Year 12 Biology Notes – Maintaining a Balance

1. Most organisms are active in a limited temperature range

Identify the role of enzymes in metabolism, describe their chemical composition and use a simple

model to describe their specifically on substrates

Role of enzymes in metabolism:

Metabolism refers to all the biochemical reactions occurring within an organism.

Enzymes are protein molecules present in cells which act as biological catalysts, thus

increasing the rate of the reactions that occur in living organisms and maintains the

temperature.

The basic unit of proteins are amino acids that form long chains called polypeptides

bonded together by peptide bonds, which have a specific shape.

They are globular molecules that have long chains or sequences of amino acids.

Without enzymes, metabolism would be too slow to maintain life.

The molecule which an enzyme acts upon is called a substrate.

An enzyme fits together with its substrate molecule at a precise place on the surface of the

larger enzyme molecule, called the active site.

In the chemical reaction, the products are the substances which the substrate becomes,

where as the enzyme is not changed or consumed by the reaction.

Models to explain specifically:

- Lock and Key Model

States that the active site is rigid and the small substrate is reciprocally shaped and fits

exactly into the active site like how a key fits into a lock.

- Induced Fit Model

States that the active site changes to accommodate the substrate which

induces/changes the shape of the enzyme.

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

The presence of Hydrogen ions makes a solution acidic.

The pH if a solution is a measure of the concentration of hydrogen ions per litre of solution.

The pH of a solution is a measurement of its acidity/ alkalinity.

The pH scale is from 0 to 14: a pH of 7 is neutral (pure water); above 7 is alkaline/basic and

below 7 is acidic.

Explain why the maintenance of a constant internal environment is important for optimal

metabolic efficiency

Enzymes control all the metabolic processes in the body and work optimally in an

environment where their optimum temperature and pH conditions are met.

Metabolic efficiency relies on a constant level of the following variables in the internal

environment:

Temperature and pH (optimal range) for enzyme functioning

Concentration of metabolites (reactants)

Water and salt concentration (osmotic pressure), which determines the volume of cells

or fluid such as blood

Absence of toxins that may inhibit enzyme functioning

Describe homeostasis as the process by which organisms maintain a relatively stable internal

environment

Homeostasis is defined as the process by which organisms maintain a constant internal

environment, regardless of changes to their behaviour and the external environment.

Through homeostasis, it allows organisms to control conditions:

- Temperature and metabolic rate

- pH levels

- Concentration of nutrients

- Concentration of dissolved salts and minerals

- Concentration of water

Homeostasis ensures that the organism operates at maximum performance.

Explain that homeostasis consists of two stages:

- Detecting changes from the stable state - Counteracting changes from the stable state

Homeostasis involves an enormous amount of coordination and control in a living organism.

Coordination in animals is controlled by two systems:

The nervous system

The endocrine system (i.e. the hormone system)

Homeostasis is brought about in two stages:

1. Detecting change: Sensory cells or receptors present within the body detect change in

the temperature and/or chemical composition within the body. This change is called a

stimulus.

- Examples of external stimuli: light, day length, sound, temperature, odours

- Examples of internal stimuli: levels of CO2, oxygen levels, water, wastes, etc

- Receptors can range from a patch of sensitive cells, to complex organs like the eyes and

ears of mammals.

2. Counteracting change: Effector organs (such as muscles and glands) then work to

reverse the change. A response that successfully reverses the change will return the

body to homeostasis – its relatively constant state.

- Effectors can be either muscles or glands:

Muscles bring about changes by movement

Glands bring about changes by secreting chemical substances

Outline the role of the nervous system in detecting and responding to environmental changes

The nervous system provides rapid coordination of internal organ systems, and detects and

responds to environmental changes.

The nervous system consists of the central nervous system (CNS – brain and spinal cord) and

peripheral nervous system (PNS – Sensory neuron, motor neuron and interneuron)

The function of the nervous system is co-ordination and this takes place in 3 steps:

1. It detects information about an animal’s internal and external environments.

2. It transmits this information to a control centre.

3. This information is processed in the control centre, generating a response to ensure the

maintenance of a relatively constant internal state.

