maintaining a balance notes

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HSC Biology Nov 2014

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Identify the Role of Enzymes in Metabolism, describe their chemical

composition use a simple model to describe their specificity on substrates

Role of enzymes in metabolism

- Metabolism: all the chemical reactions that occur within an organism

- Enzymes: biological catalysts which increase rate of chemical reactions but remainunchanged throughout entire reaction

- Without enzymes, metabolism would occur at a rate to slow to support life

- Enzymes assist metabolism by increasing reaction rate of formation, breaking downand exchanging of molecules

Chemical Composition of Enzymes

- Enzyme: protein molecule made up of long chained amino acids, joined by peptidebonds forming a polypeptide chain

- The shape of the enzyme is determined by its role and the reaction it controls

- In enzymes the polypeptide chain is folded into a 3D globular shape

- The active site is the area of the enzyme that binds to the substrate (molecules)

Specificity on Enzymes

- Enzymes are highly specific in action: each enzyme acts on one substrate only

- The shape of the active site matches the shape of the substrate material

Models to explain specificity:

- The Lock and Key Model: suggests the substrate fits exactly into the active site ofenzyme like a key/lock. It assumes that enzyme had a rigid and unchanging shape.

- Induced Fit Model: binding substrate to enzyme ‘induces’ a temporary change inshape of enzyme. New enzyme shape accommodates substrate: reaction occurs.

Lowering of activation energy

- Enzymes don’t produce activation energy they reduce amount of activation energy

- Lower activation energy to start a reaction so that reaction can proceed quicklywithout change in temperature

Example of enzyme (Sucrase)

- Sucrose: Obtained by crushing out contents of phloem tissue of sugarcane plants

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- Carb consists of 2 simpler sugar molecules: 1 glucose & 1 fructose molecule

- Sucrose- too large to be absorbed into the bloodstream from digestive system

- Molecules of glucose and fructose are small enough to be directly absorbedthrough the membranes of the digestive system into the blood stream

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

- pH is a scale which indicates the dissolved H+ concentration in a substance on ascale of 0-14

- As a result we are able to identify whether the substance is acidic (pH<7), basic(pH>7) or neutral (pH=7)

- The higher the concentration of hydrogen ions the lower the pH and vice versa

Explain why the maintenance of a constant internal environment is important foroptimal metabolic efficiency

- Metabolic efficiency relies heavily upon the optimal operation of enzymes

- However a range of factors inhibit this such as pH, Temperature and SubstrateConcentration

- It is known most enzymes can only work efficiently under a small range ofconditions

- This work of enzymes at optimal capacity is essential to maintain optimummetabolic efficiency

- It ensures that external changes do not affect entire metabolic pathways producingessential compounds. E.g. haemoglobin

- The enzyme catalase found in yeast has an optimum temperature of 35OC

- If conditions for optimal activity aren’t met (excess heat), enzyme is known todenature, where the shape of the active site is destroyed, preventing activity

Describe homeostasis as the process by which organisms maintain a relativelystable internal environment

- Homeostasis: process where organisms maintain a relatively stable internalenvironment in response to changes in the internal and/or external env.

- Meets enzyme's optimal conditions, allows efficient body work efficiently and keptas stable as possible.

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- System monitors all activities of cells, requirements and wastes they produce

- Keeps conditions as close to the optimum as possible so that the organism’smetabolism can operate as efficiently as possible

- Through homeostasis, organism maintain an internal equilibrium (stableness) byadjusting physiological processes through the use of feedback systems

- Feedback systems are a self regulating mechanism & maintain homeostasis

- Role: maintain conditions and reaction within the small range to sustain life Consists of 3 main parts: 1. Receptor- monitors/detects changes in the internal and external environment 2. Control centre (hypothalamus)- monitors information passed from the receptorand determines and appropriate response. 3. Effectors- carries a message from the control centre

Counteracting changes from the stable state

- After the receptor detects the change, it will respond by counteracting the changeto ensure a stable environment is attained and maintained

