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9.2 Maintaining a balance: 1. Temperature range

Syllabus reference (October 2002 version)
1. Most organisms are active in a limited temperature range	Students learn to: identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates identify the pH as a way of describing the acidity of a substance explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency describe homeostasis as the process by which organisms maintain a relatively stable internal environment 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 identify the broad range of temperatures over which life is found compared with the narrow limits for individual species compare responses of named Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation identify some responses of plants to temperature change	Students: 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) gather, process and analyse information from secondary sources and use available evidence to develop a model of a feedback mechanism analyse information from secondary sources to describe adaptations and responses that have occurred in Australian organisms to assist temperature regulation

Syllabus reference (October 2002 version)

1. Most organisms are active in a limited temperature range

Students learn to:

identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates
identify the pH as a way of describing the acidity of a substance
explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency
describe homeostasis as the process by which organisms maintain a relatively stable internal environment
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
identify the broad range of temperatures over which life is found compared with the narrow limits for individual species
compare responses of named Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation
identify some responses of plants to temperature change

Students:

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)
gather, process and analyse information from secondary sources and use available evidence to develop a model of a feedback mechanism
analyse information from secondary sources to describe adaptations and responses that have occurred in Australian organisms to assist temperature regulation

Extract from Biology Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW [Edit: 12 Jun 2008]

Prior learning: Preliminary module 8.2 (subsection 3); 8.4 (subsection 3) and 8.5 (subsection 3).

Science Stages 4 - 5 syllabus: Outcome 4.8 (content 4.8.5a and b), Outcome 5.8 (content 5.8.4a).

Background: All organisms are adapted to a particular environment with its characteristic temperature range. The temperature range allows the organism's enzymes to control its metabolism by operating at their optimum efficiency within this range.

Some organisms are adapted to live at high temperatures (80 - 100^oC) and these are called thermophiles. At the other end of the scale, there are organisms that are adapted to extremely cold temperatures (0-4^oC), termed psychrophiles. Most mammals and microbes are adapted to a temperature range 30 - 45^oC, averaging around 37^oC. The optimum temperature for plants is around 25^oC.

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

Enzymes are biological catalysts. This means that they lower the energy required to start a chemical reaction within a cell but do not get used up by that reaction. Every reaction and process within a cell (metabolism) is controlled by a specific enzyme.

Enzymes are globular proteins whose shapes are specialised so that other chemicals (substrates) can form a temporary bond with them. There are two models used to show how an enzyme work:

One model used to illustrate the action of an enzyme is the lock-key model. This is where only one small part of the enzyme molecule can form a complex with the substrate. This part of the molecule is called the active site. Only a specific substrate(s) can bond in that site and this makes the enzyme specific to that substrate.

The induced fit model, a more recent modification on the lock-key model, proposes that the active site slightly changes its shape to accommodate the substrate perfectly.

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

pH is a scale related to the concentration of hydrogen ions in a solution.

A pH value of 0 - 6 indicates an acid solution, where 0 is more acidic than 6, e.g. lemon juice has a pH value of 2, hydrochloric acid has a pH value of 1.

A pH value of 7 indicates a neutral solution, e.g. water.

A pH of 8 - 14 indicates a basic solution, where 14 is far more basic than 8, e.g. sodium hydroxide (drain cleaner) has a pH of 14, sodium bicarbonate has a pH of 8.

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 concentration

on the activity of named enzyme(s)

For this investigation, you need data that will assist you to determine appropriate ways in which each aspect may be researched. Enzymes that could be used include salivary amylase, trypsin and rennin.

Rennin is an enzyme found in the stomachs of young mammals that are still being fed on milk. The rennin 'curdles' or sets the protein in the milk separating it into curds (solids) and whey (liquid).

Plan your investigation using the procedure provided below.

When choosing resources, you should be able to buy rennin as a junket tablet from supermarkets.