Identify the broad range of temperatures over which life is found compared with the narrow limits

for individual species

Ambient temperature is the temperature of the environment.

Organisms can line with environments with ambient temperatures from less than 0oC

(bacteria in snow) to 100oC (Pompeii worm in undersea vents of volcanoes).

Individual organisms cannot survive this wide range of temperatures.

For example mammals can generally survive temperatures of about 0oC to 45oC, as below

0oC cells risk ice crystals forming in them and above 45oC the enzymes will become

denatured.

This means that life is found in a very wide range of temperatures, but individual species can

only be found in a narrow temperature range.

Compare responses of named Australian ectothermic and endothermic organisms to changes in

the ambient temperature and explain how these responses assist temperature regulation.

Ectotherms are organisms that have a limited ability to control their body temperature.

Their cellular activities generate little heat. Their body temperatures rise and fall with

ambient temperature changes. Most organisms are ectotherms. Examples are plants, all

invertebrates, fish, amphibians and reptiles

Endotherms are organisms whose metabolism generates enough heat to maintain an

internal temperature independent of the ambient temperature. Birds and mammals are

endotherms.

Australian Red Kangaroo – Endotherm

Cold conditions

Physiology Structural Behavioural

Increased metabolic rate to create more heat within the body

Basking in the sun

Hot conditions

Physiology Structural Behavioural

Exposed areas of skin on forelegs to increase evaporative cooling of blood for the area

Shunting of blood from tail to exposed areas of skin to increase heat loss

Basking in the sun

Sitting in the Shade

Australian Diamond Python – Ectotherm

Cold conditions

Physiology Structural Behavioural

Lies on eggs and shivers to create more heat within the body

Dark colour to absorb heat and can therefore tolerate colder temperature than most snakes

Basks in sun to raise body temperature

Hibernation in winter

Migration to warmer areas

Warm conditions

Physiology Structural Behavioural

Nocturnal – hunts at night

Burrowing during the day

Identify some responses of plants to temperature change

Plants need certain temperatures for growth and the germination of seeds.

On land, where temperature fluctuations are greater than in water, plant responses can

include:

The ability to orientate leaves vertically to reduce the surface area exposed to the sun,

reducing heat absorption and supporting convective cooling

The ability to drop their leaves if the temperature becomes too cold

Germination (some seeds will only germinate if they have been exposed to a minimum

number of hours of cold conditions)

Budding as temperature and length of day increase in the spring

Closing stomates in response to high temperatures to reduce water loss

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

develop a model of a feedback mechanism:

Homeostasis involves the detection of the change in the environment and the response to

that change

The mechanism that brings about this change is called Feedback

In feedback systems, the response alters the stimulus

In living organisms, the feedback system has 3 main parts:

- Receptors: A type of sensor that constantly monitors the internal environment

- Control Centre: Receives info from the receptors and determines the response

- Effector: Restores the set value. Keeps environments stable.

An example of a feedback system would be the control of body temperature

These receptors send their information to the control centre

The temperature control centre in mammals is the hypothalamus

The hypothalamus responds by initiating responses to increase or decrease

temperature, until it goes back to the set value (which is 37ºC)

Temperature control responses:

2. Plants and animals transport dissolved nutrients and gases in a fluid medium

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

- Carbon dioxide

When Carbon dioxide enters the blood 70% of it is transported in the form of hydrogen

carbonate ions – formed in the red blood cells, but carried in the plasma. The remaining

carbon dioxide can be dissolved into the plasma 7% and the rest 23% can bind with

haemoglobin.

- Oxygen

Haemoglobin in the red blood cells binds with this oxygen, forming a compound called

oxyhaemoglobin. This compound gives the bright red colour to blood.

- Water

Water is the universal solvent about 90% of blood plasma is water. Water is carried in

blood plasma.

