1. Cellular Processes and structure
04 Feedback
Feedback
Organisms respond to change
Interactions within organisms

2. Feedback
Curriculum Framework: 2.C.1
Holtzclaw: 75, 223, 224, 228

3. Organisms use feedback
Maintain internal environment
homeostasis
Respond to external stimuli

4. Negative feedback The response reduces the effect of the stimulus
Used to maintain dynamic homeostasis
“dynamic” because target can change

6. Negative feedback examples
Sweat and temperature
Exercise
internal temperature increases
Sweat
Internal temperature returns to normal
Plant transpiration and water availability
Stomata are open
gas is exchanged
CO2 in, water out
Water loss detected
stomata close

7. Positive feedback Response magnifies effect of stimulus Example: Labor
Oxytocin causes contractions
Contractions result in pressure on the cervix
pressure on the cervix releases more oxytocin
Example: Ripening fruit
Fruit releases ethylene gas as they ripen
ethylene gas signals fruit ripening

9. Disruption of feedback
If feedback mechanisms are disrupted, there can be negative consequences

10. Disruption of feedback examples
Diabetes Mellitus
Haemophilia
excessive bleeding caused by inability to produce clotting factors (e.g. platelets and other proteins)

11. Cellular Processes and structure
04 Feedback
Feedback
Organisms respond to change
Interactions within organisms

12. Organisms respond to change
Curriculum Framework: 2.C.2
Holtzclaw:

13. Organisms respond to changes in the environment
Behavioral mechanisms
Taxis
Movement toward or away from a stimulus
Ex. river fish orient themselves upstream
Ex. Cockroaches move away from light sources
Kinesis
Change in rate of movement
Not direction-specific
Ex: Sow bugs move fast in dry areas and slow in moist areas

14. Organisms respond to changes in the environment (cont.)
Physiological mechanisms
Passive response, usually at the level of organs or below
Ex. Phototropism
Plants “bend” toward the light by shortening cells exposed to sunlight

15. Organisms respond to changes in the environment (cont.)
Physiological mechanisms
Ex. Circadian rhythms
Any 24-hour cycle that can be entrained