HS-LS1-3: Investigating Feedback Mechanisms That Maintain Homeostasis
In plain English: HS-LS1-3 is the NGSS high school performance expectation that asks students to plan and conduct investigations that provide evidence that feedback mechanisms keep conditions inside living things within a stable range. Typical investigations track heart rate during and after exercise, stomata opening as moisture changes, and root growth at different water levels. It is usually taught in Biology.
Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.
Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.
Next Generation Science Standards · Disciplinary Core Idea: From Molecules to Organisms: Structures and Processes · Official standard
Students plan and conduct investigations whose data show feedback at work. Homeostasis means keeping conditions inside an organism, such as the carbon dioxide level of the blood or the water content of a plant, within a stable range. In a negative feedback loop, a change is detected by sensors, a control center compares it with the normal range, and effectors respond in a way that reduces the change. Students measure their own heart rate before, during and after exercise, count open and closed stomata in leaf peels from watered and unwatered plants, and plan a two-week investigation of root growth at different water levels. The focus is the practice: writing testable questions, choosing variables and controls, repeating trials, collecting data safely, and explaining why the results count as evidence of feedback.
The official Clarification Statement reads: "Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels." The Assessment Boundary reads: "Assessment does not include the cellular processes involved in the feedback mechanism." So the lesson treats feedback at the level of the organism and its organs: sensors, a control center and effectors. How cells detect signals, how guard cells change shape, and the role of hormones inside cells are beyond this standard and are not assessed.
Learning Objectives
By the end of this lesson, students will be able to:
Describe a negative feedback loop (change, sensor, control center, effector, response) and use it to explain how an organism maintains homeostasis
Plan an investigation with a testable question, independent, dependent and controlled variables, repeated trials, a data table and safety steps
Conduct a heart rate investigation, convert pulse counts to beats per minute, and find the change and the recovery time
Analyze data from stomata and root investigations and explain how they provide evidence of feedback in plants
Critique an investigation plan and a conclusion, and propose improvements
Prior Knowledge Required
Students should already be comfortable with:
The body is a system of interacting subsystems made of groups of cells MS-LS1-3
Sensory receptors respond to stimuli by sending messages to the brain MS-LS1-8
Environmental factors influence the growth of organisms MS-LS1-5
Independent, dependent and controlled variables in a fair test
Students find their pulse (two fingers on the side of the wrist, below the thumb) and count beats for 15 seconds while the teacher times. They multiply by 4 and write the result.
Warm-Up Prompt
"Predict your heart rate right after one minute of fast stepping in place, and again three minutes after you stop. Sketch the shape of the graph. Why would your body bring the rate back down instead of keeping it high?"
Collect a few sketches. Many show the rise; fewer show the return to resting. Tell students that the return is the key evidence: a feedback mechanism does not only respond to a change, it also stops responding when conditions are back in the normal range.
Direct Instruction20 minutes
Part 1: The feedback loop model. Project Diagram 1 and build the loop with the class:
Change (stimulus): a condition moves away from its normal range. During exercise, working muscles raise the carbon dioxide level of the blood.
Sensors detect the change and send signals. Sensors in blood vessels and the brain respond to the rising carbon dioxide.
Control center: the brain compares the signals with the normal range and sends signals to the effectors.
Effectors respond: the heart beats faster and breathing speeds up, moving more blood and air.
Negative feedback: the response reduces the original change. When exercise stops, the change shrinks, and heart rate returns to its resting range. In plants the same pattern appears over minutes (stomata) and days (roots).
Part 2: Turning a loop into an investigation. An investigation provides evidence of feedback when it shows both a response to a change and a return toward the normal range, or a response that reduces the change. Work through the examples below, then show Diagram 2.
Conducting: pulse counts to heart rate
A student counts 18 beats in 15 seconds at rest and 33 beats in 15 seconds right after two minutes of stepping. Find both heart rates and the percent increase.
Result: 18 × 4 = 72 bpm; 33 × 4 = 132 bpm. Increase: 132 - 72 = 60 bpm, and 60 ÷ 72 ≈ 0.833, about an 83% increase.
