Module 1 Finished

Module 1-Maintaining Balance- 2010

Module 1:

Maintaining a balance-

Dotpoint 1:

Enzymes are biological catalysts which increase the rate of chemical reactions by

lowering the activation energy.

Metabolism refers to all the chemical reactions, occurring in living organisms.

Without enzymes metabolism would be to slow to maintain life.

Most enzymes are made up of proteins which are composed of long chains of amino

acids joined together by peptide bonds. These chains are called polypeptide chains.

Part of the enzyme molecule is called the active site which attaches to the reacting

molecules (substrate).

Enzymes are highly specific, this means that each enzyme acts only on one substrate.

E.g. the enzyme catalyse is present in liver and is used to react with hydrogen

peroxide, forming water and oxygen.

The lock and key model suggests that the substrate fits the enzymes active site like a

key fits a lock. It assumes that the enzyme has a rigid unchangeable shape.


An increase in temperature will increase and enzymes activity up to the optimum

temperature.

At high temperatures, the chemical bonds maintaining the 3 dimensional shape of

the enzyme are broken, the shape of the active site is permanently altered and no

longer fits the substrate. This process is called denaturing.

Enzymes work best at the optimum temperature. To low temperatures slows down

the rate of enzyme activity and to high temperatures denatures the enzyme.

pH is the measure of acidity or alkalinity of a solution. A pH less than 7 is acidic and

greater than 7 is basic.

Enzymes work best at and optimum ph. Any change from optimum ph will slow

down the activity of the enzymes and extreme changes in ph will denature the

enzyme.

An increase of substrate concentration will increase the rate of reaction until all the

enzymes active sites are occupied.

Enzymes are essential for proper metabolic function in an organism. Enzyme

efficiency is affected by the temperature, the pH and the substrate concentration. A

constant and stable internal environment is needed for optimum enzyme activity

and metabolism.

Homeostasis is the maintenance of a relatively constant and stable internal

environment.

Homeostasis is important because metabolic reactions require enzymes and

enzymes only function in a narrow range of conditions. Furthermore homeostasis

enables enzymes to catalyse reactions by maintaining a constant and stable internal

environment.

Homeostasis consists of two stages:

Detecting stages from stable state by receptors.

Counteracting changes from stable state brought about by effectors.

Role of nervous system in maintaining homeostasis:

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

and spinal nerves).Homeostasis involves both the CNS and the PNS.

E.g. When the body temperature increases it is detected by the thermo receptors in

the brain and the skin. The message is the taken from the sensory neurons to the

CNS into the brain (hypothalamus) which processes the information and decides on a

course of action. This message is the taken to the effectors by the motor neurons

which respond in vasodilatation and sweating which lowers the body temperature.


The function of the nervous system is coordination, it works to regulate and

maintain and organisms internal environment and respond to external changes.

1. Detects information about and organisms internal and external environment.

2. Transmits this information to a control centre.

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

homeostasis.

When a change affects the organisms normal state, the response is homeostatic.

This type of response will counteract the change, maintaining a stable state.

The CNS includes the brain and the spinal cord, it acts as a control centre to

coordinate all the organisms responses. It receives information, interprets it and

initiates a response.

The PNS is a series of nerves branching from receptors to effectors. These transmit

messages (nerve impulses) to and from the CNS.

The nervous system works with the endocrine system, which produces hormones in

response to certain stimuli.

Ambient temperature refers to the environmental temperature.

The range of temperatures over which life is found on earth is broad compared to

the narrow limits for individual species.

Organisms live in environments with ambient temperature ranging from less than

0c, e.g. bacteria in snow (-70c), to 100c e.g. bacteria in hot springs, to as high as

350c e.g. bacteria in undersea volcanic vents.

Mammals generally can only survive temperatures of about 0-45c.

When a response affects the original stimuli the stimulus response model is called a

feedback mechanism.


Ectotherm: Internal temperature fluctuates with ambient temperature.

