grass limit evaporation by havingfine hairs all over their leaves. This traps a layer of air nearthe leaf so that wind cannot increase evaporation rates.

• Generally, all Australian sclerophylls have fewer stomateson their leaves to limit the water loss from transpiration.

How Plants Cope With SaltMany of the Australian coastal estuaries are home toMangrove trees which have a number of adaptations tocope with the salt water that covers their roots with everyhigh tide.

To maintain their “osmotic balance” they must bothconserve water and deal with high levels of salt. One of themost common species is the “Grey Mangrove”, Avicenniamarina, which has all the following adaptations:

• leaves with a thick, waxy cuticle and fine hairs on theundersurface, all to minimize water loss.

• salt glands in the leaves which excrete a concentrated saltbrine onto the leaf surface. The salt gets washed awaywhen it rains.

• salt is deposited in older leaves, so when they drop offthey carry a load of excess salt away.

• special tissues within their roots which allows water topass through, but reduces the passage of salt. This helps toreduce the salt intake.



Small & narrow to reduceSurface Area for less

evaporation

Droop downwards to avoid the heatof midday for less evaporation

Thick, waxycuticle

minimizesevaporation

Mangrovescoastal NSW

GUM LEAVES

Worksheet 4Fill in the blanks Check your answers at the back.

Water is vital to all living things because:1. It is the a)................................... of life, and mostsubstances are b).............................. in water solution.2. Water is involved in many c)............................... reactions,such as photosynthesis or d).............................................3. Water has very high “heat e)....................................” and“heat of f)....................................” so it is vital to temperaturecontrol4. Water g)................................ and cushions cells and organs.For example, plants rely on water in cellh).................................. to keep leaves and stems upright.Maintaining the correct balance of both water anddissolved i)................................ is another aspect ofj)......................................

In vertebrate animals, the control of water balance is doneby the k)..............................., which also are responsible forexcretion of l).................................. wastes. Different animalsproduce different wastes: the fish produce mainlym)...................................... while birds and insects producen)................................................... and mammals produceo).................................. In fish, the kidneys are used mainlyfor p).......................................... because excretion of theammonia takes place from their q)................................

Each kidney contains about 1 million units calledr)................................ There is a coiled blood vessel, thes)..................................... which is inside thet).............................. capsule. Here the process ofu).............................................. takes place, where water andmany dissolved substances leave the blood and flowthrought the v).............................................. The secondprocess is w)......................................... in which any usefulsubstances (most of the water, plus x)............................... and..................................) are absorbed back into they)...................................... by a combination of activetransport and z)..................................... Some water plus theaa).............................. are not reabsorbed but pass into aab)..................................... duct, and down theac)..................................... to the bladder to await excretion.The kidneys also have a role in ad)..........................................by adjusting the amounts of water andae)......................................... that are reabsorbed into theblood. This function is controlled by theaf)................................. which monitors “water balance” andcontrols the release of the hormone ag)..............................from the ah)................................... gland. This hormoneincreases the permeability of membranes in theai)...............................so that aj)............................. (more/less)water will be absorbed, and ak)............................ (more/less)urine formed.

So, an increase in ADH secretion leads to greateral)................................. (excretion/retention) of water, whilea decrease in ADH results in am)..........................(more/less) urine production.

Another hormone called an)....................................... isproduced by the ao).......................................... glandscontrols the reabsorption of ap).................................. Somepeople do not produce enough of this hormone and sohave a chronic salt-balance problem calledaq)................................. Disease. This disease is treated byar)................................................... Therapy (HRT).

If a person’s kidneys fail, they can have their blood“cleaned” of wastes by the process of “Renalas)..................................... This is similar to kidney functionin that both involve movement of dissolved chemicalsthrough at)............................................... membranes. It isdifferent from kidney function in that it involves onlyau)............ (number) process, which involvesav).............................. (active/passive) diffusion. Kidneyfunction has aw).................... (number) steps, and involvesboth ax).............................. (active/passive) transport andosmosis.

