MODEL OF SPECIFICITY
A simple model can be a drawing. The models on the following page show the two
main types of reactions that enzymes are involved in:
Example 1 (Figure 3): An endergonic reaction (requires energy to proceed):
Example 2 (Figure 4): An exergonic reaction (releases energy):
 Some common enzymes include:
1. Maltase:
Found in saliva and pancreatic juice, acts on maltose.
2. Sucrase: Acts on the carbohydrate sucrose.
3. Catalase: Found in all living cells acts on the poison hydrogen
peroxide.
QUESTION 1
Which of the following sequences most correctly represents the result of a reaction involving
an enzyme?
KEY: E=Enzyme, P1=Product 1, P2=Product 2, S=Substrate
A
B
C
D
P1+ S
S+E
P1 + P2 + E
S+E
P2 + E
P1 + P2
E+S
P1 + P2 + E
QUESTION 2
The diagram below shows an enzyme and substrate. Which number correctly identifies the
active site?
A
B
C
D
1
2
3
4
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Trial Exam Preparation Lectures – Biology – Book 1
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QUESTION 3 (4 marks)
Identify the role of enzymes in the process of metabolism and use a simple model to
describe their action. (Try answering on your own and then use the notes above to check
your response.)
Solution

Identify the pH as a way of describing the acidity of a substance.
The pH of a solution is the measure of concentration of _____________ ions per litre of
solution.
The pH of a neutral solution (for example, pure water) is ______. A pH value below 7
indicates an acidic solution. The lower the number is, the more acidic the solution. A
pH value above 7 and up to 14 indicates a basic solution. The higher the number is,
the more basic the solution.
The pH scale is a log scale, which means that a single number shift on the scale
changes the acidity 10x.
Most biological solutions have a pH of between 6 and 8, for example human
___________ is maintained at a pH of about 7.4. There are a few exceptions to this,
for example gastric juice in the stomach has a pH of about 2.
QUESTION 4
What does the term pH describe?
A
B
C
D
The amount of hydrogen gas in a solution.
The acidity of a solution.
The solute concentration of a solution.
The acidity of water.
© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Identify data sources, plan, choose equipment or resources and perform a
first-hand investigation to test the effect of:

Increased temperature.

Change in pH.

Change in substrate concentrations on the activity of named enzyme(s).
FIRST HAND INVESTIGATION EXPECTED RESULTS
There are various factors that affect enzyme activity. Some of these include:

Temperature: Each enzyme has an optimum temperature. In humans this is typically
37ºC. At high temperatures enzymes are denatured, that is their active sites are
permanently altered in shape. If the shape is altered, then the enzyme and substrate
cannot lock together and the enzyme won't work on the substrate. At low temperatures
enzymes become less active due to reduced molecular movement. However, they can
regain their former activity again when the temperature rises back to optimum level.

pH: Each enzyme has an optimum pH, for example pepsin has an optimum pH of 1.5
working in the human stomach, whereas trypsin, active in the small intestine, works
best at a pH of 8. A change in pH can change the shape of the enzyme active site.
© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Substrate concentration: As substrate concentration increases, rate of reaction will
also increase (assuming the presence of free enzymes) until a certain concentration
where the enzymes cannot be recycled any faster and hence the rate of reaction
plateaus.
You should have conducted three controlled experiments, one to test the effect of each
of the above factors on enzyme activity. Make sure you can describe or outline these
experiments and discuss certain aspects such as accuracy, validity and reliability.
QUESTION 5
A space probe recently returned to Earth from a distant planet with samples containing
bacteria X. Biologists are interested in comparing the activity of an enzyme found in bacteria
X with that found in bacteria E from Earth. Both bacteria contain an enzyme that produces a
gas as a product of its activity on the same substrate.
Environmental condition where bacteria were collected
Bacteria
Temperature (oC)
pH
X
50 - 80
5.5 - 7.5
E
37 - 55
6.5 - 8.5
State a hypothesis to be tested and plan an investigation you could carry out to compare
the activity of the enzyme found in the TWO bacteria under ONE of these conditions.
(7 marks)
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QUESTION 6
The sweet taste of freshly picked corn is due to the high sugar content in the kernels.
Enzyme action converts about 50% of the sugar to starch within one day of picking.
To preserve its sweetness, the freshly picked corn is immersed in boiling water for a
few minutes, and then cooked.
Which of the following explains why the boiled corn kernels remain sweet?
A
B
C
D
Boiling destroys sugar molecules so that they cannot be converted into starch.
Boiling inactivates the enzyme responsible for converting sugar to starch.
Boiling kills a fungus on the corn that is needed to convert sugar to starch.
Boiling activates the enzyme that converts starch into sugar.
© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Explain why the maintenance of a constant internal environment is important
for optimal metabolic efficiency.
Chemical reactions within a cell involve enzymes that combine and break apart many
complex molecules. The total of these reactions is called _____________________.
Some of them occur in one step, but often a complex set of reactions is involved in a
metabolic change.
If the internal environment does not remain stable, the rate of reactions that are
catalysed by enzymes decreases. This can then affect entire pathways that are
required to make essential compounds (for example, haemoglobin).
Some of the variables that need to be maintained at optimal levels for maximum
metabolic activity include __________ ____________, ion concentrations, core body
_____________, pH, oxygen levels, water levels and blood _______________.
QUESTION 7
Explain why the maintenance of a constant internal environment is important for optimal
metabolic efficiency. (3 marks)
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© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
Page 6

