Feedback Mechanisms – Negative & Positive Feedback | Class 11 Biology Chapter 13
🔵 13.1.2 FEEDBACK MECHANISMS
🟢 Introduction
Our body is constantly changing. Temperature rises and falls, blood sugar changes after meals, blood pressure increases during exercise, and hormones are released at different times.
How does the body know when to stop or continue a response?
The answer is Feedback Mechanisms.
A Feedback Mechanism (a self-regulating process in which the result of an action controls that same action) helps the body maintain homeostasis (a stable internal environment).
Figure 13.8 – Feedback Mechanism Overview Caption: Homeostasis is maintained by two types of feedback mechanisms – Negative Feedback and Positive Feedback. Attribution: Biology Online / educational resources.
🟣 What is Feedback?
Imagine you are filling a water tank. When the tank becomes full, ➡ the automatic switch turns the motor OFF.
This is feedback because the result controls the process. Our body works in exactly the same way.
🟢 Types of Feedback Mechanisms
There are two types:
1️⃣ Negative Feedback 2️⃣ Positive Feedback
🔵 NEGATIVE FEEDBACK
📖 Definition
Negative Feedback (a mechanism that reverses or reduces the original change) is the most common homeostatic mechanism. It brings the body back to its normal condition (set point).
Instead of increasing the problem, it reduces the problem.
🧠Easy Definition
Negative Feedback stops the change and returns the body to normal.
📦 Important Point
Nearly all daily body regulation works through negative feedback.
Examples include: ✅ Body temperature ✅ Blood glucose ✅ Blood pressure ✅ Water balance ✅ Hormone secretion
Figure 13.9 – Negative Feedback (Body Temperature) Caption: Negative feedback restores body temperature to its normal value (37°C). Attribution: Human Biology Pressbooks / educational resources.
🌡️ Example: Body Temperature Regulation
Suppose the weather becomes very hot.
Step 1 Body temperature rises above 37°C. ↓ Step 2 Thermoreceptors (temperature-sensing receptors) detect the increase. ↓ Step 3 Signals are sent to the Hypothalamus (temperature control centre in the brain). ↓ Step 4 The hypothalamus activates: ✔ Sweat glands ✔ Skin blood vessels ↓ Step 5 Sweat evaporates. Blood vessels widen (vasodilation). Heat leaves the body. ↓ Step 6 Temperature returns to 37°C. ↓ Step 7 The thermoreceptors stop sending signals. The response ends.
🔄 Negative Feedback Flowchart
Body Temperature ↑
│
▼
Thermoreceptors Detect Heat
│
▼
Hypothalamus
(Control Centre)
│
▼
Sweat Glands Activated
│
▼
Sweating + Vasodilation
│
▼
Heat Lost
│
▼
Body Temperature Returns to 37°C🧠Memory Trick
Negative ↓ “NEGATIVE = NORMAL” It always tries to return the body to NORMAL.
📦 Everyday Examples
| Situation | Negative Feedback Response |
|---|---|
| Hot weather | Sweating |
| Cold weather | Shivering |
| High blood sugar | Insulin released |
| Low blood sugar | Glucagon released |
| High blood pressure | Heart slows down |
🔴 POSITIVE FEEDBACK
📖 Definition
Positive Feedback (a mechanism that increases or strengthens the original change) continues the response until a particular event is completed.
Unlike negative feedback, it does NOT stop the change. Instead, it makes the change stronger.
🧠Easy Definition
Positive Feedback keeps increasing the response until the job is finished.
📦 Important Point
Positive feedback is rare in the human body. It is only used when rapid action is needed.
Common Examples ✔ Childbirth ✔ Blood clotting ✔ Milk ejection during breastfeeding
Figure 13.10 – Positive Feedback During Childbirth Caption: Oxytocin strengthens uterine contractions until the baby is born. Attribution: StoryMD / educational medical diagram.
👶 Example: Childbirth
During labour, the baby’s head presses against the cervix. ↓ Stretch receptors detect pressure. ↓ Signals travel to the Hypothalamus. ↓ The Pituitary Gland (hormone-producing gland below the brain) releases Oxytocin (a hormone that causes stronger uterine contractions). ↓ Contractions become stronger. ↓ The baby’s head presses even harder. ↓ More oxytocin is released. ↓ Even stronger contractions occur. ↓ Finally, the baby is born. The cycle immediately stops.
