Stimulus & Response

Stimulus A change in organism’s environment

Types of Stimuli A stimulus can either be external or internal. External stimuli- come from things found in the environment. Examples- temperature, predators, length of daylight, presence of water or food, etc. Internal stimuli- come from things within an organism Examples- germs, dehydration, lack of energy, pain, lack of sleep

Stimulus Is this stimulus external or internal?

Response An organisms reaction to change.

Response

Homeostasis Homeo- same Stasis- state of balance The purpose of response to stimuli in organisms is to maintain homeostasis, a balance within it’s internal systems, or protection.

Examples Stimulus = Is this internal or external? Response = Lack of water Wilting (to conserve water) Bacteria or Virus Fever (to kill germs)

Fight or Flight Response An organisms biological response to extreme stress. Can include- Increased heart and breath rate Shaking Adrenaline rush- extreme strength Freezing in place (cannot move)

Examples of Fight or Flight

Tropisms Tropism = plant’s growth response toward or away from a stimulus

Tropisms Tropism = plant’s growth response toward or away from a stimulus Positive tropism Negative tropism

Tropisms Tropism = plant’s growth response toward or away from a stimulus Positive tropism = plant grows toward a stimulus Negative tropism

Tropisms Tropism = plant’s growth response toward or away from a stimulus Positive tropism = plant grows toward a stimulus Negative tropism = plant grows away from a stimulus

Phototropism Plants grow toward a source of light Animation: http://botanical-online.com/animation8.htm

Examples

Hydrotropism Hydrotropism = a plant’s roots grow toward water Is this positive or negative?

Gravitropism A plant grows with or against gravity Also called Geotropism Positive- A plant’s roots grow down, with the pull of gravity Negative- A plant’s stems or trunk grow up, against the pull of gravity. Animation: http://botanical-online.com/animation4.htm

Regardless of the position a seed is planted in, the roots grow down with gravity and the stem up against gravity. Regardless of the slope of the land, the tree grows up against gravity.

Thigmotropism A plant grows toward or away from pressure Positive turns toward pressure Negative turns away from pressure

Working Together + phototropism - geotropism + geotropism Plant tropisms work together to maintain homeostasis within the plant + phototropism - geotropism + geotropism + hydrotropism

Turgor Pressure The pressure exerted by water inside the cell against the cell wall. This celery stalk has the least amount of turgor pressure because of water pressure in the cells This celery stalk has more turgor pressure than the 1st This celery stalk has the most turgor pressure of all because it has the greatest water pressure in the cells of the plant