Conducting: recovery as evidence of feedback
Invented data: resting 70 bpm; after exercise, 130, 112, 96, 84, 76 and 72 bpm at 0, 1, 2, 3, 4 and 5 minutes. When is the rate within 5 bpm of resting?
Result: Within 5 bpm means 75 bpm or less. At 4 minutes it is 76; at 5 minutes it is 72. Recovery time: 5 minutes. The drops per minute are 18, 16, 12, 8 and 4 bpm: the rate falls fastest when it is farthest from resting.
Planning: variables for a stomata test
Question: "Does the water supply of a plant affect how many of its stomata are open?" Identify the variables.
Result: Independent: watering (watered daily vs not watered for 5 days). Dependent: percent of stomata open in leaf peels. Controlled: plant species and size, leaf age, light, temperature, time of day, and the method of making peels. Repeat: 3 leaves per plant, 3 microscope fields per leaf.
Conducting: stomata percentages
In leaf peels, 42 of 60 stomata are open in the watered plant and 9 of 60 in the unwatered plant (invented data). Find each percent and interpret.
Result: 42 ÷ 60 = 70% open; 9 ÷ 60 = 15% open. Closing stomata reduces water loss from the leaves, which helps keep the plant's water content in a stable range: a feedback response to low water.
Analyzing: root growth over days
After 14 days, well-watered bean seedlings have a mean root mass of 0.8 g and shoot mass of 2.0 g; seedlings given less water have 0.9 g of roots and 1.2 g of shoots (invented data). Compare root-to-shoot ratios.
Result: Watered: 0.8 ÷ 2.0 = 0.40. Less water: 0.9 ÷ 1.2 = 0.75. With less water the plants put relatively more growth into roots, which can take up more water: a slower feedback response.
Point out the difference in time scale: heart rate responds in seconds, stomata in minutes to hours, root growth over days. All three are responses that reduce a change.
Guided Practice15 minutes
Pairs analyze invented class data from an investigation of exercise intensity. Each value is the mean for 8 students who did each activity for 2 minutes. Recovery time is the time until the heart rate was within 5 bpm of resting.
Mean heart rate for three exercise intensities (invented data, 8 students each)
Activity (2 minutes)
Resting (bpm)
Peak (bpm)
Recovery time (min)
Walking in place
72
96
2
Step test
71
128
4
Jumping jacks
73
152
6
Find the rise from resting to peak for each activity. (24, 57 and 79 bpm.)
Describe the pattern between the size of the rise and the recovery time. (The larger the rise, the longer the recovery: 2, 4 and 6 minutes.)
Which result is evidence of feedback, and why? (All three rates rose with demand and returned toward resting when exercise stopped.)
Name two variables the class should have controlled. (For example, the length of the exercise, how long students rested first, and how pulse was measured.)
Different students did each activity. How could the class improve the design? (Have the same students do all three activities on different days, in a different order.)
Independent Practice10-15 minutes
Students write a complete plan for one investigation from the Clarification Statement that the class has not yet planned: stomata response to temperature, or root development at different water levels. The plan must include a testable question, a prediction based on the feedback model, the independent, dependent and controlled variables, the number of trials or plants, a data table, one safety step, and a sentence explaining what result would count as evidence of feedback. Students swap plans with a partner and check them against the list in the assessment guidance.
Closure5 minutes
Exit ticket: (1) Label the sensor, control center and effector in this loop: when a person stands up quickly, blood pressure drops, sensors in large arteries detect it, the brain sends signals, and the heart beats faster. (2) A student counts 21 beats in 15 seconds. What is the heart rate? (84 bpm.) (3) Name one variable you would control in the heart rate investigation.
Differentiation Strategies
For Struggling Students
Give a feedback loop template with four boxes and arrows already drawn, and a word bank
Give a planning frame with sentence starters: "I will change...," "I will measure...," "I will keep the same..."
