Page 20 - Biology - XII
P. 20
Slide Preparation
2 Slide Preparation
EXPERIMENT - 4
Objective
To prepare a temporary mount to observe the pollen germination on a slide (Portulaca/Grass/China rose).
Principle/Theory
Pollen grains represent the male gametophyte. If the open anthers of any fl ower are seen, yellowish powdery
pollens are found. They are generally spherical in shape, about 25–50 micrometres in diameter. It has a
prominent 2-layered wall. The hard outer layer called exine is made up of sporollenin and has prominent
apertures called germ pores. The inner wall of the pollen grain is called intine and is a continuous layer
made up of cellulose and pectin.
In nature, pollen grains germinate on the compatible stigmas of carpels which is called pollen pistil
interaction. During germination, intine of pollen grain emerges out as pollen tube through one of the germ
pores in exine. However, this can also be synthetically induced using chemicals such as 10% sucrose
solution.
The percentage of pollen grains germinated is calculated by
Number of pollen grains in the microscopic fi eld = N (on the prepared slide).
Number of pollen grains germinated in the microscopic fi eld = n (on the prepared slide).
n 100 n
Percentage of the pollen germination 100 or . The time taken for germination of pollen varies
N N
for diff erent pollens of diff erent species.
Materials Required
Study material—Portulaca or China rose fl ower, slide, coverslips, microscope, chemicals—sucrose 10 g,
boric acid 10 mg, potassium nitrate 20 mg, magnesium sulphate 30 mg, 100 ml distilled water, beaker,
and a dropper
Procedure
1. Prepare nutrient medium by dissolving 10 g sucrose, 20 mg potassium nitrate, 30 mg magnesium
sulphate, and 10 g boric acid in 100 ml of distilled water.
2. Dust the pollen grains from the stamens of a fl ower on a clean and dry slide.
3. Add a drop of nutrient medium with a dropper over the pollen grains.
4. Let the slide be kept undisturbed for 10–15 minutes.
5. Observe the slide under low power of microscope.
6. Write comments and draw the labelled diagram in your practical record fi le.
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