Tropisms

The survival of an organism depends on it’s environment – all the living and non-living things in a region.

A plant’s environment must include: sufficient water, sunlight, carbon dioxide, and a proper temperature range.

If an environment is lacking, plants can react in order to survive. Plants can react to light, gravity, temperature, touch and water.

What is a plant’s environment?

What does a plant’s environment need to include?

What do plants react to?

Something that causes a response is a stimulus. The hot stove is the stimulus.

The reaction to something in the environment is called a response. Moving your hand away from a hot stove.

A response toward a stimulus is called a positive response. Roots growing towards water.

A response away from a stimulus is called a negative response. Roots growing away from dry soil.

What is a stimulus?

What is a response?

What is a positive response?

What is a negative response?

Plant responses that involve growth are called tropisms.

Plant growth toward a light is called phototropism.

Scientists believe phototropism is caused by a chemical in plants that speeds up cell growth on the dark side of the plant.

Some stimuli are more important than others. A plant will respond more to the stimulus that is most important to its’ survival. For example, roots will respond more to water than gravity.

What are plant responses that involve growth called?

What is phototropism?

What causes phototropism?

Why will a plant respond to one stimulus more than another?

Homework

1. Give two examples of stimuli that plants will respond to.

2. Describe the plants’ responses to the stimuli above, and explain how it helps the plants to survive.

3. What causes a plant to grow toward the light? Explain.

Structural Adaptations of Plants

Any structure or response that helps an organism survive is called an adaptation. Any difference between plants.

Plants have adaptations for protection against:

1. animals and insects : plants get eaten

2. plants: they compete for water and sunlight

3. weather/climate

What is an adaptation?

Why do plants have adaptations?

Some plants have poisons:

1. Wild cherry and locoweed have poisonous leaves that will kill or make sick animals or insects that try to eat them.

2. Black walnut trees have a poison in their roots to stop other black walnut trees from growing around it.

3. Horsetail and rhododendron have a bad taste or odor to keep animals and insects away.

4. Poison ivy and oak have oils that cause a rash.

What are some types of poisons plants have?

Some plants have adaptations because of their environment.

For example, plants are adapted to live in dry, hot regions.

1. Thick stems for water storage.

2. Fibrous roots that grow near the surface to collect water quickly.

3. Waxy coating to prevent evaporation.

4. Spines to keep animals from getting water from eating the stems.

5. White hairs to reflect the sunlight.

6. Seeds that have a chemical that needs to be washed off with lots of water before it will germinate.

What are some adaptations for plants in hot, dry regions?

Some plants’ leaves are adapted to live in regions with varying amounts of rainfall and sun.

For example, the needles of evergreen trees are short and thin and require only a small amount of water, so they can stay on trees for the entire year.

Why can needles on evergreens stay on trees all year?

New plants will have to compete for water and light, therefore their seeds are adapted to be carried away from the parent plant and spread away from each other.

Some adaptations of seeds are:

1. Parachutes to carry on the wind-dandelions

2. Wings to be carried on the wind-maple trees

3. Hidden in fruit to be deposited later-apples

4. Hooks or sticky to attach to animals-cockleburs

5. Shooting

6. Filament - Walking

7. Floating - coconut

Why do seeds need to have adaptations?

What are some adaptations of seeds?

Additional adaptations:

1. Bark

2. Adventitious roots, taproots and fibrous roots

3. Monocot and dicot seeds, cones

4. Green stems

5. Lobed, toothed or untoothed

6. Pinnately or palmately

7. Etc…

What are some other adaptations of plants?

Structural adaptation How does it help the plant survive?

1.

2.

3.

Biological Clock

The biological clock is the “chemical clock” in plant cells that tells a plant when to grow or bloom.

Scientists believe two main factors control a plant’s biological clock: sunlight and temperature.

Nearly all the flowers of any one kind of plant bloom at the same time. This allows pollen to be transferred.

What is a biological clock?

Why do the same kind of flowers need to blossom at the same time?

What do scientists think control a plant’s biological clock?

Scientists and florists can fool a plant’s biological clock by controlling the temperature, light and water it receives (greenhouse).

A flower clock consists of beds of flowers arranged so that different beds open or close at different times during the day.

How can someone fool a plant’s biological clock?

What is a flower clock?