Pair pulse counting with a partner who confirms the count, and allow a pulse app or monitor
For Advanced Students
Ask students to design a test that separates two effectors, such as heart rate and breathing rate, and graph both on one time axis
Ask students to compare a negative feedback loop with a positive one, such as a blood clot forming, and explain why homeostasis relies on negative feedback
Ask how the recovery time could be used to compare fitness, and what variables would make that comparison fair
Assessment Guidance
What to Look For
Strong plans have one independent variable, a measurable dependent variable with units, at least three controlled variables, repeated trials or several organisms, a data table set up before data collection, and a safety step. Strong conclusions connect the data to the loop: a change, a response, and a return toward the normal range or a reduction of the change. Watch for these errors: calling any response "feedback" without showing the return, changing two variables at once, drawing conclusions from one trial or one person, forgetting to multiply a 15-second count by 4, and mixing up sensors and effectors. Explanations of what happens inside cells are not required.
02
Classroom Activities
3 Activities
1
Heart Rate Feedback Investigation
30 minPairs
Pairs plan and conduct an investigation of how heart rate responds to exercise and how it returns to resting. They graph the results and use the recovery as evidence of a feedback mechanism.
Safety
Any student with a heart, breathing or joint condition, or who feels unwell, takes the timer and recorder role instead of exercising
Keep the exercise moderate: steady stepping, not a race. Stop at once if anyone feels dizzy, faint or short of breath
Use a sturdy step on a non-slip floor, or step in place
Plan First
Write the question, for example: "How does 2 minutes of stepping affect heart rate, and how long does it take to return to resting?"
List the variables and controls: same exercise, same length, same step height, same pulse method, seated rest before starting
Draw the data table: rest, then 0, 1, 2, 3, 4 and 5 minutes after stopping. Have the teacher approve the plan
Procedure
Sit quietly for 3 minutes, then count the pulse for 15 seconds twice and use the mean. Multiply by 4
Step up and down on the step for 2 minutes at a steady pace set by the teacher
Sit down and count the pulse for 15 seconds at once, then at the start of each minute for 5 minutes
Switch roles if time allows, then graph heart rate against time
If the Lab Does Not Work: Sample Data
Invented results for one student: resting 66 bpm; then 118, 101, 88, 79, 72 and 68 bpm at 0, 1, 2, 3, 4 and 5 minutes after stopping.
Discussion Questions
In the sample data, what was the rise from resting to the first reading? (52 bpm.) When was the rate within 5 bpm of resting? (At 5 minutes: 72 bpm at 4 minutes is still 6 above resting.)
Which part of the graph is the evidence of feedback, and why?
What was the sensor, the control center and the effector in this investigation?
How would you change the plan to find out whether the results apply to the whole class?
2
Stomata Peel Investigation
30 min (plus 5 days of preparation)Small groups (3-4)
Groups plan and carry out a test of whether a plant's water supply affects how many stomata are open. They make nail polish peels of leaf undersides, count open and closed stomata under the microscope, and connect the result to the feedback model.
Preparation
Five days before the lab, stop watering one of two potted plants of the same species and size (for example, two spider plants or two bean plants). Keep both plants in the same light and temperature, and water the other plant daily.
Safety
Use nail polish in a ventilated room, away from any flame or heat source; it is flammable
Wear goggles and handle glass slides by their edges
Carry microscopes with two hands
Procedure
Take 3 leaves from each plant at the same time of day. Paint a thin patch of clear nail polish on the underside of each leaf and let it dry for 5 minutes
Press clear tape on the dry polish, peel it off and stick it on a labeled slide
At 400× magnification, count the open and closed stomata in 3 fields of view per leaf
Record the counts in a table and find the percent open for each plant
If the Lab Does Not Work: Sample Data
Invented counts (open, closed) in three fields of view on one leaf from each plant. Watered plant: (12, 4), (11, 5), (13, 3). Unwatered plant: (3, 13), (2, 14), (4, 12).
Discussion Questions
What percent of stomata were open on each plant in the sample data? (36 of 48, or 75%, and 9 of 48, or 18.75%.)
How does closing stomata help the unwatered plant keep its water content stable?
How would you decide whether the difference between the two plants is large enough to trust?
Name one variable that could make the comparison unfair if it were not controlled.
Variation: Temperature
Groups that finish early plan a follow-up: keep two well-watered plants for 2 hours, one at room temperature and one in a warmer place, then compare peels. They choose a safe way to warm one plant, write a prediction before counting and report whether the data support it.
