08/02/2025, 17:17 Biology Paper III Essays - Evernote
The importance of responses to changes in
the internal and external environment of an
organism
The importance of responses to changes in the internal and external
environment of an organism
Internal Environment:
• Glucose concentration
• Heart rate control
• Depolarisation to action potential in presynaptic -> post synaptic neurones
resulting in muscle contraction
• Immune Response
• Transpiration
• External environment resulting in selection pressures (new species forming)
External Environment:
Evidence of the importance of responses to changes in the internal
environment of an organism can be seen in a homeostatic process of glucose
regulation. This occurs as a section of the pancreas known as the Islets of
Langerhans detects changes in the concentration of blood glucose. If the
concentration is too low glucagon is secreted by the alpha cells, if
concentration is too high insulin is secreted by the beta cells where it binds to
receptors on target cells (liver/muscles). The insulin causes a conformational
change causing the number of carrier proteins in the cell membrane to
increase so that the rate of facilitated diffusion and glucose moving into the cell
would increase. This would decrease blood glucose concentration levels
restoring them to optimum levels, also reducing the concentration of solutes in
the blood so that the blood is not too thick and blood clots which may cause
myocardial infarction would not form. This therefore also regulates the water
potential of the blood as it would not decrease (due to the high concentration
of solutes) preventing water from surrounding cells to move down a water
potential gradient and enter by osmosis. This would prevent metabolic
processes from occurring within the cells where water is necessary acting as a
metabolite in condensation and hydrolysis reactions, such as in DNA replication
d t i th i I li l ti t ithi th ll i
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, 08/02/2025, 17:17 Biology Paper III Essays - Evernote
and protein synthesis. Insulin also activates enzymes within the cells increasing
the rate of glycogenesis (converting glucose -> glycogen). Glucagon on the
other hand provides a reverse reaction increasing the rate of gluconeogenesis
(non-carbohydrate substrates -> glucose for respiration) and glycogenolysis
(glycogen -> glucose) increasing blood glucose concentration. It activates the
enzyme adenylate cyclase which converts ATP to cAMP the secondary
messenger model. This activates the enzyme protein kinase A which causes a
cascade of reactions converting glycogen to glucose. This response to a
change in the internal environment is therefore vital as without it – too high
concentration of glucose can cause kidney failure and blindness, and too low
concentrations would cause fatigue and tiredness. The detrimental effects of
this can be seen in diabetes where the protein hormones are not produced and
cause various problems.
Chemoreceptors found in the carotid arteries, medulla, and aorta detect
changes in concentration of chemicals in the blood (O2/CO2), while
baroreceptors found in the carotid arteries and aorta detect changes in
pressure. For example, if an organism is escaping predators the concentration
of CO2 in the blood would increase, and O2 decrease. The baroreceptors
would detect this and send a signal to the medulla which would activate the
sympathetic nervous system which sends a signal to the SAN where the
neurotransmitter noradrenaline would be secreted. This would increase the rate
at which the SAN sends out waves of depolarisation causing the rate of atrial
systole and therefore heart rate to increase. Blood would be pumped around
the body much faster allowing the deoxygenated haemoglobin to become
saturated with O2 again, and the O2 to be delivered to the respiring tissues and
cells. This would allow aerobic respiration to occur as respiration proceeds into
the oxidative phosphorylation stage where O2 acts as the final electron
acceptor producing the final safe product of water. This allows there to be a
very large net gain in ATP, and anaerobic respiration which produces the toxic
product of lactic acid which causes an oxygen debt is not produced. Anaerobic
respiration (which occurs solely in glycolysis) only has a net gain of 2 X ATP
which would mean the organism has less energy, would be less successful in
escaping predators, and therefore less likely to survive. The response to an
increase in CO2 is also vital as the CO2 would dissolve in the blood to form
carbonic acid decreasing the pH of blood so the enzymes/proteins in the bond
would be denatured. The low pH would cause the Bohr effect however the
more acidic blood would cause the tertiary structure of the enzymes to change
as the ionic and hydrogen bonds are disrupted and the molecules would no
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The importance of responses to changes in
