Stimulus & Stimulus & Response Response

StimulusAA change in organism’s environmentchange 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

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

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

HydrotropisHydrotropismm

HydrotropismHydrotropism = 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

- geotropism

+ phototropism

+ geotropism

+ hydrotropism