- An effector receives the message from the control centre that an undesirablechange must be counteracted, and causes a response to counteract the changeand maintain a stable state (negative feedback)

- E.g muscles that cause movement, or glands that secrete a chemical substance

Explain that homeostasis consists of two stages: (1. Decting Changes fromStable state) (2. Counteracting changes from Stable state)

Detecting Changes:

- The body needs to maintain a ‘stable state’ in order to function properly

- Changes, or deviations, from the stable state are caused by the external and

internal environment

- Any change, or information, that provokes a response is called a STIMULUS

- RECEPTORS detect stimuli; organisms then react to the change

- 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

Counteracting Changes

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- After receptors detect changes, organisms can then react to the change

- This type of response will counteract the change to ensure the stable state is

maintained

- EFFECTORS bring about responses to stimuli

- Effectors can either be muscles or glands:

• Muscles bring about change by movement

• Glands bring about change by secreting chemical substances

Outline the role of the nervous system in detecting and responding toenvironmental changes

- The nervous system: regulates & maintains animal’s internal environment inresponse to a change in the internal and/or external environment

- The nervous system consists of 2 parts: Central Nervous System (PNS) and thePeripheral Nervous System (PNS)

- The CNS: brain, spinal cord and retina. It acts as the control centre for all thebody’s responses. It receives information, interprets it and initiates a response

- The PNS: branching system of nerves that connect receptors and effectors. Theseacts as communication channels and pass messages rapidly to the CNS and back

- The stimulus response pathway occurs as follows

1. Special endings on sensory nerves in the PNS, e.g heat sensors detect stimulisuch as changes in heat, pressure or chemical condition

2. Receptors relay messages that are processed within the CNS

3. Response is formulated & message is relayed to effector. Organs/muscles respond

Identify the broad range of temperatures over which life is found compared withthe narrow limits for individual species

- Ambient Temperature refers to the temperature of the external environment

- Ambient temperature at particular areas varies daily, monthly and seasonally andthe range of ambient temperatures over the world is very large

- Life is found in this great range of ambient temperatures

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- Life can be found in a range of -70OC to 100OC (e.g. bacteria in snow, bolingsprings and undersea vents)

- While this range of ambient temperatures in which life is found is very broad, the

range of ambient temperatures in individual organism survival is very small

- E.g. Sugar Cane needs warm environment so grows in tropical/sub-tropical regions

- Mammals are generally found in an ambient temperature range of 0OC to 45 OC

Identify some responses of plants to temperature change

- Desert plants e.g Spinifex have a reduced surface area enables reduced waterloss and provide a smaller area for solar absorption

- Have shiny/hairy leaves that reflect solar radiation & reduce heat absorption

- Curling Leaves occurs in increased temps, reducing surface area exposed to sunlight. This minimises heat absorption & water loss through evap at leaf surface

- Plants e.g Eucalypts open their stomata in early morning but close them nearmidday as temperature rises to prevent water loss through evap. and transpiration

- Leaves on plants in hot dry area hang vertically to reduce their surface areaexposed to sunlight. In cold shady areas, leaves from plants have a maximumsurface area exposed to the sun

Responses to cold:

- Vernalisation: plants e.g daffodils require exposure to cold conditionsbefore they will develop flowers

- Plants may leave dormant seeds & alter growth rate; in tropical regions growth maycease below 15 degrees

- Frost-tolerant leaves

- In low temperatures, ice forms in spaces outside living cells. The inside of the celldoesn’t freeze because concentration of ions in the cytosol is greater.

- Because water concentration is decreasing outside cells (as ice produces), watermoves out by osmosis, increasing cytosol concentration, and lowering freezingpoint inside cells even further. Pliable cell membranes prevent cell rupture.

