Learning Exercise

Photomorphogenesis and Plant Tropic Responses

Non-major General Biology students will examine Plants in Motion movies of a variety of plant responses to light and gravity. The students will answer questions based on introductory material and movies viewed.
Course: Non-majors General Biology Lab

Time lapse movies of plant growth from germination to flowering, including tropic responses, nastic movement and... see more


Plants use the process of photosynthesis to convert the energy of sunlight into
chemical energy that the plant will use for growth and development. The
perception of sunlight is necessary for plant development. The absence of light
also elicits growth responses in plants. Examine the text and movies listed
below and answer the questions.

Follow the navigation links and the instructions provided below. Questions
answered will be submitted as part of Lab 6 on Photosynthesis.

Go to:

Click on: Ticket to Enter Site

Read: Introductory Text
NOTE: You will need QuickTime 5.0 to view movies
If you don?t have it download it now.

Click on: Photomorphosis
Read: Introductory Text

Click on: Sunflower dark and light
Read: Text with each movie (NOTE: Movie may take a few minutes to load on some

Create a Table:
Across the top of the table put light and dark. Down the side put:stem
elongation; leaf (cotyledon) development, chlorophyll production; hooked stems.
As you read text fill-in the table indicating how light grown and dark-grown
plants respond in each category listed.

Click on: Movie for Dark Grown Seedlings (right facing triangle) You may drag
circular slider back to the beginning to view again. The triangles with lines
next to them allow you to move forward or backward step-by-step through the

Answer these questions.
Q-1 How did the movies provide support for the table that you developed?
Q-2 Which plant is most prepared to start photosynthesizing? Explain.
Q-3 Prior to starting to photosynthesize, what was the energy source for the
young plants? By what process did the plants get energy from this source?
Q-4 The dark-grown plants had longer stems. What is a possible reason that the
longer stems might be an advantage to the plants in the dark?

Click on: Dark-grown Arabidopsis
Read: Text
View: Movie

Q-5 Compare the Arabidopsis with the dark- grown sunflower movie.

Click on: Tropisms
Read: Text

A positive tropism is when the plant grows toward the stimulus and a negative
tropism is when the plant grows away from the stimulus.

Click on: Arabidopsis shoot phototropism
Read: Text with both movies
View: Blue-light induced phototropism movie
View: Red-light enhanced phototropism movie

Q-6 Which plants responded most quickly to the blue light? Why?
Q-7 Were the plants displaying a positive or negative phototropism?

Click on: Tomato Phototropism
Read: Text
View: Movie

Click on: Corn Phototropism
Read: Text
View: Movie

Click on: Cool Corn Plants
Read: Text
View: Movie

Click on: Sunflower phototropism
Read: Text
View: Movie

Click on: Arabidopsis shoot Gravitropism
Read: Text
View: Movie

Click on: Coleus Sh oot Gravitropism
Read: Text
View: Movie

Click on: Sunflower Gravitropism
Read: Text
View: Movie

Q-8 Summarize your observations of plant stems response to gravity.
Q-9 What is the adaptive value of plants responding in this way?

Click on: Corn root gravitropism
Read: Text
View: Movie

Q-10 Make a statement regarding the adaptive value of plant roots displaying a
positive gravitropic response.

Technical Notes

Some movies may be slow to load for students with a slow modem.


Students will have completed a lab on photosynthesis and will have reviewed background information on plant structure (roots, stems, leaves).


Photomorphogenesis, Phototropism, Gravitropism

Learning Objectives

Explain how plants respond in an adaptive way to light and gravity.