Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis

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Describe homeostasis as the process by which organisms maintain a relatively stable internal environment
Explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency

Homeostasis
Of all living organisms the mammalian body has best perfected keeping internal functioning constant, no matter what changes occur in the environment. We are going to look at the regulatory systems in both plants and animals that act to maintain a balance in their internal environments. bbc.co.uk

Homeostasis
The word homeostasis comes from the Greek words homoios, meaning like or the same and stasis, meaning state. This implies a state of balance or constancy, where conditions stay the same in the internal environment of living organisms to allow them to function efficiently, despite fluctuations in the external environment.
allposters.com.au

Homeostasis
Homeostasis is defined as: the maintenance by an organism of a constant or almost constant internal state, regardless of external environmental change.
Any organised infrastructure, whether a living organism or a non-living enterprise, needs careful control and certain constants if it is to run smoothly and efficiently. jerky.com.au

Homeostasis
If we consider the smooth running of a hospital or even a household, a sudden external change, for examples a power cut, could have drastic results if the organisation cannot continue to work independently of the outside changes. If the hospital does not have a back-up plan, lives could be lost.
sesiahs.health.nsw.gov.au

Homeostasis
In order to maintain a constant internal environment, the following two steps are essential:
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2.
Detect the change
Counteract the change swallowtailconsulting.com

Homeostasis
In a similar way, living organisms must have mechanisms in place to enable them to function independently of external changes to maintain a relatively constant internal state. alaska-in-pictures.com

Homeostasis
Lets think about our hospital and home analogy. In order to maintain a constant internal environment in the event of a power cut, how would people within the hospital or home:
 Detect the changes?
 Counteract the change? newshopper.sulekha.com

Homeostasis
When we consider our analogy in more detail, it becomes clear that some organisations are better equipped to cope with change than others. Part of the back-up plan in a hospital is to have its own emergency generator. Most of us however, would not have one in our homes. generatorservicesinc.com

Homeostasis
Certain living organisms have a better ‘back-up plan’ than others when it comes to maintaining a constant internal environment.
Living organisms have developed mechanisms that ensure that they are able to maintain a constant internal state regardless of changes in the external environment. abc.net.au

In order to understand how homeostasis is maintained, we need to understand this at the cellular level. Living organisms are made of cells, which must function efficiently to maintain life. All chemical reactions within cells must occur efficiently and be effectively co-ordinated to bring about optimal metabolic efficiency. blood.co.uk

Optimal Metabolic Efficiency
Each of your cells is surrounded by a small amount of fluid called intercellular or interstitial fluid and this, together with cytoplasm inside cells, makes up their internal environment. proprofs.com

Optimal Metabolic Efficiency
Cells are extremely sensitive to changes in their internal environment and any imbalance adversely affects their functioning. The internal environment of an organism must be maintained within a narrow range of conditions. h2ooverdrive.digithinkit.com

Optimal Metabolic Efficiency
Temperature, the amount of cells or fluid and chemical content for example must be kept stable so enzymes can function effectively and metabolic efficiency can be maintained. blobs.org

Optimal Metabolic Efficiency
Enzymes are extremely sensitive to the temperature and pH of the environment and changes in concentrations of these, as well as nutrients such as glucose and oxygen, affect their activity. Cells cannot tolerate any build-up in levels of waste products such as carbon dioxide or other metabolic wastes. southeastgenetics.org

Optimal Metabolic Efficiency
Metabolic efficiency relies on a constant level of the following variables in the internal environment:
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Temperature and pH
Concentration of metabolites (reactants)
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Concentration of water and salt (osmotic pressure), which determines the volume of cells or fluid such as blood.
Absence of toxins that may inhibit enzyme functioning
All chemical reactions necessary for the cell’s survival and functioning are controlled by enzymes so it’s vital to maintain a constant environment.

Metabolites
For any chemical reaction to proceed, reactants must be present.
We call these reactants metabolite. Metabolites are chemicals that participate in chemical reactions in cells (for example, glucose and oxygen). Some are taken in from the outside environment, whereas others are products of other metabolic pathways. blog.flemingoutdoors.com

Metabolites
Many metabolic reactions rely on the availability of ATP energy in cells. If cells cannot produce sufficient energy, there is a ripple effect and other metabolic activity will be adversely affected. hyperphysics.phy-astr.gsu.edu

Metabolites
The production of energy relies on chemical respiration, which in turn relies on an ample supply of metabolites such as glucose and oxygen, as well as respiratory enzymes and their cofactors. A lack of any of these metabolites may therefore slow down or stop chemical respiration, affecting overall metabolic efficiency. phschool.com

Osmotic Balance
All chemical reaction in living organisms take place in water. For chemical reactions to proceed, the reactants must be dissolved in water.
Therefore the water concentration of cells and their surrounding fluid is of enormous importance. Dissolved substances such as salt affect the osmotic balance of fluids and so the concentration of slats and other dissolved substances must also be maintained within a narrow range. quickgym.com

An absence of toxins
A build-up of carbon dioxide and/or other wastes (as a result of chemical reactions in the cells) may be toxic to cells, affecting enzymes either directly or indirectly. drugline.org

An absence of toxins
Some interact directly by blocking the active site of enzymes, while others act indirectly by altering the optimal conditions for enzyme functioning. For example, carbon dioxide alters the pH of fluid. In either case, enzyme functioning is inhibited and to these wastes must be removed to ensure metabolic efficiency. beachandbay.com.au

-Students to write and answer the following questions in their notebooks:
1.
Explain why organisms devote a lot of energy to maintaining a constant internal environment
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3.
Define homeostasis
Identify body processes that are controlled by homeostasis