Compare responses of named Australian ectothermic and endothermicorganisms to changes in the ambient temperature and explain how these

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Identify data sources, plan, choose equipment or resources and perform afirst-hand investigation to test the effect of:increased temperature | change in pH | change in substrate concentration

on the activity of named enzyme(s)

1. Changing pH:

- Many enzymes work best at a pH that is just slightly alkaline

- Decreasing or increasing acidity from the optimum (the best possible) pH reducesthe activity of an enzyme.

- Enzymes change shape and are denatured (take away natural qualities) when thepH varies too much from their optimum

- Any change in pH above or below the Optimum will quickly cause a decrease in therate of reaction, since more of the enzyme molecules will have Active Sites whoseshapes are not, or at least less, Complementary to the shape of their Substrate.

- Small changes in pH above or below the Optimum do not cause a permanentchange to the enzyme, since the bonds can be reformed but extreme changes are

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irreversible.

2. Changing temperature

- Decreasing temperature = decreases activity of an enzyme & molecules have lowerenergy

- Increasing temperature = increased activity until shape of the enzyme begins to alter

- If the temperature is high enough to permanently change the enzyme’s shape thenthe enzyme is denatured and can no longer catalyse the reaction

- Human optimum temp- 35-40’c

- Enzymes that are partially denatured by heat may regain their correct shape

on cooling but complete denaturation is irreversible

3. Changing substrate concentration

- Decreasing the concentration of substrate decreases the activity of an enzyme

- Increasing concentration of substrate = increased activity until all enzyme is involvedin catalysing reactions

- If substrate concentration increases, enzyme concentration stays the same & rate of

reaction increases to a point and remains constant —> caused by active sites on theenzyme molecule being occupied —> known as the saturation point.

- Increase in substrate molecules doesn’t increase rate of reaction —> causes noactive sites available.

- Cofactors: inorganic chemicals that help catalyse, by binding tightly to the enzyme’sactive site as permanent residents or bonding loosely alone with the substrate

- Coenzymes- perform same function but are organic molecules

- Enzyme inhibitors: chemicals that inhibit the action of specific enzymes, by attachingto the active site/changing its shape.

1.2.2 Gather, process and analyse information from secondary sources and useavailable evidence to develop a model of a feedback mechanism

- Homeostasis involves the detection of the change in the environment and theresponse to that change to maintain a stable internal environment

- The mechanism that brings about this change is called a feedback mechanism. Infeedback systems, the response alters the stimulus

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- In Endotherms a constant internal temperature of 36.1OC to 37.8OC is maintained byan inbuilt thermostat called the hypothalamus

- Its role is to regulate the internal temperature by detecting and responding to

changes in the stable state caused by stimuli

- Thermoreceptors within the skin inform the hypothalamus of changes in the internaland external temperature

- The hypothalamus can then respond to an increase in temperatures by sendingmessages through the PNS and activating cooling mechanisms such as vasodilation( blood vessels dilate, moving closer to the skin surface allowing heat to escape),sweating and panting

- The hypothalamus can then respond to a decrease in the internal temperature by

directing the PNS to activate heating mechanisms such as increased muscle activity(shivering), vasoconstriction (constricts blood vessels, reducing heat loss tosurrounding areas).

- The involvement of the hypothalamus and PNS in dealing with temperature regulationis an example of a negative feedback mechanism

Identify form(s) in which each of following is carried in mammalian blood: carbondioxide, oxygen, water, salts, lipids, nitrogenous waste/other products ofdigestion

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Explain the adaptive advantage of haemoglobin

- Haemoglobin is protein and a respiratory pigment carrying oxygen needed forrespiration. Globule-shaped protein containing four polypeptide sub-units

- Oxygen fuses with haemoglobin where concentration of oxygen in blood is low;

lungs. It makes an unstable compound – oxyhaemoglobin and where oxygen is

needed, oxygen bond easily breaks and the oxygen is used.