Procedures to investigate the activity of an enzyme

A. To demonstrate the effect of increased temperature:

Make a rennin solution by dissolving a junket tablet in distilled water.
Add the same amount of rennin solution to a number of test tubes of milk, eg 7 test tubes.
Place test tubes in different water baths at temperature ranges such as 0^oC, 10^oC, 20^oC, 30^oC, 40^oC, 50^oC and 60^oC. Make sure each water bath is kept at the temperature it has been allocated.
Time the interval between adding the rennin and curdling of the milk for each temperature.
Note that the variables kept constant in each test tube are the junket solution, the pH of the solution, the type of milk and the quantity of milk in each test tube.
Comment on which temperature is the most effective in curdling the milk. Could a different temperature be better?

B. To demonstrate the effect of change in pH:

Make a rennin solution the same as was done in A and add pH solution to each with known concentrations of pH solutions from for example pH 3, pH 4, pH 5, pH 6, pH 7 and pH 8.
Add the same amount of rennin solution with the varying pH to six test tubes of milk.
Place in a water bath kept at a constant temperature of 37^oC.
Time the interval between adding the rennin and curdling of the milk in each test tube.
Note that the variables kept constant in each test tube are the junket solution, the type of milk, the temperature of 37^oC, and the quantity of milk in each test tube.
Comment on which pH is the most effective in curdling the milk.

C. To demonstrate the effect of change in substrate concentration:

Make different concentrations of the substrate by diluting the milk using different amounts of powdered milk to get different concentrations.
Add the same amount of rennin solution to each test tube of milk.
Place in a water bath kept at a constant temperature of 37^oC.
Time the interval between adding the rennin and curdling of the milk.
Note that the variables kept constant in each test tube are the type of milk, the temperature of 37^oC, and the quantity of milk in each test tube.
Should smaller increments of milk concentrations have been used?

Perform the investigation by using the procedures above and carrying them out, recognising where and when modifications are needed and analysing the effect of any adjustments that you make.

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

Enzymes control all the metabolic processes in the body.

Enzymes work optimally in an environment where their optimum temperature and pH conditions are met. At temperatures and pH values other than the optimum, the enzymes fail to work as efficiently as they should or not at all.

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

Homeostasis is the process by which the internal environment is kept within normal limits regardless, of the external environmental conditions. This includes conditions, such as temperature, pH, gas levels, water and salt concentrations. This allows the enzyme's optimal conditions to be met and the body to work efficiently and kept as stable as possible.

explain that homeostasis consists of two stages:

detecting changes from the stable state

counteracting changes from the stable state

Background

For a state of homeostasis to exist, the body must have some way of detecting stimuli that indicate a change in the body's internal or external environment.

A receptor detects a change in some variable in the organism's internal environment, for example, sensory neurons in the skin pick up a decrease or increase in temperature of air surrounding the body.

An appropriate response occurs that counteracts the changes and thus maintains the stable environment, for example, shivering to generate heat in muscles.

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

The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal chord and the PNS consists of the sensory nerves and the effector nerves. When the environmental temperature begins to exceed a comfortable level for the body, temperature sensors in the skin detect the temperature change and a sensory neuron conducts a nervous impulse to the hypothalamus found in the brain. Nerve impulses pass this information from the receptors to effector neurons then onto effectors, such as blood vessels, sweat glands, endocrine glands and muscles.

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

Background

The body has some effective mechanisms to alter body temperature. To reduce temperature, heat can be expelled by sweating or radiation of heat from the skin. To increase heat, the body can respond by shivering or by contracting the skin. These responses can be activated by heat receptors. If a mechanism is activated, it will operate until receptors indicate that the optimum temperature has been reached.

