MAINTAINING A BALANCE

Contextual Outline

Multicellular organisms have specialised organ systems that are adapted for the uptake and transport of essential nutrients from the environment, the utilisation or production of energy and the removal of waste products arising from cellular activities.

The basis of healthy body-functioning in all organisms is the health of their cells. The physical and chemical factors of the environment surrounding these cells must remain within narrow limits for cells to survive. These narrow limits need to be maintained and any deviation from these limits must be quickly corrected. A breakdown in the maintenance of this balance causes problems for the organism.

The nervous and endocrine systems in animals and the hormone system in plants bring about the coordinated functioning of these organ systems. They are able to monitor and provide the feedback necessary to maintain a constant internal environment. Enzyme action is a prime example of the need for this balance. Enzymes control all of the chemical reactions that constitute the body’s metabolism. As enzymes normally function only within a narrow temperature range, even a small rise in body temperature can result in the failure of many of the reactions of metabolism that are essential to life.

This module increases students’ understanding of the applications and uses of biology, implications for society and the environment and current issues, research and developments in biology.

  1. Most organisms are active in a limited temperature range

Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates.

Things to consider:

-What does identify mean?

-What does describe mean?

-Understand what you are going to write before you write your answer down.

All chemical reactions taking place within a cell and all chemical processes within the organism is known as its metabolism. The organism’s metabolism is maintained by special large proteins called enzymes. The role of these enzymes is to catalyse steps in metabolic pathways as well as produce essential molecules for cells. (Maintaining a balance)

Other facts about enzymes:

  • They can be used over and over again
  • Only small quantities required in cells
  • Made by the cell and controlled by nucleus
  • Different cells make different enzymes

The major chemical composition of enzymes is proteins. These proteins are made up of amino acids which are joined by peptide bonds. Certain amino acids code for certain proteins. The chemical composition can determine the active site, which binds to the substrate.

Enzymes are highly specific which means that enzymes have a specific substrate and that substrate only can incur a reaction. The models below illustrate enzymes specificity to a substrate.

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LOCK AND KEY MODEL

The above model shows that the enzyme is specific for only one type of substrate. The enzyme can only react with a substrate which is the reciprocal to its shape. The substrate binds to the enzyme at the active site whereby a reaction occurs. Once the reaction is complete the enzyme returns to its regular state and two products are formed.

It is called the lock and key model due to the substrate fitting to the enzyme like a key going into a lock.

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INDUCED FIT MODEL

The above model shows that an enzyme is adaptable to the shape of the substrate. Once the substrate has attached itself to the enzyme at the active site the reaction occurs and the once complete the enzyme returns to its regular state and two products are formed.

It is called the induced fit model due to the enzyme changing its shape to accommodate the substrate. (Inducing itself)

Identify the pH as a way of describing the acidity of a substrate.

Things to consider:

-What does identify mean

-Be succinct in your answer

The pH scale is a scale which illustrates the hydrogen ion concentration within a substance. Acidity is when a substance has a large amount of hydrogen ions present in solution. Acidic substances fall between the pH ranges of 1 – 7. If a substance is neutral it is said to have a pH of 7. Alkalinity or a base is a substance that contains very little hydrogen ion’s. Basic substances fall between the pH range of 7 -14. If we use this scale we can determine how many hydrogen ions are present in a substrate therefore determining the optimum pH range for an enzyme.

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

Things to consider:

-What does explain mean?

-Underline key words

-Define key words. Know what they mean!

There are three main factors that affect the enzymes there activity and hence metabolic efficiency. These factors are:

  • Temperature
  • pH
  • Substrate concentration

All enzymes have a specific temperature in which they function the best, (optimum temperature.) If the temperature is low enzymes are “sluggish,” and reactions occur at a slow rate. When the temperature increases, reaction rates increase until the enzyme is at its optimum temperature. If the temperature continually increases reactions rates dramatically decrease. This increase in temperature causes the peptide bonds to break, which in turn makes the active site inactive, effectively destroying the enzyme. This process is called denaturation.

All enzymes have an optimum pH. This means that if an enzyme carries a pH level of 6 it needs to be in an environment which has a pH of around 6. Changing the pH slightly will change the enzyme activity, while changing the pH dramatically will cause irreversible changes in the enzyme.

Substrate concentration also affects metabolic activity. If we increase the substrate concentration the enzyme activity increases to a certain point until all active sites are being occupied by a substrate. So how does the substrate concentration stay at a level which enables the enzyme to continually function at the optimum level? Enzymes are continually reacting with substrates to produce a product, these products are then metabolised by another enzyme. A process called feedback regulates enzyme activity, a key factor in metabolic efficiency. Feedback also controls temperature and pH.