- Salts

Salts are carried in the blood as ions dissolved in plasma, referred to as electrolytes.

- Lipids

Some lipids are insoluble, they are packaged into small droplets, which pass into the

lymphatic system and then into the bloodstream.

- Nitrogenous waste

Nitrogenous wastes in the form of ammonia, urea, uric acid and creatinine are all carried

dissolved in blood plasma.

- Other products of digestion

Glucose and amino acids are water soluble and so they are transported in the

bloodstream dissolved in plasma.

Explain the adaptive advantage of haemoglobin

Haemoglobin is a complex molecule within red blood cells which enable them to carry

oxygen.

Adaptive advantages:

- It increases the oxygen-carrying capacity in blood. Haemoglobin contains four haem

units – giving one molecule the ability to bond with four oxygen molecules. Thus, far

more oxygen can be carried in blood cells by haemoglobin than would be carried

dissolved in plasma.

- Its ability to bind oxygen increases once the first oxygen molecule binds with it. The

binding of each oxygen molecule changes the shape of the haemoglobin – making it

easier for each subsequent oxygen molecule to bind to it. This increases the rate and

efficiency of oxygen intake.

- Its capacity to release oxygen increases when CO2 is present. It is important for

haemoglobin to release the oxygen from the blood in tissues where the oxygen

concentration is low so that oxygen is delivered to the cells that need it. Metabolising

cells release CO2 which (indirectly) causes more oxygen to be released from

haemoglobin.

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

The function of arteries and veins is to carry blood over relatively long distances, from one

organ to another, whereas capillaries form branching networks to carry blood over relatively

short distances within organisms.

Arteries carry blood away from the heart

Veins return blood to the heart

Capillaries bring the blood into close contact with tissues, allowing for the exchange of

chemical substances between them.

Structure Function related to structure

Arteries Walls of arteries are relatively thick (compared to veins)

Walls of arteries have a large proportion of elastic fibres

No valves

The walls are thick to suit blood pumping out of the heart in regular bursts of high pressure

Elastic fibres allow the arteries to expand and accommodate for the increases in blood volume with each heartbeat

No valves – pressure of heartbeat ensures one way flow

Veins Few elastic fibres

Thinner wall than arteries

Valves

Few elastic fibres as no stretch or recoil necessary

Thinner wall due to blood flowing through is at a lower pressure than blood through arteries

Valves ensure one way flow of blood

Capillaries Very thin walls

Vast network

Wall is only one-cell thick to allow efficient diffusion between blood/body cells

Vast network allows a large surface area of exchange with cells

Describe the main changes in the chemical composition of the bloody as it moves around the body

and identify tissues in which these changes occur

An increase in oxygen and a decrease in carbon dioxide concentrations are evident in the

blood that has passed through the lungs; whilst a decrease in oxygen and an increase in

carbon dioxide is evident in blood that has passed through any organ other than the lungs

(i.e. in any organ where cellular respiration has occurred).

An increase in digestive end products is evident in blood that has passed through the small

intestine (which absorbs digested food). These products then travel through the

bloodstream to the liver.

A decrease in digestive end products and an increase in nitrogenous wastes (e.g. glucose and

fatty acids) are evident once blood has passed through the liver.

A decrease in nitrogenous wastes is evident in blood that has passed through the kidneys,

since they filter nitrogenous wastes out the blood and excrete them.

Outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is

essential

Oxygen is necessary for respiration, a process by which cells release energy from glucose.

Energy is needed for the growth, repair of tissues, movement, excretion and reproduction.

Without oxygen, this chemical energy stored in glucose and other food molecules cannot be

released; thus preventing the metabolic processes within cells.

Carbon dioxide is produced in cells as a waste product of cellular respiration. It must be

removed from cells to prevent a change in the pH, as carbon dioxide reacts with water in the

body to form carbonic acid. A build-up of carbon acid is toxic, as it lowers pH of cells –

reducing the efficiency of enzymes and affecting the overall homeostatic balance within an

organism. Therefore, the removal of carbon dioxide is essential for the normal functioning of

cells.