🔄 Positive Feedback Flowchart
Baby Pushes Against Cervix
│
▼
Stretch Receptors Activated
│
▼
Hypothalamus
│
▼
Pituitary Releases Oxytocin
│
▼
Stronger Contractions
│
▼
More Pressure
│
▼
More Oxytocin
│
▼
Baby Born⚠ Unregulated Positive Feedback
Normally, positive feedback stops after completing its task. Sometimes, it becomes dangerous.
For example, during severe infection, immune cells release Cytokines (small proteins that allow immune cells to communicate).
Too many cytokines can cause a Cytokine Storm (an uncontrolled immune response) leading to excessive inflammation and damage to healthy tissues.
📊 Comparison Table
| Feature | Negative Feedback | Positive Feedback |
|---|---|---|
| Purpose | Restores normal conditions | Increases the response |
| Goal | Maintain homeostasis | Complete a process |
| Common? | Very common | Rare |
| Stops When | Body returns to normal | Event is completed |
| Examples | Sweating, Shivering, Blood Sugar | Childbirth, Blood Clotting |
🧠Easy Memory Trick
❄️ Negative Feedback N = Normal Returns the body to Normal.
🔥 Positive Feedback P = Pushes Process Forward Keeps pushing until the work is complete.
⭐ Board Exam Tips
Frequently Asked Short Questions ✅ Define Negative Feedback. ✅ Define Positive Feedback. ✅ Give two examples of Negative Feedback. ✅ Explain Positive Feedback with the example of childbirth.
Frequently Asked MCQs ✔ Human body temperature is controlled by → Hypothalamus ✔ Oxytocin is released from → Pituitary gland ✔ Sweating is an example of → Negative Feedback ✔ Childbirth is an example of → Positive Feedback
📌 Quick Revision Box
✔ Homeostasis depends mainly on Negative Feedback. ✔ Negative Feedback reduces the original change. ✔ Positive Feedback increases the original change. ✔ Sweating and shivering are examples of Negative Feedback. ✔ Childbirth and blood clotting are examples of Positive Feedback. ✔ Positive Feedback stops only after the process is completed.
30 MCQs – Feedback Mechanisms
(Based on Past Paper Patterns of Punjab Boards)
1. Homeostasis is mainly maintained by: A) Positive feedback B) Negative feedback C) Neutral feedback D) Both A and B
Answer: B) Negative feedback
2. Which of the following is an example of negative feedback? A) Childbirth B) Blood clotting C) Sweating D) Milk ejection
Answer: C) Sweating
3. Positive feedback: A) Reverses the original change B) Increases the original change C) Maintains set point D) Stops the response immediately
Answer: B) Increases the original change
4. The control centre for body temperature is: A) Cerebrum B) Cerebellum C) Hypothalamus D) Medulla oblongata
Answer: C) Hypothalamus
5. Oxytocin is released from: A) Thyroid gland B) Adrenal gland C) Pituitary gland D) Pancreas
Answer: C) Pituitary gland
6. Childbirth is an example of: A) Negative feedback B) Positive feedback C) Both D) None
Answer: B) Positive feedback
7. In negative feedback, the response: A) Amplifies the stimulus B) Reduces the stimulus C) Has no effect D) Continues indefinitely
Answer: B) Reduces the stimulus
8. Which of the following is NOT an example of negative feedback? A) Regulation of blood glucose B) Regulation of body temperature C) Uterine contractions during labour D) Regulation of blood pressure
Answer: C) Uterine contractions during labour
9. When body temperature rises above 37°C, the hypothalamus causes: A) Vasoconstriction B) Shivering C) Sweating D) Increase in metabolic rate
Answer: C) Sweating
10. The set point of human body temperature is: A) 35°C B) 36°C C) 37°C D) 38°C
Answer: C) 37°C
11. Positive feedback continues until: A) Set point is reached B) The event is completed C) Stimulus is removed by negative feedback D) Hormones are finished
Answer: B) The event is completed
12. Which hormone is involved in positive feedback during childbirth? A) Insulin B) ADH C) Oxytocin D) Glucagon
Answer: C) Oxytocin