3
Root Response to Water Levels
20 min planning, then 5 min every 2 days for 2 weeksSmall groups (3-4)
Groups plan and set up a two-week investigation of how the amount of water affects root growth in radish seedlings, then analyze the results as evidence of a slower feedback response.
Plan First
Write a testable question and a prediction based on the feedback model
Choose three watering amounts, for example 10, 20 and 40 mL every 2 days, and list everything to keep the same: cup size, soil, seed type, light, temperature
Plan to grow 5 seedlings per cup and 2 cups per watering amount, and design the data table
Procedure
Plant 5 radish seeds against the side of each clear cup so the roots will be visible, 1 cm deep
Water each cup its amount every 2 days and keep all cups in the same place
After 14 days, gently wash the soil off and measure the longest root and the shoot height of each seedling
Wash hands after handling soil
If the Lab Does Not Work: Sample Data
Invented means after 14 days. 10 mL every 2 days: root length 9.5 cm, shoot height 4.0 cm; 20 mL every 2 days: root length 8.0 cm, shoot height 6.0 cm; 40 mL every 2 days: root length 5.5 cm, shoot height 7.0 cm.
Discussion Questions
Find the root-to-shoot ratio for each amount in the sample data. (About 2.4, 1.3 and 0.8.)
Which amount gave the longest roots, and how could longer roots help a plant with little water?
Why grow several seedlings per cup and use two cups per amount?
How is this response slower than stomata closing, and why might a plant need both?
Modification for Distance Learning
Students analyze the sample data, graph root length against the watering amount, and write a claim, evidence and reasoning paragraph about feedback.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Feedback Loop Model
A change in the blood during exercise is detected by sensors, the brain acts as the control center, and the heart and lungs act as effectors. Their response reduces the change, which is why this is negative feedback. The same four parts can be used to plan investigations of stomata and roots in plants.
Diagram 2: Heart Rate Recovery After Exercise
The graph is drawn to scale for the invented data in the second worked example. Heart rate jumps from 70 bpm at rest to 130 bpm and then falls toward resting, fastest at first. It first reaches the dashed line (75 bpm, within 5 of resting) at 5 minutes. The return is the evidence that feedback maintains homeostasis.
04
Homework Assignment
~30 min
HS-LS1-3 Homework: Investigating Feedback
Directions: Show calculations. In every plan, name the independent, dependent and controlled variables and the number of trials. In every explanation, connect the data to a feedback loop (change, sensor, control center, effector, response). All data sets are invented for practice.
Part 1: Feedback Models (Problems 1-2)
Draw a feedback loop model for body temperature on a hot day, when a person sweats, and a second loop for a cold day, when the person shivers. In each, label the change, the sensor, the control center, the effector and the response. Explain why both loops are negative feedback.
A plant in dry soil on a hot, windy afternoon starts to lose water from its leaves faster than its roots take it in. (a) Draw a feedback loop that explains how stomata help the plant keep its water content stable. (b) Closing the stomata also affects how much carbon dioxide can enter the leaf. Explain the trade-off for the plant.
Part 2: Planning Investigations (Problems 3-4)
Plan an investigation to answer: "Does air temperature affect the percent of open stomata in well-watered plants?" Include a prediction, the independent, dependent and controlled variables, how many plants, leaves and fields of view you will use, a data table, one safety step, and what result would support your prediction.
A student writes this plan: "I will run up the stairs as fast as I can for a while, then do push-ups, and check my heart rate once when I finish. If it is high, that proves feedback." (a) Identify three problems with the plan. (b) Rewrite the plan so it can provide evidence that feedback maintains homeostasis.
Part 3: Conducting and Analyzing (Problems 5-6)
A student counts pulse beats for 15 seconds: 16 at rest; then 36, 30, 24, 17, 16 and 16 at 0, 1, 2, 3, 4 and 5 minutes after 2 minutes of jumping. (a) Convert every count to beats per minute. (b) Find the rise from resting to the first reading after exercise. (c) When was the rate first within 5 bpm of resting? (d) Explain how these data provide evidence of a feedback mechanism.