Describe current theories about processes responsible for the movement of materials through

plants in xylem and phloem tissue

Xylem:

- Transpiration is the loss of water from plant leaves. Transpiration stream is the

movement of water in the xylem vessels up the plant, from the roots to the leaves

- The processes involved in the transpiration stream can be explained by the transpiration

(evaporation) - tension- cohesion mechanism.

- Transpiration: water is evaporated from the leaves through the stomates, pulling water

from cells and xylem tissue

- Cohesion: water molecules stick together and have the ability to instantaneously

transfer pressure and tension

- Tension: As water is evaporated from the leaves, it causes tension in the water column

within the xylem. Due to the cohesion of the water molecules, water moves up the

xylem like a wire being pulled up, and replaces the water lost

- Adhesion: when the pull stops, water sticks to the side of the xylem vessel and does not

fall down

Phloem:

- Translocation is the movement of sugars and small amounts of other nutrients in

phloem from sugar sources in the plant to sugar ‘sinks’

- The current theory explaining translocation uses the pressure-flow mechanism and is

called the ‘source to sink’ model.

- The sugars from the leaves (source) are loaded into the phloem by active transport,

causing the osmotic pressure to shift (due to the difference in sugar/water

concentrations) and thus water follows in by osmosis.

- The opposite occurs at the sugar ‘sink’. Sugar and materials are removed from the

phloem by active transport, reducing osmotic pressure in the phloem (due to higher

water concentration), and water moves out by osmosis.

- These two processes produce a difference in hydrostatic pressure in the phloem, causing

the sap (sugar solution) to move from source to sink. Pressure flow, therefore drives the

sugars in the phloem from photosynthetic/storage sites to other parts of the plant.

Analyse information from secondary sources to identify current technologies that allow

measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and

explain the conditions under which these technologies are used

Current technologies that allow measurement of oxygen saturation and carbon dioxide

concentrations in blood are:

- Pulse oximeters

Pulse oximeters are used to measure the amount of oxygen in the patient’s blood. A clip

with a sensor is placed on the finger or earlobe and the sensor is connected to a monitor

that shows the pulse rate and oxygen saturation level. Two wavelengths of light: red and

infra-red pass through the finger from the light source to the photo detector. The

amount of light absorbed by the haemoglobin (and consequently the amount of light

reaching the detector) depends on its degree of saturation with oxygen.

Note that most oximeters don’t measure carbon-dioxide levels (it is only as recently as

2005 that some oximeters with a carbon dioxide sensor were developed)

Conditions under which it is used:

When a non-invasive technique is required

When rapid, continuous monitoring of arterial blood is needed

Examples: during anaesthesia, during recovery phase or in intensive care units during

mechanical ventilation. Oximeters are useful in such situations as it can quickly detect

problems with oxygenation.

- Arterial blood gas (ABG) analysis

Arterial blood gas analysis is a more invasive technique of analysis, and involves

removing blood from an artery (usually in the arm) and performing a blood test using a

sensor which translates the chemical properties of the blood into an electrical signal that

can be measured. It reveals far more detail about the levels of chemicals in the blood,

including partial pressure of oxygen and carbon dioxid, the pH and level of bicarbonate

ions.

Conditions under which it is used:

Invasive, and there could be delay between sampling and availability of results

When more detailed information about oxygen, carbon dioxide and pH levels are

required

Examples: provides vital information for critically ill patients who are on ventilators or

respiratory therapy, studies of lung diseases, or in severe cases of breathing disturbance.

Analyse information from secondary sources to identify the products extracted from donated

blood and discuss the uses of these products

Red blood cells – they help increase the amount of oxygen that can be carried to the body’s

tissues (by increasing haemoglobin levels) while not increasing blood volume. They are given

to people with anaemia (whose bone marrow doesn’t make enough red blood cells), those

who have kidney failure or acute blood loss.

