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HSC YEAR 12 BIOLOGY
MAINTAINING A BALANCE
First I would like to say that this document should be used as a guideline in building your own
syllabus answers, rather than copied and memorised. The latter strategy will work against you in
exams...
Identify the role of enzymes in metabolism, describe their chemical composition and use a
simple model to describe their specificity on substrates
Enzyme composition and purpose
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Enzymes are composed of catalytic amino acids chains (polypeptides) folded into proteins
with a globular structure, with each amino acid composing of elements carbon, nitrogen,
oxygen and hydrogen. Enzymes are found in all forms of life. Their purpose is to reduce the
energy required to initiate chemical reactions. It achieves this by using its composition and
shape. The globular structure contains surface grooves called active sites. These have
highly specific boundaries bind with the enzyme’s target substrate. That is, enzymes are
substrate specific. Once actual bonding with the substrate has occurred, the new composite
structure is called the enzyme-substrate complex. The catabolic amino acids on the surface
of the active site significantly reduce the energy required for a substrate reaction to occur.
Thus overall, enzymes speed up metabolic activities to the required rate within the body, to
maintain life. After the reaction, the product(s) are released and the enzyme remains
unchanged. This means that very little enzyme is produced as they can be reused again and
again.
Factors that influence enzyme activity
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Enzymes are most active within very small range of conditions, factors that may throw
enzymes out of this optimum range includes:
•
Substrate concentration – increasing the substrate concentration levels fills more active
sites, raising the enzyme activity rate. However saturation point is reached when all the
active sites are filled. To further increase activity, enzyme concentration must increase.
•
pH levels – Amino acids in the enzyme are basic, hence changes in from the optimal pH
will change the globular structure of the enzyme, so its active sites no longer complement
its substrate. This reduces enzyme activity and metabolic rate.
•
Temperature – high temperatures breaks the hydrogen bonds in the enzyme, again
changing its globular structure, so its active sites no longer complement its substrate. This
reduces enzyme activity and metabolic rate. However initial minute temperature raise will
give substrate molecules higher thermodynamic energy, allowing a higher chance to bind
with the active site, allowing higher rate of reaction.
•
If enzymes are exposed to extreme variation in temperature or pH, the enzyme structure
will be irreversibly altered, leading to metabolic rates that are too slow to maintain life.
Such enzymes are termed denatured enzymes.
•
Some enzymes require the coenzymes and cofactors to activate them and to aid them in
catabolic function.
Models for enzyme activity
•
•
The lock and key models shows that enzyme are substrate specific, in that only one type
of substrate is shaped to fit the active site of the enzyme to form the enzyme-substrate
complex, a reaction occurs and the products are released while the enzyme remains
unchanged.
The induced fit model shows that enzymes are able to slightly alter the shape of its active
site, so is able to fit more closely to its substrate allowing higher rate of reaction
Identify the pH as a way of describing the acidity of a substance
•
pH is a way of describing acidity, or the hydrogen ion concentration. pH of 7 is neutral,
less than 7 is acidic and more than 7 is alkaline.
Explain why the maintenance of a constant internal environment is important for optimal
metabolic efficiency
•
Metabolic activities are vital in life as they are needed to:
1. obtain energy
2. build new chemicals for growth and repair
3. making substances required by cells
•
An example of metabolic activity the breakdown of sucrose by the enzyme sucrase into
glucose needed for respiration.
•
Maintenance of constant internal environment is vital as metabolic reactions within the
body can only occur efficiently within a small range of conditions. Variations reduce
enzyme activity and thus metabolic rate. Under extreme variations, enzymes will denature
and metabolic rate will be too slow to maintain life.
Describe homeostasis as the process by which organisms maintain a relatively stable
internal environment
•
Homeostasis is the process by which organisms maintain a relatively stable internal
environment despite changes in the external environment. Features to be controlled
include water volume, salt levels, o2 and co2, temperature and pH. Homeostasis allows
enzymes to work efficiently and thus allowing the chemical reactions that are vital for life
to occur at the required rate.
Explain that homeostasis consists of two stages:
-detecting changes from the stable state
-counteracting changes from the stable state
Outline the role of the nervous system in detecting and responding to environmental
changes
•
Homeostasis is consisting of 2 stages, detecting the change and counteracting the
change.
•
The nervous system consists of the brain, spinal cord and all nerve cells.