Insects process their nitrogenous wastes into the chemicalay)......................................... which has very low solubility.This allows them to excrete “urine” which is almost entirelyaz)........................... Many Australian mammals excrete veryba)................................ (small/large) amounts ofbb)................................... (dilute/concentrated) urine. Theyachieve this by having increased ability to reabsorbbc)............................... from the nephron tubules, and canbd).................................... (actively/passively) pump ureafrom be)............................. into the bf)...................................

When an organism can maintain homeostasis despitesignificant variations in the environment, this is calledbg).......................................... A good example is the way thatestuarine animals can maintain bh)......................................balance despite the fluctuations in salt concentrations as thebi)......................... change. Mangrove plants deal with salt byspecial root tissue to bj).............................. its entry, or bybk).................................. salt onto their leaves, or bybl).......................... salt in older leaves which are later shed.Many Australian plants are well-adapted to conserve waterby such features as leaves which arebm)............................................ (shape & size) and arecovered with a thick, waxy bn)...........................................They often have fewer bo)......................................... on theirleaves, or may be covered with bp)..................................... totrap a layer of air.

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HSC Biology Topic 1Copyright © 2005-2007 keep it simple science www.keepitsimplescience.com.au


WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES




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Blank “Mind Map”Use this scaffold to try and learn all the parts of this topic.Some students find that if they know what’s in the topic,

they also remember the facts & concepts that need to be learnt.

MMAAIINNTTAAIINNIINNGGAA

BBAALLAANNCCEE

Practice QuestionsThese are not intended to be "HSC style" questions, but tochallenge your basic knowledge and understanding of the topic,and remind you of what you NEED to know at the K.I.S.S.principle level.

When you have confidently mastered this level, it is stronglyrecommended you work on questions from past exam papers.

Part A Multiple Choice1. Which of the following is NOT true about enzymes?Enzymes:-A. are catalysts which speed up chemical reactions.B. are carbohydrate molecules of a special shape.C. will only work within a narrow range of temperature & pH.D. are substrate-specific; each only works for one substrate.

The graph shows the rate ofan enzyme-catalysed reaction.Questions 2 and 3 refer to it.

2. Which part of this graph (A,B,C or D) corresponds to theenzyme having the best 3-dimentional shape to fit itssubstrate?

3. At point D on this graph, youcould describe the enzyme as:A. saturated with substrate.B. optimum shape.C. decomposed.D. denatured.

4. This graph compares the performance of 2 enzymes atdifferent pH levels.

It would be reasonable to conclude that:A. “P” is a stomach enzyme, “Q” is an intra-cellular enzyme.B. “P” is from a plant cell, “Q” is from a mammal cell.C. “Q” performs better than “P” under all conditions.D. Both would be at their optimum activity at about 40oC.

5. The effect on enzyme activity of increasing the substrateconcentration is best described as:A. Activity rises to an “optimum” level, then declines again.B. Activity always rises as substrate concentration increases.C. Activity declines as substrate concentration increases.D. Activity rises, then levels off as the enzyme becomessaturated.

6. Which of the following is least likely to be controlled bya negative feedback system?A. Body temperature B. Blood sugar levelsC. Rate of digestion D. Water & salt levels.

7. The “control centre” for homeostasis involving thenerve system is the:A. Hypothalamus B. CerebrumC. Cerebellum D. Pituitary gland

8. Which of the following is a response by an effectororgan which would be appropriate when the body is toowarm?A. Muscles begin shivering.B. Blood vessels dilated.C. Body hairs erected, forming “goose bumps”.D. Metabolic rate increased by the hormone thyroxine.

9. Which statement is correct?A. Ectotherms such as fish, generate their own body heat.B. Endotherms such as birds, rely on their surroundings tosupply their body heat.C. Ectotherms such as mammals, generate their own bodyheat.D. Ectotherms such as reptiles, rely on their surroundingsto supply their body heat.