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

Things to consider:

-A definition of homeostasis

-What does describe mean?

-Underline key words

-Be succinct in your answer

No matter what is happening on the external environment, the human body is capable of maintaining a constant internal environment. For example our blood sugar remains fairly constant, (90mg/100mL) body temperature (37 degrees Celsius) and pH of the blood (7.38 – 7.42). This constant internal environment is known as homeostasis. Homeostasis is the constant internal composition of a cell or an organism and the mechanisms that maintain it. In simple terms homeostasis is the steady state of an organism. Homeostasis does not merely occur. Certain stimuli that cause an imbalance will in effect illicit a response, in turn returning the organism to its steady state.

OTHER FACTS:

  • Idea of homeostasis introduced by Claude Bernard in 1859, did not call the process homeostasis.
  • Term homeostasis first coined by Walter Cannon 1929.

Explain that homeostasis consists of two stages:

-Detecting changes from the stable state

-counteracting changes from the stable state

Things to consider:

-What does explain mean?

-Determine the best way to answer the question

-Diagram?

The human body uses the homeostatic response to maintain a balance in a variety of ways including body temperature. The homeostatic system has three main parts; the receptor (detector), the control centre and an effector. The role of the receptor (detector) is to detect changes within the surrounding internal and external environment. These changes are known as stimuli. When and if a change takes place the receptor relays a message to the control centre. The control centre then determines whether or not to illicit a response or maintain the balance. This response or maintaining a balance is carried out by the effector. This process is known as feedback:

Receptor/detector  control centre  effector.

Therefore homeostasis is a two stage process whereby receptors detect changes from the stable state and counteract these changes to return to the stable state. (E.G. shivering/sweating)

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

Things to consider:

-What does outline mean?

-What does the nervous system contain?

-Underline key words and be succinct

The nervous system consists of two parts the central nervous system (CNS) and the peripheral nervous system (PNS). The role of the central nervous system is to coordinate all the organisms’ responses. The CNS receives the information, interprets the information and initiates a response. The PNS is a system of nerves that branches out and around the body. These nerves are connected to receptors and effectors. When the PNS detects a stimuli it rapidly relays the message to the CNS and to the control centre to illicit a response.

The endocrine system also plays a pivotal role in maintaining a balance. The endocrine system secretes certain hormones in response to certain stimuli.

E.G. Thermoreceptors detect a change in the surrounding air temperature, (hot). A message from the PNS is relayed to the CNS which in turn interprets the message. The CNS then initiates a response. Effectors start to produce sweat and dilate blood vessels in order to lose heat, and therefore maintain a balance.

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

Things to consider:

-What does identify mean?

-What does compare mean?

-Be succinct, make sure in your answer you include a variety of species

On Earth organisms face a vast variety of temperatures ranging from over 100 degrees to -70 degrees Celsius. All organisms have a certain optimum temperature range. When out of their temperature range the organism risks death or damage to their cells. For example most terrestrial organisms are found to function best between 0 – 45 degrees. Any higher or lower and the organism risks their cells and proteins denaturing, or their cells becoming frozen. In comparison thermoacidophiles love a hot climate around 100 degrees. If the temperature drops below 55 degrees the thermoacidophiles will eventually become inactive and die.

Compare responses of named Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation.

Things to consider:

-What does compare and explain mean?

-Know the key words in this statement such as ectothermic and endothermic.

AUSTRALIAN ECTOTHERM - ENDOTHERM / RESPONSE TO CHANGE IN AMBIENT TEMPERATURE / EXPLANATION OF CONTROL
Frilled Neck Lizard / Flatten or narrow body shape. (Sunbaking)
Access areas of cooler ambient temperature (Shade/burrows.)
Dormant states of reduced metabolic activity. / Frilled neck lizards will flatten their body to absorb as much sun as possible in order to increase their body temperature.
Frilled neck lizards will narrow their body if the ambient temperature is too high or if their own body temperature is too high. This is performed in order to reduce their surface area.
Frilled neck lizards move into shades or burrows to cool down from the rising ambient temperature. The temperature in burrows is fairly constant, which enables the lizard to cool down. Burrows in particular also minimise water loss which is beneficial to the lizard.
Due to the ambient temperature being too cold frilled neck lizards can go into a state of torpor whereby their body shuts down for the winter and their metabolic rate is slowed.
Kangaroos / Surface area to volume ratio.
Changing patterns in blood flow.
Cooling by evaporation of water.
Fur.
Regulating metabolic rates. / Kangaroos have a relatively large surface area. This larger surface area enables the kangaroo to maintain and lose body heat during periods of high temperatures.
Kangaroos have a dense network of blood vessels particularly in their forearms. These blood vessels dilate when the ambient temperature is high. This dilation increases blood flow to the forearms and promotes heat loss. To increase cooling kangaroos lick their forearms.
Kangaroos cool themselves by sweating. This evaporation of the water cools the organism down. However in times whereby the kangaroo needs to conserve water it will increase its body temperature a couple of degrees in order to maintain water.
Kangaroo’s fur has two main processes when the ambient temperature increases/decreases. When the temperature decreases the fur stands on end in order to reduce heat loss and maintain body heat. When the ambient temperature increases the fur insulates the kangaroo from the hot air surrounding it.
Kangaroos regulate their metabolic rates in order to regulate their body temperature. This is done by remaining crouched in the shade during times of extreme heat.