Bean seedlings were grown for 14 days in tall tubes of sand. In one set, water was added only to the bottom layer; in the other, water was added at the top (invented data). Root depths for 5 seedlings in each set: bottom-watered 12, 13, 11, 14 and 10 cm; top-watered 6, 7, 5, 6 and 6 cm. (a) Find each mean. (b) By what percent is the bottom-watered mean greater? (c) Explain the result as a response that helps the plant maintain its water balance. (d) Name two variables that should have been controlled.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
No Credit (0 pts)
Feedback Model
All parts of the loop labeled correctly; response reduces the change
Several variables changed at once, or no measurement
Data Analysis
Conversions, means and percents correct with units
Correct method with one error
Calculations missing or wrong method
Evidence of Feedback
Explains how the data show a response and a return, or a reduction of the change
Response described but not linked to homeostasis
Data not used as evidence
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Pick or write an answer for each question, then reveal the explanation. The counter tracks your correct answers, and Reset quiz clears everything for a new try. All data are invented.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which statement best describes homeostasis?
Answer: C
Homeostasis is keeping conditions within a range, not at one fixed value. Choice A is too strict: heart rate and body temperature vary within a range. Choice B describes the opposite: a body that matched the environment would lose control of its internal conditions.
Question 2 of 20 · Multiple Choice
Which of these is an example of negative feedback?
Answer: A
The heater's response (warming) reduces the change that triggered it (cooling), and it stops once the room is back in range, which is negative feedback. Choice B is positive feedback: each change makes the next one larger. Choice D is a response with no sensor checking the result, so there is no feedback.
Question 3 of 20 · Multiple Choice
During exercise, carbon dioxide in the blood rises, sensors detect it, the brain sends signals, and the diaphragm and rib muscles contract faster so breathing speeds up. In this loop, the diaphragm and rib muscles are the
Answer: D
The diaphragm and rib muscles carry out the response, so they are effectors. The sensors detect the rising carbon dioxide, and the brain is the control center. The stimulus (choice C) is the rise in carbon dioxide itself.
Question 4 of 20 · Multiple Choice
A student counts 26 pulse beats in 15 seconds. What is the heart rate?
Answer: B
26 beats in 15 seconds is 26 × 4 = 104 beats per minute. Choice A adds 15 instead of multiplying by 4. Choice C forgets to convert to a full minute. Choice D multiplies by 15.
Question 5 of 20 · Multiple Choice
A student's heart rate rises from 64 bpm at rest to 120 bpm after exercise. What is the percent increase?
Answer: C
The rise is 120 - 64 = 56 bpm, and 56 ÷ 64 = 0.875, an 87.5% increase. Choice A gives the rise in bpm, not a percent. Choice B divides by the new value, 120, instead of the starting value. Choice D is the new rate as a percent of the old one.
Question 6 of 20 · Multiple Choice
In an investigation of heart rate and exercise, which is a controlled variable?
Answer: A
A hot room can raise heart rate by itself, so keeping the room temperature the same for every trial makes the comparison fair. Choices B and D are dependent variables, measured as results. Choice C is the independent variable when the question is about exercise type.
Question 7 of 20 · Multiple Choice
A class asks: "Does exercise intensity affect peak heart rate?" What is the independent variable?
Answer: B
The independent variable is the one the investigators change on purpose: the intensity. Choice A is the dependent variable they measure. Choice D should be measured, and kept similar, before each trial.
Question 8 of 20 · Multiple Choice
Invented data: Student X recovers to within 5 bpm of resting in 3 minutes after a step test; Student Y takes 7 minutes after the same test. Which conclusion is best supported?
Answer: D
Both rates returned toward resting, which is the evidence of feedback; only the time differs. Choice A is contradicted by Student Y's return. Choice B has no support: the question says both did the same test.
Question 9 of 20 · Multiple Choice
Leaf peels from a watered plant show 32 open stomata out of 40; peels from a plant not watered for 5 days show 5 open out of 40 (invented data). Which interpretation fits the feedback model?