Endotherm: Maintain a constant internal temperature by using their internal

metabolism to generate heat.

Example of Australian Ectotherm: Black snake-

Increase in ambient temperature:

The snake moves into a sheltered or shady spot.

It reduces day time activity and may become active in the evening.

Decreases in ambient temperature:

Shelters from cold and basks in sunlight when available.

It becomes less active; metabolism slows down and uses fat reserves.

Eg.2. Central Netted dragon-


Burrows or seeks shelter under rocks.

Change colour on back from dark to pale to reduce heat absorbed.


Bask in sunlight.

Change colour of back form pale to dark to absorb heat.

Example of Australian Endotherm: Red Kangaroo-


Pant and sweat as a cooling mechanism

Lick forearms so that the surface blood vessels will lose heat as the evaporation of saliva

takes heat from their body.

Inactivity, lie in the shade in the cooler exposed soil beneath a tree.


Shiver which causes muscles to generate more heat.

They also grow a thick layer of fur, closer to the skin.

They bath in sunlight, absorbing heat from the sun.

Eg.2. Bilby-


Large thin ears (large surface area to volume ratio) that lets heat escape from blood

vessels close to the skin.

Shelter in deep burrows away from heat.

Shelter during the day and active during the night.


Plant response to temperature change:

Eucalyptus: Eucalyptus leaves hang vertically. This reduces the surface area exposed

to the sun and reduces the water loss from the leaves.

The leaves are also covered by a thick waxy cuticle, this provides a shiny surface to

reflect the suns heat, and this also reduces transpiration.

Spinifex (porcupine grass): The porcupine grass leaves curl, so that the stomata are

enclosed in a tight area. This also reduces transpiration.

The upper epidermis is covered by a thick waxy cuticle; this provides a shiny surface

to reflect the suns heat, thus reducing transpiration.

The major function of the circulatory system is to transport water, gasses, nutrients

and waste. It is also involved in blood clotting and acts as a defence against disease.

The forms the following are carried in the blood in:

Oxygen: Oxygen combines with haemoglobin to form oxyhaemoglobin

Carbon dioxide:

70% as hydrogen carbonate ions

23% as carbaminohaemoglobin

7% is dissolved directly into the plasma

H20: water molecules

Salts: ions

Lipids: transported as chylomicron

Nitrogenous wastes: urea

Other products of digestion: mainly water soluble and are transported dissolved in

plasma

Adaptive advantages of haemoglobin:

Haemoglobin increases the oxygen carrying capacity of the blood by 100 times.

If oxygen was dissolved directly into the blood, 100 ml could only carry 0.2 ml of

oxygen. With haemoglobin the same amount can carry 20 ml of oxygen.

Increased oxygen levels provide mammals a considerable advantage as it enables

them to produce more energy, which can be used in growth or metabolic processes.

Haemoglobin is a globular protein made of 4 polypeptide chains each of which has

an iron/haem containing group at its centre.

Oxygen is essential for living cells for aerobic respiration. It also produces carbon

dioxide as a waste product.

Too much carbon dioxide is toxic to cells.

Carbon dioxide dissolves in water to form carbonic acid which lowers the ph of the

blood and this affects enzyme function hence disrupting metabolism.


Arteries:

Veins:

Capillaries:

Thick walled, elastic and muscular. The thick muscular walls withstand the high pressure of blood in arteries. The elastic fibres allow the arteries to expand and recoil with each heartbeat. This maintains the pressure of blood in the arteries.

Thinner walls. There is less muscle and elastic fibres because blood flows at very low pressure and no stretch is necessary.

Very thin walls to allow efficient diffusion of substances.

No valves Valves prevent the backflow of blood.

Are one cell thick

The relatively large lumen offers less resistance to the flow of blood

Blood flow slows down in the capillaries, small lumen forces red blood cells to pass through in single file, increasing the exposed surface area for gas exchange.