the internal and external environment of an
organism
The importance of responses to changes in the internal and external
environment of an organism
Internal Environment:
• Glucose concentration
• Heart rate control
• Depolarisation to action potential in presynaptic -> post synaptic neurones
resulting in muscle contraction
• Immune Response
• Transpiration
• External environment resulting in selection pressures (new species forming)
External Environment:
Evidence of the importance of responses to changes in the internal
environment of an organism can be seen in a homeostatic process of glucose
regulation. This occurs as a section of the pancreas known as the Islets of
Langerhans detects changes in the concentration of blood glucose. If the
concentration is too low glucagon is secreted by the alpha cells, if
concentration is too high insulin is secreted by the beta cells where it binds to
receptors on target cells (liver/muscles). The insulin causes a conformational
change causing the number of carrier proteins in the cell membrane to
increase so that the rate of facilitated diffusion and glucose moving into the cell
would increase. This would decrease blood glucose concentration levels
restoring them to optimum levels, also reducing the concentration of solutes in
the blood so that the blood is not too thick and blood clots which may cause
myocardial infarction would not form. This therefore also regulates the water
potential of the blood as it would not decrease (due to the high concentration
of solutes) preventing water from surrounding cells to move down a water
potential gradient and enter by osmosis. This would prevent metabolic
processes from occurring within the cells where water is necessary acting as a
metabolite in condensation and hydrolysis reactions, such as in DNA replication
d t i th i I li l ti t ithi th ll i
https://www.evernote.com/client/web#/notebook/6023ecd6-5695-e5af-51bd-423d67e1dfa4/note/f8800091-8030-0dde-8416-eb72e985699e i 1/5
, 08/02/2025, 17:17 Biology Paper III Essays - Evernote
and protein synthesis. Insulin also activates enzymes within the cells increasing
the rate of glycogenesis (converting glucose -> glycogen). Glucagon on the
other hand provides a reverse reaction increasing the rate of gluconeogenesis
(non-carbohydrate substrates -> glucose for respiration) and glycogenolysis
(glycogen -> glucose) increasing blood glucose concentration. It activates the
enzyme adenylate cyclase which converts ATP to cAMP the secondary
messenger model. This activates the enzyme protein kinase A which causes a
cascade of reactions converting glycogen to glucose. This response to a
change in the internal environment is therefore vital as without it – too high
concentration of glucose can cause kidney failure and blindness, and too low
concentrations would cause fatigue and tiredness. The detrimental effects of
this can be seen in diabetes where the protein hormones are not produced and
cause various problems.
Chemoreceptors found in the carotid arteries, medulla, and aorta detect
changes in concentration of chemicals in the blood (O2/CO2), while
baroreceptors found in the carotid arteries and aorta detect changes in
pressure. For example, if an organism is escaping predators the concentration
of CO2 in the blood would increase, and O2 decrease. The baroreceptors
would detect this and send a signal to the medulla which would activate the
sympathetic nervous system which sends a signal to the SAN where the
neurotransmitter noradrenaline would be secreted. This would increase the rate
at which the SAN sends out waves of depolarisation causing the rate of atrial
systole and therefore heart rate to increase. Blood would be pumped around
the body much faster allowing the deoxygenated haemoglobin to become
saturated with O2 again, and the O2 to be delivered to the respiring tissues and
cells. This would allow aerobic respiration to occur as respiration proceeds into
the oxidative phosphorylation stage where O2 acts as the final electron
acceptor producing the final safe product of water. This allows there to be a
very large net gain in ATP, and anaerobic respiration which produces the toxic
product of lactic acid which causes an oxygen debt is not produced. Anaerobic
respiration (which occurs solely in glycolysis) only has a net gain of 2 X ATP
which would mean the organism has less energy, would be less successful in
escaping predators, and therefore less likely to survive. The response to an
increase in CO2 is also vital as the CO2 would dissolve in the blood to form
carbonic acid decreasing the pH of blood so the enzymes/proteins in the bond
would be denatured. The low pH would cause the Bohr effect however the
more acidic blood would cause the tertiary structure of the enzymes to change
as the ionic and hydrogen bonds are disrupted and the molecules would no
https://www.evernote.com/client/web#/notebook/6023ecd6-5695-e5af-51bd-423d67e1dfa4/note/f8800091-8030-0dde-8416-eb72e985699e 2/5
