Tropisms and Turgor Pressure Notes: Stimulus and Response in Plants Stimulus = Light Stimulus = Touch

INternal Stimuli in Plants Turgor Pressure The outward pressure that occurs in a plant cell when the cytoplasm and vacuoles fill up with water and the cell membrane pushes against the cell wall. Presence of water  turgid cell aka healthy plant cell Absence of water  flaccid (limp) cell aka dying plant cell KEY Stimulus Response Draw this picture and label each as turgid or flaccid.

Turgor Pressure Animation Read Only Turgor Pressure Animation Click on the picture or hyperlink to watch an animation that shows a plant cell gain and lose Turgor Pressure. Watch it for about 2 minutes in order to see the effect of a full vacuole and a low-pressure vacuole. The PPT must be in Slide Show Mode to access the link. Click HERE to view the animation

EXternal Stimuli in Plants Tropisms Tropisms: a plant’s growth in response to an external stimulus. Positive (+) tropism: Plant growth toward a stimulus (water, sunlight) Negative (-) tropism: Plant growth away from a stimulus (spilled gas, toxins, too much sun or not enough)

Emergence of Seedlings (plants coming out of their seed) Seeds are actually immature plants (seedlings) with a thick, hard coat covering them. The seed coat (outside of a seed) protects the beginning of a root, the beginning of a stem, either one or two seed leaves, and the seed’s food supply. The seedling’s stem and roots exert a strong force that enable it to break free of the coat or hard shell when conditions are right. Factors necessary for most seed emergence: Warm/moist soil Longer days of sunlight (spring) VIDEO: Click HERE to observe seedling emerging Stem Broken seed coat Roots Pecan sprouting

Phototropism Growth of a plant in response to light. The stalk displays positive phototropism growing towards the light. The roots display negative phototropism growing away from the light.

Geotropism (Gravitropism) Earth Growth Gravity Growth Growth of a plant in response to earth / gravity. The roots display a positive geotropism growing towards earth (with gravity.) The stalk displays a negative geotropism growing away from gravity. Negative Positive

Seed placement (orientation) Read Only It does not matter which way you plant a seed in the ground. The root cells will always grow down towards earth because of their response to gravity (geotropism). The stem cells will always grow towards light (phototropism). Root Top of seed

Hydrotropism Growth of a plant in response to water. The roots display a positive hydrotropism growing towards water. The stalk display a negative hydrotropism growing away from water. Positive Water

Thigmotropism Moves or grows in response to touch or contact stimuli. Growth Moves or grows in response to touch or contact stimuli. A vine displays a positive thigmotropism growing towards touch Vine growing against a wall Venus Fly Trap closing when touched The leaves display negative thigmotropism growing away from touch

The PPT must be in Slide Show Mode to access the link. Read Only View the video below to hear a teacher who created a song about tropisms. Click HERE for the Tropisms Song The PPT must be in Slide Show Mode to access the link.

Tropisms Notes Assignment Phototropism Geotropism Draw a picture of each tropism showing its positive response to each stimulus listed. Label what is happening in each picture. Hydrotropism Thigmotropism Color is optional.