- If blood carried oxygen without haemoglobin, the oxygen would have to be dissolved

directly into the plasma (into water). However, oxygen is not very soluble in water

- Presence of haemoglobin increases oxygen carrying capacity of blood by 100 times

- Dissolved oxygen results in 0.2 ml oxygen being carried per 100 ml blood, whereas

the presence of haemoglobin results in 20 ml oxygen being carried per 100 ml blood

- This ability of blood to carry large quantities of oxygen gives mammals a survival

advantage because mammalian cells need a lot of energy and therefore must have a

continual supply of OXYGEN for CELLULAR RESPIRATION

- Organisms with blood (containing haemoglobin) are able to deliver oxygen to cellsmore efficiently than other organisms with blood that has no haemoglobin.

- The net effect is that these organisms are more effective operators in a given

environment than their competitors.

- This higher rate of respiration allows an increase in amount of released energy which

allows the animal to: move faster, grow large, live in cold areas and give mammals

the ability to maintain a constant body temperature enabling them to be active in a

large temperature range for example.

- The structure of haemoglobin is also an adaptive advantage because it is a type of

molecule that can combine with oxygen loosely at the respiratory surfaces and then

release the oxygen freely in capillaries.

- The extra energy allows mammals to be active, as well as grow large.

NOTE: Cellular respiration is the conversion of stored energy into usable energy

• Glucose combines with oxygen to produce ATP (useable energy)

• The waste gas and by product is carbon dioxide

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• Equation: Glucose + oxygen " CO2 + Water + energy (ATP)

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

ARTERIES:

- Carry blood away from heart (high blood pressure)

- The pressure created by the heart’s pumping creates great stress in the arteries

- This is why the arteries are thick walled, elastic and muscular .

- The arteries are not motionless; they have muscle fibres in them which can contract

and relax.

- This contracting maintains the pressure on the blood, so that the blood travels inspurts towards the body tissues (the contracting and relaxing also creates the pulseon your wrist or neck).

- The muscle fibres of the arteries also maintain the rate of the flow of blood.

- Arteries usually carry oxygenated blood

- Arteries lead to arterioles (small arteries).

CAPILLARIES:

- Capillaries are an extension of the inner layers of the arteries and veins

- They join arterioles and venules (small veins)

- Capillaries are only one cell thick, and are so narrow, that only one red blood cell canpass at a time.

- Capillaries surround all tissue cells

- Thus, they provide a very large surface area over which exchange of materialsbetween blood and body can occur.

VEINS:

- Veins carry blood back to the heart

- The capillaries join to form venules, which join to form veins

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- Veins are not under a lot of stress - blood pressure is low

- This is why they have thinner walls than arteries, less muscle and a wider diameter.

2.1.4 Describe the main changes in the chemical composition of the blood as itmoves around the body and identify tissues in which these changes occur

Pulmonary circuit:

- It is mainly composed of the lungs and the heart.

- Blood enters the right atrium of the heart via the vena cava:

- The blood is deoxygenated, and high in carbon dioxide

- It is low in glucose and other nutrients; it is also high in urea, other nitrogenouswastes and various poisons.

- As the heart beats, the right ventricle pumps the blood through the pulmonary artery,to the lungs:

- Here the blood gains oxygen, and loses its carbon dioxide.

- The blood then enters the left atrium via the pulmonary vein.

SYSTEMIC CIRCUIT (Body):

- The left ventricle pumps oxygenated blood to the body through the aorta.

- In the body, various changes occur to the blood. The blood loses oxygen and gains

carbon dioxide in all body cells, as respiration occurs. Glucose levels also drop.

# LIVER:

- Levels of glucose are regulated – excess glucose is changed to glycogen, or

glycogen stores are changed to glucose (if needed)

- Excess amino acids are changed to ammonia, and then to urea

- Poisons are also reduced, as the liver changes them to less toxic forms

# In the INTESTINES:

- Levels of nutrients from digestion increase.

- Glucose, amino acids, ions, lipids and other substances from food enter the

blood. The increase is through the small intestines reabsorption of food

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# In the KIDNEYS:

- Salt and water levels are regulated

- All urea is removed, toxins are excreted into the urine

# Changed blood, again highly deoxygenated, flows back to pulmonary circuit.

Outline the need for oxygen in living cells and explain why the

removal of carbon dioxide from cells is essential:

– All living cells need oxygen for respiration.

