Homeostasis: how the body keeps things steady

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   The run lasts from minute 0 to minute 15, and the set point is about 37 °C. Kira reads the exercise card. After minute 15, temperature, skin blood flow and sweat all fall. What does this show about the loop?

   • The set point fell, so less cooling was needed
   • The loop switched off because the temperature reached exactly 37 °C
   • The stimulus shrank as the temperature fell, so the response eased
   • The response grew stronger as the temperature fell, pushing it further
2. 2.

   Esme reads a graph of the glucose level after meal A and meal B. Which statement does the graph support?

   • Meal A took longer than meal B to return inside the range
   • Both lines end at exactly 90 mg/dL, so the loop holds the set point
   • Meal A kept rising after 30 minutes, so the response pushed it further
   • Meal B raised the level higher and took longer to return inside the range
3. 3.

   Bo edits a model of the body temperature loop: the arrow from the control center to the effectors is cut. Body temperature then rises above 37 °C. What does the model predict?

   • The temperature falls back, because the sensors make the response themselves
   • The temperature stays above the set point, because the effectors get no order
   • The temperature rises faster, because the cut arrow makes the loop positive
   • The temperature stays at exactly 37 °C, because the set point holds it there
4. 4.

   In a model, Jun changes the loop so that, after a meal, the pancreas releases glucagon instead of insulin. What happens to the glucose level?

   • It falls, because negative feedback lowers a level
   • It stays inside the range, because the loop still reverses the change
   • It rises further, because glucagon raises the glucose level
   • It stays the same, because glucagon has no effect after a meal
5. 5.

   “model, not to scale” Noah tests a model of the ADH loop when body fluid volume is low. Which change would make the model lose less water?

   • More ADH reaches the kidneys, so they release more water
   • Less ADH reaches the kidneys, so they take back more water
   • More ADH reaches the kidneys, so they take back more water
   • The kidneys release ADH, so the pituitary takes back more water

6. Read this first

   Use this

   Notebook (model data), 4 rows. Columns: line, what it says. 1, Temperature sensors detect a rise in body temperature. 2, The control center compares the value with the set point. 3, The sensors then make the response, such as sweating. 4, The response brings body temperature back toward the set point.

7. 6.

   Ari reviews a classmate's notebook on the body temperature loop. Exactly one line is wrong. Which line, and why?

   • Line 3, because the effectors, not the sensors, make the response
   • Line 2, because the sensors compare the value with the set point
   • Line 1, because the control center detects a rise in temperature
   • Line 4, because the response makes the temperature rise more

8. Use this

   Notebook (model data), 4 rows. Columns: line, what it says. 1, In a negative loop, the response reverses the change. 2, In a positive loop, the response pushes the change further. 3, A positive loop in the body runs until it reaches an end point. 4, Positive feedback is the usual kind in the body, and negative is rare.

9. 7.

   Pia reviews a classmate's notebook on kinds of feedback. Exactly one line is wrong. Which line, and why?

   • Line 1, because a negative loop lowers a level instead of reversing a change
   • Line 3, because a positive loop has no end point
   • Line 4, because negative feedback is the usual kind in the body
   • Line 2, because a positive loop reverses the change that started it

10. Use this

    Two models (not to scale). Model 1, body temperature: when body temperature rises above about 37 °C, sweat is released and the temperature falls back. Model 2, clotting boxes: early clotting factor activates next clotting factor, which activates thrombin; thrombin activates more early clotting factors until a clot is complete.

11. 8.

    Ren compares the body temperature loop with the clotting boxes. Which statement compares them correctly?

    • Both models push their change further until an end point, so both are positive
    • Model 1 reverses its change, while Model 2 adds to its change until an end point
    • Model 1 is harmful because it is negative, while Model 2 is the helpful kind
    • Model 1 is negative, while Model 2 is the helpful positive loop that keeps the body steady

12. Use this

    Two loops (model, not to scale) for the glucose level, normal range about 70 to 100 mg/dL. Loop 1: the level rises above the range, insulin is released, and the level falls. Loop 2: the level falls below the range, glucagon is released, and the level rises.

13. 9.

    Tala claims the glucose system is not negative feedback, because glucagon raises the level. Is the claim sound?

    • No: each loop reverses a change, so raising a low level is also negative feedback
    • Yes: negative feedback lowers a level, and glucagon raises it
    • Yes: the glucagon loop helps the body, and negative feedback is the harmful kind
    • No: raising a low level helps the body, so Loop 2 is positive feedback

14. Use this

    Two loops (model, not to scale). ADH loop: body fluid volume is low, ADH reaches the kidneys, and they take back more water. Glucose loop: the glucose level rises after a meal, insulin is released, and liver, muscle and fat cells take up glucose.

15. 10.

    Zee compares the ADH loop with the glucose loop after a meal. What do the two loops have in common?

    • In each, the sensor is the part that carries out the response
    • Each has a response that pushes the change further until an end point
    • Each has a response that reverses the change that started it
    • In each, the controlled value stays at exactly its set point