Describe homeostasis as the process by which organisms maintain a
relatively stable internal environment.
Homeostasis is one of the key characteristics of living things. It is the condition of
maintaining a relatively stable ______________ environment regardless of the
conditions in the external environment. The ‘internal environment’ consists of the body
_________ and cells while the ‘external environment’ is that outside the body.
Homeostasis = staying the same.
We need to keep key variables in our bodies within a narrow range so they can function
optimally – for example so that enzymes can perform a variety of chemical reactions.
These variables include body temperature, pH (percent H+ ions), water, gas
concentrations (CO2) salt concentrations (Na+, Cl-, Ca+) and glucose levels.
In animals, homeostasis is achieved through the action of _______________ and
______________. In plants, homeostasis is achieved through the action of hormones
only as plants do not have a nervous system. If homeostasis is not maintained the
organism will be unable to function properly and is likely to die.
QUESTION 8
Which process is an example of homeostasis?
A
B
C
D
Heart rate increasing with exercise.
Blood pressure increasing with exercise.
Body temperature falling in cold weather.
Removal of glucose from the blood.

Explain that homeostasis consists of two stages:

Detecting changes from the stable state.

Counteracting changes from the stable state.
DETECTING CHANGES FROM THE STABLE STATE
For homeostasis to take place there must be an external _______________
(Eg. the temperature going up) telling our bodies the stable state has changed.
A ____________ (Eg. Thermo-receptors in our skin) must recognise this.
© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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COUNTERACTING CHANGES FROM THE STABLE STATE
There must also be a _____________ (sweating) by our bodies in order to correct the
change in temperature detected by the ______________. An _______________ (pores in
the skin) must initiate the response. Homeostasis allows a change to take place. If it is a
counter change, it is known as a _______________ feedback system.

