Stimulus and Response Notes. April 4, 2013

Transcription

1 Stimulus and Response Notes April 4, 2013

2 Stimulus and Response Stimulus (stimuli): A change in an organism's environment that causes the organism to respond (react) -Anything that can be observed that causes a reaction Response: An action or change in behavior that occurs as a result of a stimulus

3 Types of Stimuli External Stimulus: A change that occurs outside of the body that causes a response Examples: You see a scary movie and scream in response You watch someone eating a lemon and your face puckers You hear a loud noise and you jump You smell a steak cooking and your mouth starts to water You feel cold wind on your skin and you get goose-bumps You taste a piece of sushi and spit it out You enter a dark room and your pupils dilate (get larger) to let in more light You enter a bright room and your pupils constrict to reduce the amount of light entering your eye

4 Types of Stimuli Internal Stimulus: A change that occurs inside of the body that causes a response Examples: Your blood sugar level drops and you feel hungry Your testosterone level increases and you grow facial hair You are infected by a virus and you get a fever and begin to vomit Your blood sugar level increases and your pancreas releases insulin The amount of water in the central vacuole of a plant decreases and the plant begins to wilt The amount of human growth hormone in your body increases and you grow really tall

5 Types of Responses Fight or flight response Phototropism Geotropism Wilting Feeling sick

6 Fight or Flight Response When organisms face a dangerous situation (external stimulus) the adrenal glands of the endocrine system release the hormone adrenaline Adrenaline increases the heart rate and oxygen flow in the organism as it prepares to do one of the following: Fight (face the dangerous situation) or Flight (run away from the dangerous situation)

7 Phototropism Response The tendency of an organism to turn/move toward or away from light The stems/flowers of plants turn or grow toward light sources (positive phototropism) Roots don't respond to light (they are underground where there is no light)! Animals sometimes move toward light (positive phototropism), and sometimes they move away from it (negative phototropism)

8 Geotropism Response Plants grow against (negative) or with (positive) the external stimulus of gravity Also called gravitropism Plant stems grow up against the pull of gravity (negative) Plant roots grow down with the pull of gravity (positive)

9 Wilting and Turgor Pressure Plant stems are able to stand up against the pull of gravity due to the turgor pressure of the water in the central vacuoles of their cells If the plant cells use up the water in the central vacuoles (internal stimulus) the turgor pressure decreases and the plant begins to wilt (bend over due to gravity)

10 Fever and Vomiting When bacteria and viruses infect the body (internal stimulus) the body responds by vomiting (removing the bacteria/viruses) and starting a fever (increase in temperature kills the viruses and bacteria) If the fever or vomiting lasts too long it can kill the organism that is infected!

11 Homeostasis Stable internal environment Everything is balanced inside of the body Balance = homeostasis Examples: 98.6 o F temperature, correct amount of blood sugar levels, correct amount of water The goal of stimulus and response is to maintain homeostasis! Organisms maintain homeostasis through a mechanism called negative feedback

12 Negative Feedback A process in which a system is turned off by the condition it produces Example: 1. Blood sugar levels increase (stimulus) causing the pancreas to release insulin (response) 2. Insulin causes the blood sugar levels to decrease (stimulus) which causes the pancreas to stop producing insulin (response) The process (releasing insulin) was turned off by the lower blood sugar (which was caused by the insulin)

13 Negative Feedback: Thermostat