yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

2015 AP Biology free response 5


3m read
·Nov 11, 2024

Phototropism in plants is a response in which a plant shoot grows toward a light source. The results of five different experimental treatments from classic investigations of phototropism are shown above.

Part A: Give support for the claim that the cells located in the tip of the plant shoot detect the light by comparing the results from treatment group one with the results from treatment group two and treatment group three.

So, we want to compare these first three treatment groups. You see, when you have an unaltered tip, the whole plant is going to bend in the direction of the light. When you remove the tip, it no longer bends in the direction of the light. Or if you were to cover the tip with some type of an opaque cap so the light can't go through it, it's still not going to bend.

So, this is pretty good evidence that there's something about the tip of the plant that allows the phototropism to occur. It allows the plant to know which direction the light is and then somehow causes it to bend in that direction.

So, I'll just write that down: give support for the claim. We can say that phototropism only occurred when there is an unaltered tip that has access to light. No bending occurred when either the tip was removed (that was treatment two) or the tip had an opaque cover (that was treatment three).

So, that's all there is to it. It only occurred when there was an unaltered tip, so that was treatment one, that has access to light. No bending occurred when either the tip was removed in treatment two or treatment three.

So, it's a pretty good indication that you need that tip, and it needs to have access to the light. Something about the tip lets the plant know what direction to start bending in.

All right, let's do Part B now.

Part B: In treatment groups four and five, the tips of the plants are removed and placed back onto the chute on either a permeable or impermeable barrier. Using the results from treatment groups four and five, describe two additional characteristics of the phototropism response.

Well, when the tip was placed on top of a permeable barrier, the phototropism still happens; the plant still bends. So, even though the tip is disconnected, because this barrier is permeable, the tip must be able to sense the light and release some type of substance or hormone or chemical or something that's able to go through this permeable barrier.

Some type of substance goes through this permeable barrier and signals to the rest of the plant to bend in the right direction. Because when you put an impermeable barrier right over here, the tip might be trying to release those same substances, but they can't get through. So, the rest of the plant doesn't know to bend or in what direction to bend.

So, we could say the tip must release some type of hormone or chemical that signals to the rest of the plant to bend and in which direction. We know this because only treatment four, where the barrier is permeable to that substance, shows phototropism, not treatment five.

We could say this because of the two treatments four and five; only treatment four, where the barrier is permeable to that substance, shows phototropism. That's the only explanation here. It's not doing it through somehow doing it through radio waves or releasing substances that somehow float in the air to the rest of the plant.

Some type of substance is going through directly from the tip to the rest of the plant, and when you block it, it's not able to send those chemical signals. That's the best explanation that I can think of for this behavior that we see between treatments four and five.

More Articles

View All
LearnStorm Growth Mindset: Dr. Michael Merzenich on growing your brain
But we’ve actually trained athletes, you could say, on the sort of academic side of training you would not necessarily imagine. And guess what? It improves our performance on the field. What’s happening for a couple of reasons. One reason is that you’re …
Pain in the Crevasse | Continent 7: Antarctica
Okay team, let Mark the shear zone, so come on nice and close behind us. Thank you. The RAS shelf team has traveled about 30 miles, and they’re facing the most dangerous part of their traverse. Oh, we’re just about to enter into the shear zone here. We j…
The Seven Years' War part 2
So we’ve been discussing the Seven Years’ War in North America, also commonly called the French and Indian War. But as I mentioned in the last video, I think “Seven Years’ War” is a better name for this conflict because it was the first global war that ha…
15 Money Mindsets That Speed Up Your Growth
Do you know what your money mindset is? You know research shows that most people have four core money beliefs: money avoidance, money worship, money status, and money vigilance. Those beliefs often, especially when you don’t understand where they come fro…
TIL: Wild Lions Live in India | Today I Learned
[Music] Most people think about lions in Africa, but very few people know that they actually exist in India too. It looks, uh, not very different from the African lion. It is, however, a bit smaller. It does have flappy skin on the stomach that looks diff…
How Hidden Technology Transformed Bowling
A portion of this video was sponsored by Salesforce. This is the biggest, most in-depth video about bowling ever. How bowling balls are made, the best way to throw them, maximize strikes, how the lanes are oiled, what it takes to be a pro, and how this sp…