XII BIOLOGY
PRACTICAL-6
Q. 2 Make a temporary
preparation to show pollen germination.
Draw neat and labelled diagram of the same.
Preparation (pollen germinationslide)…… 2 Marks.
Diagram of pollen grain showing pollen germination…1
Mark.
Total -3 Marks
To study pollen
germination on a slide
Requirements:
Flowers of Catharanthus (Periwinkle), slide,
cover slip, compound microscope, petri dishes with covers, filter paper,
needles, forceps. boric acid, sucrose, magnesium sulphate, potassium nitrate,
distilled water, beaker, dropper, glass rod.
Procedure:
(1)
A nutrient medium for germination of pollen grains is prepared by dissolving 10
g sucrose, 30 g magnesium sulphate, and 20 g potassium nitrate in 100 ml of
distilled water. Add a small pinch of boric acid.
(2)
Take two drops of this solution on a clean glass slide.
(3)
Dust a few pollen grains from the anther of the flower over the nutrient
medium.
(4)
Place a cover slip on the preparation of pollen grain and observe the slide
under a compoun microscope.
(5)
Observe the slide after every five minutes till a protuberance emerging from
the polle grain is seen.
Ans-Board Exam
Requirements: -Flower of Catharanthus, glass
slide, cover slip, compound microscope, sugar solution, etc.
Observation: -In the nutrient medium, pollen
grain germinates, and pollen tube comes out through germ pore.
Qestions-
Q.1. Note the shape, colour and ornamentation of pollen grain?
Ans- The shape of the pollen grain is commonly found in round, ovule, triangular, disc or in a bean-shape with a smooth to spiky texture. The natural colour of pollen grains are white, which may also vary depending on the plant species. Some are yellow in colour, or orange, or cream and so on..
Q.2. What are the specific terms used for inner and outer walls of pollen grain? Ans= The outer thick wall of pollen grain is called exine and the inner thin wall is called intine.
Q.3. Name the chemical component of the inner wall of pollen grain? Ans= The intine, or inner layer, consists primarily of cellulose andp pectins.
Q.4. What does a mature pollen grain represent? Ans= The pollen grains represent the male gametophyte.
Q.5. Where do the pollens germinate naturally? Ans- Pollen germinates in the pollen chamber, located beneath the micropyle, underneath the integuments of the ovule.
Q.6. Name the nutrient element which plays major role in pollen grain germination.? Ans= The results of many studies indicate that calcium is a critical element that is strongly related to pollen germination and pollen tube growth.
Q.7. Draw a well labelled diagram of male gametophyte in Angiosperms as observed by you?
Multiple choice Questions.
1.Movement of pollen tube
towards an embryo sac is …….
a. thermotactic b. phototactic
c. chemotropic d. thigmotropic
2 Outer wall of pollen grain is made up
of ………….
a.
sporopollenin b.
pectocellulose
c. protein d. lipids
3 How many mitotic divisions take place
during germination of pollen grain and its development into mature gametophyte?
a. 3 b.
1 .
c. 5 d.
2
4. Triporate pollen grain is commonly
found in……………..
a. monocot plants b. dicot plants
c. pteridophytes d. gymnosperms
5. How many prothallial cells develop
during development of mole gametophyte in Angiosperms?
a. One prothallial
cell b. No prothallial cell
c. Equal to number of gametes produced d. Equal to number of tube cells produced
6
.Uniporate or monocolpate pollen grain is found in
a. monocot plants b. dicot plants
c. gymnosperms d. pteridophytes
Ans =
1.-c. chemotropic ; 2.- a. sporopollenin ; 3. -d. 2
4.- a. monocot plants ; 5.- b. No prothallial cell ; 6.- a.
monocot plants .
or
Aim-To study pollen germination on a slide.
Materials &
Apparatus
Freshly plucked from
china rose,10mg boric s,
beaker, boric acid, sucrose, microscope and cavity slide,Beaker,Microscope,Sucrose(10g),Coverslips,Slide,Dropper,Magnesium
sulphate (20 mg),Calcium nitrate (30 mg).
Procedure
- The first step involves the preparation of a nutrient solution.
- This is done by dissolving 10g of sucrose as well as 10mg of boric acid in 100ml of water.
- Pour a few drops of this solution onto the cavity slide.
- Then, use a brush or fingers to gently dust a few pollen grains from the stamen of mature flowers.
- Let the slide set for 5 mins. Then, use the microscope to view the slides in 30-minute intervals.
Observation
- The pollen grains will germinate when submerged in the nutrient-rich medium.
- This is characterized by the enlargement of the vegetative/tube cell.
- It emerges through one of the germ pores, eventually forming a pollen tube.
- The generative cell nucleus grows into the pollen tube and makes two male gametes.
- The male gamete is either spherical or lenticular in outline.
- The first step is to prepare the nutrient solution by dissolving the sucrose and boric acid in water, Then this mixture has to be dropped using a dropped on the cavity slip.
- Then using a brush or simply by fingers, brush off a few pollen grains and let the slide for 15 minutes.
- Then the microscope has to be used to observe the slide at intervals of 30 minutes.
Precautions
- The observation slide should be a cavity slide, meaning that it has a depression in the centre.
- There are precautions to be observed while performing this experiment:
- Dirty or previously used slides should not be used for dusting pollen grains. Slides should be clean and dry for use.
- Only a few drops of the nutrient medium is required for germination. 2-3 drops of the solution are enough, more than that may hinder the process of pollen germination.
- Only freshly plucked flowers should be used and the experiment should be conducted within some time of plucking.
- The cavity slide used for observation should have depression at the centre so that the solution can be held in that cavity and does not flow.
Factors Affecting Germination
Several factors influence the success of pollen germination:
1.Pollen viability: Fresh, mature
pollen from healthy flowers is more likely to germinate.
2.Compatibility: Pollen grains must
be compatible with the stigma they land on for successful germination and
fertilization.
3.Temperature and humidity: Warmth and moderate humidity provide optimal conditions
for pollen tube growth.
4.Nutrient availability: The sugar solution provides essential energy for the germinating
pollen.
Further Exploration:
- Trying different types of flowers and observing variations in pollen size, shape, and germination patterns.
- Investigating the role of different sugars or other nutrients on pollen germination.
- Exploring the fascinating world of incompatibility mechanisms in plants.
- Remember, scientific curiosity is a powerful tool. So, grab your microscope, embrace the spirit of discovery, and embark on your journey into the captivating world of pollen germination!
Conclusion-