Platelets – essential for blood clotting. They are given to people who have cancer of the

blood or lymph. Patients undergoing cancer therapy do not make enough platelets and are

also given platelets from donated blood.

Plasma – contains blood clotting factors. It us used to treat people with clotting disorders

such as haemophilia. It can also be used to adjust the osmotic pressure of blood and to pull

fluids out of the tissues.

White blood cells - infection fighting component of the blood. White blood cells are only

used occasionally to treat life-threatening situations when the cell count is very low or the

white blood cells are not functioning properly (in most cases, antibiotics is used rather than

white blood cell transfusions).

Whole blood – only used when absolutely needed, for example when a person has lost more

than 20% blood volume

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

of artificial blood and use available evidence to propose reasons why such research is needed

Artificial blood or blood substitutes are designed to carry oxygen and carbon dioxide. They

are not involved in clotting, coagulation and immune defence.

The need for research in the development of artificial blood is as follows:

- It can be stored for long periods and time and is easily transported.

- It does not need to be cross-matched for different blood types (i.e. it is universally

accepted by all blood groups).

- Can be produced at large quantities at low cost (meaning it can be readily available in

large supplies, solving the problem of a shortage of blood donors).

- It is completely safe (has no toxic effects, is free of disease and does not trigger an

immune response).

Proposed replacements for blood include:

- Perfluorocarbons (PFC)

Biologically inert materials

Relatively inexpensive to make

Can be made without biological materials, eliminating possibility of spreading an

infectious disease via blood transfusion

However, it is not soluble in water, meaning that they need to be combined with other

materials (emulsifiers) to mix with blood

Also, it can carry much less oxygen than haemoglobin-base d products, meaning that a

lot of PFC must be used

- Haemoglobin-based products

Unlike whole blood, haemoglobin products do not have the problem of blood typing.

Raw haemoglobin cannot be used because it breaks down into smaller, toxic compounds

within body. There are also problems with the stability of haemoglobin in solution.

Modifications, such as cross-linking molecules or using recombinant DNA technology are

currently undergoing trial phases for eventual commercial use.

3. Plants and animals regulate the concentration of gases, water and waste products of

metabolism in cells and in interstitial fluid

Explain why the concentration of water in cells should be maintained within a narrow range for

optimal function

Water makes up 70-90% of living things and is essential for life.

Water is the solvent for all metabolic reactions in living cells, and can take part in it (i.e

respiration).

Isotonic: Concentration of solutes outside the cell is the same as inside the cell. No overall

movement of water.

Hypertonic: Concentration of solutes is greater outside the cell than inside. Water tends to

move out of the cell.

Hypotonic: Concentration of solutes is greater inside the cell than out. Water tends to move

inside the cell.

Living cells work best in an isotonic environment, so the water level must be constant.

Any change in the concentration of solutes will result in a change in the levels of water in

cells which usually results in death (either dehydration or cell bursting).

Enzymes also require specific conditions of functioning, some of which could relate to the

levels of water and solutes in cells.

This is why the concentration of water must be kept constant: To ensure the proper

functioning of living cells.

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

As a result of metabolism, many waste products are formed (i.e. Carbon dioxide and

Ammonia).

If these were allowed to accumulate, they would slow down metabolism and kill the cells

(e.g. excess CO2 increases pH, affecting enzyme function or when protein and lipids are

broken down, deamination, produces nitrogenous waste, ammonia, which is highly toxic).

Other reasons for their removal is because some are poisonous, some take up space and

some would create problems for osmoregulation.

This is why they need to quickly be removed, or converted into a less toxic form.

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

The kidney plays a central role in homeostasis, forming, filtering and excreting urine while

regulating water and salt concentration in the blood.

Regulating water and salt levels is known as osmoregulation.

Fish do not excrete nitrogenous wastes through their kidneys; they use their gills.

Marine Fish: Their kidneys conserve water, excrete salts and nitrogenous wastes. These fish

are in a hypertonic environment.

