CP 14 Flashcards
What is the role of gibberellin during germination?
It is secreted by the embryo, then it diffuses to the aleurone layer of the endosperm to stimulate the production of amylase. Amylase hydrolyses starch to
maltose
IV DV
IV: Concentration of Gibberellin (GA)
DV: Size of Clear Area Around the Grain
control variables
- Size, number of seeds
- Temperature (no more than
- 30℃)
- Incubation time
- Starch concentration on agar
- Volume of GA
- Soaking time in GA
- Species of seed
Why are sterile conditions used
sterile conditions are used to:
- prevent the growth of bacteria that would produce amylase
- prevent bacteria/fungi from decomposing the seeds
How is the effect of gibberellin concentration on
amylase production investigated?
- Dilute gibberellin to produce several concentrations.
- Cut seeds in half, use only the half with the endosperm.
- Dip in sodium hypochlorite solution and wash with water.
- Place seeds in each gibberellin solution and leave.
- Place seeds in a petri dish and starch agar, and leave for 12-48 hours.
- Pour potassium iodide onto the plates and measure the clear zone.
What does the zone of inhibition indicate?
The clear zone indicates that starch has been hydrolysed by amylase (hence not stained by iodine).
The larger the zone of inhibition, the higher the amylase concentration
Why are the seeds placed in sodium hypochlorite
solution?
To sterilise the seeds
What is the effect of gibberellin concentration on
amylase production?
Increasing gibberellin concentration increases the area of the clear zone, indicating an increased production of amylase and more starch hydrolysed.
What are some sources of error in this practical?
The existing gibberellin and amylase
content of the seeds may be different
EVALUATION ISSUES
● Not all the seeds will have started to germinate before embryo removal which will reduce the sample size and reliability of the mean
● Wrong end of the seed used will prevent accurate results
● Not sterilising the seed halves properly could lead to contamination of the plate
BIOLOGICAL EXPLANATION
A cereal grain contains a store of starch within the endosperm.
During germination the starch must be made soluble so that it can be transported to the embryo to support the growth of the seedling.
The embryo is much smaller than the endosperm and is situated at the more pointed end of the grain. The developing embryo releases gibberellins that act on a layer of cells on the outside of the endosperm, stimulating these cells to release the starch-digesting enzyme amylase.
The production of amylase will be assessed using a starch agar assay. Cereal grains that have had the embryo removed are first soaked in gibberellic acid, then placed onto the starch agar plates and incubated. The agar plate is then flooded with iodine solution, which stains starch blue-black. The areas where starch has been digested will not stain. The size of the clear area around a cereal grain indicates the amount of amylase produced by the seed.
Why were the embryos removed from the seeds used in this investigation?
The embryos would produce gibberellin in unknown quantities, reducing the validity of the
results
It was important to avoid contamination of the Petri dishes by microorganisms. Contamination would present a potential biohazard, but could also affect the validity of the results. Explain why this is the case
Microorganisms such as fungi and bacteria may produce amylase, which would produce clear zones.
If there had been contamination close to the seeds this would make the measured results invalid
Explain why clear areas appeared around some seeds
Gibberellin at certain concentrations stimulates the production of amylase by the aleurone layer
around the endosperm.
This hydrolyses starch to maltose. Iodine only stains the areas that contain starch
