Flower Structure and Pollination

Flower Structure and Pollination

A flower is the reproductive structure of an angiosperm. It is mainly concerned with sexual reproduction and contains the male and female reproductive organs. The major events associated with flowering plants include formation of male and female gametes, pollination, fertilisation and seed formation.

1. Basic Structure of a Flower

A typical flower consists of four floral whorls (floral parts arranged in circles around the central axis). These are:

Floral Whorl	Individual Unit	Main Function
Calyx	Sepals	Protects the flower bud
Corolla	Petals	Attracts pollinators
Androecium	Stamens	Male reproductive whorl; produces pollen grains
Gynoecium	Carpels/Pistils	Female reproductive whorl; contains ovules

2. Calyx

The calyx is the outermost floral whorl. Its individual members are called sepals.

• Sepals are usually green in colour.
• They protect the flower during the bud stage.
• In some flowers, sepals may remain attached even after flowering.

Example: In a typical flower, the green leaf-like structures surrounding the flower bud are sepals.

3. Corolla

The corolla is the second floral whorl and is made up of petals.

• Petals are generally large and brightly coloured.
• They may produce fragrance.
• They help in attracting insects and other pollinating agents.
• Some petals also provide nectar guides to pollinators.

4. Androecium – Male Reproductive Whorl

The androecium represents the male reproductive part of a flower. Its individual members are called stamens.

A typical stamen consists of two main parts:

Part	Description	Function
Filament	A long, slender stalk	Supports the anther
Anther	The terminal part of the stamen	Produces and stores pollen grains

5. Structure of a Typical Anther

A typical angiosperm anther is generally bilobed. The two lobes are connected by a connective.

Each anther lobe usually contains two pollen sacs. Therefore, a typical anther generally contains four microsporangia (pollen sacs).

Structure	Number/Feature
Anther	Generally bilobed
Anther lobes	Two
Microsporangia per lobe	Two
Total microsporangia	Four

6. Microsporangium

The microsporangium is the structure in which pollen grains are produced. It is commonly called the pollen sac.

A young microsporangium is generally surrounded by four wall layers:

Wall Layer	Important Feature
Epidermis	Outermost protective layer
Endothecium	Helps in anther dehiscence
Middle Layers	Usually degenerate at maturity
Tapetum	Innermost layer; provides nourishment to developing pollen grains

7. Gynoecium – Female Reproductive Whorl

The gynoecium is the female reproductive part of a flower. It is made up of one or more carpels. A carpel may also be referred to as a pistil.

A typical pistil has three main parts:

Part	Position	Function
Stigma	Uppermost	Receives pollen grains
Style	Middle	Connects stigma with ovary
Ovary	Basal portion	Contains ovules

Stigma → Style → Ovary

8. Ovary and Ovules

The ovary is the swollen basal part of the pistil. It contains one or more ovules.

Each ovule is attached to the placenta through a stalk called the funicle. The point of attachment of the funicle with the ovule is called the hilum.

After fertilisation:

• Ovule develops into a seed.
• Ovary develops into a fruit.
• Ovary wall develops into the pericarp.

9. Types of Flowers Based on Sexuality

On the basis of the presence of male and female reproductive organs, flowers may be bisexual or unisexual.

Type	Meaning	Examples
Bisexual Flower	Contains both androecium and gynoecium	Hibiscus, Mustard
Unisexual Flower	Contains either stamens or carpels	Papaya, Watermelon

10. What is Pollination?

Pollination is the transfer of pollen grains from the anther to the stigma of a flower.

The pollen grain first reaches the stigma. If the pollen is compatible, it germinates and forms a pollen tube. The pollen tube then grows through the style towards the ovary.

Anther → Pollen Grain → Stigma → Pollen Tube → Style → Ovary

11. Types of Pollination

Based on the source of pollen grains, pollination can be classified into three main types:

1. Autogamy

Autogamy is the transfer of pollen grains from the anther to the stigma of the same flower.

Easy Rule: Same flower = Autogamy

Example: Pea is a common example where self-pollination occurs.

2. Geitonogamy

Geitonogamy is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same plant.

Easy Rule: Different flowers + Same plant = Geitonogamy

3. Xenogamy

Xenogamy is the transfer of pollen grains from the anther of one plant to the stigma of a flower on a different plant.

Easy Rule: Different plants = Xenogamy

Type	Source	Destination	Easy Memory
Autogamy	Same flower	Same flower	Same flower
Geitonogamy	One flower	Another flower of same plant	Same plant
Xenogamy	One plant	Flower of another plant	Different plant

12. Agents of Pollination

The agents that help in the transfer of pollen grains are called agents of pollination. They may be abiotic or biotic.

Abiotic Agents

• Wind
• Water

Biotic Agents

• Insects
• Birds
• Bats
• Other animals

Agent	Term	Example
Wind	Anemophily	Maize
Water	Hydrophily	Vallisneria, Zostera
Insects	Entomophily	Many flowering plants

13. Wind Pollination – Anemophily

Pollination through wind is called anemophily.