Freshwater Fish: Their kidneys excrete excess water and nitrogenous wastes (produce large

amounts of dilute urine), conserve salt. These fish are in a hypotonic environment.

Mammals: Their kidneys conserve water and salts when required, excrete excess water and

salts and excrete nitrogenous wastes.

The kidney ensures that both the concentration of blood and interstitial fluid are constant.

Explain why the processes of diffusion and osmosis are inadequate in removing dissolved

nitrogenous wastes in some organisms

Osmosis is a selective form of diffusion in which the cell membrane acts as a selectively

permeable barrier that allows the passage of water but not larger molecules.

The processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous

wastes because:

- Diffusion is too slow, relying on random movement of molecules and is not able to

selectively reabsorb useful solutes.

- Osmosis would mean that wastes would stay in the body and water would leave.

In the kidney, some useful products are reabsorbed into the body – this would not be

possible with diffusion (active transport needed).

Osmosis without active reabsorption of water would result in excess water loss.

These problems are resolved by having a kidney that dumps everything ‘outside’ the body

and then selectively reabsorbs the still-useful material.

Distinguish between active and passive transport and relate these to processes occurring in the

mammalian kidney

Active transport uses energy to transport substances across a membrane it would normally

not be able to cross due to a diffusion gradient or its own properties.

Passive transport is the movement of substances across a membrane without energy

expenditure (this is diffusion and osmosis) – completely random.

In a mammalian kidney, water reabsorption is a passive process, whereas reabsorption of

salts is an active process.

Glucose and amino acids are also actively reabsorbed

Explain how the processes of filtration and reabsorption in the mammalian nephron regulate body

fluid composition

The functional unit of the kidney is the nephron. Each nephron has three main parts:

Bowman’s capsule, the glomerulus and a long, thin tubule.

Filtration occurs in the glomerulus, where blood pressure forces the movement of small

molecules from the bloodstream into the Bowman’s capsule (urea, glucose, amino acids,

salts and water). These form the glomerular filtrate.

Reabsorption occurs in the tubules (proximal, distal tubules and the Loop of Henle). It

involves both passive and active transport – whereby solutes required by the body are

moved back into the bloodstream via the capillary network (ALL glucose and amino acids,

SOME ions and water)

- Glucose and amino acid reabsorption takes mainly in the proximal tubule. At frist,

movement of glucose and amino acids is by facilitated diffusion (as the concentration is

higher in the glomerular filtrate than the bloodstream) but once the concentrations

become equal, active transport is utilised, until all glucose and amino acids are

eventually reabsorbed.

- Salt reabsorption occurs in the proximal, distal tubule and the loop of Henle (sodium,

chloride, potassium, calcium and hydrogen bicarbonate ions – HCO3-).

- Water is reabsorbed along the length of the tubule by the passive process of osmosis. As

the reabsorption of solutes occurs, osmotic pressure is altered and water flows out

passively together with the solutes.

Note this is for understanding; not part of syllabus:

Secretion involves the selective movement of further substances from the bloodstream

across the wall of the nephron into the filtrate by the process of active transport (some

drugs, hydrogen ions and toxin molecules). It occurs in the proximal and distal tubules and is

highly selective.

Excretion is where excess water and solutes are eliminated via collecting tubules in the form

of urine (passing into renal, pelvis, ureter and then bladder for storage).

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

of water and salt levels in blood

Antidiuretic hormone (ADH) or vasopressin is produced by the hypothalamus and stored by

the posterior pituitary gland. Osmoreceptor cells in the hypothalamus monitor water and

salt levels in the blood; when the water levels become too low, ADH is released – changing

the water permeability of collecting duct walls so that more water is reabsorbed into the

bloodstream from the ducts. It also increases the permeability of the duct walls to urea,

which diffuse in from the bloodstream. These two effects cause the urine concentration to

increase

Aldosterone is a hormone produced by the adrenal cortex in the adrenal gland when a

decrease in the concentration of sodium ions is detected. It increases the permeability of the

nephron to sodium, causing more reabsorption sodium ions, and consequently increased

reabsorption of chloride and water (which follows by osmosis) as they follow the sodium

ions. Thus there is more salt conservation within the body causing in a rise in blood volume

and pressure (and also a reduction of the salt concentration of urine).