Changes in the composition of the blood as it moves around the body:

Pulmonary circuit (heart lungs heart)

The blood entering the lungs has high carbon dioxide concentration, low oxygen

concentration and high glucose concentration.

In the lungs oxygen and carbon dioxide are exchanged and glucose is used by respiring

cells.

The blood leaving the lungs is high in oxygen concentration, low in carbon dioxide

concentration and low in glucose concentration.

Systematic circuit (heart body heart)

Blood travelling to the body is high in oxygen and glucose concentration and low in

carbon dioxide and urea concentration.

The cells in the body use up the oxygen and glucose give out carbon dioxide and produce

urea as waste.

The blood leaving the body is high in carbon dioxide and urea concentration and low in

oxygen and glucose concentration.

Kidneys:

Blood is taken to the kidneys via the renal artery and it is high in oxygen, glucose and

urea concentration but low in carbon dioxide concentration.

In the kidneys oxygen and glucose are used by the respiring cells and urea is removed

from the blood.

The blood leaves the kidneys via the renal veins and is low in oxygen, Glucose and urea.

Intestines:

The blood going to the intestines is high in oxygen concentration but low in carbon

dioxide and glucose concentration.

In the intestines, blood collects the products of digestion such as amino acids, glucose

and fats.

The blood leaving the intestines is high in carbon dioxide and glucose but low in oxygen

concentration.

Liver:

Blood entering the liver is high in glucose but low in urea concentration.

The liver converts excess glucose into glycogen and excess amino acids into urea.

The blood leaving the liver is low in glucose and high in urea concentration.


Current technologies measuring oxygen and carbon dioxide concentration:

Pulse Oximeter: Non-invasive-

Measures the level of oxygen in blood and pulse.

Uses two wavelengths of light and the amount of absorption of light as the light passes

through the finger from the light source to the photo detector. A small clip with a sensor

is attached to the earlobe, toes or fingers of the patients and a cable connects the

sensor to the pulse oximeter. The colour of the blood changes due to the amount of

oxygen dissolved in it. Oxygenated blood is bright red, deoxygenated blood is dark red.

It is used when a non-invasive technique is needed or rapid continuous monitoring of

arterial blood is needed (e.g. to monitor premature babies, during anaesthesia or people

on ventilators, asthmatics)

If the oxygen level falls below 95% it may lead to cell death.

ABG (Arterial blood gas) analysis: Invasive (penetrates skin)-

ABG analysis is an invasive method (requires a blood samples) of measuring the oxygen

and carbon dioxide concentration in the blood, as well as the bicarbonate content of the

blood and the pH of the blood.

ABG analysis evaluates how effectively the lungs are delivering oxygen and removing

carbon dioxide

In the analyser the oxygen is measured in a cell using 2 electrodes while carbon dioxide

is also measured in a cell with 2 chambers one for the blood specimen and one for the

hydrogen electrode.

It is used in intensive care units, monitor people with respiratory diseases and people in

accidents and emergency facilities.

Donated blood: When blood is donated it can immediately be used as whole blood

or it can be separated into various components, including:

1. White blood cells: Used to combat infections. It is given to people with cancer of the

blood (leukaemia).

2. Platelets: Used for blood clotting. It is given to people with leukaemia and severe

bleeding cases.

3. Plasma: Also used for blood clotting. It is used to treat people with haemophilia and

severe bleeding cases.

4. Immunoglobins: Used to treat people who have difficulty fighting infections, or

whose immune systems are not working properly (aids sufferers).

5. Red blood cells: Used to increase haemoglobin levels in the blood without increasing

blood volume, used for people with anaemia.


Artificial blood: Reasons why research is important:

There is a shortage of donor blood; donor blood needs screening for diseases e.g.

mad cow disease.

Donor blood can only be stored for a few of weeks, artificial blood can be stored for

up to a year which is useful in emergencies, wars and underdeveloped countries.

Donor blood needs to be cross matched whereas artificial blood doesnt. This makes

it useful in emergencies.