13. Negative feedback is also called: A) Amplifying feedback B) Corrective feedback C) Destructive feedback D) Neutral feedback
Answer: B) Corrective feedback
14. When the body becomes cold, negative feedback causes: A) Vasodilation and sweating B) Vasoconstriction and shivering C) Decrease in metabolic rate D) Release of oxytocin
Answer: B) Vasoconstriction and shivering
15. Which of the following statements is correct about positive feedback? A) It is very common in the body B) It restores normal conditions C) It is rare and used for rapid processes D) It always maintains homeostasis
Answer: C) It is rare and used for rapid processes
16. Thermoreceptors detect change and send signals to: A) Effectors B) Control centre C) Muscles only D) Glands only
Answer: B) Control centre
17. In the water tank example, turning off the motor when the tank is full is an example of: A) Positive feedback B) Negative feedback C) Both D) None
Answer: B) Negative feedback
18. Blood clotting is an example of: A) Negative feedback B) Positive feedback C) Both A and B D) Neither
Answer: B) Positive feedback
19. The hypothalamus is called the body’s: A) Thermostat B) Pump C) Filter D) Sensor only
Answer: A) Thermostat
20. Which of the following occurs in negative feedback for high body temperature? A) Shivering B) Vasoconstriction C) Vasodilation D) Increase in thyroxine
Answer: C) Vasodilation
21. Cytokine storm is an example of: A) Regulated negative feedback B) Unregulated positive feedback C) Normal homeostasis D) Thermoregulation
Answer: B) Unregulated positive feedback
22. The most common type of feedback in the human body is: A) Positive feedback B) Negative feedback C) Both equally common D) Neutral feedback
Answer: B) Negative feedback
23. During labour, stretch receptors in the cervix send signals to: A) Pituitary gland directly B) Hypothalamus C) Thyroid gland D) Adrenal gland
Answer: B) Hypothalamus
24. Negative feedback always tries to: A) Increase the change B) Return the body to set point C) Complete a process D) Amplify the stimulus
Answer: B) Return the body to set point
25. Which of the following is a correct pair? A) Sweating – Positive feedback B) Childbirth – Negative feedback C) Shivering – Negative feedback D) Blood clotting – Negative feedback
Answer: C) Shivering – Negative feedback
26. Oxytocin causes: A) Relaxation of uterine muscles B) Stronger uterine contractions C) Decrease in pressure D) Stoppage of labour
Answer: B) Stronger uterine contractions
27. In negative feedback for high blood glucose: A) Glucagon is released B) Insulin is released C) ADH is released D) Oxytocin is released
Answer: B) Insulin is released
28. Positive feedback loop stops when: A) Set point is restored B) The stimulus is removed (e.g., baby is born) C) Hormones are depleted D) Temperature becomes normal
Answer: B) The stimulus is removed (e.g., baby is born)
29. Which statement is TRUE? A) Positive feedback maintains homeostasis B) Negative feedback is rare C) Negative feedback reverses the change D) Positive feedback reduces the original stimulus
Answer: C) Negative feedback reverses the change
30. The main purpose of negative feedback is to: A) Amplify changes B) Maintain stable internal environment C) Complete rapid processes D) Increase hormone secretion continuously
Answer: B) Maintain stable internal environment
Quick Answer Key
1-B, 2-C, 3-B, 4-C, 5-C, 6-B, 7-B, 8-C, 9-C, 10-C, 11-B, 12-C, 13-B, 14-B, 15-C, 16-B, 17-B, 18-B, 19-A, 20-C, 21-B, 22-B, 23-B, 24-B, 25-C, 26-B, 27-B, 28-B, 29-C, 30-B
Sources / Pattern Mention: These MCQs are prepared according to the pattern of Punjab Board past papers (especially BISE Lahore, Faisalabad, Gujranwala, Multan) and standard FSc resources. Questions on negative feedback (sweating, shivering, body temperature) and positive feedback (childbirth + oxytocin) are among the most frequently repeated objective questions
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