– As a result of respiration, carbon dioxide is produced and when dissolved in

water, it makes carbonic acid.

– Carbonic acid makes the body cells (& the blood) acidic which increases

breathing

– This means that if a lot of carbon dioxide is produced, the body cells (and the

blood and lymph) will become acidic.

– As studied before, enzymes can only function within a specific pH range

– So an increase in carbon dioxide will result in a lowering of pH, which will affect

the overall metabolism of the body.

Describe current theories about processes responsible for the movement of

materials through plants in xylem and phloem tissue:

XYLEM:

- Transport of water is passive and depends on transpiration and the physical

properties of water:

• Transpiration: Evaporation of water from the leaf cells through the stomates

initiates the pull of the TRANSPIRATON STREAM. Water is then drawn up the

xylem tubes to replace this loss. The low concentration of water at the roots

allows diffusion of water in.

• Cohesion: Water molecules tend to bind together, forming a continuous

column in the xylem, which replaces any loss

• Adhesion: Water molecules stick to the sides of the xylem tubes (cellulose

walls), pulling the water up the tubes.

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- The movement of water through narrow tubes is called CAPILLARITY

- It is caused by the two forces of COHESION and ADHESION

PHLOEM:

- Movement of organic molecules, e.g sugars, in the phloem is called translocation

- Materials are transported both up and down the stem to the growing points &

reproductive structures

- Flow of materials in the phloem is an active process that requires energy

- It is thought to occur by a mechanism called the source-path-sink THEORY:

- Plants have sources of nutrients, e.g. leaf cells are sources of glucose. As glucose

builds up, cells transport glucose by active transport into phloem tubes, 2 ways:

• SYMPLASTIC LOADING: Sugars and nutrients move in the cytoplasm from

the mesophyll cells to the sieve elements through plasmodesmata joining

adjacent cells

• APOPLASTIC LOADING: Sugar and nutrients move along the cell walls to

the sieve tube. Then they cross the cell membrane by active transport.

- As sugars enter the phloem the concentration of phloem sap increases.

- This causes the entry of water by osmosis from the surrounding cells.

- This resulting pressure causes water and dissolved solutes to flow towards a SINK.

• A sink is a region of plant where sugars and other nutrients are actively removed

from the phloem. As sugars move out of the phloem, water flows out with them.

• This reduces the pressure in the sieve cells at the sink region.

Explain why the concentration of water in cells should be maintained within anarrow range for optimal function

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

- Essential that the concentration of water in cells is kept constant as even smallincreases or decreases can lead to death.

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- Water —> solvent of all metabolic reactions in living cells, and sometimes directlytakes part in it (eg. Respiration).

- It is a solvent in which all metabolic reactions take place.

- It is a transport medium for sugars, salts, hormones, wastes.

- The concentration must be kept within a narrow range as the amount of wateraffects the concentration of solutes, which affects ability to diffuse in & out of cells.

- Lack of water causes dehydration.

- Blood pressure falls and circulation fails.

- It can absorb and release large amounts of heat and requires a large amount of heatto vaporize, and therefore plays an important role in regulating temperature.

- It maintains the shape of the cell membrane – too much water can cause a cell toburst and it cushions and protects body organs

- The osmotic pressure of living tissue can also affect the pH in cells - e.g little waterleads to increase in concentration of solutes e.g C02. This lowers pH. Both osmoticpressure and pH must be maintained within a narrow range so that enzymes canfunction under optimal conditions, to allow effective metabolism.

RECALL:

- Isotonic : Concentration of solutes outside the cell is the same as inside the cell. Nooverall movement of water.

- Hypertonic : Concentration of solutes is greater outside the cell than inside. Watertends to move out of the cell.

- Hypotonic : Concentration of solutes is greater inside the cell than out. Water tendsto move inside the cell.

