Question
2,4-D is a synthetic plant auxin that is used as a weedkiller.
Researchers investigated the effectiveness of different treatments of 2,4-D on the control of the
weed Conyza canadensis in fields of maize, Zea mays.
The results are shown in Table 5.1.
(a) (i) Maize farmers that had been using treatment C were advised by the researchers to
change to treatment F.
Discuss the advantages and disadvantages of changing to treatment F.
(ii) Suggest two factors that could decrease the effectiveness of 2,4-D.
1
2
(iii) Explain how 2,4-D acts as a weedkiller
(b) Auxin causes the shoots of a plant to grow away from gravity.
State the name of this response.
Answer/Explanation
Ans
5 (a)(i) advantages
1 lower (dry) mass ;
2 fewer weeds / lower weed density ;
3 less competition ;
4 therefore higher yield of crop ;
disadvantages
5 more treatments ;
6 higher cost / time / effort ;
7 idea of increased environmental impact ;
8 increased health risks ;
5 (a) (ii) increased strength of wind ;
increased precipitation ;
resistance ;
type of weed ;
AVP ;; e.g. ref. to amount / too much time between treatments
5 (a) (iii) 1 absorbed by (broad leaved) weeds / selective for weeds ;
2 less absorption by (narrow leaved) crops ;
3 increase the growth (rate) of weeds ;
4 plant cannot produce enough, glucose / photosynthesise fast enough ;
5 weeds cannot maintain rate of growth ;
6 AVP ; e.g. falls over and can’t absorb sunlight
5 (b) gravi / geo ;
tropism ;