10. A typical response of an ectotherm to over-heating is:A. sweating B. sun-bakingC. seeking shade D. shivering

11. An important adaptation in Australian mammals to helpkeep cool in a desert environment is:A. a lot of sweat glands in the skin.B. a “stocky”, thick-set shape to minimize heat absorption.C. large ears to acts as heat radiators.D. thick fur to prevent heat getting to their body.

12. A blood vessel with relatively thin muscle layer andequipped with one-way valves is most likely a:A.Vein B. ArterioleC. Artery D. Capillary

13. As blood flows through a capillary in an active muscle,you would expect changes in the substances carried in theblood, as follows:A. Increase in CO2, decrease in O2 and sugars.B. Decrease in CO2 and sugars, increase in O2C. Inrease in CO2 and sugars, decrease in O2D. Decrease in CO2 and O2, decrease in sugars

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Temperature

Rate

of r

eact

ion

AA

BB

CC

DD

1 2 3 4 5 6 77 8 9 10 ppHH

Enzy

me

Activ

ity

Enzyme Q

Enzyme P

14.Which line correctly identifies the way in which most of theoxygen and carbon dioxide gases are carried in the blood?

Oxygen Carbon DioxideA. dissolved in plasma, in haemoglobinB. in haemoglobin, dissolved as bicarbonate ionC. in white cells, in haemoglobinD. in haemoglobin, dissolved as carbonic acid

15.The “Oximeter” is able to measure percentage oxygensaturation of the blood because, depending on the amountof oxygen present:A. the blood pH changes B. the ratio of red and white cells changesC. the blood flows at a different rateD. haemoglobin absorbs light differently

16.Which statement about plant transport systems is correct?A. Xylem use active transport for Transpiration.B. Xylem cells are alive and carry out TranslocationC. Phloem cells use active transport to move nutrientsD. Phloem tubes carry out Transpiration by passive means

17.A freshwater fish:A. produces a large volume of dilute urineB. produces a small volume of concentrated urineC. excretes urea in large amounts via the kidneysD. excretes water from its gills and must drink to replace it

18.In the mammalian kidney nephrons the formation of urineoccurs in 2 stages. Which line describes correctly thelocation of each process?

Filtration ReabsorptionA. Glomerulus Bowman’s capsuleB. Renal tubules UreterC. Glomerulus Renal tubulesD. Bowman’s capsule Collecting duct

19.An increase in the level of the hormone “ADH” wouldcause the kidney nephrons to:A. reabsorb less saltB. reabsorb more waterC. reabsorb more saltD. reabsorb less water

20.Insects conserve water by excreting their nitrogenouswastes in the form of:A. a semi-solid paste of uric acidB. a small volume of urine, highly concentrated in ureaC. a large amount of ammonia-containing urineD. pellets of solid urea

Part B Longer Response QuestionsMark values given are suggestions only, and are to give you an ideaof how detailed an answer is appropriate.

21. (4 marks) Discuss the importance of shape to the characteristics ofan enzyme, with specific reference toa) why each enzyme will usually only catalyse only onereaction.

b) why enzymes only work within fairly narrow ranges oftemperature and pH.

22. (8 marks) The following data was collected in an experiment in whichthe time taken for a chemical reaction catalyzed by anenzyme, was measured at different temperatures.

Temp (oC) Time taken for reaction (min.)5 4.0

10 2.015 1.020 0.225 2.530 10

a) Tabulate this data appropriately, adding a third columnfor “Reaction Rate” and calculating values for this.

b) Construct a graph of Temperature v Rate.

c) Is it likely that this is a human enzyme? Explain.

23. (5 marks) a) What is meant by “Homeostasis”b) What is the link between the necessity for homeostasisand enzymes?c) Using a simple example, explain the concept of“negative feedback” as a way to maintain stability of anysystem.

24. (8 marks)a) Discuss the role of the hypothalamus in the regulation ofbody temperature in a mammal.

b) Give an outline of how the blood vessels function as“effectors” in the regulation of body temperature.

c) List 3 other effectors (apart from blood vessels) involvedin temperature regulation.

