homeostasis and negative feedback Flashcards
What is homeostasis?
The maintenance of an organism’s internal environment within restricted limits.
Why is homeostasis important for enzymes?
Enzymes are proteins and rely on constant conditions for their structure. A change in temperature or pH will affect the H-bonds in the tertiary structure of the active site, changing the shape so it is no longer complimentary to the substrate. This will reduce the rate of reaction.
Why is homeostasis important for cells?
Changes to water potential due to the number of ions or glucose in the blood or volume of water will causes cells to shrink or expand (even bursting). To stop this a constant environment is needed.
Why is homeostasis important for independence?
Being able to maintain a constant internal environment means organisms can move round the environment so has a greater range.
Describe negative feedback.
A receptor detects a change from the optimum, the coordinator tells an effector to bring about a corrective measure to return the system to the optimum. The receptor detects the return to the optimum and turns off the corrective measure.
Describe positive feedback.
A receptor detects a change, the feedback causes the system to deviate further from the optimum.
Give an example of positive feedback.
In neurones- when a stimulus causes a small influx of sodium ions (generator potential) and the influx increases the permeability of membrane to sodium ions (by opening the voltage gated sodium ion channels) so more sodium ions enter causing an action potential.
Explain why negative feedback is important.
A change can occur, negative feedback brings the change back to the optimum, limiting the effect of the change.
How many different control mechanisms are needed for positive feedback?
Two separate mechanisms controls departures in different directions from the original state, giving a greater degree of control
