Forces and Work in the Natural World

WORK• Is force over a

distance• If force is applied to

an object, and the object moves work has been done

• Plants can do work!

Osmosis in plant cells

• Osmosis – movement of water through the semipermeable cell membrane

• When most plants are given water the roots take up as much water as it needs which is stored inside the cells (vacuoles) and the plant looks normal

Osmosis in Plants

• When a plant does not receive enough water there is a higher concentration of water inside the plant cells than outside so the water diffuses out of the cell

• This causes the plant to wilt

Turgor Pressure• Pressure of

water molecules against the cell wall that allows plants to stand up straight.

Turgor Pressure

• Remember plant cells are surrounded by a rigid (resists bending) cell wall. Just beneath the cell wall is the cell membrane

Turgor Pressure

• Also remember the plant cell has a much larger vacuole than an animal cell

• This vacuole is used to store food and water for the plant cell

Turgor Pressure

• When a plant has the right amount of water then the turgor pressure inside the cell will help support the plant and the plant will stand upright

• When a plant does not have enough water the turgor pressure inside the cell is decreased and the plant is not able to stand upright as well

• If the plant does not get any water, it will wilt completely and eventually die

No Turgor Pressure Turgor Pressure

Tropism• Tropism – a plant’s response that results in

plant growth toward or away from a stimulus.–Positive – growing TOWARD the stimulus–Negative – growing AWAY from the

stimulus

Stimulus: Light

• Response: Phototropism

• Tendency for plants to grow towards sunlight

• Why is this beneficial for the plant?

• 18 Sec Video

Stimulus: Gravity• Response: Geotropism (or Gravitropism)• A plant’s growth in

response to gravity.–Negative: Stems grow

away from gravity–Positive: Roots grow

towards gravitySeeds growing in response to gravity – select CORN

Stimulus: Touch• Response:

Thigmotropism – a plants growth in response to touch

• Examples:–Vines –Carnivorous

Plants–Roots avoiding

contact

Venus Fly Trap Video