25. (6 marks) a) Explain the difference between an ectotherm and anendotherm.

b) Using a named Australian example, outline how anectotherm regulates its body temperature.

c) Using a named Australian example, outline 2 adaptationsof desert-living endotherm to keep their bodies cool.

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26. (3 marks) Describe some adaptations of sclerophyll plants which helpthem minimize absorption of heat from the Sun.

27. (5 marks) Describe the structural difference(s) of veins and arteries,and relate these differences to the functions of these bloodvessels.

28. (9 marks) a) Contrast the way(s) that the gases oxygen and carbon dioxideare carried in the blood.

b) These gases are described as the “respiratory gases” because oftheir involvement in cellular respiration. Summarize this processwith a chemical equation.

c) How is the release of oxygen from the bloodstream facilitatedby the high concentration of carbon dioxide in the body tissues?

29. (4 marks) Identify 2 of the “blood products” extracted from donate blood,and describe the uses of these products.

30. (6 marks) Construct a table to contrast the processes of Transpiration andTranslocation in plants. Your answer should cover:

• the name and nature of the vessels involved• the substance(s) transported• the basic nature of the processes

31. (4 marks)Discuss briefly the importance of water in living organisms,identifying 4 functions of water.

32. (4 marks)Outline the processes of Filtration and Reabsorption in thenephron of a mammalian kidney. Identify where each processoccurs and the main events occurring.

33. (6 marks)Compare and contrast the role of the hormones “ADH” and“Aldosterone” in the maintenence of mammal homeostasis. Youranswer should include

• source of each hormone• precise effect on the target organ• how this contributes to Homeostasis

34. (5 marks)a) Outline the process of excretion of nitrogenous wastes ininsects, explaining how it contributes to conservation of water intheir bodies.

b) Using a named example of an Australian mammal, explain howthe excretion of nitrogenous wastes is achieved with minimumwater loss.

35. (8 marks)a) What is “Enantiostasis”? Give an example of an environmentwhere this process is vital and outline some of the strategies forachieving enantiostasis in the named environment.

b) Identify strategies for conservating water in 2 named Australianplants.

c) Describe 2 strategies used by mangrove trees to maintain waterbalance in a saline environment.

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Worksheet 1 (continued)

Part Ca) stable / at the same level b) temperaturec) pH d) watere) blood sugar f) negativeg) receptor h) control centrei) effectors j) nervousk) hypothalamus l) brain

Worksheet 2

a) hypothalamus b) effectorc) dilation d) moree) sweat f) perspirationg) evaporates h) hormonesi) thyroid j) constrictedk) the skin l) raised / erectedm) insulate n) shivero) ectotherms p) reptilesq) Sun r) Blue-tongue lizards) sunbakes t) seeks shadeu) copperhead snake / corroboree frogv) becoming dormant w) endothermsx) & y) mammals & birds z) feathersaa) blubber (fat) ab) earsac) lose water ad) fore armsae) insulation af) shunted back into the bodyag) deciduous ah) shed their leavesai) stomates aj) needle / spineak) light al) sclerophyllam) narrow an) droop downwards

Worksheet 3

Part Aa) plasma b) redc) haemoglobin d) oxygene) bicarbonate f) waterg) carbonic h) plasmai) sugars j) amino acidsk) urea l) proteinm) arteries n) pressureo) heart p) Veinsq) valves r) flowing backwardss) one cell t) tissuesu) digested nutrients v) liverw) processing & storage x) ureay) kidneys z) water & saltsaa) oxygen ab) carbon dioxideac) blood ad) cellsae) oxygen af) carbon dioxide

Answer Section

Worksheet 1Part Aa) metabolism b) speeds upc) used up / consumed d)enzymese) protein f) amino acidsg) 3-dimensional shape h) substrate(s)i) specific j) & k) temperature & pHl) shape m) & n) acidity & alkalinityo) 7 p) belowq) above 7 r) 7 / neutrals) stomach t) acidic

Part B1. graph

2.a) reaction rate (=activity)increases as temp. goes upbecause molecules are more likelyto collide and react with eachother.

b) Above the optimum the shape of the enzyme protein beginsto change and be distorted. The substrate(s) no longer fit theenzyme perfectly, and activity declines rapidly.

