UNIT_4_AP_BIO_Teacher__Lesson_2_

Lesson Overview

• Aim: Understand the difference between positive and negative feedback mechanisms.

Feedback Mechanisms

Positive Feedback

• Definition: Amplifies or increases a response to a stimulus.

• Examples:

  • Childbirth: Hormones increase contractions.

  • Blood clotting: Platelets release chemicals that attract more platelets.

  • Fruit ripening: Ethylene production signals neighboring apples to ripen.

Negative Feedback

• Definition: Slows down or stops a response, helping to maintain homeostasis.

• Examples:

  • Regulation of body temperature: Sweat production to cool the body.

  • Blood sugar levels: Insulin decreases glucose levels.

  • Breathing rate: Increases with CO2 levels in blood.

Learning Objectives

ENE 3A

• Describe positive and/or negative feedback mechanisms.

ENE 3B

• Explain how negative feedback helps to maintain homeostasis.

ENE 3C

• Explain how positive feedback affects homeostasis.

Homeostasis

• Definition: The state of relatively stable internal conditions.

• Importance: Essential for organisms to detect and respond to stimuli.

• Mechanism: Maintained through feedback loops.

Set Points

• Definition: Values the body tries to maintain for physiological conditions.

• Example of Body Temperature:

  • Set Point: 98.6°F

  • Normal Range: 97°F to 99°F

Feedback Loops

Components

• Stimulus: A variable that causes a response.

• Receptor/Sensor: Organs that detect a stimulus and send information to the control center (brain).

• Effector: Muscle or gland that responds to the stimulus.

• Response: Change that modifies the effects of the stimulus.

Types of Feedback Loops

• Negative Feedback: Most common; reduces the effect of the stimulus.

• Positive Feedback: Increases the effect of the stimulus.

Detailed Examples of Feedback Mechanisms

Negative Feedback in Action

• Body Temperature Regulation:

  • Stimulus: Heat

  • Receptor: Skin receptors

  • Effector: Sweat glands

  • Response: Sweating to cool down.

  • Cold Response:

  • Stimulus: Cold

  • Receptor: Skin receptors

  • Effector: Muscles

  • Response: Shivering to warm up.

Insulin & Glucagon

• Hormones involved in regulating blood glucose levels through negative feedback.

Positive Feedback Example

• Childbirth Process:

  • Stimulus: Baby pushes against cervix

  • Receptor: Nerve cells in cervix send signals to brain

  • Effector: Pituitary gland releases oxytocin

  • Response: Increased contractions.

• Fruit Ripening Process:

  • Ripe apple produces ethylene

  • Signals neighboring apples to ripen via ethylene production.

Homeostatic Imbalances

• Reasons for failure in maintaining homeostasis include:

  • Genetic disorders

  • Drug or alcohol abuse

  • Extreme environmental conditions (heat or cold).

Diseases related to Homeostasis

• Cancer: Unregulated cell growth.

• Diabetes: Poor regulation of blood glucose levels.

Review Questions

Feedback Mechanism Statements

1. Feedback mechanisms help maintain steady state conditions in the body.

2. Which statements exemplify feedback mechanisms, e.g., insulin regulation of blood sugar or guard cells in plants?