Wind-pollinated flowers show several adaptations because wind is an unpredictable pollinating agent.

• Pollen grains are generally light and dry.
• A large quantity of pollen is produced.
• The stigma may be large, exposed and feathery.
• Flowers are generally not brightly coloured.
• Flowers usually do not need to produce strong fragrance to attract insects.

Example: Maize.

14. Water Pollination – Hydrophily

Pollination through water is called hydrophily. It is relatively rare among flowering plants.

Examples include Vallisneria and Zostera.

15. Insect Pollination – Entomophily

Insect-mediated pollination is called entomophily. Insects such as bees, butterflies and other insects may carry pollen grains from one flower to another.

Insect-pollinated flowers commonly possess:

• Brightly coloured petals
• Fragrance
• Nectar
• Sticky pollen grains

These features help the flower attract and retain insects.

16. Outbreeding Devices

Many flowering plants have mechanisms that prevent self-pollination and encourage cross-pollination. These mechanisms are called outbreeding devices.

1. Dichogamy

In dichogamy, the anther and stigma of a bisexual flower mature at different times. इससे self-pollination की possibility कम हो जाती है.

2. Herkogamy

In herkogamy, the anther and stigma are positioned in such a way that pollen cannot easily reach the stigma of the same flower.

3. Self-Incompatibility

Self-incompatibility is a genetically controlled mechanism in which pollen from the same or genetically similar plant is unable to fertilise the ovule successfully.

4. Unisexuality

In unisexual flowers, male and female reproductive organs are present in separate flowers. This can prevent autogamy.

17. Pollen-Pistil Interaction

After pollination, the pollen grain comes in contact with the stigma. The interaction between pollen and pistil determines whether the pollen is compatible or incompatible.

1. Pollen grain reaches the stigma.
2. The stigma recognises the pollen.
3. Compatible pollen germinates.
4. A pollen tube develops from the pollen grain.
5. The pollen tube grows through the style.
6. It ultimately reaches the ovary and the ovule.

18. Pollination vs Fertilisation

Pollination	Fertilisation
Transfer of pollen from anther to stigma	Fusion of male and female gametes
Occurs before fertilisation	Occurs after successful pollination
No fusion of gametes occurs	Gamete fusion takes place

19. Self-Pollination and Cross-Pollination

Self-Pollination	Cross-Pollination
Pollen generally reaches the stigma of the same flower or same plant.	Pollen is transferred between flowers of different plants in xenogamy.
Genetic variation is generally lower.	Genetic variation is generally higher.
External pollinating agent may not always be required.	Usually requires a pollinating agent.

20. Important Terminology

Term	Meaning	Hindi Meaning
Androecium	Male reproductive whorl	पुमंग
Gynoecium	Female reproductive whorl	जायांग
Stamen	Individual unit of androecium	पुंकेसर
Carpel	Individual unit of gynoecium	अंडप
Anther	Produces pollen grains	परागकोष
Stigma	Receives pollen grains	वर्तिकाग्र
Style	Connects stigma with ovary	वर्तिका
Ovary	Contains ovules	अंडाशय
Ovule	Develops into seed after fertilisation	बीजांड
Pollination	Transfer of pollen to stigma	परागण

21. Board Important Questions

1. Describe the structure of a typical flower.
2. What is androecium? Describe the structure of a stamen.
3. Describe the structure of a typical anther.
4. What is gynoecium? Describe the structure of a pistil.
5. Define pollination. Explain its different types.
6. Differentiate between autogamy, geitonogamy and xenogamy.
7. What are the different agents of pollination?
8. Explain anemophily with its important adaptations.
9. What is hydrophily? Give suitable examples.
10. What is entomophily? Mention important characteristics of insect-pollinated flowers.
11. What are outbreeding devices? Explain them.
12. Explain dichogamy, herkogamy and self-incompatibility.
13. Explain pollen-pistil interaction.
14. Differentiate between pollination and fertilisation.

