Homeostasis

**Area of Study 2: Detecting and responding**
 * VCE Biology Unit 3: Signatures of life**

__**Big Idea: Homeostasis**__ // This big idea is concerned with how an organism maintains particular internal conditions (coordination and regulation) in order to stay alive. Such conditions are kept stable by a variety of systems, in particular the nervous and endocrine systems. An understanding of these mechanisms is needed where environmental stimuli that may cause unwanted side effects within the organism, are sometimes beyond the ability of homeostatic processes to modulate. Knowledge of such systems then allows for external treatment (medicine, drugs). //

Homeostasis refers to an organism being able to maintain its internal environment within a stable range given factors that influence the external environment. A multicellular organism’s internal environment refers to the extra cellular fluid that surrounds the cells. The external environment refers the surrounds an organism lives in.

Homeostasis controls many aspects of the internal environment, for example: Homeostasis in vertebrates occurs through the integration of the nervous and endocrine systems. The hypothalamus is the main nervous system 'switchboard' for homeostasis. It resides in the brain stem’s upper end and it controls many body activities that affect the maintenance of a stable internal environment in the body.
 * Body temperature
 * Blood concentrations of: Glucose, hormones, Carbon dioxide and inorganic ions
 * Oxygen levels
 * Blood pH
 * Blood pressure
 * Solute concentration ( Water balance)

The hypothalamus also controls the endocrine glands. The pituitary gland lies just below the hypothalamus, and is a small endocrine gland that secretes a variety of hormones. When the hypothalamus detects certain body changes, it releases chemicals that stimulate or inhibit the pituitary gland. The pituitary gland then releases or blocks various hormones. Due to this close association between the nervous and endocrine systems, together they are called the neuroendocrine system.

These systems regulate activities within the body so as to keep the internal environment of the organism within set conditions. This system however relies on a negative feed back response mechanism. This is when a change in the external environment is picked up by receptors, which then kicks the effectors in the body into gear. Once the effectors are activated a response to the stimulus occurs. In a negative feedback system the response reduces the size of the stimulus to restore the original state of Homeostasis. Conversely in a Positive feedback system, the response increases the original stimulus to restore Homeostasis. Below is an example an a negative system. Source: []

Neurotransmitter substances and hormones are chemicals within the body that help communicate between cells. They do this by binding themselves to receptor molecules on target cells and hence transmit a signal.

Source: [] (2007) Hormones are molecules that:
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: justify;">Are made of protein or lipids
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: justify;">Are carried through the bloodstream
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 14px; text-align: justify;">Are produced in the endocrine glands
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 14px; text-align: justify;">Originate in one part of the body but carry out their role in another part

<span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 14px; text-align: justify;">Homeostasis also happens in plants to a certain degree. They can control certain aspects of their internal environment for example: water loss and salt concentration. <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 14px; text-align: justify;">This occurs through pores in the leaf surface known as stomata. These pores are bound by guard cells, and they open and close the stomata to control:
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 14px; text-align: justify;">rate of water lost through transpiration
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 14px; text-align: justify;">gas exchange

<span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 14px; text-align: justify;">Below is a diagram of stomata. [|] [] Last updated: 10/3/11 <span style="display: block; font-family: arial,helvetica,sans-serif; text-align: justify;"><span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**__Learning Activities:__**





<span style="display: block; font-family: arial,helvetica,sans-serif; text-align: justify;"><span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**__Text Books:__**
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Heinemann Biology 2 VCE Units 3 and 4
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 13px; text-align: justify;"><span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Nelson Biology VCE Units 3 and 4
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">Jacaranda Nature of Biology

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**__Useful Links:__**

<span style="color: #0070c0; font-family: Arial,Helvetica,sans-serif; font-size: 110%;">http://www.phys.unsw.edu.au/biosnippets/ <span style="color: #0070c0; font-family: Arial,Helvetica,sans-serif; font-size: 110%;">[|http://www.distance.mun.ca/media/samples/homeostasis/04_audio.swf] <span style="color: #0070c0; font-family: Arial,Helvetica,sans-serif; font-size: 110%;">[] <span style="color: #0070c0; font-family: Arial,Helvetica,sans-serif; font-size: 110%;">[] <span style="color: #0070c0; font-family: Arial,Helvetica,sans-serif; font-size: 110%;">[]

<span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 110%; text-align: justify;">**__Curriculum refer to:__**
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 110%; text-align: justify;">Victorian Curriculum Assessment Authority – Victorian Certificate of Education: Study Design 2010 pg. 21 – 25
 * <span style="display: block; font-family: arial,helvetica,sans-serif; font-size: 110%; text-align: justify;">Australian Curriculum, Assessment and Reporting Authority - current national curriculum design for science []