No eyes. No brain. So how does a seedling respond to light?
A seedling near a window has a curved stem. Did it grow that way by chance—or did something in its environment affect its growth?
Your mission: compare light directions, look for a pattern, and build an explanation from evidence.
How can a plant respond to a change in its environment?
WICOR focus: Inquiry—make a prediction, compare conditions, and explain a pattern using evidence.
- I can distinguish an observation from an inference.
- I can compare light directions while keeping other conditions consistent.
- I can explain a modeled growth response and identify a limitation of the model.
A plant with a mystery curve.
Imagine two matching seedlings. Both begin upright. After time passes, the seedling near a side window has a curved shoot. A second seedling, lit evenly from above, remains upright.
Pause and think: What do you directly observe? What are you only assuming? What could you change to investigate the cause?
Observation or inference?
“The stem is curved toward the window.”
Move the light. Compare the response.
Testable question: How does the direction of light affect the direction of a young shoot’s growth?
Before running the model, predict what will happen if light comes from the left, from above, or from the right. Which comparison would help you test your explanation?
Observe: the modeled direction of shoot curvature.
Keep consistent: seedling type, age, starting position, water, soil, temperature, light intensity at the shoot, and modeled growth interval.
Starting upright. Run the model to see the response.
Starting upright. Run the model to see the response.
Choose two different light directions for a comparison.
Model rules: Side lighting produces shoot curvature toward that side; balanced overhead lighting produces an upright shoot. Each run starts with a new pair of identical modeled seedlings. The short animation represents growth over time, not an instant movement. Curvature and timing are illustrative and have no measured units. Results are programmed, with no natural variation.
Static model results: Light from left → shoot curves left. Balanced light from above → upright shoot. Light from right → shoot curves right. Compare these conditions and use the comment prompts below.
Does the pattern follow the light?
- Compare light from one side with light from above.
- Swap the settings between A and B and run again.
- Try the opposite side. Does the response follow the seedling’s label or the direction of light?
| Run | A: light | A: response | B: light | B: response |
|---|---|---|---|---|
| Run a comparison to add results. | ||||
The log stays only while this page is open. Reset clears it. These are outputs from a teaching model, not observations of real plants.
Need a hint for interpreting the pattern?
Compare the light’s direction with the shoot’s direction. Swapping A and B checks whether the pattern follows the condition rather than the label. Repeating a programmed result does not provide new biological evidence.
Does a plant need to “see” to respond?
One student claims, “The plant decides where to go.” Another says, “Light triggers a growth response.” Which explanation could scientists investigate? What evidence would help distinguish them?
After investigating: reveal the life science connection
Phototropism is a growth response to directional light. Many young shoots show positive phototropism: they grow toward a light source.
Light sensing can change how the growth-regulating hormone auxin is distributed across a young shoot. Greater elongation on the shaded side causes the shoot to curve toward the light. This is a growth response, not a decision made by a brain.
Connect structure and function: Light sensing and uneven growth help orient shoots toward light used in photosynthesis. This model does not show photosynthesis, hormone movement, or individual cells.
Think critically: The simulation illustrates an established idea. Its programmed results cannot prove that mechanism. Real responses vary with species, developmental stage, light conditions, and time.
Explore the research: Primary research on auxin transport and phototropism. For background: Georgia Tech: Plant Hormones and Sensory Systems.
Stretch your thinking: design a real investigation
How would you test this pattern with real seedlings? Describe a side-lit group and an overhead-lit comparison group. Include several seedlings in each group, consistent growing conditions, a fixed observation schedule, and a way to record curvature. Why would multiple seedlings be more useful than just one?
Extension question: What might happen to new growth after you reverse the light direction? Our model starts fresh each run, so it cannot answer that question.
Take your evidence to the comments.
Write one comment below this post with all four parts:
- My prediction: What did you expect when the direction of light changed?