Artificial blood can be sterilised, eliminating the possibility of infection from diseases

such as aids.

Perfluorocarbons/chemicals:

Synthetic, inert materials.

Can dissolve 50 times more oxygen than plasma

Cheap to produce

Free of biological material, no risk of infection.

Disadvantages /Reasons for future research for artificial blood:

It can only transport oxygen

It doesnt supply nutrients and hormones and there arent any substitutes for

immune defence or blood clotting yet.

XYLEM PHLOEM

What Is transported Water and dissolved minerals Sugars (Sucrose) and products of photosynthesis

In what direction are the substances transported

From roots to leaves, only in upwards direction

Any direction, from where sugar is produced to where energy is needed

Is energy required by the plant

No- Passive. The suns energy causes evaporation of water from the leaves

Yes- energy required to move materials against concentration gradient (loading and unloading)

What are the distinctive characteristics of the tissue

Dead cells- often reinforced with secondary thickening (thick lignin) Xylem always have larger cells

Living cells Sieve tube elements Companion cells to provide energy and keep sieve tubes alive

Main Processes Transpiration-cohesion-adhesion-tension mechanism

Pressure- Flow mechanism/translocation(occurs by source path sink mechanism)


Xylem:

Transpiration-cohesion-adhesion-tension mechanism accounts for the passive

movement of water up the xylem vessel. Evaporation from the stomates in the leaves

known as transpiration, draws water from the leaves of the plants creating a negative

tension in the xylem vessel causing water to move up to replace it. A continuous

transpiration stream is maintained due to the physical properties of water. Cohesion

refers to the attraction forces between water molecules which enables a continuous

stream of water to form. Adhesion refers to the attracting forces between the water

molecules and the walls of the xylem. Capillarity which is the tendency for water to

move unassisted to a certain height up narrow tubes. Thus the combined effects of the

transpiration stream, cohesion, adhesion and capillarity allows the water molecules to

move all the way form the roots to the leaves.


Phloem:

The movement of organic molecules (e.g. sugars and amino acids) by the phloem is

called translocation. This is thought to occur by the source-path-sink mechanism.

In this mechanism sugars are actively loaded form the source (e.g. leaf) into the

phloem sieve tube cells.

a) Symplastic loading: The organic materials move into the cytoplasm from the

mesophyll cells, to the sieve tubes through plasmodesmata.

b) Apoplastic loading: The organic materials move along the cell wall to the sieve tube.

They then cross the cell membrane by active transport.

As the sugars enter the phloem the concentration of the phloem sap increases, causing

the entry of water by osmosis form the surrounding cells. This increase the hydrostatic

pressure at the source end. This resulting pressure causes water and the dissolved

solutes to flow towards the sink (i.e. the sap moves passively).

One loaded at the source, the materials flow towards a sink. A sink is a region of the

plant where sugars and other nutrients are actively being removed from the

phloem(e.g. roots, stems, flowers storage areas of the plant. As the sugars are actively

taken out from the phloem, water flows out with them by osmosis. This reduces the

pressure in the sieve cells in the sink region.

This pressure difference between the source and sink ends of the phloem tubes drives

the phloem sap flow.

The direction of the flow depends on where the sink regions of the plant are operating.


The concentration of water in cells should be maintained within a narrow range for

optimal function.

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

Water is the solvent for metabolic reactions in living cells.

Living cells work best in an isotonic environment and any change in the

concentration of solutes will lead to cell death by dehydration or bursting.

Enzymes require specific conditions and the levels of water and solutes must be

maintained within a narrow range so metabolism can take place.

The removal of wastes is essential for continuous metabolic activity. Metabolic

wastes are toxic to cells and must be removed quickly. If not removed, their levels in

the body will increase and alter the internal environment, inhibiting enzyme

functions and preventing normal metabolic activity.

E.g. the build up of wastes such as urea is toxic to cells; therefore they must be

removed immediately.