3. graph

4. At the optimum pH the shapeof the enzyme is a perfect “lock& key” shape to fit the substrate,so activity is at a maximum.

5. At pH’s either side of optimumthe shape of the enzyme changes so that the “fit” with thesubstrate is no longer perfect, so activity declines.

6. graph

7. a) As the concentration ofsubstrate molecules increases, itbecomes more likely that theywill collide with an enzyme andundergo the reaction. Soreaction rate increases.b) However, once all the available enzyme molecules are beingused, (they are “saturated” with substrate) increasing theconcentration cannot increase reaction rate any further, so thegraph levels off.

Temp

Activ

ity

Substrate concentration

Activ

ity

pH

Activ

ity




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Worksheet 4 (continued)ac) ureter ad) homeostasisae) salt af) hypothalamusag) ADH ah) pituitaryai) renal tubules aj) moreak) less al) retentionam) more an) aldosteroneao) adrenal ap) saltaq) Addison’s ar) Hormone Replacementas) Dialysis at) semi-permeableau) one av) passiveaw) two ax) activeay) uric acid az) solid / dryba) small bb) concentratedbc) water bd) activelybe) blood bf) tubules / urinebg) enantiostasis bh) water & saltbi) tides bj) limitbk) secreting / excreting bl) storing / accumulatingbm) small & narrow bn) cuticlebo) stomates bp) hairs

Practice Questions

Part A Multiple Choice1. B 5. D 9. D 13. A 17. A2. B 6. C 10. C 14. B 18. C3. D 7. A 11. C 15. D 19. B4. A 8. B 12. A 16. C 20. A

Part B Longer ResponseIn some cases there may be more than one correct answer possible. The following “model”answers are correct, but not necessarily perfect.

21.a) Enzymes are protein molecules and each has a a particular 3-dimensional shape which fits its substrate like a key fits a lock.Usually each enzyme will only “fit” one particular substrate, so itwill only catalyse one reaction.b) Any change in temperature or pH can change the shape of anenzyme, by causing the protein chain to alter the way it is foldedand twisted. As its shape changes, its ability to “fit” the substratewill change too. Thus each enzyme only works fully withinrelatively narrow ranges of temperature and pH.

22.a) Table should • be ruled • have clear headingsThe values in the 3rd column should be:

Reaction Rate (min-1)0.250.51.05.00.40.1

(These values are calulated as 1/time taken)

Worksheet 3Part B1. Carbon dioxide reacts with water to form carbonic acid

CO2 + H2O H2CO3Carbonic acid is a weak acid which partly ionizes

H2CO3 H+ + HCO3-

Carbon dioxide is mostly carried as bicarbonate ion.

2. The equations show that carbon dioxide reacts withwater forming an acid. If allowed to accumulate, this wouldlower the pH, which could seriously affect the activity ofenzymes and disrupt metabolism.

3. As shown in the equations above, the presence of carbondioxide lowers the pH. In tissue capillaries, the slightlylowered pH alters the shape of the haemoglobin moleculesslightly. This causes them to release the oxygen moleculesthey are carrying, which then diffuse into the cells.

Part Ca) red b) ironc) haemoglobin d) 4e) oxyhaemoglobin f) carbon dioxideg) release h) diffusei) percent oxygen saturation j) 95%k) Oximeter l) red light & infra-red lightm) absorbed n) Redo) immunity p) Plateletq) Plasma r) blood volumes) stored t) immune-responsesu) diseases v) Haemoglobinw) Oxygen x) Perfluorocarbons

Part Da) xylem b) rootsc) leaves d) deade) passive f) transpirationg) evaporates h) cohesivei) phloem j) translocationk) nutrients / sugars l) alivem) active n) use energy