Both ADH and Aldosterone help the kidney carry out its homeostatic functions of

osmoregulation:

- Regulation of solute concentration in blood – regulating the amount of sodium and

other ions that are reabsorbed or secreted in urine.

- Regulation of blood volume – maintaining a constant fluid volume by producing either

concentrated or dilute urine.

Aldosterone brings about conservation of salts in the body; ADH brings about water

conservation in the body.

Note that aldosterone conserves salt in the body but subsequently more water is reqbsorber

via osmosis.

So aldosterone also increases blood volume not just salts.

Define enantiostasis as the maintenance of metabolic and physiological functions in response to

variations in the environment and discuss its importance to estuarine organisms in maintaining

appropriate salt concentrations

Enantiostasis is the maintenance of metabolic and physiological functions in response to

variations in the environment.

It is important for organism living in estuarine environment where salinity varies greatly.

An estuary is where a river meets the sea, and freshwater mixes with saltwater.

From low tide to high tide, water can flow in from either the salty ocean, or from freshwater

rivers causing great variation in the levels of salt in the water.

Osmoregulators are organisms that avoid changes in their internal environment and

have the ability to keep the solutes at an optimal level (‘regulate’ solute concentrations

within the body), regardless of the differing external environment. This includes excreting

salts and concentrating urine.

Organisms living in such an environment need to have mechanisms to cope with such

changes in order to survive they are known as osmoconformers.

The mechanisms are all collectively called enantiostasis.

Many plants and marine invertebrates rely on enantiostsasis to survive, meaning that the

composition of their body fluids varies along with the environment.

Adjustments are made in their physiology, such as to keep enzymes functioning despite

changes in conditions or metabolic pathways so their needs are met.

Animals (like fish) can move to avoid changes (or shellfish opening and closing).

E.g. Eels have special cells in their gills that can act as salt absorbers and salt excretors.

Both homeostasis and enantiostasis are essential in maintaining the diversity of estuarine

ecosystems.

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

Mechanisms that minimise water loss:

Examples

Reducing the internal temperature

Eucalyptus trees and banksias have coarse, leathery leaves with a thick cuticle to reduce evaporation (from the epidermal cells) which would occur with thinner leaf cuticles.

Reducing exposure of leaves to the sun

Australian she-oaks have cladodes, which are green needle-like structures that are modified stems. Tiny brown scale leaves occur at regular intervals along the cladodes, a feature to reduce the SA of leaves and their exposure to the sun – thus minimising water loss.

Reducing difference in water The coastal banksia has epidermal hairs, which trap a moist

concentration between plant and outside air

layer of air – resulting in a smaller difference between concentration of water in the leaf tissue and water vapour in the layer of air trapped by the hairs.

Features related to water storage

The desert plant parakeelya has fleshy stems and leaves which swell up and retain moisture when it becomes available, so that during dry periods, it can survive by using up this moisture.

Gather, process and analyse information from secondary sources to compare the process of renal

dialysis with the function of the kidney

People with dysfunctional kidneys are not able to remove wastes such as urea and other

toxins.

They have to undergo renal dialysis to regulate their blood.

The process:

- The blood is extracted from the body from a vein (invasive) and passed into a dialyser,

which is a bundle of hollow fibres made of a partially permeable membrane.

- The dialyser is in a solution of dialysing fluid, which has similar concentrations of

substances as blood.

- The dialyser only allows wastes to pass through, and not blood cells and proteins. In this

way it is similar to the filtrations stage of the nephron.

- The wastes diffuse into the solution, and it is constantly replaced.

- The anti-clotting agent, heparin, is also added to prevent clotting.

- The blood is then returned to the body.

Comparison of dialysis and normal kidney function:

Present information to outline the general use of hormone replacement therapy in people who

cannot secrete aldosterone.