Answer: C
32 ÷ 40 = 80% and 5 ÷ 40 = 12.5%, and both counts are out of 40 stomata, so the total is the same. Closing stomata reduces water loss, the response that helps keep water content stable. Choice A misreads the data. Choice B reverses the direction: stomata release water vapor, they do not take in water.
Question 10 of 20 · Multiple Choice
Why should students count stomata in several fields of view on several leaves?
Answer: A
Counts differ from field to field and leaf to leaf, so repeating the count gives a more reliable percent. Choice B has nothing to do with sample size. Choice D is false: a single field usually contains many stomata.
Question 11 of 20 · Multiple Choice
Invented results after 14 days: radish seedlings given 10 mL of water every 2 days have a mean root length of 12 cm and shoot height of 3 cm; seedlings given 50 mL have roots of 6 cm and shoots of 10 cm. Which statement is best supported?
Answer: B
The root-to-shoot ratio is 12 ÷ 3 = 4.0 with little water and 6 ÷ 10 = 0.6 with more water. Longer roots can reach more water, a response that reduces the water shortage. Choice A is contradicted: roots were longer with less water. Choice D is contradicted by the change from 3 cm to 10 cm.
Question 12 of 20 · Multiple Choice
Invented data from two students who did the same 2-minute step test. Student 1: 70 bpm at rest, 120 bpm right after, and still 120 bpm ten minutes later. Student 2: 70 bpm at rest, 120 bpm right after, and 72 bpm six minutes later. Which data set is better evidence that feedback controls heart rate?
Answer: D
Feedback means the response depends on the condition, so the rate should fall once exercise stops. Student 2 shows the rise and the return. Choice B counts only the rise, which shows a response but not control. Student 1's data would call for rechecking the measurement or the student's health, not show feedback.
Question 13 of 20 · Multiple Choice
In the temperature follow-up to the stomata lab, a group wants to keep one well-watered plant warmer than another for 2 hours. Which method is safest?
Answer: A
A lamp at a distance warms the plant gently, and keeping the cord away from water prevents shocks. Choices B and C add high heat and, for C, an open flame near flammable nail polish. Choice D puts an electrical device next to water.
Question 14 of 20 · Multiple Choice
A plan tests whether low water affects root growth, but every cup gets 10 mL of water every 2 days. What is the most important change to the plan?
Answer: B
Without a second water level there is nothing to compare, so the plan cannot show an effect of water. Choice A and choice D add new variables, which makes the test unfair. Choice C gives roots too little time to respond.
Question 15 of 20 · Short Answer
Pulse counts for 15 seconds (invented): 16 at rest; 34, 28, 24, 20, 17 and 16 at 0, 1, 2, 3, 4 and 5 minutes after exercise. Convert to beats per minute and find when the rate is first within 5 bpm of resting.
Rest: 16 × 4 = 64 bpm. After exercise: 136, 112, 96, 80, 68 and 64 bpm. Within 5 bpm of resting means 69 bpm or less, so the rate is first within range at 4 minutes (80 at 3 minutes is still 16 above resting).
Question 16 of 20 · Short Answer
Plan an investigation of whether the length of exercise affects heart rate recovery time. Name the independent, dependent and three controlled variables, and describe your trials.
Independent: length of exercise (for example, 1, 2 and 3 minutes of stepping). Dependent: recovery time, the minutes until heart rate is within 5 bpm of resting. Controlled: type and pace of exercise, step height, rest before each trial, pulse method, time of day. Trials: several students each do every length on different days, in a different order, with the mean used for each length. Safety: moderate pace, and anyone who feels unwell stops.
Question 17 of 20 · Short Answer
On a hot day a person has not had anything to drink for several hours. Draw or describe a feedback loop that brings the body's water content back to its normal range. Label each part.
Change: the body's water content falls. Sensor: sensors in the brain detect the change. Control center: the brain. Effectors: the person feels thirsty and drinks (muscles carry out the drinking), and the kidneys release less water in urine. Response: water content rises back toward normal, which reduces the change, so this is negative feedback.
Question 18 of 20 · Short Answer
Invented data after 14 days: seedlings watered only at the bottom of deep pots have a mean root mass of 1.4 g and shoot mass of 1.6 g; seedlings watered at the top have 0.6 g of roots and 1.6 g of shoots. Find both root-to-shoot ratios and explain what they show.