An increase in nitrogenous wastes such as ammonia can cause an increase in the ph

of cells, resulting in them becoming more alkaline. Whereas an accumulation of

carbon dioxide lowers the ph, resulting in the internal environment to become more

acidic (carbon dioxide when dissolved in water becomes carbonic acid).

This change to the acidity or alkalinity of the cells slows down or inhibits enzyme

functioning in metabolism.

Why diffusion and osmosis are inadequate in removing nitrogenous wastes:

Diffusion and osmosis are both examples of passive transport (i.e. they do not require

energy as they occur along the concentration gradient)

Diffusion is non-specific and is too slow for the normal functioning of the body.

Furthermore not all wastes can be removed by diffusion. E.g. uric acid needs to be

removed against the concentration gradient.

Osmosis only deals with the movement of water and therefore it cannot move any

nitrogenous wastes.


A nephron is a regulatory unit of the kidney that is it absorbs and secretes

substances to maintain homeostasis and a constant body fluid composition.

This regulation maintains a constant composition of body fluids.

The three main processes involved in urine formation are filtration, reabsorbtion and

secretion.

Filtration occurs in the glomerulus which separates substances from the blood based on

their size. The high blood pressure in the glomerulus forces small molecules such as

urea, water, glucose and amino acids out of the blood into the Bowmans capsule.

The composition of the glomerulus filtrate is adjusted as it flows along the nephron.

As the blood flows along the remainder of the nephron, substances that the body needs

(glucose and amino acids etc) are reabsorbed from the filtrate in the bloodstream

furthermore water and salts are also reabsorbed throughout the nephron as osmotic

balance is vital for normal cell and enzyme functioning .

Additional wastes that may still be in the bloodstream (urea) are secreted into the fluid,

which later on leaves the body as urine.

The processes of filtration and reabsorbtion are able to regulate the body fluid

composition by getting rid of waste products such as urea, excess salts and water and

the reabsorbtion of useful substances back into the blood stream.

However if body fluid composition was not regulated, metabolic and physiological

functions would cease to function effectively due to chemical and water imbalance.

Active and passive transport in the kidney:

Active transport involves the expenditure of energy against a concentration gradient.

Passive transport involves no expenditure of energy, along a concentration gradient.

In the mammalian kidney both active and passive transport occur.

Passive transport occurs in the glomerulus during filtration and osmosis (reabsorbtion)

of water back into the blood.

However active transport is needed for the removal of nitrogenous wastes, some

substances must be reabsorbed against the concentration gradient. This requires energy

and is therefore active transport.


Kidney function: Renal dialysis:

Differences:

A natural body process (natural

membrane).

An artificial process to replace damaged

kidneys (artificial membrane-dialysis

tubing).

Removes wastes continuously.

Involves both passive and active

transport.

Only involves passive transport.

Involves filtration, reabsorbtion and

secretion.

Only involves filtration.

Performed by two fist-sized organs.

Performed by a large machine

controlled by computers and other

equipment.

Similarities: Both remove nitrogenous wastes e.g. urea.

Both processes use a semi-permeable membrane.

The role of the kidney in the excretory system of fish and mammals:

The kidney is an organ of the excretory system in both fish and mammals.

It plays an important role in homeostasis forming and excreting urine while regulating

salt and water balance in the blood. It maintains a precise balance between waste

disposal and the animals need for water and salt.

In mammals the kidneys function is to remove or excrete nitrogenous wastes as well as

maintain osmoregulation (water and salt balance).

In fish, kidneys mainly serve to maintain water and salt balance. Nitrogenous wastes

such as ammonia are excreted by the gills.

The role of kidneys in fish is dependent on their environment

In marine (salt water) environments, the kidneys excrete small amounts of concentrated

urine, which helps conserve water and excrete excess salts which they gain from their

environment.

In freshwater fish, the kidneys work continuously to excrete large amounts of dilute

urine, which has very low salt concentration. This helps remove excess water gained

from the environment.