Worksheet 4

a) solvent b) dissolvedc) chemical d) metabolic / chemicale) capacity f) vaporizationg) supports h) vacuolesi) salts j) homeostasisk) kidneys l) nitrogenousm) ammonia n) uric acido) urea p) water balanceq) gills r) nephronss) glomerulus t) Bowman’su) filtration v) renal tubulesw) reabsorption x) sugars / salts / amino acidsy) bloodstream z) osmosisaa) urea ab) collecting




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25.a) Endotherms are animals which generate their own body heat.Ectotherms rely on their environment to supply their body heat;they do not generate internal body heat.b) Ectotherms such are the Blue-Tongue Lizard often useinstinctive behaviours to regulate temperature. When too cold, itwill sunbake, flattening its body to increase the surface areaexposed to the Sun. When too hot, it will seek shade and avoid theheat of the Sun.c) Desert-living endotherms, such as the Bilby, cannot afford thewater loss involved with sweating to cool off. Instead, they havelarge ears to radiate heat away. They seek shade in the heat of theday and are active only in the evenings and early morning. Insteadof sweating, they “pant” so that evaporation from the mouth andthroat has a cooling effect.

26.Sclerophyll plants have• small, narrow leaves to reduce surface area exposed to Sun• shiny leaf cuticle to reflect some radiant heat• leaves which “droop” downwards. This allows for absorption oflight for photosynthesis in the cool of the morning, but avoidsheat absorption in the heat of midday.

27.Arteries have thick, muscular walls. This allows them to withstandthe high pressure blood they carry as the heart pumps. Beingelastic, the walls can expand outwards under pressure, thencontract and help squeeze the blood on its way.Veins have thinner walls since the blood they carry back to theheart is at low pressure. Veins are equipped with valves to preventback-flow. The thin walls of a vein allow them to be compressedby neighbouring muscles, which helps squeeze the blood forward.

28.a) Oxygen is carried attached to the haemoglobin molecules in thered blood cells.Most carbon dioxide is carried in solution in the blood plasma asbicarbonate ion, HCO3

-.b) C6H12O6 + 6O2 6CO2 + 6H2O + ATPc) The high concentration of dissolved CO2 causes the pH to beslightly lower (because CO2 reacts with water forming carbonicacid). This change in pH causes a change in the shape of thehaemoglobin molecule, which causes it to release oxygen, whichcan then diffuse into the surrounding body cells.

29.Red Cell Concentrate contains about 2x as many red cells asnormal blood. It is used to treat people with severe anaemia, orfollowing severe blood loss.Platelet Concentrate is given to patients who need extra blood-clotting capability, such as leukemia sufferers.

22. (continued)b)

c) No.The graph showsthat at humanbody temp. (37C)the enzyme’sactivity is almostzero. Thisenzyme wouldNOT function ina human body.

23.a) Homeostasis is the process of maintaining a stable,internal environment, for such things as temperature, pH,water balance, etc.b) Homeostasis is vital so that the optimum conditions (oftemp., pH etc) for enzymes to function efficiently aremaintained. Efficient enzyme activity is essential so that thereactions of metabolism occur at a rate appropriate for lifefunctions.c) example: thermostat control of an ovenA temperature sensor constantly monitors the temp.If oven is too cool, the control mechanism sends anelectrical signal to turn the heating element on. (effector)If the oven is too hot, a signal is sent to turn the heatingelement off, so the oven will cool down.By always taking action in the opposite direction (negativefeedback) a relatively stable temperature is maintained.

24.a) The hypothalamus is both the receptor and controlcentre for regulation of body temperature.Blood flowing through the hypothalamus is constantlymonitored by special, heat-sensitive cells lining the bloodvessels. If body temperature is even slightly high or low, thehypothalamus sends nerve messages to various effectororgans to either warm or cool the body back to its correcttemperature.b) The peripheral blood vessels are “effector organs” fortemperature regulation. Veins and arteries can beconstricted (narrowed) to reduce the blood flow to the skin.This reduces the amount of heat lost through the skin,thereby helping to warm the body. The opposite process ofdilating (widening) the blood vessels allows more bloodflow to the skin. This allows more heat to be lost from theskin, thereby cooling the body.c) Three other effector organs:Sweat glands (perspiration), skeletal muscles (shivering),thyroid gland (hormone thyroxine), body hair muscles(goose bumps).

