Photo by: Andrey Armyagov

Tropisms And Turgor pressure 7th Grade Science Ms. DeFreese September 24, 2012 Photo by: AndreyArmyagov

Plants can react and adjust • Since plants must make their own food to survive the ability to capture as much of this light energy as possible is crucial to its survival. • Thus, plants have developed a chemical response to light or the lack of it that causes their stems to bend toward the stronger light.

Tropisms • Tropisms are directional movement responses in plants that occur in response to a directional stimulus. • Tropisms are controlled by a plant hormone called auxin.

A Tropism is a growth movement • Direction is determined by the direction from which the stimulus strikes the plant. • Positive = the plant, or a part of it, grows in the direction from which the stimulus originates. • Negative = growth away from the stimulus.

Tropisms are namedbased upon the stimulus. • Phototropism • The way a plant grows or bends in response to light. • Gravitropism • The way a plant grows or bends in response to gravity or earth.

Phototropism = Light Response • Stems are positively phototropic. • Roots are negatively phototropic.

Gravitopism = Gravity Response • Stems are negatively gravitropic while • roots are positively gravitropic.

The adaptive value of these tropisms is clear. • Roots growing down and/or away from light are more likely to find the soil, water, and minerals they need. • Stems growing up and toward the light will be able to expose their leaves so that photosynthesis can occur.

Roots growing down and/or away from light are more likely to find the soil, water, and minerals they need. Stems growing up and toward the light will be able to expose their leaves so that photosynthesis can occur. The adaptive value of these tropisms is clear.

Turgor Pressure The pressure exerted by water inside the cell against the cell wall.

Journal Assignment Use the folding Venn to compare and contrast phototropism and gravitropism. Be prepared to share

Photo by: Andrey Armyagov