(Solved): Gibberellin causes stem elongation in plants. Fig. 17.1 shows the effect of gibberellin on cabbage ...

Gibberellin causes stem elongation in plants. Fig. 17.1 shows the effect of gibberellin on cabbage plants. Fig. 17.1 Gibberellin causes an increase in the distance between the leaves on the stem, which is known as the internodal length. (a) Explain why gibberellin is classed as a plant hormone. (ii) Gibberellin causes an increase in internodal length. State one other role of gibberellin in plants. [1] (c) A student carried out chemical tests on cabbage leaves to investigate which molecules were present. The student's method was as follows: - Add $50{\mathrm{cm}}^3$ of distilled water to 2 large cabbage leaves and blend into a smooth liquid using a food mixer. - Place $1{\mathrm{cm}}^3$ of the blended cabbage leaf liquid into 5 test tubes: - Tube 1: Add 5 drops of biuret reagent and mix. - Tube 2: Add $2{\mathrm{cm}}^3$ of Benedict's solution, mix, then place tube into a water bath for $5\min$. Remove and cool. - Tube 3: Add 2 drops of iodine solution and mix. - Tube 4: Add $2{\mathrm{cm}}^3$ of ethanol and mix. Then add $2{\mathrm{cm}}^3$ of distilled water and mix. - Tube 5: Insert a glucose test strip into the liquid then compare the colour to the colour chart provided (see Fig. 17.2 on the Insert). (i) Name a type of food molecule that the student will not be able to detect using these chemical tests. (ii) The table below is a summary of some of the student's findings. Complete the table by writing in the missing observations and conclusions. [2] (iii) The student then used a colorimeter to measure the absorbance of the contents of Tube 2. Explain how the use of a colorimeter could improve the student's conclusion.