How do Organisms Reproduce? · Lesson 9 of 14
Sexual Reproduction in Flowering Plants
“Flowers quietly handle pollen delivery, fertilisation, seeds and fruit.”
• Identify reproductive parts of a flower. • Distinguish unisexual and bisexual flowers. • Compare self-pollination and cross-pollination. • Distinguish pollination from fertilisation. • Trace pollen-tube growth and gamete fusion. • Explain seed fruit and seedling formation.
A flower is more than a colourful structure that attracts animals. It contains organs that produce gametes, receive pollen and protect the developing seed.
Reproductive Parts Of A Flower
The stamen is the male reproductive part. Its anther produces pollen grains containing male germ cells. The pistil is the female reproductive part and consists of a stigma, style and ovary. Ovules inside the ovary contain egg cells.
| Part | Structure or position | Function |
|---|---|---|
| Anther | Top of stamen | Produces pollen grains |
| Stigma | Top of pistil | Receives pollen |
| Style | Connects stigma and ovary | Provides path for pollen tube |
| Ovary | Swollen base of pistil | Contains ovules |
| Ovule | Inside ovary | Contains female gamete and later becomes seed |
Unisexual And Bisexual Flowers
A unisexual flower contains either stamens or pistil, as in papaya and watermelon. A bisexual flower contains both, as in Hibiscus and mustard. Sepals protect the bud, while petals can attract pollinating animals.
Pollination
Pollination is the transfer of pollen grains from anther to stigma.
Self-pollination transfers pollen to the stigma of the same flower or another flower on the same plant. Cross-pollination transfers pollen between different plants of the same species. Wind, water and animals can act as agents.
Fertilisation And Pollen-Tube Growth
After compatible pollen lands on the stigma, it germinates. A pollen tube grows through the style toward an ovule. The male germ cell travels through the tube and fuses with the egg, forming a zygote. Pollination is therefore transfer; fertilisation is gamete fusion.
From Zygote To Seed And Fruit
The zygote divides to form an embryo within the ovule. The ovule develops a protective coat and becomes a seed. The ovary enlarges and ripens into a fruit. Other flower parts often shrivel and fall. Under suitable water, oxygen and temperature conditions, the embryo resumes growth during germination.
| Before fertilisation | After fertilisation |
|---|---|
| Zygote | Embryo |
| Ovule | Seed |
| Ovary | Fruit |
| Ovary wall | Fruit wall |
| Other floral parts | Usually shrivel and fall |
Observing A Germinating Seed
Soak Bengal gram seeds, keep them under a wet cloth and prevent drying. Open softened seeds carefully. Identify the seed coat, stored food and embryo. The activity shows that a seed already contains a young plant and reserves supporting early growth.
Problem
Pollen reaches a stigma but gametes have not fused. Which process has occurred?
- 1.Pollen transfer from anther to stigma is pollination.
- 2.No fusion has yet taken place.
- 3.Therefore pollination has occurred, but fertilisation has not.
Problem
Trace a male germ cell from anther to egg.
- 1.A pollen grain forms in the anther.
- 2.Pollination places it on a suitable stigma.
- 3.The pollen grain germinates and grows a tube through the style.
- 4.The male germ cell travels down the tube to an ovule.
- 5.It fuses with the egg during fertilisation.
Problem
Pollination occurs, but the pollen tube cannot grow. Predict the result.
- 1.Pollen has reached the stigma, so pollination is complete.
- 2.The male germ cell cannot reach the ovule.
- 3.Fertilisation does not occur.
- 4.A zygote and embryo do not form, so normal seed formation fails.
Pollen is not a seed. A pollen grain carries the male reproductive contribution; a seed forms from an ovule after fertilisation and contains an embryo.
Quiz
Which part produces pollen?
What is cross-pollination?
Where are ovules located?
What does an ovule become?
What distinguishes fertilisation from pollination?
Practice Problems
- Label the main reproductive parts of a flower in words.
- Compare unisexual and bisexual flowers with examples.
- Trace events from pollination to fertilisation.
- Explain conversions after fertilisation.
- Predict consequences of removing anthers before pollen matures and discuss how cross-pollination could still allow seed formation.
Key Takeaways
• Stamens produce pollen and the pistil contains ovules. • Flowers may be unisexual or bisexual. • Pollination transfers pollen to stigma. • Self-pollination and cross-pollination differ in pollen source. • A pollen tube carries the male germ cell to the ovule. • Fertilisation forms a zygote. • Ovules become seeds and the ovary becomes fruit. • Germination resumes embryo growth under suitable conditions.