If receptors in the skin detect heat, they relay information via the nerves to the hypothalamus, which also contains receptors sensitive to the heat of passing blood. This triggers the sympathetic nervous system to dilate skin capillaries and activate sweat glands. When receptors in the skin detect a low temperature, a negative feedback mechanism is activated to stop the original action. If skin temperature is still low, the hypothalamus may activate thyroid hormones to increase metabolic rate, activate the sympathetic nervous system to shut down skin capillaries and sweat glands and activate food metabolism in the liver to produce heat. In this way, the body can maintain a stable body temperature.

Gather samples of feedback mechanisms from biology texts, from scientific journals or from the Internet. Often, analogies, such as the operation of a thermostat in a refrigerator or an air conditioning system, are used.

Process the samples to identify the common elements of each system. Evaluate the validity of your sources by checking the reputation of the sources and by looking to see how consistently the information compares.

Analyse and use the information to design a creative model to represent a feedback mechanism. The model might be a physical model, e.g. may be based on a see-saw action, or it might be a conceptual model, based on an analogy.

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

Life, in some form, can be found at extremes ranging from - 40^oC to +120^oC. However, the great majority of living organisms are found in the - 2^oC to +40^oC range and for each individual species the range is even narrower. Below 0^oC, cells risk ice crystals forming in them and above 45^oC, proteins within cells may denature.

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

Background

Endotherms derive most of their body heat from cell metabolism. Mammals and birds are endothermic animals. Australian endotherms include: the kangaroos and the platypus (temperate regions); the rabbit-eared bandicoot (desert dweller); and the alpine pygmy possum (alpine dweller)

Ectotherms derive most of their body heat from their surroundings. All invertebrates and fish, reptiles and amphibians are ectothermic. Australian ectotherms include the blue-tongued lizard, the green tree frog and barramundi.

Some sites to get you started are:

A land of lizards University of Texas, Austin, Texas, USA

Alpine Pygmy possum University of Michigan, Museum of Zoology, Ann Arbor, Michigan, USA

Crocodiles Crocodile Specialist Group, Florida Museum of Natural History, University of Florida, Gainesville, Florida, USA

Ecology: distribution and adaptations of organisms . This site has useful information on a range of plants. University of Winnipeg, Manitoba, Canada (All the above websites were last accessed on 22 December 2005.)

You can analyse the information by designing a table like the one below. Describe adaptations or responses of the organisms that assist temperature regulation.

Australian organism	Endotherm or ectotherm	Adaptation or response to temperature regulation

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

Endotherms

In hot conditions, the red kangaroo licks the inside of its paws, where skin is thinner, and blood supply is closer to surface, so that heat can be easily dumped to the outside. Evaporation from saliva promotes the loss of heat from the blood.

The large ears of the rabbit-eared bandicoot provide a large surface area to pass excess heat when it is burrowing during the heat of day and when it is active at dusk.

Ectotherms

Magnetic termites (Amitermes meridionalis) pack the walls of their mounds with insulating wood pulp and align their mounds north-south to maximize exposure to the sun in the mornings and evenings when the air is cooler and to minimize exposure during heat of day.

Bogong moths are able to avoid their bodies freezing by supercooling their tissues. This process involves reducing the temperature of body fluids below their usual point of freezing and as a result, ice crystals do not form and destroy the cells.

Insects in alpine areas, as a rule, tend to be smaller, darker and use basking behaviours to absorb what heat is available.

Antarctic ice fish produce antifreeze (glycoproteins) that prevent ice formation.

identify some responses of plants to temperature change

Plants can be damaged at temperature extremes when enzyme structures are altered or membranes change their properties. As many important enzymes that are involved in photosynthesis and respiration are embedded in plant membranes, extremes of temperature can be a major problem.

In cold conditions, extracellular ice formation causes dehydration. Some plants can tolerate freezing temperatures as low as - 50^oC by altering their solute concentrations and through the lack of ice-nucleating sites in cells to prevent intracellular freezing.

In hot desert conditions, plants have to develop a compromise between access to gases for photosynthesis and access to gases for respiration by keeping their stomates open and cooling by evaporation. This risks dehydration of the plant.