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

- Any accumulation of wastes may be toxic to cells and so metabolic wastes must beremoved from the body to maintain homeostasis.

- If wastes not continuously removed, levels in body will increase & alter conditions ininternal environment. This inhibits enzyme function & prevents cells from normalmetabolic activity.

- Examples are:

• The build-up of nitrogenous wastes such as ammonia, which causes an increasein pH in cells, resulting in them becoming more alkaline, affecting enzyme activity

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• Carbon dioxide accumulation, which lowers pH, resulting in internal env.becoming more acidic. These changes to acidity or alkalinity of cells slow downor inhibit enzyme functioning in metabolism. Accumulation of wastes that don’talter pH may cause other problems—increased solute conc. interfere with

reaction rates & an osmotic imbalance adversely affects membrane functioning.- Urea —> not as toxic as ammonia but can soon build up to toxic levels in the blood,

poisoning the cells and retarding metabolism

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

- Primary role of kidney: osmoregulation (regulation of salt & water levels in the body)

- Fish excrete nitrogenous wastes through gills. Urine contains excess water & salts

- Mammals’ urine contains urea as well as water and salts. The kidneys ensure that the

concentration of blood and interstitial fluid is constant

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

dissolved nitrogenous wastes inn some organisms

- Diffusion/Osmosis are e.g of passive transport, rely on random movement of

molecules.

- Diffusion: too slow for normal functioning of body and isn’t able to selectively

reabsorb useful solutes.

- Osmosis: only deals with movement of water and thus would only allow water to

move out of the body, not the nitrogenous wastes

- In the kidney, some useful products are reabsorbed into the body, which would not

be possible with diffusion because active transport needed

- Osmosis, without active reabsorption of water, would result in excess water loss

- The kidney functions by excreting all the blood substances in the nephron ‘outside’

the body and then selectively (actively) reabsorbing useful materials.

- Solution: Active transport which requires energy, quicker & more effective " moves

wastes as ions are moved against a concentration gradient

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Distinguish between active and passive transport and relate these to processesoccurring in the mammalian kidney

- Active transport uses energy to transport substances across a membrane. It wouldnot be able to cross due to a diffusion gradient or its own properties

- Passive transport: movement of substances across membrane without energy (this is

diffusion and osmosis).

- Kidney: made up of a million nephrons. Within nephrons, processes of filtration,

reabsorption & secretion occur.

- The STRUCTURE of a nephron:

- A nephron is a long twisted tubule made up of sections: a Bowman’s capsule,connected to (1) a proximal tubule, leading to the (2) loop of Henle, which connects

to (3) the distal tubule. This all joins to the collecting duct which leads to the bladder.

- The nephrons are densely surrounded by capillaries (this is to provide a large surface

area for excretion).

Three processes occur in the nephrons (kidneys):

• Filtration: Most water & solutes are forcefully filtered out of blood into Bowman’s

Capsule as blood pressure is high. Blood cells & large proteins remain in blood.

• Reabsorption: Materials required by body, such as glucose, are reabsorbed into

the blood. Water and salts also selectively reabsorbed to restore water balance.

• Secretion: body actively transports substances from blood into nephron. Toxins,

e.g urea, tend to diffuse back into blood, so must be secreted back into nephron.

Secretion regulates salt and water levels again & removes additional toxins.

Explain how the processes of filtration and reabsorption in the mammalian

nephron regulate body fluid composition

- Nephron: regulatory unit & absorbs or secretes substances in order to maintain

homeostasis. This regulation maintains the constant composition of body fluids.

• Salts & water are adjusted to maintain fluid concentration

• Different ions also adjusted to maintain pH.

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These different processes happen in the different sections of the nephron:

Proximal Tubule:

- Bicarbonate ions are reabsorbed into the capillaries into the blood from the nephron,hydrogen ions are secreted out which maintains the pH of the blood.

- Drugs, such as aspirin, are secreted out of the blood

- Regulation of salts occurs here - Sodium ions & potassium ions are actively

reabsorbed and chlorine ions follow passively.

