Temperature 8.1

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Inquiry Question 1: How is an organism’s internal environment maintained in response to a changing external environment?

Content Descriptor: Construct and interpret negative feedback loops to show homeostasis by using a range of sources, including but not limited to:

Temperature: (8.1.1)

Feedback loops:




Glucose: (8.1.2)


Content Descriptor: Investigate the various mechanisms used by organisms to maintain their internal environment within tolerance limits, including:

Trends and patterns in behavioural, structural and physiological adaptations in endotherms that assist in maintaining homeostasis: (8.1.3)

Heat Exchange:

Organisms must protect their core body temperature, as the lowering of core temperature reduces the speed of metabolism and bodily functions causing cell and eventually organism death. Endotherms have better physiological adaptations for thermogenesis and thus do not need to gain heat energy from the sun. Ectotherms rely mostly upon behavioural and structural adaptations to maintain temperature homeostasis.


Counter current heat exchange - Veins and arteries to and from extremities are adjacent, allowing warm blood heading to the extremities to warm the cool blood returning.


Body size – Smaller organisms have a higher surface area to volume ratio. This makes it harder to smaller animals to retain heat.

Feathers, blubber and fat – Insulation


Vasodilation and vasoconstriction – Muscle contracts to move blood vessels closer to or away from the surface of the skin.


Sweating – Sweat released evaporated removing heat from the skin.


Seeking shade and basking – Movement to different locations takes advantage of the natural heat differences.

Huddling – Reduces surface area and thus reduces size which heat can be lost across.

Plant temperature control:

  • Temperatureaffects germination times
  • Undergroundbulbs which stay dormant until temperatures decrease
  • Vernalisation –Tthe delaying of flowering until they have been exposed to a certain level of
  • Smallwaxy leaves

Internal coordination systems that allow homeostasis to be maintained, including hormones and neural pathways: (8.1.4)

The nervous system:

  • Involvedin the coordination of messages throughout the body
  • Canbe broken down into:
  • CNS– Brain and spinal cord
  • Peripheral nervous system – Consists of all nerves outside the brain and the spinalcord
  • Stimulusresponse model:
    1. Receptor– A part of the body which can receive stimuli
    2. Sensoryneurone – Carries message from the receptor to the CNS
    3. Connectorneurones – Located in brain and spinal cord, assist in delivering message
    4. CNS– Receives the message and processes
    5. Motorneurone – Carry messages from the brain to muscles and effector organs
    6. Effectororgans – Carries out the desired response

Compare nervous and endocrine systems:


  • Maydetect internal or external
  • Proprioceptors– Muscle and movement
  • Mechanoreceptors – Respondingto touch pressure and pain
  • Chemoreceptors –Activated by binding to chemicals, mouth and nose
  • Photoreceptors– In the retina


  • Simpleendocrine pathway – Stimulus leads to secretion of hormone which reacts with target cells
  • Simple neuroendocrine pathway – Stimulus is detected by a sensory neuron stimulating aneurosecretory cell to release a neurohormone
  • Examples include glucagon and oxytocin. ADH is also secreted by hypothalamus causingincreased water absorption into the blood by kidneys

Mechanisms in plants that allow water balance to be maintained: (8.1.5)

Xerophytes are plants adapted to arid regions

  • Generally,have leaves with thick waxy cuticles
  • Smallerleaves
  • Largeroot systems
  • Tightlypacked epidermis layer
  • Stomatesare small pores in the leaves of plants, these are closed to reduce water loss
  • Leaves sometimes roll to cover stomates and prevent water lossHydrophyte needs large amounts of water

Hydrophyteneeds large amounts of water

  • Single layer for upper and lower dermis for air pockets 
  • Mesophyteneeds moderate amounts of water


  • Osmoconformers allow the osmorality of their intestinal fluid to follow that of theenvironment
  • Osmoregulatorsuse active transport to maintain constant osmorality
  • Mangrovesuse pneumatophores to absorb oxygen for roots
  • Accumulatesalt on leaves and old branches to be 

Inquiry Question Review: How is an organism’s internal environment maintained in response to a changing external environment? (8.1.6)

You should be able to:

  • Drawand interpret feedback loops
  • Describethe variety of mechanisms in organism that enable homeostasis