Stimulus & Response TEKS 7.13B describe and relate responses in organisms that may result from internal stimuli such as wilting in plants and fever or vomiting in animals that allow them to maintain balance TEKS 7.13A investigate how organisms respond to external stimuli found in the environment such as phototropism and flight or fight

Stimulus A change in organism’s environment

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

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.

Examples Stimulus = Lack of water Is this internal or external? Response = Lack of water Wilting Bacteria or Virus Fever

Examples Stomach virus Stimulus = Is this internal or external? Response = Stomach virus vomiting Saber-tooth Tiger Fight or flight

Just as animals respond to the environment, plants do as well.

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

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

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

Examples

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

Geotropism A plant grows with or against gravity Also called Gravitropism 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.

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