EXTERNAL STIMULI INTERNAL STIMULI HOMEOSTASIS What is the

EXTERNAL STIMULI & INTERNAL STIMULI & HOMEOSTASIS

What is the difference between a stimulus & a response? Stimulus: an action or condition that provokes a response. (Cause) Response: Any behavior of a living organism that results from an external or internal stimulus. (Effect)

Internal Stimulus: A signal that comes from within an organism. Examples: Thirst Adrenaline Blood sugar levels Pathogens Hunger Oxygen Toxins

External Stimulus: A signal that originates from outside of an organism & causes a response within the organism. Examples: Touch Pressure Heat

Learned Response: This is a behavior/response that is learned by observation or training. Examples: Bear cub taught to fish (hunger)

Innate Response: Instinct This is a behavior/response that is not taught. It is a natural automatic response. Migrate: to move to another area in order to increase the chance for survival of the species.

Fight or Flight: The response to an organism’s acute stress or danger. The response could be “fight” or “flight”. Hormones are released that stimulate the heart, raise blood pressure, constricts small blood vessels, & releases sugar stored in the liver. It relaxes some involuntary muscles & contracts others.

Tropism: The turning or bending movement of a living organism or part toward or away from an external stimulus Light = Phototropism Gravity = Geotropism Touch = Thigmotropism Heat = Thermotropism “+” (Positive) = Toward the stimulus “-” (Negative) = Away from stimulus

Phototropism A plant grows in the direction of the light.

What type of tropism? �Geotropism • Thermotropism • Phototropism

How do you think phototropism relates to a plant’s chance for survival? • Phototropism is a response by plants that promotes maximum photosynthesis, & therefore plant growth & optimal overall plant health. Without this response, many plants would die & never reproduce.

What is the difference between phototropism & photosynthesis? • Phototropism is the response of plants to light (usually “+”) that help them to collect sunlight for photosynthesis. • Photosynthesis is the process of plants to create food energy from sunlight energy.

Homeostasis: Refers to the body’s ability to regulate it’s body in response to changing outside elements.

What is the role of homeostasis in an organism? Examples: • If you are hot, then you sweat • If you are cold, then you shiver • If you are exercising, then you breathe faster to feed more oxygen to your muscles.

Examples of Homeostasis �Drink too much water, excretory system is more active, you go to the bathroom more. �Working muscles need more oxygen and create more carbon dioxide, so to balance this, the circulatory and respiratory systems are more active. �Get pollen in your nose, you sneeze to get unwanted spores out of your airway.

Homeostasis in Plants �Turgor Pressure �Water moves in & out of cell in response to mineral levels �Concentration of sodium/minerals is too high, water moves in to balance it out �Concentration too low, water will pass out of the cell to maintain the same balance

Homeostasis in Plants �Transpiration �Stomata open and close in response to how much water the plant has access to �Not enough water, stomata stays closed for water retention �Guard Cells open and close depending on the amount of water that is available.

Homeostasis in Humans �Temperature -Sweating when hot, shivering when cold. �To keep body temperature at 98. 6, your body automatically makes adjustments. Goosebumps form, which makes your hair stand up to help insulate your body. If that doesn’t help then you start to shiver. Shivering is an attempt by your body to create heat through movement. • Infection -To fight infection, our body heats up (fever) to make it an uncomfortable place for bacteria to live.