•
A receptor detects a change and sends a message via messager nerve cells to the spinal
cord (some message are directly interpreted by the spinal cord) which relays it to the
brain which interprets the change and sends a message via nerve cells to an effector
organ to produce a response to counteract the change. This reduces the effect of the
stimulus and restores the body back to a stable state. Once this is achieved, the brain
sends another message to stop the response.
Compare responses of named Australian ectothermic and endothermic organisms to
changes in the ambient temperature and explain how these responses assist temperature
regulation
• Endotherms are organisms that use their internal metabolic activities to generate heat.
They can maintain a constant internal temperature under most conditions.
• Ectotherms are organisms that use behavioural adaptations to regulate its temperature.
Its temperature fluctuates with the ambient temperature, thus does not usually remain
constant.
• Endotherms example: Red kangaroo
When hot - seeks shelter to avoid heat, blood vessels dilate to increase blood flow to the
surface of the skin to dissipate heat to the environment, licks its forearm and pants to
induce evaporation, light coloured skin to reflect light,
When cold - blood vessels near the skin constrict to retain heat in the area, bask in the
sun, hair rise to trap heat, increase in physical activity
• Ectotherm example: Blue Tongue lizard
When hot -seeks shelter away from heat, rises the body 90 to the sun, to reduce
exposure
When cold- bask in the sun with maximum surface area ie stick out tongue, uncurl tail
Identify some responses of plants to temperature change
Describe adaptations of a range of terrestrial Australian plants that assist in minimising
water loss
Extreme temperatures can be a problem for plants since enzymes involved with photosynthesis
would be denatured.
Colder temperatures
The groundsel is a plant found in temperature ranges of -10 to 3 degrees. The plant is short so
that it is buried under snow, as it acts as an insulating layer. The plant shed their leaves to
prevent the frozen water inside them from doing any damage. A hairy layer also reduced
likelihood of freezing.
Hotter temperature
•
The Bankia disperses its seeds once stimulated by extreme heat.
Preservation of water prevents overheating of the plant in arid environments.
•
Spinifex has the following characteristics:
1. Extensive root systems that can reach underground water.
2. has long thin blades of leaves with low surface area, reduces sun exposure and
transpiration
3. the coiling of the leaves protects stomates from heat, traps humid air and water, and
reduces sun exposure and transpiration
4. The positioning and the few numbers of the sunken stomates, reduces sun exposure and
the water evaporated from stomates are trapped in the sunken cavity.
5. The hairs on the leaves of the spinifex traps air and water molecules again reducing water
lost.
•
the eucalyptus has the following:
1. hangs its leaves vertically to reduce exposure to the sun,
2. Its leaves are cover with a layer of waxy cuticles that traps water since it’s an oily
substance, and also reflects sun light thus reducing water lost.
Identify the form(s) in which each of the following is carried in mammalian blood:
. carbon dioxide
. oxygen
. water
. salts
. lipids
. nitrogenous waste
. other products of digestion
•
co2 - 7% are dissolved directly in the plasma as CO2 gas and 23% are attached to the
haemoglobins to form carbaminohaemoglobin in the red blood cells, while 70% are found
as bicarbonate ions dissolved in the plasma (co2 forms carbonic acid which in turn forms
bicarbonate ions in water.) CO2 + H20 --> H2CO3 --> H+ and HCO3-
•
o2 - some are dissolved directly in the plasma as o2 gas. While most are attached to
haemoglobin in red blood cells as oxyhaemoglobins.
•
h20- made up 90% of the blood plasma hence carried as h20 molecules in the plasma
•
salts- carried as ions dissolved in the plasma e.g. potassium ions and sodium ions
•
lipids - lipids are encases in a protein coat, and becomes lipoproteins dissolved in plasma
•
nitrogenous wastes - urea, uric acid are dissolved directly in the plasma
•
products of digestion - sugars, amino acids, vitamins are dissolved directly in the plasma
Explain the adaptive advantage of haemoglobin
•
Haemoglobin is a respiratory pigment found in red blood cells of most vertebrates that
gives blood its colour. It is an iron containing metalloprotein that has the ability to carry o2.
Since o2 does not dissolved very well in blood, the presence of haemoglobin increases
the o2 capacity of the blood by 100 folds. Haemoglobin readily attaches with o2 in the
lungs to form oxyhaemoglobins and can release o2 to cells easily. The net effect of
having haemoglobin for organisms is more o2 for respiration, hence production of more
energy through respiration. This extra energy can be used to maintain a body
temperature, thus vertebrates can be active in a larger range of conditions. This extra
energy generally allows organisms to grow larger and live longer.
