Stimulus & Stimulus & Response Response

TEKS 7.13A investigate

how organisms respond to external

stimuli found in the

environment such as

phototropism and flight or

fight

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

StimulusAA change in organism’s change in organism’s

environmentenvironment

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

HomeostasisHomeo- sameStasis- state of balance

The purpose of response to stimuli in organisms is to maintain homeostasis, a balance within it’s internal systems.

ExamplesExamples

StimulusStimulus = =

Is this internal or external?Is this internal or external? ResponseResponse = =

StimulusStimulus = =

Is this internal or external?Is this internal or external? ResponseResponse = =

Lack of water

Wilting

Bacteria or Virus

Fever

ExamplesExamples

StimulusStimulus = =

Is this internal or external?Is this internal or external? ResponseResponse = =

StimulusStimulus = =

Is this internal or external?Is this internal or external? ResponseResponse = =

Stomach virus

vomiting

Saber-tooth Tiger

Fight or flight

Just as Just as animalsanimals respondrespond to the to the environment, environment, plantsplants do as do as well. well.

TropismsTropisms Tropism Tropism = plant’s growth response = plant’s growth response

toward or away from a stimulustoward or away from a stimulus

TropismsTropisms Tropism Tropism = plant’s growth response = plant’s growth response

toward or away from a stimulustoward or away from a stimulus

Positive tropismPositive tropism

Negative tropismNegative tropism

TropismsTropisms Tropism Tropism = plant’s growth response = plant’s growth response

toward or away from a stimulustoward or away from a stimulus

Positive tropismPositive tropism = plant grows toward = plant grows toward a stimulusa stimulus

Negative tropismNegative tropism

TropismsTropisms Tropism Tropism = plant’s growth response = plant’s growth response

toward or away from a stimulustoward or away from a stimulus

Positive tropismPositive tropism = plant grows toward = plant grows toward a stimulusa stimulus

Negative tropismNegative tropism = plant grows away = plant grows away from a stimulusfrom a stimulus

HydrotropismHydrotropismHydrotropismHydrotropism = a plant’s = a plant’s

rootsroots grow toward watergrow toward water

Is this positive or negative?Is this positive or negative?

PhototropismPlants grow toward a source of light

Animation:

http://botanical-online.com/animation8.htm

Examples

ThigmotropismA 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

Negative- A plant’s stems or trunk grow up, against the pull of gravity.

Positive- A plant’s roots grow down, with the pull of gravity

Animation:

http://botanical-online.com/animation4.htm

Regardless of the slope of the land, the tree grows up against gravity.

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

Working Together

Plant tropisms work together to maintain homeostasis within the plant

Plants in Motion Video

- geotropism

+ phototropism

+ geotropism

+ hydrotropism