Identify some responses of plants to temperature change.

Things to consider:

-What does identify mean?

-Be succinct

Desert plants or plants which are exposed to high temperatures elicit a few responses due to temperature change. For example due to increasing temperature a desert plant will have smaller leaves which in turn decreases their surface area which leads to a decrease in water loss and solar radiation.

An Australian example where a plant reacts to temperature change is the eucalypt. The eucalypts leaves hang down, vertical in nature. This in turn provides a large surface area for the rising sun, and at this time of the day it is generally cool in nature. When the sun is higher in the sky around midday, the ambient temperature generally increases. At this time the eucalypts leaves are still hanging vertically which in turn reduces the surface area of the leaf as well as maximising water retention. In some very dry and hot conditions the eucalypt may even close its stomates in order to stop transpiration from occurring.

Therefore particularly in Australia there are numerous responses of plants to temperature change.

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)

Things to consider:

-What does identify mean?

-This experiment is referred to frequently in past HSC papers. Understand the task when it is performed in class.

-Underline key words and know their definitions.

Part A: The effect of temperature on an enzyme

EQUIPMENT:

You need to know what equipment was used in this experiment, as this dot point asks you to “choose equipment.” Refer to page 274 for the equipment list.

METHOD:

Ensure you have written your own method. This dot point asks you to PLAN your experiment so in the HSC there is no reason why they can’t ask you to re-write the method you followed. Refer to pages 274 – 275 of the textbook.

RESULTS:

  • Ensure that you have a table of results
  • Construct a graph of your results and answer the following questions.

QUESTIONS:

-From your results which temperature clotted the quickest?

-From your results which temperature clotted the slowest?

-From your results what relationships can you describe between temperature change and enzyme activity. Include possible reasons as to why 10 degrees and 80 degrees did no clot as well as the phrases, “optimum temperature” and “denaturation.”

-What was the purpose of test tube “B?”

-Write down ONE safe working practice you used throughout this experiment.

-Write a conclusion. (Did your experiment answer your aim?)

WRITE UP PART B: EFFECT OF pH ON ENZYME ACTIVITY (Pg 275 – 276). It must be in your own words!

EQUIPMENT:

You need to know what equipment was used in this experiment, as this dot point asks you to “choose equipment.” Refer to page 275 for the equipment list.

METHOD:

Ensure you have written your own method. This dot point asks you to PLAN your experiment so in the HSC there is no reason why they can’t ask you to re-write the method you followed. Refer to pages 275 – 276 of the textbook.

RESULTS:

  • Ensure that you have a table of results
  • Construct a graph of your results and answer questions 1 – 3 on page 276.

WRITE UP PART C: EFFECT OF SUBSTRATE CONCENTRATION ON ENZYME ACTIVITY (Pg 276 – 277). It must be in your own words! (“PLAN”)

EQUIPMENT:

You need to know what equipment was used in this experiment, as this dot point asks you to “choose equipment.” Refer to page 276 for the equipment list.

METHOD:

Ensure you have written your own method. This dot point asks you to PLAN your experiment so in the HSC there is no reason why they can’t ask you to re-write the method you followed. Refer to pages 276 – 277 of the textbook.

RESULTS:

  • Ensure that you have a table of results
  • Construct a graph of your results and answer questions 1 – 3 on page 277.

Gather, process and analyse information from secondary sources and use available evidence to develop a model of a feedback mechanism.

Things to consider:

-What does gather, process and analyse information mean?

-What does use available evidence mean?

-Underline key words and be succinct in your answer, if you are unsure of what your answer should be ask another student or the teacher.

Feedback Systems good site

Analyse information from secondary sources to describe adaptations and responses that have occurred in Australian organisms to assist temperature regulation.