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
Safari Live - Day 316 | National Geographic
This program features live coverage of an African safari and may include animal kills and carcasses. Viewer discretion is advised. Good afternoon, everybody! Welcome to Juma in the Sabi Sands in South Africa, where we have found a beautiful European roll…
Khanmigo for teachers
Hi! I’m Michelle, a professional learning specialist here at KH Academy and a former classroom teacher, just like you. Meet Kigo, your AI-driven companion, who’s revolutionizing teaching for a more engaging and efficient experience. Kigo has many excitin…
The early Temperance movement - part 2
Hey, it’s Becca, and this is Temperance Part Two. Um, in this video, I’ll be talking more about how exactly, over the course of the 1830s until mostly the 1860s, the temperance movement took root in America and how it became this national phenomenon. So,…
how to ACTUALLY CHANGE your life in 2023 (step by step guide)
We all experienced failure at some point in our lives. Maybe you didn’t get that promotion you were hoping for, or you didn’t accomplish a personal goal you set for yourself. But for some reason, when it gets closer to New Year’s, we tend to be more hopef…
Pitch Practice with FlavorCloud, Holly Liu, and Adora Cheung
So the next thing we’re going to do is bring up Flavor Cloud, who is going to pitch Holly, who is the investor here, and then go from there. Yep, so I guess we’re gonna be sharing. Sorry, so I’m gonna be an angel investor, and I’ve done some angel investi…
Khan Academy Needs Your Help This Back to School
Hi everyone, Sal Khan here from Khan Academy. I just want to remind everyone that, as we’re going through what’s clearly a very difficult time, especially, well, in the world generally, but especially in education, the entire team here at Khan Academy is…