A student placed populations of duckweed in two identical controlled-environment ponds. Only Lemna gibba was placed in pond A. Equal amounts of Lemna albba and Spiradela polyrhiza were placed in pond B. each pond was provided with suitable nutrients for duckweed growth. Every week a square metre sample of plants growing on the surface of each pond was removed and the weight of Lemna gibba plants in each sample was measured. The samples were then returned to the ponds. The following table shows the change in weight of Lemna gibba in pond A and in pond B over the eight weeks of the investigation. Time since experiment began (weeks) 0 1 2 3 4 ii. 5 6 7 8 Pond A Weight of Lemna gibba when grown alone (g) 60 110 190 255 285 335 330 340 360 Pond B Weight Lemna gibba when grown with Spiradela polyrhiza (g) 60 85 105 85 90 80 75 40 35 a) State one hypothesis that this investigation may have been designed to test. b) State the dependent variable in this investigation. c) Both ponds contained equal amounts of Lemna gibba at the start if this investigation. State two quantities that should have been deliberately kept the same for pond A and B. d) Describe the changes in the weight of Lemna gibba population in pond B over the eight weeks of the investigation. e) State one conclusion that can be reached by comparing the data for pond A and pond B. f) The student did not repeat this investigation. i. State why the validity of the results is reduced because the student did not repeat this investigation. The lack of repetition is a weakness in the design of this investigation. State one other weakness in the design of this investigation.