0 5 10 15 20 25 30

Temperature (oC)

Reac

tion

Rate

(1/m

in)

1

2

3

4

5

Reaction Rate v Temp. Graph




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34.a) The insect equivalent of kidneys are the “malphigiantubes” which run all though the body and collect andconcentrate nitrogenous wastes in the form of uric acid.Since this is basically insoluble, the “urine” can beconcentrated to a semi-solid paste by reabsorbing virtuallyall the water, before passing the wastes into the rectum forexcretion with the digestive wastes. This means there isvirually no loss of water during excretion.

b) The Spinifex Hopping Mouse is a desert-dweller whichproduces very small amounts of very concentrated urine.This is achieved because:• the nephron tubules are very long, allowing for morereabsorption of water, and less volume of urine.• the cells lining the tubules are able to actively transporturea from the blood into the urine. This allows the urine tobe even more highly concentrated than in other mammals.

35.a) Enantiostasis is a special case of homeostasis, in whichan organism maintains a stable internal environmentdespite significant changes in the environment around it.An example of a habitat where this is important is a tidalestuary, where the tides cause the salinity of theenvironment to fluctuate.To maintain their “osmotic balance” while their evironmentchanges from virtual fresh water, to salty and back again,requires estuarine organisms to cope by strategies such as:• burrowing into the mud where the salinity is moreconstant. (eg crabs & yabbies)• adjusting the functioning of their kidneys from waterexcreters to water conservers as the tides change. (eg fish)

b) Spinifex Grass has fine hairs all over its leaves. This trapsa layer of still air near the leaf, reducing the evaporativeeffect of the wind.Gum trees, such as the River Red Gum, has leaves with veryfew stomates, and a thick, waxy cuticle to minimize waterlosses.

c) Mangroves:• secrete salty brine onto the leaf surface. This washes awaywhen it rains.• accumulate salt in older leaves which are then shed,carrying away a load of excess salt.

30.Transpiration Translocation

Vessels Xylem PhloeminvolvedSubstances Water & dissolved Nutrients, especiallytransported minerals sugarsProcesses Passive transport Active transportinvolved

31.Water is the solvent of lifeAll the chemical reactions of metabolism take place inwater solution, and the transport of materials in cytoplasm,blood or phloem takes place mainly in water solution.Water is involved in life chemistryWater is a reactant or product of many metabolic reactions.The reactions of photosynthesis and cellular respiration arejust two of the many examples.Water is vital in temperature regulationWater has a very high specific heat capacity. This helpsstabilize the temperature of all living things.Evaporation ofsweat is an important cooling mechanism in mammals.Water supports and cushions cells and organsAnimals such as worms rely on the hydraulic pressure ofwater in their tissues to support their body and maintain itsshape. In vertebrate animals the water solutions in thetissues helps to cushion organs against bumps and impacts.(eg cerebrospinal fluid around the brain)

32.Filtration occurs in the glomerulus. Some of the water ofthe blood plasma and its dissolved sugars, minerals, urea etcseep out of the blood vessel, like water through a filterpaper. Blood cells and proteins cannot leak out.This “filtrate” flows along the renal tubules wherereabsorption occurs. Useful nutients (sugars, amino acids)are actively transported back into the bloodstream. Most ofthe water in the filtrate flows back to the blood by osmosis.A portion of the water with dissolved urea flows on to beexcreted as urine.

33.ADH is secreted by the pituitary gland (under control ofthe hypothalamus) It alters the permeability of the renaltubules to water. Increased ADH allows greater waterreabsorption, and less urine production.Aldosterone is secreted by the adrenal glands. It stimulatesthe cells lining the renal tubules to actively transport moresodium ions back into the blood from the renal fitrate. Thisretains more salt in the body to adjust “osmotic balance”.

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Bio5.Maintaining a Balance