Outline the role of the nervous system in detecting and responding to
environmental changes.
The nervous system is only found in multi-cellular animals and involves rapid
responses which only last for a short time, i.e. it forms the quick source of
communication between cells.
It is composed of the brain, spinal cord (______________ nervous system) and all the
surrounding nerves of the body (_________________ nervous system).
The nervous system coordinates the responses between the receptors and the
effectors via the _____________________ in the brain and the network of nerves
around the entire body. Receptors detect a change from external stimuli. Humans have
light receptors in their eyes, gravity and sound receptors in their ears, chemical sensors
in their noses and tongues, pressure and pain sensors on their skin. These sensors
send an electro-chemical signal along many interconnected nerve cells (peripheral
nervous system) to the hypothalamus (central nervous system) in the brain. Here, the
effect is coordinated and transmitted via the peripheral nervous system.
Stimulus →
→ Transmission of Message → Effector →
QUESTION 9
Homeostasis involves two stages. (1) Detecting changes from a stable state and (2)
Counteracting changes from the stable state.
Using an example, describe the role of the nervous system in the above stages. (3 marks)
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© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Gather, process and analyse information from secondary sources and
use available evidence to develop a model of a feedback mechanism.
Feedback is the mechanism by which homeostasis is maintained. It is called this
because information about the change has been fed to the control centre, which then
feeds back a response to the system in which the set value is being maintained.
Homeostasis involves the operation of feedback mechanisms, whereby the response
affects the original stimulus. If a set value or point deviates from this value, negative
feedback causes the system to correct the deviation and return the value to the set
Value – negative feedback __________________ the change. For example, if the
blood glucose levels get too high from eating a high GI meal, the response counteracts
this change by stimulating processes that reduce the blood sugar concentration.
Negative feedback is the commonest type of feedback in biological systems.
SECONDARY SOURCE INVESTIGATION
You would have drawn a model of a negative feedback mechanism for a plant, human,
animal other than a human or a machine such as a heater.
QUESTION 10
Draw a labelled diagram to show how a specific feedback mechanism plays a role in
homeostasis. (4 marks)
© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Identify the broad range of temperatures over which life is found compared
with the narrow limits for individual species.
Most organisms prefer to live in an environment with temperatures between 0°C and
45°C. Water freezes at 0°C, and as it expands when it freezes, cell membranes can
break and rupture if the water in them freezes. Similarly, temperatures above 45°C can
cause the enzymes in an organism to denature.
Most individual species have a very specific temperature range in which they can exist.
They are most comfortable in a temperature range where their adaptations allow them
to survive, be active and reproduce. For example, you would not find giraffes in the
Arctic as their adaptations would not allow them to survive at such low temperatures.
QUESTION 11
The table below shows information about four species of bacteria and their reproductive
rates at different temperatures.
Bacterial Species
Temperature range found in
(°C)
Generations per hour
(average)
Species W
-2 to 20
0.8
Species X
15 to 46
2.0
Species Y
42 to 70
3.0
Species Z
69 to 94
2.5
What conclusion can be drawn from this table?
All bacterial species can adapt to a broad range of temperatures:
A
B
C
D
Individual species can reproduce in a broad range of temperatures.
All bacterial species are limited to a range between 0°C and 100°C.
Species Y is able to reproduce the best across all temperature ranges.
Individual species reproduce in a relatively narrow range of temperature
© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Compare responses of named Australian ectothermic and endothermic
organisms to changes in the ambient temperature and explain how these
responses assist temperature regulation.
ECTOTHERM
Ectotherms use (mostly) the energy in their _________________ to control their internal
temperatures. Reptiles, amphibians and _________ are ectotherms.
ENDOTHERM
Endotherms use (mostly) their __________ energy to maintain their internal temperatures.
Birds and ________________ are endotherms.
AMBIENT TEMPERATURE
The ambient temperature is the immediate environmental temperature. Australia has a great
range of environmental conditions, from Alpine regions (for example, The Snowy Mountains)
to desert in Central Australia. Australian animals possess various responses to cope with the
environments within which they live.
RESPONSE
A response is a type of adaptation. Not all adaptations are responses. A response is
something that takes place after a stimulus rather than a feature that exists constantly.
For example, a kangaroo licking its paws when it is hot is an adaptation and a response.
The large ears of a bilby used to dissipate heat are an adaptation.
QUESTION 12
Compare responses of Australian Ectotherm and Endotherm to changes in ambient
temperature. (3 marks)
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© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Identify some responses of plants to temperature change.

Eucalypts can hang their ______________ downward during the hottest part of the day
so they are pointing away from the sun. This reduces the surface facing the direct heat.

Frangipanis slow their growth rate in response to low temperatures i.e. below 15°C.

Banksia release seeds in response to the heat of a bushfire.

Many plants keep their ________________ closed during the hottest part of the day.
QUESTION 13
Which adaptation assists temperature regulation in plants?
A
B
C
D
Large leaves for cooling.
Increased production of seeds.
Movements of glucose to roots.
Evaporation of water from stomates.
QUESTION 14
Identify a response of a named plant to temperature change. (2 mark)
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© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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
Analyse information from secondary sources to describe adaptations and
responses that have occurred in Australian organisms to assist temperature
regulation.
SECONDARY SOURCE INVESTIGATION
You will have used various resources to prepare case studies of a few Australian plants and
a few Australian animals showing the adaptations and responses that have assisted them in
regulating their temperature.
ANALYSE
Look at the relationship between the adaptations/responses and the benefit they provide for
the organism. How common are some of the adaptations/responses?
QUESTION 15
A small Australian mammal that lives in the alpine regions of New South Wales has specific
features that enable it to retain body heat. Identify the features that are most likely to be
present in the mammal described.
A
B
C
D
Long ears, rounded body, long legs.
Short ears, rounded body, short legs.
Short ears, slender body, long legs.
Short ears, slender body, short legs.
QUESTION 16
Outline how you made sure the information you analysed to describe adaptations and
responses that have occurred in Australian organisms to assist temperature regulation
was reliable. (2 marks)
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© The School For Excellence 2011
Trial Exam Preparation Lectures – Biology – Book 1
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