The difference in urine between different organisms including terrestrial mammals,

freshwater fish, saltwater fish and insects:

The urine composition varies between animals and is dependent mostly on the

environment that the organisms occupy.

In terrestrial mammals, the urine concentration and volume varies according to the

organisms needs.

It can be more concentrated than the blood and for mammals that live in the desert;

they produce small amounts of concentrated urine, to conserve water.

Freshwater fish have a well developed glomerulus for filtration. The concentration of

body solutes is higher than that of the environment. As a result water moves inside the

body and they need to get rid of this excess water. Therefore they produce large

amounts of dilute urine.

Salt water fish live in an environment where the solute concentration is much higher

than that of their body, as a result water tends to move out of their body and in order to

conserve water marine fish produce small amounts of concentrated urine.

Insects have solved the problem of conserving water and excreting excess nitrogen, by

excreting uric acid. If uric acid is excreted almost no water is lost.

Uric acid is excreted through special tubules (malpighian tubules) or uric acid crystals are

deposited in various parts of the body.

E.g. the white scales on the wings of some butterflies are uric acid deposits.

Desert mammals provide good examples of how terrestrial mammals overcome the

problem of conserving water and excreting nitrogenous wastes.

Red kangaroo: the kidneys produce highly concentrated urine (urea).

Mulgara: small carnivorous mammal (dasyurid). The mulgara doesnt drink; the large

amounts of urea produces by a carnivorous diet are excreted in highly concentrated

urine.

Murid hopping mouse: lives on dry seeds with no drinking water and has the greatest

ability to concentrate urine.

Ammonia: is produced by fish and is the most toxic and the most soluble hence it

requires a large amount of water to be excreted and this is only possible in aquatic

organisms. It is very toxic and must be removed immediately. It requires a small

amount of energy to be produced.

Urea: is less toxic and soluble that ammonia and is produced by mammals.

Uric acid: is the least toxic and the least soluble and almost no water is lost however

requires large amounts of energy to produce. It is produced by insects, birds reptiles

and land snails.


Aldosterone is a steroid hormone produced by the adrenal cortex.

Its function is to regulate the transfer of sodium and potassium in the kidneys.

Aldosterone is secreted in response to lower sodium levels in the blood. It causes the

Loop of Henley, Distal tubule and the Collecting duct to reabsorb more sodium ions

which in turn decreases potassium levels. Water follows by osmosis resulting in the

homeostatic balance of blood pressure (causes a rise in blood pressure and volume).

When sodium levels increase aldosterone stops being released.

Anti-diuretic hormone (ADH) also called vasopressin controls the reabsorbtion of

water in the nephrons (distal tubule and collecting duct).

When the level of fluid in the blood drops, the hypothalamus stimulates the pituary

gland to release ADH. This increases the permeability of the collecting ducts and the

distal tubule to water, allowing more water to be absorbed into the blood resulting

in concentrated urine.

When the level of fluid is high osmoreceptors in the brain cause the hypothalamus to

reduce the production of ADH, decreasing the amount of water reabsorbed in the

blood resulting in large quantities of dilute urine.

Aldosterone is released in response to low sodium level in the blood. While ADH is

released in response to low level of fluid concentration in the blood.

Hypoaldosteronism is the condition where people fail to secrete aldosterone. This

results in Addisons disease which is caused by the shrinking or destruction of the

adrenal cortex. If the body cannot secrete aldosterone water and salt balance cannot

be maintained. When this balance is upset blood volume drops and blood pressure

drops also. The replacement hormone is called fludrocortisone.

However the hormone replacement thereapy needs to be carefully monitored in

order to prevent fluid retention and high blood pressure.

Salt bush:

Actively transports excess salts into bladder cells on the tip of leaves. These bladder

cells then burst releasing salts into environment.


