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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:

Students:

Extract from Biology Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW

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


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

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

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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 concentration

on the activity of named enzyme(s)

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).


Procedures to investigate the activity of an enzyme

A. To demonstrate the effect of increased temperature:

  1. Make a rennin solution by dissolving a junket tablet in distilled water.
  2. Add the same amount of rennin solution to a number of test tubes of milk, eg 7 test tubes.
  3. Place test tubes in different water baths at temperature ranges such as 0oC, 10oC, 20oC, 30oC, 40oC,  50oC and 60oC. Make sure each water bath is kept at the temperature it has been allocated.
  4. Time the interval between adding the rennin and curdling of the milk for each temperature.
  5. 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.
  6. 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:

  1. 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.
  2. Add the same amount of rennin solution with the varying pH to six test tubes of milk.
  3. Place in a water bath kept at a constant temperature of 37oC.
  4. Time the interval between adding the rennin and curdling of the milk in each test tube.
  5. Note that the variables kept constant in each test tube are the junket solution, the type of milk, the temperature of 37oC, and the quantity of milk in each test tube.
  6. Comment on which pH is the most effective in curdling the milk.

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

  1. Make different concentrations of the substrate by diluting the milk using different amounts of powdered milk to get different concentrations.
  2. Add the same amount of rennin solution to each test tube of milk.
  3. Place in a water bath kept at a constant temperature of 37oC.
  4. Time the interval between adding the rennin and curdling of the milk.
  5. Note that the variables kept constant in each test tube are the type of milk, the temperature of 37oC, and the quantity of milk in each test tube.
  6. Should smaller increments of milk concentrations have been used?
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explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency

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

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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.

 

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

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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.

 

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

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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 (external website) University of Texas, Austin, Texas, USA

Alpine Pygmy possum (external website) University of Michigan, Museum of Zoology, Ann Arbor, Michigan, USA

Thermoregulation (external website) Wikipedia.

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















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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

Endotherms

Ectotherms

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identify some responses of plants to temperature change

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