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5a-b, Responses to the environment

Phototropism investigation.

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  • starky ultimate style avatar for user Greacus
    On cellular, or even molecular level, how does phototropism work exactly? Are there enzymes in the shoot, that are not present in the rest of the plant (stem)? If yes, how do they work?
    (9 votes)
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    • female robot grace style avatar for user Chiara
      Based on what I know, the tip contains some specific hormones or chemicals that the rest of the plant do not have, so the tip releases those hormones so that the rest of the plant will bend towards the light source. I'm not an expert on this, but I hope this helps you! :)

      Edited:
      From my research, a chemical called auxin is contained in the tip of the plant, so when it receives light, the auxin moves toward the darker side and sort of "pushes" the part that receives less light causing that part to elongate and bend towards the light source. You can search phototropism at Wikipedia if you want a better explanation (looking at images can be really helpful). :)
      (9 votes)
  • mr pants teal style avatar for user Tig
    Part 5b asked for TWO additional characteristics of the phototropism response. This video only gives one.
    (7 votes)
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    • leafers ultimate style avatar for user Yousef Sheikh
      I looked it up the 2015 AP Scoring Guidelines and it said two possible characteristics are:

      1. Tip produces a substance/signal/hormone (auxin) in response to light that causes plant to bend
      2. Substance/signal/hormone must diffuse from the tip and cause the plant to bend

      So Sal kinda mentioned the second part, but I think you may want to be a little more thorough, even if it seems too obvious
      (15 votes)
  • blobby green style avatar for user DHRUV MN
    could not understand what photoperiodism is
    (1 vote)
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    • starky sapling style avatar for user shounak Naskar
      Photoperiodism is the response of a plant to the relative length of day and night (24 hrs cycle).
      Some plants flower only when then exposed to day lengths shorter than or below a certain critical value . This is their response (photoperiodism ) and they are called short day plants (SDP). eg. Chrysanthemum
      Long Day Plants(LDP) require a photoperiod more than critical length . Eg. Hordeum vulgare
      Day neutral plants have no specific requirements . eg Tomato
      (5 votes)
  • blobby green style avatar for user Victory Lee
    Is this free response a short or a long response?
    (2 votes)
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  • aqualine ultimate style avatar for user rugphantom
    can someone please explain what phototropism is, because i dont understand what it means
    (2 votes)
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  • blobby green style avatar for user Josephine Turay
    Is there a possibility that the shoot will grow away from the light?
    (1 vote)
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  • marcimus purple style avatar for user Amina
    Didn't the question say "describe TWO additional charecteristics?" Sal only explained one, or did i get something wrong? thanks
    (1 vote)
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  • aqualine seedling style avatar for user mjaumjau
    What material could those barriers be? Wouldn't the impermeable barrier block everything else (water, nutrients) too, so the tip couldn't actually live with this kind of barrier? And is this an experiment that somebody has actually done?
    (1 vote)
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Video transcript

- {Voiceover] 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 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 wanna compare these first three treatment groups, and you see when you have an unaltered tip that 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 is there is 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 makes somehow causes it to bend in that direction. So I'll just write that down. Give support for the claim, so we can say that phototropism phototropism phototropism only occurred only occurred when there is an unaltered tip unaltered tip that has access to the light that has access to light. No bending occurred no bending occurred occurred when either the tip was removed the tip was removed that was that was treatment two so treatment treatment two, or the tip was tip had an opaque cover, the tip had an opaque cover, that was treatment treatment 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 this one, 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 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, so that's these two treatment groups right over here, the tips of the plants are removed and placed back onto the shoot 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 that goes through this permeable barrier, and somehow 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 and so the rest of the plant doesn't know to bend or in what direction to bend. So we could say, we could say tip, tip must release some type of hormone hormone I say chemical chemical that signals to rest of plant to bend to bend and in which direction which direction we know this, we know this, because only the or only I could say treatment four only treatment four treatment four permeable barrier, and I'll say where the barrier's permeable to that substance, where the barrier is permeable to that substance that substance we know this because only treatment four where the barrier is permeable to the substance shows shows phototropism, phototropism. Not treatment treatment five. We know this, we could say, because of the two, of four and five, only treatment four where the barrier's permeable to that substance shows phototropism. That's the only explanation here, that it's not doing somehow doing it through radio waves or releasing substances that somehow float in the air to the rest of the plant, that somehow some type of substance is going through 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 that's the best explanation that I can think of for this behavior that we see between between treatments four and five.