The Loop of Henle: (has a descending & ascending limb)

- In the descending limb, it is permeable to water, not salt.

- Water passes out of the nephron and into the capillaries by osmosis

- In the ascending limb, the walls are permeable to salt, but not water

• Ascending limb is thin-walled at the bottom, and thick-walled at the top.

- Salt passively passes out into the capillaries at the bottom, thin-walled section, but is

actively passed out in the top, thick-walled section.

The Distal Tubule:

- Selective reabsorption of sodium ions and potassium ions occurs here to regulate the

pH of the blood & concentration of salts.

The Collecting Duct:

- This is the end of the nephron, and connects to the ureters.

- The walls are permeable to water only & water is transported out accordingly to the

needs of the body. Urine is the final filtrate

- Hormones: chemically controlled substances secreted by endocrine glands directlyin bloodstream

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Outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in theregulation of water and salt levels in blood

ALDOSTERONE:

- Produced and released by the adrenal glands, which sit above the kidneys

- Controls amount of salt in blood by regulating the reabsorption of salt in the nephrons

High Salt Levels:

- High blood volume and blood pressure due to water diffusing in.

- Levels of aldosterone decreased

- Less salt reabsorbed, less water diffusing in

- Salt level decreased, blood volume and pressure decreases

Low Salt Levels:

- Low blood volume and blood pressure due to water diffusing out.

- Levels of aldosterone increased

- More salt reabsorbed, more water diffusing in- Salt levels increase, blood volume and pressure increase

ADH (ANTI-DIURETIC HORMONE)

- Controls the reabsorption of water by adjusting the permeability of the collecting

ducts and the distal tubules.

- It is made in the hypothalamus in the brain, but stored in the pituitary gland

- ADH doesn’t control salt levels in blood. It controls salt conc. through water retention.

- Receptors in hypothalamus monitor the concentration of the blood:

High Salt Levels:

- ADH levels increased

- Collecting ducts and distal tubules become more permeable to water

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- More water reabsorbed & concentration returns to normal. (Concentrated urine)

Low Salt Levels:

- ADH levels reduced

- Collecting ducts and distal tubules less permeable

- Less water absorbed & concentration returns to stable state. (Dilute urine)

Define enantiostasis as the maintenance of metabolic and physiological functionsin response to variations in the environment and discuss its importance to estuarine

organisms in maintaining appropriate salt concentrations

- An estuary is where a river meets the sea & freshwater mixes with saltwater

- Enantiostasis is the maintenance of metabolic and physiological functions in

response to variations in the environment

- In such an environment, the salinity levels are always changing dramatically.

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

freshwater rivers (This causes great variation in the levels of salt in the water.)

- Organisms living in such an environment need to have a mechanism to cope with

such changes in order to survive, called enantiostasis

- Animals (fish) can move to avoid changes. Plants must have mechanisms to help

them cope with these changing environmental conditions.

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

water loss

- Xerophytes are plants living in arid conditions & possess adaptations that allow them

to achieve balance between evaporative cooling & prevention from dehydration.

- Saltbush has waxy leaves with a thick cuticle which protects them from excessive

sunlight by insulation yet also reduces small amounts of evaporation

- Eucalyptus leaves hang vertically which reduces the surface area exposed to the sun

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- Hakeas have reduced leaves, meaning each leaf is divided into pinna or leaflets thus

there is fewer stomata, ensuring less water loss.

- Hakeas have sunken stomata (stomata lower than main surface of leaf) which allows

moist air to be trapped in pit. This reduces difference in water potential outside stoma

- Banksias have hairy/shiny leaves which reduce the transpiration by trapping water

- Hummock grass involves leaf curling whereby leaves roll up to form cylinder. This

reduces surface area & traps humid layer of air reducing water loss.

- Succulents have water storage whereby water is stored in trunk, leaves or roots.

Plants survive by using the moisture from the water during dry periods

maintaining a balance notes

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