Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    can anyone help me out with the following question?

    Herbicides (weedkillers) interfere with electron transport by accepting electrons. Suggest how this causes plants to die (3 marks)

    so far i've written:

    NADPH in the plant can no longer accept the electrons. this means that NADPH no longer provides energized electrons to the calvin cycle

    I'm not sure if what i've written is correct, though


    why does it take longer in a light dependent reaction far a plant in NH3OH to change colour rather than water.

    is this something to do with photlysis.
    • Study Helper
    Offline

    17
    ReputationRep:
    You already asked the last question on the other thread

    What you put for the first part is correct I believe. But something else happens in the electron transport chain, ATP is synthesised by the electrons losing energy when transferring to the next chlorophyll molecule, I would also mention something to do with less ATP is synthesised, but thats not the main reason, the main reason is what you've said, no electrons are available to reduce the co enzyme, which is very important. I'm doing AQA Biology, so I will go other this again in more detail over the weekend.
    Offline

    1
    ReputationRep:
    NADPH does not accept electrons. It is reduced already!

    The problem is that NADP cannot accept electrons.
    Offline

    1
    ReputationRep:
    (Original post by l4ith)
    NADPH does not accept electrons. It is reduced already!

    The problem is that NADP cannot accept electrons.
    Your grades seem to speak for themselves. I have a small question....in non-cyclic photophosphorylation, is ATP produced by the same mechanism that produces it during respiration via ATP synthase? Also during cyclic photophosphorylation, does the energy released from the electron transport chain directly join ADP to Pi to produce ATP without the need for protons to be pumped into the thylakoid lumen and then through ATP synthase?
    Offline

    1
    ReputationRep:
    (Original post by sc0307)
    Your grades seem to speak for themselves. I have a small question....in non-cyclic photophosphorylation, is ATP produced by the same mechanism that produces it during respiration via ATP synthase? Also during cyclic photophosphorylation, does the energy released from the electron transport chain directly join ADP to Pi to produce ATP without the need for protons to be pumped into the thylakoid lumen and then through ATP synthase?
    ATP is produced in the same way in photosynthesis as it is in respiration. Non-cyclic photophosphorylation involves the movement of H+ ions (or H3O+ to be more accurate) across the thylakoid membrane into the stroma and through this ATP synthase is activated.
    Offline

    2
    ReputationRep:
    (Original post by usmana)
    can anyone help me out with the following question?

    Herbicides (weedkillers) interfere with electron transport by accepting electrons. Suggest how this causes plants to die (3 marks)

    so far i've written:

    NADPH in the plant can no longer accept the electrons. this means that NADPH no longer provides energized electrons to the calvin cycle

    I'm not sure if what i've written is correct, though


    why does it take longer in a light dependent reaction far a plant in NH3OH to change colour rather than water.

    is this something to do with photlysis.
    I think you have the basic idea, but you have to relate it to how this kills the plant.

    ATP and NADPH is required for the light-independent reaction AKA Calvin cycle, which provides the compounds with which the plant makes glucose, starch,e.t.c. Herbicides prevent the plants from making these organic materials necessary for its growth by preventing the production of NADPH. Hence, the link between the light dependent stage and light-independent stage of photosynthesis is compromised and the plant will eventually die because of lack of NADPH which is required for the production of organic materials the plant uses for growth.

    This should give you your whole point...
    Offline

    2
    ReputationRep:
    (Original post by Eloades11)
    You already asked the last question on the other thread

    What you put for the first part is correct I believe. But something else happens in the electron transport chain, ATP is synthesised by the electrons losing energy when transferring to the next chlorophyll molecule, I would also mention something to do with less ATP is synthesised, but thats not the main reason, the main reason is what you've said, no electrons are available to reduce the co enzyme, which is very important. I'm doing AQA Biology, so I will go other this again in more detail over the weekend.
    Actually ,the level of ATP produced is not compromised...as this is not dependent on the "final electron" acceptor... As you have correctly hinted, this is not the main reason.......But I would go further by saying is not a reason at all.....ATP is not compromised here....the problem here is that NADPH will not be formed which is required for the Calvin cycle......
    Offline

    2
    ReputationRep:
    (Original post by sc0307)
    Your grades seem to speak for themselves. I have a small question....in non-cyclic photophosphorylation, is ATP produced by the same mechanism that produces it during respiration via ATP synthase? Also during cyclic photophosphorylation, does the energy released from the electron transport chain directly join ADP to Pi to produce ATP without the need for protons to be pumped into the thylakoid lumen and then through ATP synthase?

    Yes, ATP synthase uses the electrochemical gradient across the thylakoid membrane ( photosynthesis) and inner mitochondrion membrane( respiration) to make ATP.