22. Multiple Choice Questions

1. The male reproductive whorl of a flower is:
   (a) Calyx   (b) Corolla   (c) Androecium   (d) Gynoecium
   Answer: (c) Androecium
2. The female reproductive whorl is:
   (a) Androecium   (b) Gynoecium   (c) Corolla   (d) Calyx
   Answer: (b) Gynoecium
3. A typical stamen consists of:
   (a) Stigma and style   (b) Filament and anther   (c) Ovary and ovule   (d) Sepal and petal
   Answer: (b) Filament and anther
4. Pollen grains are produced in:
   (a) Stigma   (b) Style   (c) Anther   (d) Ovary
   Answer: (c) Anther
5. The receptive part of the pistil is:
   (a) Ovary   (b) Style   (c) Stigma   (d) Ovule
   Answer: (c) Stigma
6. Transfer of pollen grains from anther to stigma is called:
   (a) Fertilisation   (b) Pollination   (c) Germination   (d) Syngamy
   Answer: (b) Pollination
7. Pollination within the same flower is called:
   (a) Xenogamy   (b) Geitonogamy   (c) Autogamy   (d) Hydrophily
   Answer: (c) Autogamy
8. Pollination between two flowers of the same plant is:
   (a) Autogamy   (b) Geitonogamy   (c) Xenogamy   (d) Anemophily
   Answer: (b) Geitonogamy
9. Pollination between genetically different plants is:
   (a) Autogamy   (b) Geitonogamy   (c) Xenogamy   (d) Hydrophily
   Answer: (c) Xenogamy
10. Wind pollination is known as:
    (a) Hydrophily   (b) Anemophily   (c) Entomophily   (d) Ornithophily
    Answer: (b) Anemophily
11. Water pollination is called:
    (a) Anemophily   (b) Hydrophily   (c) Entomophily   (d) Xenogamy
    Answer: (b) Hydrophily
12. The innermost wall layer of microsporangium is:
    (a) Epidermis   (b) Endothecium   (c) Middle layers   (d) Tapetum
    Answer: (d) Tapetum
13. After fertilisation, an ovule develops into:
    (a) Fruit   (b) Seed   (c) Pericarp   (d) Pollen grain
    Answer: (b) Seed
14. After fertilisation, the ovary generally develops into:
    (a) Seed   (b) Fruit   (c) Pollen   (d) Embryo sac
    Answer: (b) Fruit
15. The main function of tapetum is:
    (a) Protection of stigma   (b) Nourishment of developing pollen grains   (c) Formation of ovary   (d) Attraction of insects
    Answer: (b) Nourishment of developing pollen grains

23. Very Short Answer Questions

1. What is a flower?
2. What is calyx?
3. What is corolla?
4. What is androecium?
5. What is gynoecium?
6. Name the two parts of a stamen.
7. Name the three parts of a pistil.
8. Where are pollen grains produced?
9. What is a microsporangium?
10. What is the function of tapetum?
11. Define pollination.
12. Define autogamy.
13. Define geitonogamy.
14. Define xenogamy.
15. What is anemophily?
16. What is hydrophily?
17. What is entomophily?
18. What is dichogamy?
19. What is herkogamy?
20. What is self-incompatibility?

24. Short Answer Practice

1. Explain the structure of a typical stamen.
2. Explain the structure of a typical pistil.
3. Describe the wall layers of a microsporangium.
4. Differentiate between autogamy and geitonogamy.
5. Differentiate between geitonogamy and xenogamy.
6. Explain the characteristics of wind-pollinated flowers.
7. Explain the role of insects in pollination.
8. What are outbreeding devices?
9. Explain any three outbreeding devices.
10. Differentiate between pollination and fertilisation.

25. Long Answer Practice

1. Describe the structure of a typical flower and explain the functions of its four floral whorls.
2. Describe the structure of a typical anther in detail.
3. Describe the structure of gynoecium with reference to stigma, style and ovary.
4. Define pollination and explain autogamy, geitonogamy and xenogamy.
5. Explain different agents of pollination with suitable examples.
6. Explain the different outbreeding devices that promote cross-pollination.
7. Describe pollen-pistil interaction from pollen deposition to the formation of the pollen tube.

26. Fill in the Blanks

1. The outermost floral whorl is called ________.
2. The male reproductive whorl of a flower is called ________.
3. The female reproductive whorl is called ________.
4. A stamen consists of filament and ________.
5. Pollen grains are produced in the ________.
6. The innermost wall layer of microsporangium is ________.
7. The receptive part of pistil is ________.
8. Ovules are present inside the ________.
9. Pollination within the same flower is called ________.
10. Pollination between different flowers of the same plant is called ________.
11. Pollination between different plants is called ________.
12. Wind pollination is called ________.
13. Water pollination is called ________.
14. After fertilisation, ovule develops into a ________.
15. After fertilisation, ovary develops into a ________.

27. Match the Following

Column A	Column B
1. Anther	a. Female reproductive whorl
2. Gynoecium	b. Wind pollination
3. Anemophily	c. Pollen production
4. Hydrophily	d. Water pollination
5. Tapetum	e. Nourishment of developing pollen grains

Answers: 1-c, 2-a, 3-b, 4-d, 5-e

28. Quick Revision Table

Concept	One-Line Revision
Calyx	Made up of sepals; protects the flower bud.
Corolla	Made up of petals; commonly attracts pollinators.
Androecium	Male reproductive whorl.
Gynoecium	Female reproductive whorl.
Stamen	Filament + Anther.
Pistil	Stigma + Style + Ovary.
Anther	Produces pollen grains.
Tapetum	Provides nourishment to developing pollen grains.
Pollination	Transfer of pollen grains from anther to stigma.
Autogamy	Pollination within the same flower.
Geitonogamy	Pollination between different flowers of the same plant.
Xenogamy	Pollination between flowers of different plants.
Anemophily	Pollination by wind.
Hydrophily	Pollination by water.
Entomophily	Pollination by insects.
Ovule	Develops into seed after fertilisation.
Ovary	Develops into fruit after fertilisation.