CP4: the effect of sucrose concentrations on pollen growth or germination

method

1. dilute the stock sucrose solution to several set concentrations

2. place a moist piece of filter paper into a petrish to dish to form a humid chamber

3. put a few drops of sucrose solution and an equal volume of mineral salt medium into a clean microscope slide.

4. Use mounted needle to rub the anther of the flower so they shed some pollen onto the microscope slide. Don’t add cover slip to prevent conditions becoming anoxic

5. Place slides into the petri dish until it is time to observe them.

6. start stopwatch/note time

7. place slides under microscope + use calibrated eyepiece graticule to measure pollen tube growth

independent variable

sucrose concentration

why equal volumes of sucrose and mineral salt solution

graphical analysis

plot graph of sucrose concentration vs pollen tube growth and curve

dependent variable

measuring length of 5 pollen tubes using calibrated eyepiece graticule and find mean

control variables

• time in which growth is happening

• maturity

• temperature

• equal volume of mineral salt solution

petri dish with moist filter paper

so pollen grains don’t dry up

why no cover slip

to prevent anoxic conditions so that germination/pollen tube growth isn’t affected.

risks/hazard

• allergies, soil bacteria, contamination - wash hands

• cuts from sharps (eg. scalpel) - cut away from body

• injury from broken glass - microscope slides etc - don’t remove glass from wounds

explain the results of the experiment

• as sucrose conc. increases, mean pollen tube growth also increases up to an optimum

• after, as sucrose conc, increases, mean pollen tube decreases - due to osmotic effects of increasing concentrations of sucrose, (water moves out of pollen grain into sucrose solution - water needed to start pollen germination and growth)

how to calculate rate of growth of pollen tubes from raw data?

• divide length of pollen tube mm

• by time in seocnds

• calculate growth rate mms-1

why is mineral salt solution used?

to provide the essential ions and nutrients that pollen need for successful germination and tube growth

keep osmotic balance