To Prepare a Temporary Mount to Observe Pollen Germination

Do you know some pollen grains are thousands of years old? But how are these pollen grains still alive? These pollen grains have a hard sporopollenin layer resistant to all environmental changes. Pollen grains are the male gametophyte of flowering plants. Initially, pollen grains are uninucleated, but later they become multinucleated by dividing into vegetative and generative cells. Pollen grains germinate on the stigma and divide into two types of cells. Vegetative cells convert into pollen tubes, and generative cells convert into male gametes.

Table of Content

• Aim

• Apparatus Required

• Theory

• Procedure

• Observations

• Results

• Precautions

• Lab Manual Questions

• Viva Questions

• Practical Based Questions

• Summary

Aim

To prepare a temporary mount to observe pollen germination. 

Apparatus Required

• Freshly plucked flower

• Coverslip

• Beaker

• Boric acid(10mg)

• Sucrose(10g)

• Slide

• Dropper

• Magnesium sulfate 

• Calcium nitrate

Theory

Pollen germination is defined as the physiological or chemical changes in the pollen grains. Various events occur during pollen germination. Some of the events are described below: 

• Pollen Attachment 

Pollen after shedding from the flower is attached to the stigma (only if the stigma allows pollen to attach).

• Pollen Tube Growth 

After attachment, the intine layer gets hydrated and ruptures the exine layer and the stigma releases various nutrients such as boron and calcium for pollen grains. Then vegetative cells convert into a pollen tube inside a pistil and make way for male gametes. The entire content of the pollen grain goes into the pistil through the pollen tube.

• Pollen-Pistil Interaction 

Pollination does not always ensure the transfer of the right type of pollen. Sometimes incompatible pollen may reach some flowers. So, there is a mechanism to identify whether the right type of pollen is transferred or not. That mechanism is known as pollen-pistil interaction. Only compatible pollen can germinate and produce a pollen tube. It is a dynamic process and involves pollen recognition followed by approval or denial. If it is the right type and compatible pollen it will be accepted by the stigma, if it is incompatible or the wrong type of pollen, it will be rejected by the stigma.

Procedure

1. First, we will prepare a nutrient solution for pollen grains,

2. For this, we have to dissolve 10g sucrose and 10 g boric acid in water. 

3. After dropping this mixture on a cavity slip using a dropper,

4. Then brush off a few pollens grains on this mixture using a brush and keep the solution untouched for 5 minutes,

5. After 30 minutes place this slide under a microscope to see pollen germination, and then observe it regularly for about half an hour.

Observations

The pollen grain will germinate after submerging sometimes in nutrient media.

During germination, pollen grain divides into two cells- a vegetative cell and a generative cell. Later on, this vegetative cell converts into a pollen tube through which male gametes come out of the pollen grain. Two male gametes are formed by the division of a generative cell. Male gametes may be lenticular or spherical. Pollen germination under a microscope can be seen for about half an hour. 

Results

Pollen germination can be observed when a slide is placed under a microscope.

Precautions 

Following precautions must be taken while experimenting.

1. Always use a new slide for dusting pollen grains.

2. Flowers used for the experiment must be freshly plucked,

3. Only a few drops of nutrient media  should be used,

4. Mounting should be free from air bubbles.

5. Staining should be proper and moderate.

Lab Manual Questions

1. What is the shape of a pollen grain?

Ans: Pollen grains are of various shapes. Some are circular, globular, lenticular, etc. 

2. What is the composition of the wall of pollen?

Ans: Pollen grain has two layers: intine and exine. Intine is made of cellulose and pectin, whereas exine is made of sporopollenin.

3. What is the importance of tectum to taxonomists?

Ans: It helps taxonomists to identify the type, nature, and family of the pollen grain.

4. What is a tectum?

Ans: Tectum is the innermost layer of the microspore.

Viva Questions

1. What is palynology? 

Ans:  Study of pollen grains of plants, spores, and some microscopic organisms.

2. What is the composition of the wall of pollen?

Ans: The outer wall of the pollen grain is composed of sporopollenin, and the inner wall is composed of cellulose and pectin. 

3. What is a tectum?

Ans: Tectum is like protrusion on a pollen grain's outer surface or spore.

4. What is the shape of the pollen grain?

Ans: There are a variety of shapes of the pollen grain; some are spherical, some are cylindrical, and some are oval. 

5. What are the different types of cells of pollen grain? 

Ans: There are two types of cells in pollen grain - one is vegetative and another type is generative cell.

6. What is the importance of tapetum?

Ans: Tapetum is the innermost layer that provides nutrition to developing pollen grains.

7. Why does pollen survive for many years?

Ans: Pollen grains can survive for many years because of the presence of the sporopollenin layer, which is the hardest substance.

8. What is the importance of germ pores?

Ans: Germ pore helps male gametes to come out of pollen grain, it makes a pollen tube through which male gametes come out of pollen grain.

9. Why do some athletes use pollen as an energy source?

Ans: Pollen grains are a very rich source of nutrients, they contain large amounts of nutrition, and that's why athletes use pollen as a source of energy.

10. What is the meaning of viability?

Ans: Viability Means the ability to survive in adverse conditions.

Practical Based Questions

Q1. Name the area of the pollen grain where the tube arises.

1. Germ pore

2. Intine

3. Sporopollenin

4. None of the above

Ans: (1) Germ pore

Q2. Which solution is used for pollen germination?

1. Methylene blue

2. Sucrose

3. Protein

4. None of the above

Ans: (2) Sucrose

Q3. If there are 20 pollen grains, then how many meiotic divisions will occur?

1. 5

2. 4

3. 10

4. 20

Ans: (1) 5 meiotic division 

Q4. Which of the following is not a layer of microsporangium?

1. Endothecium

2. Middle layer

3. Epithelial layer

4. None of the above

Ans: (3) Epithelial layer

Q5. Who induces pollen germination?

1. Calcium

2. Magnesium

3. Boron

4. Iron

Ans: (3) Boron

Q6. Which stain is used for pollen fertility?

1. Saccharine 

2. Methylene blue

3. Iodine

4. None of the above

Ans: (3) Iodine 

Q7. Why is potassium nitrate used for pollen germination?

1. To Slow metabolism

2. To increase metabolism

3. Both of the above

4. None of the above

Ans: (2) To increase the metabolism 

Q8. Who is responsible for pollination?

1. Birds

2. Air

3. Water

4. All of the above

Ans: (4) All of the above

Conclusion

In this article, we have studied pollen germination class 12 practical experiment. Pollen germination can be studied by dusting pollen grains on the slide and observing them under a microscope. We can see pollen grains dividing into vegetative and generative cells

We can also observe the growth of the pollen tube.