Science 7–10 · Year 9

Pollen tube growth on a slide: watching the step before fertilisation

Science understanding: Biological sciences (ACARA Year 9 reproduction, AC9S9U02; NSW Science 7–10 (2023) names pollination nowhere in its Stage 4 or Stage 5 content, and SC5-GEV-02 is cited for the Stage 5 content point on how genetic information is passed on to offspring by sexual and asexual reproduction, the step this practical shows)

PracticalLow risk

The idea

A pollen grain grows a tube toward the ovule when it lands on a suitable surface, and that growth can be watched and measured on a slide within a double lesson.

What you need

Fresh pollen from a ripe anther of a species the SAPS pollen tube sheet lists as successful and that flowers locally at the time (for example Ceanothus or Viburnum in spring); SAPS notes that success depends on the species and the age of the pollen
Sucrose solution at 0.6 mol/L (20.5 g made up to 100 mL), the simplified SAPS medium, plus 0.2, 0.4 and 0.8 mol/L solutions (6.8, 13.7 and 27.4 g made up to 100 mL) for comparison, and distilled water
Cavity slides, coverslips, petroleum jelly, a warm bench
Compound microscope with a calibrated field of view, stopwatch

How to do it

Put one drop of 0.6 mol/L sucrose in a cavity slide, dust pollen from a ripe anther onto it and ring the coverslip with petroleum jelly to stop drying.
Note the time and view at 100x. Locate a field with several grains and keep it.
Every 10 minutes for the double lesson, record whether tubes have emerged and measure the length of three tubes against the field of view.
Set up slides at the other sucrose concentrations and one in distilled water; compare how many grains grow tubes and the tube length at 60 minutes.
Plot tube length against time for the best concentration, and length at 60 minutes against concentration.

What you should see

In a suitable sucrose concentration tubes emerge and lengthen during the lesson; the SAPS image series shows pollen tube growth over about an hour. SAPS warns that the practical has a reputation for being unreliable because it depends on pollen age, species and medium, so a slide with no tubes is a result to report, not a failure to hide. The distilled water slide shows whether this species needs sucrose at all; SAPS reports that chestnut pollen forms rudimentary tubes even in water. The learner knows it worked when the same grains are measured at each interval and the length-time plot rises.

What changes

What you change: Sucrose concentration (mol/L)
What you measure: Fraction of grains with tubes and tube length at 60 minutes
What you keep the same: Pollen source and age
Temperature
Drop volume
Slide sealed against drying

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Fertilisation happens when pollen touches the stigma; the tube must first grow to the ovule.
Pollen grains are the male gametes; they carry them.
Plants reproduce only by seeds.

Safety card

Low riskLearners carry it out

Hazards

Pollen allergy
Glass slides and coverslips

Controls

Anyone with hay fever handles slides prepared by a partner; wash hands
Handle coverslips by the edge; report breakages

Note

No hazardous chemicals; record a RiskAssess risk assessment for the activity as school procedure requires.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7–10 Syllabus (2023)SC5-GEV-02 SC5-WS-01 SC5-WS-05
Australian Curriculum v9AC9S9U02AC9S9I03AC9S9I04

Sources

The pages the author read to write this activity.

All Concept Studio activities