Homeostasis

Effects of Tolerance Limit Deviation

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Ben Whitten

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What are the effects of tolerance limit deviation?
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Any deviation outside the tolerance limits can affect the functioning of cells and the health of the organism. There are many potential effects for cells and living organisms when major factors deviate from the tolerance range.


The five key factors which are covered in the WACE Biology course are;


  • Temperature

  • Nitrogenous waste

  • Water

  • Salts

  • Gases


These factors must be regulated in order to stay within their tolerance ranges to enable cells to live, reproduce and function normally.

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What are the effects of moving outside temperature limits?
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A small increase in temperature can lead to an increase in enzyme activity, hence increasing metabolic rate as enzymes are biological catalysts for essential biochemical pathways; however, a larger, more significant increase in temperature can cause enzymes to denature, leading to a critically slow cell metabolism - cells can die.


When the human body, for example, reaches temperatures of up to 39.2 degrees Celsius, a number of symptoms can occur;


  • Decline in cognitive skills

  • Heat stress

  • Heat exhaustion

  • Heat stroke (up to 39.6 degrees Celsius)


In critically high temperatures, cell membranes become too fluid; this allows for unwanted substances to flow into cells, or wanted substances out of cells. In plants, photosynthesis can slow down, affecting plant growth and productivity.


A decrease in temperature below the optimal range can alternatively lead to a decrease in enzyme activity, hence decreasing metabolic rate. At low temperatures, cell membranes can become rigid, slowing the transport of substances across them.


When there is a decrease in temperature bellow the tolerance range, mammals can suffer from hypothermia and sometimes even lose limbs as a result. Some animals may survive but cannot reproduce until temperatures return to within their tolerance range.

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What are the effects of moving outside nitrogenous waste limits?

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Proteins and nucleic acids are required by organisms for survival, and they both contain the element nitrogen. When organisms break down both proteins and nucleic acids, a highly nitrogenous waste known as ammonia forms. Most terrestrial animals convert this to urea, but urea still needs to be dissolved in water and excreted as it is moderately toxic. 


As nitrogenous wastes increase in concentration, they become more toxic.


An increase in ammonia in the blood can lead to an increase in pH. Enzymes can only function within a certain pH tolerance range, and perform at their peak when within an optimal pH range. When the cellular pH is outside the optimal range, enzyme activity can decrease. When the cellular pH is outside the tolerance range, the enzymes can denature, resulting in a critically slow cell metabolism.


High levels of nitrogenous waste also affect the water balance. Cells may lose water to dilute the waste in an attempt to maintain pH homeostasis.

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What are the effects of moving outside water limits?
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Water is the universal solvent. It dissolves salts and minerals by breaking salts into ions. For example, sodium chloride (NaCl) can be dissociated into Na+ and Cl- ions. The ions are then ready to partake in metabolic reactions. Metabolic reactions occur in a solution composed mostly of water; an increase in the water content leads to a decrease in the collision rates of the reactants involved in biochemical pathways, slowing down metabolism.


The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration is called osmosis.


An increase in water content to above the tolerance range will lead to a hypotonic solution surrounding the cells in the blood and in the tissues. Water will then move into the cells, down a concentration gradient, in order to reach equilibrium; if too much water enters the cells, animal cells can swell and burst (cell lysis). If cells swell, the resulting solute concentration can be too low, leading to a decrease in collisions of reacting particles, slowing the rates of reactions. Thus, if the concentration inside cells becomes too dilute, there are insufficient interactions occurring between enzymes and substrates.


Too little water inside cells also results in an inability to regulate the concentration of solutes such as salts. A hypertonic solution surrounding the cells in the blood and in the tissues may lead to water moving out of the cells by osmosis, leading to dehydration. Cells can shrink and plant cells can undergo plasmolysis. In an environment that has a water content below the tolerance range, ions are unable to move their reaction sites at a fast enough rate, slowing the metabolic rate.


When cells are surrounded by fluid of the same water concentration, the surrounding solution is described as isotonic and there is no net movement of water.

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What are the effects of moving outside salt limits?
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Salts dissociate into ions, and these ions such as sodium and calcium are required to be in concentrations within a narrow range for the normal functioning of;


  • Muscles

  • Neurons (nerve cells)

  • Other body cells


If the salt concentration increases outside of cells, water may be transported out of the cells by osmosis. This leads to cell shrinkage and dehydration. Salts are needed at optimal levels in order to regulate water balance.


For example, calcium triggers muscles to contract. Low calcium levels in the blood can lead to the cramping of muscles in the legs and back.


Low blood sodium levels affect water balance, blood pressure and the nervous system. If the sodium concentration drops too low outside cells, water moves into the cells, the cells swell with too much water, leading to;


  • Weakness

  • Fatigue

  • Confusion

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What are the effects of moving outside gas limits?
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Living cells need a continuous supply of oxygen in order to carry out cellular respiration for the production of energy.


Carbon dioxide is a waste product of respiration. It readily dissolves in water, forming carbonic acid, and then further dissociating into hydrogen ions and bicarbonate ions. High levels of carbon dioxide can lead to a high concentration of hydrogen ions in solution, which lowers the pH of the blood, making it more acidic. pH is a measure of how acidic or alkaline an aqueous solution is.


If carbon dioxide levels increase above the tolerance range, blood pH becomes more acidic and this can affect enzyme activity, and even denature enzymes.


If carbon dioxide levels get too low, this can lead to a lower ventilation or breathing rate in animals, and a lower rate of photosynthesis in plants.


If oxygen levels increase above the tolerance range in animals, this can result in cell damage, nausea, dizziness and breathing problems.


If oxygen levels get too low, this leads to a reduction in the respiration rate and thus the rate of ATP production (energy).

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