- My evidence: Describe at least two runs, including a swap of A and B. Name each light setting and the response.
- My explanation: Explain phototropism in your own words. How can unequal growth make a shoot curve?
- My next question: Identify one model limitation and propose a question to test with real plants.
Respond to a classmate: Ask about their evidence or suggest one way to improve their proposed investigation.
Submit in the website’s comments section below. The model does not save or submit a written response.
22 Responses
The plant seems to go into the same direction as the Sun so there might be some sort of force that pulls it to the Sun like a magnetic connection of some kind.
When doing the run, the plants with the sun facing the side of the plant curved to the side where the sun was. I think the plants bend towards the sun so it gets more sunlight. I also think the genes in the plant cause it to bend towards the sun to help it grow better.
I predicted the plants to be different sizes.. In Run A, light came from the left,and the shoot bended the plant. After swapping A and B, plant A remaind standing straight up while plant be curved to the left.. The pattern suggests that the sun can bend plants different ways or it wont effect it at all. The shaded side didn’t curve, causing the other plant bent. One limitation is one plant in larger. Next, I would investigate a different size color plant.
I predicted that the plant would go to were the sun is on the left the plant would lean to the left. In Run 1, light came from the left . After swapping A and B, making B left and A right. The pattern suggests light makes the plant. The shaded side is where the plant would not go , causing is to die because it had no sunlight.. One limitation is shade because it can kill a plant. Next, I would investigate why the plant is so dependent on light while some are not.
Plants respond to environmental changes through growth movements tropisms rapid physical movements. Because plants cannot move to a new location when conditions change, they alter their growth patterns and internal systems to survive. even tho they cant see or have a brain they can still grow to the sun and as long as you water them they will grow.
I predict I thought that it would grow toward the light. In simulation 1 the light was on the left and plant A left curve, while plant B stayed straight as the light was over it. When I moved the light from plant 1 to plant 2, the plant with light on the side bent toward it. This is because the shaded side grows faster and the plant bends toward the light.
How can a plant respond to a change in its environment? It will alter how it grows producing chemicals or adjusting their cycles. My prediction is if the light is right it will bend right and if the light is left it will bend left. When I used the simulation and I put the light left or right it went in that direction. And phototropism is when the plant reacts to the light and like grows towards the light I think. And the next thing I would investigate is like see if different soil does the same thing or he does something different to the plant.
I predicted the plants to be different sizes.. In Run A, light came from the left,and the shoot bended the plant. After swapping A and B, plant A remaind standing straight up while plant be curved to the left.. The pattern suggests that the sun can bend plants different ways or it wont effect it at all. The shaded side didn’t curve, causing the other plant bent. One limitation is one plant in larger. Next, I would investigate a different size color plant.
I predicted that the plant would curve to the direction of the sunlight. In Run 1, light came from the left and the plant curved to that direction. After swapping A and B, It curved to the direction of sunlight again. The pattern suggests that the plants somehow are able to know in a way where to grow for sunlight. One limitation is that the simulation starts fresh for each run. From what I saw, it suggests that the plants somehow learned, from I think to be evolution, to curve to the direction of sunlight.
According to my prediction, the plant would lean to the left where the sun is on the left. Light came from the left in Run 1. After A and B are switched, B is on the left and A is on the right. The pattern implies that the plant is made by light. The plant would not travel to the shaded side and would eventually die from lack of sunshine. Shade is one restriction since it can harm a plant. I would then look into why some plants are so reliant on light while others are not.
I predict that the plant would go to where the sun is on the left and the plant would lean to the left. In Run 1, light came from the left . After swapping A and B, making B left and A right. The pattern suggests light makes the plant. The shaded side is where the plant would not go , causing is to die because it had no sunlight.. One limitation is shade because it can kill a plant. Next, I would investigate why the plant is so dependent on light while some are not.
plants can respond to different environments because it can help it grow more.and soil will help grow more.my prediction is if the light is right it will bend to the right if the light it is on the left it will turn left.i put the light left or it went in that direction.and the next thing I would investigate is like see if different soil does the same thing.
