Forces in Living Things

Forces• Unbalanced forces cause motion• Force in the form of pressure allows plants to

stand upright• When force is applied to an object and the

object moves, work is done.• Because most forces in living systems are

small, it is difficult to measure the amount of work done, so we will be looking at large work examples.

Seeds•How do they grow?•Why do they grow?•Where do trees and plants come from?•Where do seeds come from?•What is in a seed that responds to the environment?•What does a seed need to grow?•What does a seed look like?

Seeds•Seeds, though they look dead, contain the life that will create a new plant.•A seed will grow (or germinate) into a plant with the help of water, sun, and the right temperature.•If a seed does not germinate within a certain amount of time, it will die.

Seeds•Plants will respond to different external stimuli.•They can respond to:•Touch – thigmotropism•Light – phototropism•Gravity – geotropism

Seeds•A plants response may be positive or negative to the stimulus.•If a plant moves toward the stimulus it is a positive response•If a plant moves away from the stimulus it is a negative response

Seeds•The part of the seed that we see is the seed coat•Inside the hard outer coat, there is the cotyledon, which is the fleshy portion that provides the food for the growing plant.•Also inside the seed coat is the embryonic plant. There is a tiny root, stem, and the beginning of leaves.

Seeds•The embryonic stem (hypocotyl) emerges from the seed and pushes the cotyledons upward until the stem and leaves can reach sunlight.

Seeds and Beans

What is a tropism?

Tropism ~ a response of a plant to an environmental

stimulus.

What is phototropism?

Phototropism ~ a tendency of plants to grow toward a

source of light.

What is thigmotropism?

Thigmotropism ~ the response of plants to touch.

What is geotropism?

Geotropism ~ a tendency of a plant to grow in a direction in

response to the force of gravity.