Biology 9700/52 — May/June 2013

A student saw an advertisement about using the plant growth regulator gibberellin (GA) to stimulate the germination and early growth of seeds.

The student obtained some of the advertised growth regulator.

The information on the packet received from the supplier gave the following information.

1. The GA is supplied as a stable powder in pre-weighed sachets.
2. The contents of each sachet when dissolved in $1\ \text{dm}^3$ water gives a concentrated solution of $1\ \text{g dm}^{-3}$ ($3\ \text{mmol dm}^{-3}$).
3. The concentrated solution can be diluted according to the type of seed germinated.
4. Seeds should be soaked in the concentration required for the particular type of seed before planting.

The student decided to test the growth regulator on barley to find out if the advertisement was true.

Research into the germination of barley provided the following information.

• Barley needs to be soaked in water for 24 hours before germinating.
• Barley germinates best at a temperature between $15\text{--}20\ ^{\circ}\text{C}$ and without light.
• Embryos will develop into young plants with visible roots in 3 days and a shoot within 7 days.
• Germinating barley dries out very quickly and dies.
• The concentration of GA in barley tissue is normally $1\ \mu\text{mol dm}^{-3}$.
• Food stores in the endosperm of barley are hydrolysed by enzymes stimulated by GA and translocated into the developing embryo.

Fig. 1.1 shows a germinated barley grain.

Fig. 1.1 shows a germinated barley grain.

The student tested the hypothesis:

As the concentration of GA increases to an optimum the rate of germination of barley grains and the early growth of the young plants increases.