Compare the structure of arteries, capillaries and veins in relation to their function
•
arteries - thick muscular, highly elastic walls, it carries blood away from the heart at high
pressures, the muscular walls contract and expand to withstand and maintain the
pressure needed to pump the blood.
•
Veins - has larger diameter than arteries but has thin, less muscular, less elastic walls
and contain valves. It carries blood back to the heart under low pressure and against
gravity. Thus valves prevent the backflow of blood. The muscles around the vein press on
the veins to pump the blood.
•
Capillaries - one cell thick therefore it has large surface area to volume ratio; it connects
arteries and veins and transfers material between blood and cells. The large surface area
allows quick and easy diffusion.
Outline the need for oxygen in living cells and explain why removal of carbon dioxide from
cells is essential
•
O2 is required for respiration to produce energy that is required to maintain metabolic
processes, to survive and reproduce.
•
Respiration: Glucose + oxygen --> carbon dioxide + water + energy
•
CO2 is a waste product formed due to the process of respiration. It must be removed
since it forms carbonic acid when dissolved in plasma. This decreases the pH of the
cellular environment, and reduces enzyme activity and thus metabolic rate. If co2 is not
removed and carbonic acid is left to accumulate, enzymes would eventually denature and
metabolic rate would be too slow to maintain life. CO2 also decreases o2 capacity of the
blood, by attaching to haemoglobins, this result in net energy lost, and impairing health.
Describe current theories about processes responsible for the movement of materials
through plants in xylem and phloem tissue
•
The pressure flow theory
The transport of photosynthetic materials in multiple directions in the phloem requires
both active and passive transport and is known as translocation.
There are 3 stages:
1. The material is transported from the source end (the leaves) to the phloem tube
against the concentration gradient using active transport.
2. The material is transported through the phloem tube by an osmotically driven
pressure gradient.
3. The material is unloaded from the phloem tube to the sink end, again by active
transport.
•
The passive transport of water and inorganic salts (minerals) in one direction in the xylem
is carried out by the cohesion, adhesion and transpiration mechanism
Cohesion - the water molecules sticks to each other forming one continuous stream of
water
Adhesion - the water molecules sticks to the walls of the xylem, so that water remains in
the xylem
Transpiration - the water molecules moves up to replace the water lost to evaporation due
to the osmotic behaviour of water. Together with cohesion and adhesion this results in
one continuous stream of water moving up the xylem vessel.
Explain why the concentration of water in cells should be maintained within a narrow
range for optimal function
• Cells functions are optimal in isotonic environments. A change in water concentration, ie a
concentration gradient, results in osmosis, thus the heavy intake or lost of water will
cause damage to cells. Change in concentration of water would also impair metabolism
since water is the major solvent for chemical reactions in the body and also water
concentration affects solute concentration in the body. (ie a drop in concentration of water
will increase co2 concentration, lowering the pH of the blood.) Water balance is important
since water aids in temperature control and giving structure to cells.
Explain why the removal of wastes is essential for continued metabolic activity
•
Wastes products such as co2 and urea are formed due to metabolic reactions however
they must be removed since they are toxic to cells and a build up of waste increases
cellular solute concentration. They also decrease the ph of cellular environment distorting
H bonding in enzymes, lowering their activity and metabolic rate. if they are not removed
enzymes would be denatured and rate of metabolism would not maintain life
Identify the role of the kidney in the excretory system of fish and mammals
•
The kidney is an organ that aids in removal of nitrogenous waste formed due to metabolic
activities. It also maintains salt and water balance.
•
The mammalian kidneys produce urine with a concentration depending upon the water
availability of its environment, its water intake and its physical activities. When water is
highly available, urine concentration is low, when water is scarce, concentration is high.
Mammalian kidneys also regulate salt levels. Its nitrogenous waste is in the form of urea
because of its low toxicity.
•
Freshwater fish live in hypotonic environment, water constantly enters into their body via
osmosis, and salt will diffuse out. Its kidneys releases large amounts of urine composing
of ammonia, small amounts of salt and large volume of water, thus its urine is dilute to
expel excess water gained from the environment. Its nitrogenous waste is in the form of
water soluble ammonia because of its watery environment.
