Multiple choice

Which of the following herbicides act by interfering in light reaction of photosynthesis?

  1. 2,4-Dichlorophenoxyacetic acid
  2. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea
  3. N-(phosphonomethyl)glycine
  4. 1-Chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine

  1. 1 and 2

  2. 1 and 3

  3. 1 and 4

  4. 2 and 3

  5. 2 and 4
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Two major classes of herbicides that block photosynthetic electron flow are derivatives of urea and triazine herbicides. These herbicides interfere in PS II with binding of plastoquinone (Q) and thus, blocks the transfer of electrons to plastoquinone and also blocks electron transport between PS II and PS I. Examples: Urea derivatives: 3-(4-chlorophenyl)-1-methoxy-1-methylurea and 3-(3,4-Dichlorophenyl)-1,1-dimethylurea Triazine derivatives: 6-Chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine and 1-Chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine.

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