Plant Systems: Explain I – Teacher Directions
KMAC Objectives: 4.10.3, 4.10.5, 4.10.6
EXPLAIN I: Advanced Preparation
Print one copy of the “Plant Systems: Explain I - Student Answer Sheet” for each student
Print one copy (two copies if necessary) of “Plant Systems: Explain I - Stations 1-6”
OPTIONAL: Display videos of different tropisms at each station in addition to the informational worksheets. You
may find these videos online by simply searching for them.
EXPLAIN I: Procedure
1. Place students into cooperative groups of 2-4.
2. Tell the students that they will be completing a concept map involving plant movement and plant hormones
3. Instruct the students to read the passages at each station, perform the analysis or activity, and then answer the
questions on their ”Plant Systems: Explain I – Student Answer Sheet”
4. Utilize this time to review lab safety in terms of moving about a science laboratory by asking safety oriented
questions, such as:
a) How should groups move from one station to the next?
In an orderly and calm fashion…
b) Why is it important to move in an orderly and calm fashion from one station to the next?
So no one gets hurt and nothing gets damaged
c) What should you do if someone gets injured during a lab setting?
Notify the teacher immediately
5. Have each group answer the questions at each station
NOTE: If a student has difficulty with answering a question, ask the student what he or she thinks the question is
asking, then rephrase the question based on their understanding.
6. Have each group elect a spokesperson to share their concept map and answers during a class discussion.
7. Use the Scaffolding Questions to facilitate a whole-group discussion
EXPLAIN I: Scaffolding Questions
Answers will vary, but look for student understanding consistent with the ideas presented in this key
Station 1: Phototropism
1. Summarize (in your own words) the experiment by Francis and Charles Darwin.
Answers should accurately describe their experiment.
2. Using the above graphic, explain why the seedling at the far right is curved.
The seedling curved because there was more auxin on the shaded side of the stem.
3. Utilizing your knowledge about phototropism, why do you need to rotate your houseplants every so
often?
Over time, plants will bend towards the strongest light source (usually a window) and as a result need to
be rotated to prevent them from growing in only one direction.
Station 2: Gravitropisms
1. How can you determine if the plants in photograph B are expressing negative or positive gravitropism?
Photograph B is expressing positive gravitropism because the shoots are bending upwards, away from
gravity’s influence.
2. What would happen if you accidentally planted a seed wrong side up?
The gravitropic response would cause the root to grow downward with the pull of gravity and the stem
to grow upward against gravity.
3. Why did the root tip in photograph A with the end cut off not express any form of gravitropism?
Auxin is produced in the apical meristem and without the root tip there would be no auxin production
and thus no gravitropic response.
Station 3: Thigmotropism
1. How would a plant’s tendrils respond to a trellis?
A plant’s tendrils would coil around a trellis in an attempt to support itself as it grows.
2. Why might climbing plants have a survival advantage over some nonclimbing plants in a densely grown
forest?
Being able to climb allows the plants to grow high enough to expose their leaves to light without a
sizable energy investment in producing a tall,, strong trunk.
3. How do plants know to grow thicker in windy areas?
Plants can sense the movement caused by the wind, triggering a response to grow thicker in order to
strengthen its trunk and prevent damage to the plant caused by the wind.
Station 4: Auxin & Plant Growth
1. At what auxin concentration are the stems stimulated to grow the most?
Maximum stem growth occurs at about 10-6 particles/L
2. How is the growth of the roots affected by the auxin concentration at which stems grow the most?
That concentrations inhibits the growth of roots.
3. Use the data in the graph to describe the relationship between the concentration of auxins and the growth
of carrot plant stems.
Concentrations between approximately 10-9 and 10-3 particles/L promote stem growth. Concentrations
above about 10-2 particles/L inhibit stem growth.
4. If you were a carrot farmer, what concentration of auxin should you apply to your fields to produce the
largest-sized carrots?
Because carrots are roots, a concentration of approximately 10-10 to 10-9 particles/L would produce the
largest-sized carrots.
Station 5: Plants are HORMONAL!?!?
1. Where are hormone-producing cells in a plant?
In apical meristems, young leaves, roots, and growing flowers and fruits.
2. What are target cells?
Cells that contain a hormone receptor and are affected by particular hormones.
3. How do hormones affect target cells?
By changing their metabolism, affecting their growth rate, or activating the transcription of certain
genes.
4. How can a gardener use this knowledge of hormones produce fuller, bushier plants?
The gardener could cut off the apical meristem of the plant. The gardener could also apply hormones to
the plant to stimulate cell division, elongation, or general increase in size.
Station 6: One bad apple spoils the bunch
1. Apples are harvested in the autumn; however you may enjoy an apple at anytime of the year. How are
apples prevented from over ripening once they are picked?
If the ethylene is removed, then over ripening of the apples will be inhibited. Thus apples can be enjoyed
throughout the entire year from a single harvest.
2. Summarize what might happen to your houseplants if you were to have a small gas leak inside of your
house.
The leaves would fall off and the growth would be stunted.
3. Why is understanding plant hormones, such as ethylene, important to grocery stores?
Through understanding plant hormones, grocery stores can display the most attractive fruit and keep it
looking attractive.
EXPLAIN I: Resources
Prentice Hall Biology – Chapter 25