The adrenal cortex produces aldosterone.

Without aldosterone, the body would not be able to reabsorb salt (specifically sodium ions)

and this would cause severe dehydration, and excessive potassium.

Many functions are disrupted as a result of this aldosterone drop and can lead to death.

The replacement hormone is called fludrocortisone which can be used as a treatment for

people who cannot secrete aldosterone (due to the destruction of shrinking of the adrenal

cortex; Addison’s disease).

Fludrocortisone does the job of aldosterone.

Analyse information from secondary sources to compare and explain the differences in urine

concentration of terrestrial mammals, marine fish and freshwater fish

Freshwater Fish:

- Osmotic Problem: They are hypotonic to their environment. Water will tend to diffuse

INTO their bodies. Salts will diffuse out.

- Role of Kidney: Removes excess water. Produces large amounts of dilute urine. Kidneys

also reabsorb salts. They also rarely drink water.

- Urine: Large amount but dilute.

Marine Fish:

- Osmotic Problem: Hypertonic to environment. Water diffuses out. High salt levels

present in the water

- Role of Kidney: Continually drinks water. Kidneys reabsorb water, while actively

secreting salts. Small amounts of concentrated urine. Salt is also excreted across gills.

- Urine: Small, concentrated amount

Terrestrial Mammals:

- Osmotic Problem: Water needs to be conserved.

- Role of Kidney: Regulates concentration of blood, while at the same time excretes urea

and conserves water.

- Urine: Concentration changes with the availability of water, as well as temperature and

water loss through sweat. Water levels in blood rise, urine amount rises, and

concentration decreases and vice versa.

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

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

terrestrial mammals

Ammonia is the direct result of amino acid breakdown (deamination) and is a waste product

of all organisms. It is very water soluble, but VERY toxic, and must be removed quickly, or

changed to a less toxic form.

The removal of ammonia would require large volumes of water, and this is not possible for

animals or insects that seek to conserve water.

Aquatic Animals and Fish: These organisms directly release AMMONIA into the

environment. This uses a lot of water, but they have no need to conserve it. Ammonia is very

water soluble and is excreted through the gills.

Terrestrial Animals: Releasing ammonia would be impossible due to lack of water. Instead,

land-dwellers change ammonia into less toxic forms and release it periodically. Mammals

change it into UREA and release it as urine. (e.g. Kangaroos, wallabies, hopping mice, koalas,

etc.) Australian animals release very concentrated urine, and are able to tolerate high levels

of urea in their bodies.

Birds: Birds change ammonia into URIC ACID, a whitish paste which uses hardly any water.

This is lighter than using urea, and helps in flight.

Insects: Insects also change ammonia to URIC ACID (E.G. Acacia psyllids).

Process and analyse information form secondary sources and use available evidence to discuss

processes used by different plants for salt regulation in saline environments

Halophytes are plants that have adapted to saline environments.

They are commonly found in estuaries.

Examples:

- Grey Mangroves:

Salt Exclusion: Special glands in the mangroves can actively exclude the salt from the

water, so that the water absorbed has a lower salt concentration than the water in the

environment.

Salt Accumulation: Salt is accumulated in old leaves that drop off, so that the salt is out

of the plant’s system

Salt Excretion: Salt can be excreted from the underside of the leaves of the mangrove

plants; salt crystals form under the leaves.

- Saltbushes:

Salt Accumulation: This plant stores its excess salt in swollen leaf bases, which drop off,

ridding the plant of salt.

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

the conservation of water

Saltbush:

The saltbush has waxy leaves that reflect heat and light

Eucalyptus:

Waxy, hard leaves: Reduces water loss by reducing the rate of transpiration from the

leave surface.

The leaves hang vertically, and this reduces the water loss, conserving water.

Banksia:

Leaves have sunken stomates – this reduces transpiration.

Wattle:

Leaves are small and hairy – the small size means less evaporation of water, and the

hairy leaves reduce the transpiration by trapping water.