Bottom-watered: 1.4 ÷ 1.6 = 0.875. Top-watered: 0.6 ÷ 1.6 = 0.375. The bottom-watered plants put relatively more growth into roots, which reach the water deep in the pot. This response reduces the plant's water shortage, so it helps maintain water balance over days.
Question 19 of 20 · Short Answer
A plant in dry soil has closed most of its stomata. It is then watered well. Use the feedback model to predict what happens to its stomata over the next few hours, and explain why.
The stomata open again. Watering removes the change (low water content) that triggered the response, so the signal to close ends. Open stomata let carbon dioxide into the leaf again, though the plant also loses more water vapor. This shows negative feedback: the response lasts only while the change it reduces is present.
Question 20 of 20 · Short Answer
A student measures their own heart rate once before and once after a 1-minute sprint and concludes: "Everyone's heart rate doubles after exercise, and it never goes back down." Critique the conclusion.
The conclusion goes beyond the evidence: one person and one trial cannot show what happens to everyone, and a single reading after exercise cannot show whether the rate goes back down. An improved investigation measures several students, repeats trials, and records the rate every minute for several minutes after exercise, which would show the return to resting that is the evidence of feedback.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS1-3 mean?
HS-LS1-3 asks students to plan and conduct an investigation that provides evidence that feedback mechanisms maintain homeostasis. Students do not only describe feedback: they design a fair test, collect data, and explain how the data show an organism responding to a change and returning to a stable range.
What investigations work for HS-LS1-3?
The Clarification Statement suggests heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels. All three can be done safely in a classroom: pulse counts before and after stepping, nail polish peels of leaves, and radish or bean seedlings grown with different amounts of water.
Does HS-LS1-3 include hormones and cell signaling?
No. The Assessment Boundary says assessment "does not include the cellular processes involved in the feedback mechanism." Students work with the loop at the level of the organism: sensors, a control center and effectors. What happens inside cells, such as how guard cells change shape, is beyond this standard.
Is a rise in heart rate enough evidence of feedback?
Not on its own. A rise shows a response. Evidence of feedback also shows that the response depends on the condition: when exercise stops, heart rate falls back to its resting range. That is why investigations should record heart rate for several minutes after exercise.
Is HS-LS1-3 taught in Biology?
Yes, it is usually taught in high school Biology or Life Science, often right after HS-LS1-2, since feedback depends on systems that interact. It also fits naturally with lab skills units because it is built around planning and conducting investigations.
How do I keep the heart rate investigation safe?
Keep the exercise moderate and short, such as 2 minutes of steady stepping. Students with a heart, breathing or joint condition, or anyone who feels unwell, take the timer or recorder role. Stop anyone who feels dizzy or faint. The data from a few volunteers are enough for the whole class to analyze.
What mistakes do students make when planning HS-LS1-3 investigations?
Frequent ones are changing two variables at once, measuring only once, testing one person and generalizing to everyone, having no comparison group, and calling any response "feedback" without showing the return to the normal range. A planning checklist catches most of these.
Why do stomata count as evidence of homeostasis?
Stomata are pores in leaves that let water vapor out and carbon dioxide in. When a plant is short of water, many stomata close, which reduces water loss and helps keep the plant's water content stable. Comparing peels from watered and unwatered plants shows this response directly.
What is the difference between negative and positive feedback?
In negative feedback the response reduces the change, which keeps conditions stable; homeostasis relies on it. In positive feedback the response makes the change larger until some event ends it, such as the steps in forming a blood clot. HS-LS1-3 focuses on negative feedback.
What comes after HS-LS1-3?
Students use the same systems thinking in ecology: HS-LS2-6 asks how complex interactions in ecosystems keep numbers of organisms relatively stable, a kind of balance at a larger scale. The planning skills carry over to every later investigation, including engineering tests in HS-ETS1-3.
07
Related Standards
5 standards
These standards connect to HS-LS1-3: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS1-3Prerequisite
Argue with evidence that the body is a system of interacting subsystems of cells
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