    During cyclic photophosphorylation, the electron basically just "dances" around one photosystem center (p700, to be specific)....As it does this, energy is liberated...the energy is used to create the H+ gradient that is used by ATP synthase....so NO, the energy is not used directly to join ADP to Pi..instead, it is used to create the electrochemical gradient.
    • Study Helper
    Offline

    17
    ReputationRep:
    (Original post by int_applicant)
    Actually ,the level of ATP produced is not compromised...as this is not dependent on the "final electron" acceptor... As you have correctly hinted, this is not the main reason.......But I would go further by saying is not a reason at all.....ATP is not compromised here....the problem here is that NADPH will not be formed which is required for the Calvin cycle......
    Oh right I see, thanks for letting me know, otherwise this would have went onto my exam paper
    Offline

    1
    ReputationRep:
    (Original post by int_applicant)
    Yes, ATP synthase uses the electrochemical gradient across the thylakoid membrane ( photosynthesis) and inner mitochondrion membrane( respiration) to make ATP.

    During cyclic photophosphorylation, the electron basically just "dances" around one photosystem center (p700, to be specific)....As it does this, energy is liberated...the energy is used to create the H+ gradient that is used by ATP synthase....so NO, the energy is not used directly to join ADP to Pi..instead, it is used to create the electrochemical gradient.
    Thank you! So, during non-cyclic, the electrons rather than 'dancing around' p700 and electron carriers, it goes to the last electron acceptor and along with protons reduces NADP to NADPH? Also, the electrons must be at a high energy level to release the energy it does when it jumps across electron carriers, do the electrons, now at a low energy level, go back to a high energy level once it goes back to p700 from photons in the sunlight?
    Offline

    2
    ReputationRep:
    (Original post by sc0307)
    Thank you! So, during non-cyclic, the electrons rather than 'dancing around' p700 and electron carriers, it goes to the last electron acceptor and along with protons reduces NADP to NADPH?
    Yes. Also, note that NADP is the final electron acceptor


    Also, the electrons must be at a high energy level to release the energy it does when it jumps across electron carriers, do the electrons, now at a low energy level, go back to a high energy level once it goes back to p700 from photons in the sunlight?
    yes, once it gets to p700, it gets excited again through resonance ( dont worry about this, if it doesnt make sense)...Bottom line is that once it gets to the photosystem (p700), it gets excited again by photons in the sunlight...
    Offline

    2
    ReputationRep:
    (Original post by sc0307)
    Thank you! So, during non-cyclic, the electrons rather than 'dancing around' p700 and electron carriers, it goes to the last electron acceptor and along with protons reduces NADP to NADPH?
    Yes. Also, note that NADP is the final electron acceptor


    Also, the electrons must be at a high energy level to release the energy it does when it jumps across electron carriers, do the electrons, now at a low energy level, go back to a high energy level once it goes back to p700 from photons in the sunlight?
    yes, once it gets to p700, it gets excited again through resonance ( dont worry about this, if it doesnt make sense)...Bottom line is that once it gets to the photosystem (p700), it gets excited again by photons in the sunlight...
    Offline

    1
    ReputationRep:
    (Original post by int_applicant)
    Yes. Also, note that NADP is the final electron acceptor




    yes, once it gets to p700, it gets excited again through resonance ( dont worry about this, if it doesnt make sense)...Bottom line is that once it gets to the photosystem (p700), it gets excited again by photons in the sunlight...
    Thank you so much! The book is quite vague about this topic and my teachers couldn't seem to give me a straight answer.
    Offline

    2
    ReputationRep:
    (Original post by sc0307)
    Thank you so much! The book is quite vague about this topic and my teachers couldn't seem to give me a straight answer.
    no worries...I totally understand..goodluck with ur A levels and ping me , if you have further questions/concerns....I normally scan through this forum...
    Offline

    1
    ReputationRep:
    (Original post by int_applicant)
    no worries...I totally understand..goodluck with ur A levels and ping me , if you have further questions/concerns....I normally scan through this forum...
    Thanks. Good luck to you too!
    Offline

    2
    ReputationRep:
    (Original post by int_applicant)
    I think you have the basic idea, but you have to relate it to how this kills the plant.

    ATP and NADPH is required for the light-independent reaction AKA Calvin cycle, which provides the compounds with which the plant makes glucose, starch,e.t.c. Herbicides prevent the plants from making these organic materials necessary for its growth by preventing the production of NADPH. Hence, the link between the light dependent stage and light-independent stage of photosynthesis is compromised and the plant will eventually die because of lack of NADPH which is required for the production of organic materials the plant uses for growth.

    This should give you your whole point...
    +rep
    How about the 2nd Q!?
    Has anybody got a bit more question for this experiments?! :rolleyes:
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.