Feedback Loops Flashcards
Feedback Loops
Feedback loops occur when a change in some quantity causes a later change in the same quantity
Why do we need mathematical models?
Systems with feedback often behave counterintuitively, so we need mathematical models to study them.
Negative Feedback
occurs when an increase in a quantity causes a later decrease in that quantity, and a decrease in a quantity causes a later increase in that quantity. Essentially maintaining equilibrium.
Positive Feedback
occurs when an increase in a quantity causes a later increase in that same quantity, and a decrease in a quantity causes a later decrease in that quantity.
Time Series
A graph that shows how quantities change over time
Time Delay
The period of time between input of feedback stimulus and the system’s response to it.
What is positive feedback also called and why?
reinforced feedback bc positive feedback reinforces change
Sharks/Tuna
What type of feedback is this?
When the tuna population increases, there is more food for sharks, so their population increases. The sharks eat the tuna, so an increase in the shark population causes a decrease in the tuna population.
Negative Feedback
Population Growth
What kind of feedback is this?
Animals have young, which increases the population. The larger the population is, the more babies are born, which makes the population even larger. As long as resources
are available, the population will keep growing.
Positive Feedback
CO2 Emissions
What kind of feedback is this?
Carbon dioxide emissions trap heat, which raises global temperatures. At higher
temperatures, soil microbes have faster metabolic rates, which means that they break down soil
organic matter faster, releasing even more CO2.
Positive Feedback
Insulin/Blood Sugar
Blood sugar increases, which leads to increase in insulin, which causes a decrease in blood sugar
Negative Feedback
Hormone Regulation
. For example, the gonadal hormones estradiol and
progesterone (in females) and testosterone (in males) are under negative feedback regulation
by the brain/pituitary system.
Negative Feedback
Methane Emissions
Methane is a greenhouse gas 25 times more potent than CO2. Large amounts
of methane are trapped in Arctic permafrost and at the bottom of the ocean. Rising temperatures
cause this methane to be released, contributing to further temperature increases
Positive Feedback
Gene Regulation
Many genes inhibit their own transcription, resulting in oscillating gene expression. For example, one protein that is essential in the early development of the embryo is called Hes1. Hes1 protein is produced by transcription from messenger RNA (mRNA). But then the protein inhibits its own transcription.
Negative Feedback
Stock Market Bubbles/Crashes
In a market bubble, investors buy into a stock, which causes the price to rise, which encourages more investors to buy, on the grounds that the stock is “going up.” In a crash, investors sell the stock, which lowers the price, which convinces others to sell
because the stock is “going down.
Positive Feedback
