Science: Modeling Feedback Loops in Systems Worksheet

Question 1

A thermostat is set to 20°C. When the room temperature falls below 20°C, the heater turns on. When the room reaches 20°C, the heater turns off. Identify the feedback loop type and explain how it affects the system.

Accepted Answer

This is a negative feedback loop because the system responds to a change by reducing that change. When temperature drops, the heater raises it back toward the set point, helping maintain a stable room temperature.

Question 2

In a warming climate, Arctic sea ice melts. Dark ocean water absorbs more sunlight than bright ice, which causes more warming and more ice melt. Identify the feedback loop type and explain the cause-and-effect pattern.

Accepted Answer

This is a positive feedback loop because the initial warming is amplified. Warming melts reflective ice, darker water absorbs more solar energy, and that extra heat causes even more melting.

Question 3

Complete this feedback model using plus or minus signs: More exercise leads to increased body temperature. Increased body temperature leads to more sweating. More sweating leads to lower body temperature. Is the overall loop positive or negative?

Accepted Answer

Exercise has a positive relationship with body temperature, body temperature has a positive relationship with sweating, and sweating has a negative relationship with body temperature. The overall loop is negative because it counteracts the rise in body temperature.

Question 4

A population of rabbits grows when food is abundant. As the rabbit population increases, available food decreases. As food decreases, rabbit birth rates decrease. Explain why this is a negative feedback loop.

Accepted Answer

This is a negative feedback loop because population growth creates conditions that slow further growth. More rabbits reduce the food supply, and less food lowers birth rates, which helps limit the rabbit population.

Question 5

A student writes, 'All feedback loops are bad because they make systems unstable.' Correct this statement using examples of both positive and negative feedback.

Accepted Answer

The statement is incorrect because feedback loops can either stabilize or amplify change. Negative feedback, such as a thermostat, can keep a system stable, while positive feedback, such as melting sea ice lowering reflectivity, can make a change grow larger.

Question 6

During childbirth, pressure from the baby on the cervix causes the release of oxytocin. Oxytocin strengthens contractions, which increases pressure on the cervix and releases more oxytocin. Identify the loop type and explain when the loop stops.

Accepted Answer

This is a positive feedback loop because contractions and oxytocin release amplify each other. The loop stops when the baby is delivered, which removes the pressure on the cervix.

Question 7

A lake receives fertilizer runoff from nearby farms. Extra nutrients increase algae growth. When algae die, decomposers use oxygen, which lowers oxygen levels for fish. Create a simple causal chain and describe one possible feedback effect if fish populations decline.

Accepted Answer

A causal chain is fertilizer runoff increases nutrients, nutrients increase algae growth, dead algae increase decomposition, and decomposition lowers dissolved oxygen. If fish decline, fewer organisms may graze or disturb parts of the food web, which can change algae dynamics and may allow some imbalances to continue depending on the ecosystem.

Question 8

In a predator-prey system, an increase in deer provides more food for wolves. More wolves then hunt more deer, which can reduce the deer population. Explain how this feedback can help regulate the deer population.

Accepted Answer

This feedback can regulate the deer population because an increase in deer eventually supports more wolves, and more wolves increase predation on deer. The increased predation reduces deer numbers, which counteracts the original population increase.

Question 9

A model shows this loop: more atmospheric carbon dioxide leads to higher global temperature, higher temperature leads to thawing permafrost, and thawing permafrost releases more carbon dioxide and methane. Identify the feedback type and name one limitation of this simple model.

Accepted Answer

This is a positive feedback loop because warming can cause greenhouse gas release, which can cause more warming. One limitation is that the model leaves out factors such as plant growth, soil moisture, human emissions, and different rates of permafrost thaw.

Question 10

A person has high blood glucose after a meal. The pancreas releases insulin, which helps cells take in glucose and lowers blood glucose levels. Identify the feedback loop type and the regulated variable.

Accepted Answer

This is a negative feedback loop because the response lowers blood glucose back toward a normal range. The regulated variable is blood glucose concentration.

Question 11

Compare a stock market panic with a thermostat. In a panic, falling prices can cause more investors to sell, which lowers prices further. Explain which system is more likely to show positive feedback and which shows negative feedback.

Accepted Answer

The stock market panic is more likely to show positive feedback because falling prices encourage more selling, which can lower prices even further. The thermostat shows negative feedback because it acts to reduce temperature differences from the set point.

Question 12

A scientist builds a computer model of a forest fire system. The model includes temperature, dry vegetation, wind speed, and burned area. Explain how positive feedback could occur in this model and name one factor that could limit the feedback.

Accepted Answer

Positive feedback could occur if a growing fire dries nearby vegetation, making it easier for the fire to spread and burn a larger area. A limiting factor could be lack of fuel, lower wind speed, rain, firebreaks, or firefighting efforts.

Question 13

Two students disagree about a feedback diagram. Student A says a negative arrow always means the feedback loop is negative. Student B says the whole loop must be considered. Which student is correct, and why?

Accepted Answer

Student B is correct because the type of feedback depends on the effect of the entire loop, not just one arrow. A negative arrow shows an inverse relationship between two variables, but the full loop determines whether the original change is amplified or reduced.

Question 14

A city installs more bike lanes. More bike lanes make biking safer and easier. As more people bike, public support for bike infrastructure grows, leading to even more bike lanes. Identify the feedback loop type and explain one possible real-world limit.

Accepted Answer

This is a positive feedback loop because more bike lanes can increase biking, which can increase support for adding more bike lanes. A real-world limit could be available road space, funding, political opposition, weather, or the number of people willing to bike.

Question 15

Design a feedback loop model for one system of your choice, such as climate, ecosystems, the human body, economics, or technology. Name at least three variables, label the loop as positive or negative, and explain what the model predicts.

Accepted Answer

Answers will vary, but a complete response should name at least three connected variables, identify whether the loop is positive or negative, and explain the predicted system behavior. For example, in body temperature regulation, increased body temperature increases sweating, sweating increases cooling, and cooling lowers body temperature, so the model predicts negative feedback that helps restore a normal temperature.

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Science: Modeling Feedback Loops in Systems

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