I predicted that it would move where the sun is. In the run, the light came from the right for A, then for B the light came on the left. After swapping A and B. The pattern suggests that the plant moves where the sun is at. The shaded side blocked the sun, causing the plant to stand still. One limitation is that the plant curves. Next, I would investigate why the plant does this, it’s because the plant needs sunlight for it to grow.
I predicted that it would probably shrink or not grow since the sun is pointing directly at it. In Run 1, light came from the left and the plant was curving to the left. When I used the simulation and the light was on left or it was above it went almost in the direction. When it was above it wasn’t really moving it just stood there. The shaded side makes the plant to not react to it. causing no growth. What I think is causing it is that the plant only grows when it’s toward the light. Next, I would investigate to see how it would be if the plant would grow if there was no sun.
After running the growth model and moving the sun in different direction I observed that wherever the sun is thats the direction the plants curves to, so I started thinking if the plant can feel where the sun is. Maybe the plant wants direct sunlight so it moves with the sun, and the plant knows that it needs sun to survive and grow. I also observed that when the sun was straight above the plant the plant stayed facing up, it didn’t curve. Maybe the plant has mechanisms to know where the sunlight is coming from so it also knows where to move. I would like to learn about what plants feel and how they know where the sun is because that seems interesting.
“I predicted that the plant would bend the opposite way the sun is facing. In Run or simulation 1, light came from the left and the plant slightly bended twards the sun. After swapping A and B, A left and B right. The pattern suggests where ever the sun faces the plant would bend towards that direction. The shaded side causes the shoot to curve toward the light. One limitation is not enough water or Missing essential minerals in the soil. Next, I would investigate what would happen if I reversed the light direction.”
I predict that the plant would go to where the sun is on the left and the plant would lean to the left. In Run 1, light came from the left . After swapping A and B, making B left and A right. The pattern suggests light makes the plant. The shaded side is where the plant would not go , causing is to die because it had no sunlight.. One limitation is shade because it can kill a plant. Next, I would investigate why the plant is so dependent on light while some are not.
Plants can respond to different environments because it can help it grow more.and soil will help grow more.my prediction is if the light is right it will bend to the right if the light it is on the left it will turn left.i put the light left or it went in that direction.and the next thing I would investigate is like see if different soil does the same thing.
I would rather sleep than stay awake, but I think you’re right.
After a month I have growth into a plant so my owner fed me and gave me sunlight every day so I am just a plant the only thing I can do I grow and eat water and get sun light that only thing I do ever single day so after a it became December I grow a lot so big than my owner but me in a different vase I was very big I even started to blame flowers pink with withe and orange and yellow I looked really pretty my owner decided to put me outside because I was getting really big so she put me because I was getting so big that I was taken so much space so she grabbed me and put me outside the next two years i was so big and had so much flowers my owner still gave me water and sun light like when she was little .
I predicted that they just grow in whatever way the roots are faced. In Run 1 , light came from the left and the plant curved left. After swapping A and B, they went the direction of the sun. The pattern suggests that a plant curves to the way the sun is facing. The shaded side has no sun, causing the plant to grow away from the shade. One limitation is that no sun could make a plant die. Next, I would investigate why the plant curves towards the sun.
I predict that the plant will grow in whatever way that the sun is shining in. In the simulation if the sun is on the left side the plant will grow towards the sun. Although if the sunlight is coming from above the plant keeps on growing straight and tall because not just one stop is getting sunlight, most of the plant is. When the plants are young they have phototropism and that makes them grow in the direction that the sunlight is . If the sun is only hitting one side of the plant , it will grow more towards that side because the other side will be shaded and get no sun. I wonder if the plant has already grown to the left side if the sun direction changes to the right side will the plant move.