Grey mangroves use the following mechanisms to maintain salt concentration:

Secretion: excess salt is concentrated in the leaves by salt glands from where it is

either washed away by rain or blown away by wind.

Exclusion: special tissues in roots prevent salt from entering while letting water in

Accumulation: Excess salt accumulates in older leaves which then fall off.

River red gum (Eucalyptus):

The tree sends down extremely long roots so that they only grow where there is a

reliable source of water, in the deep soil.

Eucalyptus leaves hang vertically which means there is little surface area exposed to

the midday sun. This reduces the amount of heat absorbed by each leaf and reduces

water loss from the leaves.

The leaves are also covered by a thick waxy cuticle. This gives the leaf a shiny

surface to reflect the suns heat, this also reduces transpiration.

Spinifex (porcupine) grass:

The leaves curl around the under surface, into a needle shape so that the stomata,

which are predominantly on the under surface, are enclosed in a tight area. This

reduces the ability of water vapour to leave the area and thus reduces transpiration.

The stomata are located in sunken grooves, which further reduce transpiration.

The upper epidermis is covered with a waxy cuticle. This limits the ability of water to

diffuse out and also provides a shiny surface to reflect the suns heat. Hence

overheating is reduced in the leaf, which in turn reduces transpiration.

Plants that live in dry areas are known as xerophytes.


Define enantiostasis:

Enantiostasis is the maintenance of metabolic and physiological function in response

to variations in the environment.

Describe the environment of estuarine organisms:

One of the most extreme environments for living things is the estuary.

Organisms are bathes in freshwater during flood and saltwater at high tide.

Therefore the salt level is always changing.

Many organisms are left high and dry at low tide, exposed to the drying sun and

oxygen, while needing gills at high tide.

The current also varies between strong and nil.

If salt and water levels arent maintained within an organism. Organisms need

mechanisms to survive such changes and these mechanisms are called enantiostasis.

Describe using examples of osmoconformers:

Osmoconformers maintain the concentration of their internal fluids at approximately

the same level as the external environment.

E.g. estuarine (fiddler) crabs and sharks use small organic molecules to vary their

cellular solute concentration to match their environment. They alter the

concentration of these chemicals so that the osmotic pressure in their internal

environment is the same as the external environment. When in salt water they

accumulate solutes into their bodies and in freshwater they pump out.

Explain how Osmoconformers differ from Osmoregulators:

Osmoconformers modify the salt concentration in their body to match fluctuations

in external conditions. Whereas Osmoregulators maintain a constant salt

concentration in their bodies, despite environment fluctuations. E.g. Mussels and

Salmon are osmoregulators.

If salt water concentration falls mussels close their valves and keep a salt

concentration close to that of seawater within their mantle cavity (shells). Thus they

maintain a small habitat of seawater around their bones.

Give a point against enantiostasis:

Organisms need to spend large amounts of energy in order to carry out

enantiostasis.

Explain how enantiostasis could have arisen from natural selection:

It is possible to hypothesise that an ancestral population of estuarine organisms

were restricted to the fringes of the estuarine habitat, that didnt exhibit large

fluctuations in salt concentration.

It is possible that some members of the population were not effective

osmoregulators and that their osmotic pressure varied with the salt concentration.

They survived to reproduce more often, eventually leading to the development of a

population of osmoconformers.


Common verbs used in examinations: Account: Give reason for.

Assess: Determine the value or quality.

Compare: Similarities and differences.

Discuss: For and against.

Evaluate: Make a judgement.

Explain: Cause and effect.

Justify: Give reason in support of.

Types of Graphs-

1. Line graphs-

Are used when both variables are continuous. They are useful for showing how

changing one variable (e.g. light intensity) affects another (e.g. rate of

photosynthesis)

2. Column graphs-

Should be used when the data is discrete and is grouped into separate categories

(e.g. car colour)

3. Histograms-

Should be used with data grouped into class sized intervals rather than data sorted

into discrete categories (e.g. height in humans [100-120]...)

Documents

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