How many plants are there in the whole world

Ascience research group is testing a new type of plant food. one trial is conducted in a controlled experiment. the data from the trial show that the plant that received the new food grew faster than the control plant. the group announces that the new plant food makes plants grow faster. what is the main weakness in this scientific claim?

2. which is the last step in the scientific method?

Fredrick griffith made a scientific discovery in 1928