•
Saltwater fish live in hypertonic environment, water leaves their body via osmosis, and
salt diffuses in. It releases concentrated, low amounts of urine composing of ammonia,
large amount of salt and small volume of water, this prevents dehydration. Salt is also
excreted in their gills.
•
Ammonia is the direct results of breakdown of amino acids. It is very toxic thus it needs to
be removed quickly or changed into less toxic forms. Ammonia is however very water
soluble thus watery environments allow marine animals to directly expel nitrogenous
waste in the form of ammonia. Terrestrial animals must conserve water, thus releasing
waste in the direct form of ammonia is not an option. Mammals instead convert ammonia
into less toxic urea and release it as urine with concentrations adjusted to water
availability. Birds and insects convert ammonia into uric acids, which is highly
concentrated to preserve water. Uric acids are also very low weight, to aid insects and
birds in flight.
Explain why the processes of diffusion and osmosis are inadequate in removing dissolved
nitrogenous wastes in some organisms
Diffusion and osmosis both involve passive random movement of molecules across a
semi permeable membrane, from high concentration to low concentration. Diffusion is
inadequate in removing wastes since it is too slow and non selective thus wastes along
with needed materials are lost. Osmosis involves the movement of water, thus waste
would not be removed while water is lost.
Distinguish between active and passive transport and relate these to processes occurring
in the mammalian kidney
•
Active transport involves moving material against the concentration gradient, from low
concentration to high concentration, this requires energy.
•
Passive transport involves moving material according to the concentration gradient, from
high concentration to low concentration, this does not require energy.
•
In the kidneys salt ions, amino acids, sugars are actively reabsorbed against the
concentration gradient from the tubules back into the blood of the capillaries surrounding
the tubules. This increases the solute concentration of the blood and hence stimulates the
passive re absorption of water via osmosis, from the tubules back into the blood.
Explain how the processes of filtration and re absorption in the mammalian nephron
regulate body fluid composition
•
Filtration - The glomerular filtrate consisting of small solute molecules such as urea, water,
salts, amino acids, vitamins are forced through the glomerulus filter by the pressures in
the renal artery, then they enter the Bowman's capsule and then the tubules. The blood
components are too large to enter.
•
Reabsorption - salt ions, amino acids and sugars are actively reabsorbed against the
concentration gradient from the tubules back into the blood of the capillaries surround the
tubules. This increases the solute concentration of the blood and hence stimulates the
passive reabsorption of water via osmosis, from the tubules back into the blood. The
amount of materials reabsorbed can be altered by hormones such as ADH and
Aldosterone according to the body's needs. Hence the process of filtration and
reabsorption determines the blood composition and concentration.
Outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in the
regulation of water and salt levels in blood
•
Aldosterone is a hormone produced and released from the adrenal gland situated above
the kidneys. The hormone stimulates the tubules to increase the active reabsorption of
sodium ions against the concentration gradient from the tubules back into the blood of the
capillaries surrounding the tubules. This increases the solute concentration of the blood
and hence stimulates the passive reabsorption of water via osmosis, from the tubules
back into the blood. This ultimately corrects the blood pressure.
Release of aldosterone also stimulates the intestines to absorb more sodium ions which
cause a decrease in potassium ion concentration. The release of aldosterone
INCREASES the blood pressure and concentrations of urine
Patients that suffer from addison's disease cannot excrete sufficient amounts of
aldosterone due to damage to the adrenal gland and would require hormone replacement
therapy which involves taking florinef tablets daily. Without the therapy there will be
incorrect salt levels in the body and dangerously high potassium levels which can cause
hypertension, electrolytes imbalances and cardiac failures. Hence hormone replacement
therapy is of great importance.
•
ADH, anti diuretic hormone is produced in the hypothalamus and is released from the
pituitary gland. The hormone increases the permeability of the walls of the tubules in the
kidneys to increase passive reabsorption of water via osmosis, from the tubules back into
the blood. This ultimately increases the water volume of the body.
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 extremely important for organisms living in estuarine
environment as they face strong salt level changes. Such organisms include crabs and
starfish. They cannot regulate salt and water levels instead they must exhibit
enantiostasis to tolerate these salt level changes in order to survive. Grey mangroves
exhibit enantiostasis. Saltwater fish actively excrete salt through their gills. Mussels close
their valves, to maintain a constant salt concentration in the cavity of their shells.
© 2009 k02033 (from the Bored of Studies forum).
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