Reproduction: How Life Continues · Lesson 3 of 12
Sexual Reproduction in Flowering Plants
“Flowers look peaceful while quietly running a very busy reproductive workshop.”
• Identify the four major parts of a complete flower. • Describe the structures and functions of stamens and pistils. • Locate male and female gametes in a flower. • Analyse observations from flower dissection. • Explain how the pea-flower investigation demonstrates the need for pollen transfer.
Flowering Plants
A flower may appear to be a coloured decoration, but its arrangement is highly functional. Protective parts surround a young bud, attractive parts help bring pollinating agents, and the inner structures produce and receive the cells involved in sexual reproduction.
Flowering plants are called angiosperms. Their roots absorb water and minerals, stems support and transport, and leaves carry out photosynthesis. The flower performs the reproductive role. Its colour, fragrance and nectar can help bring pollen from one flower to a suitable stigma.
Activity: Let us explore
Collecting several flower types reveals that flowers do not all look alike and may not display every part in the same way. Observation should begin at the outer whorl and move inward. Record whether sepals, petals, stamens and a pistil are present, and note features such as fusion, colour, texture and position.
Sepals usually form the outermost green whorl. They enclose and protect the developing bud. Petals form the next whorl and are often coloured or fragrant. Their appearance can help attract animals that transfer pollen. Sepals and petals may be separate or fused in different flowers.
A complete flower contains sepals, petals, stamens and a pistil.
The stamen is the male reproductive part. A slender filament supports the anther. The anther produces pollen grains, and these grains contain the male gametes. Position matters: the anther must release pollen where wind, water or visiting animals can carry it.
The pistil is the female reproductive part. Its stigma is at the tip and may be flat or sticky, helping it receive pollen. The style is a slender tube connecting the stigma with the ovary. The ovary contains ovules, and each ovule contains an egg cell, the female gamete.
| Flower part | Structure or position | Main contribution |
|---|---|---|
| Sepal | Usually green and outermost | Protects the bud and other flower parts |
| Petal | Often coloured or fragrant | Helps attract some pollinating animals |
| Stamen | Filament topped by anther | Produces pollen containing male gametes |
| Stigma | Tip of pistil; may be sticky | Receives pollen |
| Style | Tube between stigma and ovary | Provides the route towards the ovary |
| Ovary | Swollen base of pistil | Contains ovules |
| Ovule | Inside the ovary | Contains an egg cell |
A longitudinal section follows the length of the ovary and can show how the style connects with the ovary. A transverse section cuts across the ovary and can show the arrangement of ovules. Drawing both views helps connect a three-dimensional structure with two different sections.
Problem
A flower part has a sticky tip, a long tube and a swollen base containing ovules. What is it?
- 1.The sticky tip is the stigma.
- 2.The long tube is the style.
- 3.The swollen base is the ovary.
- 4.Together these structures form the pistil, the female reproductive part.
Activity: Let us investigate
The pea-plant investigation compares buds and flowers under several treatments. Some have stamens removed, some remain intact, some are wrapped in muslin bags and one remains uncovered. The aim is to determine whether pollen must reach the stigma for fruit formation.
Removing stamens from a young bud prevents that flower from supplying its own pollen. Wrapping it in a muslin bag reduces the chance of receiving pollen from elsewhere. If this treatment fails to form fruit while suitable comparison flowers form fruits, the missing pollen transfer is the important difference.
Problem
Why may a freshly opened flower still form fruit even if its stamens are removed at that time?
- 1.The flower has already opened.
- 2.Pollen may have been released or may already have reached the stigma before removal.
- 3.Removing stamens after pollen transfer does not remove pollen already present on the stigma.
- 4.A young unopened bud provides a stronger treatment because its stamens can be removed before pollen release.
An uncovered flower provides a comparison under ordinary conditions. A wrapped intact flower tests whether pollen already present within the flower can be sufficient. Fair observation requires flowers on the same plant or under comparable conditions, similar stages of development, careful handling and enough time for fruits to develop.
Pollination is the transfer of pollen grains from an anther to the stigma of a flower.
Quiz
Which description best matches Complete flower?
Which description best matches Pollination?
Which term matches this description: A complete flower contains sepals, petals, stamens and a pistil.
Which term matches this description: Pollination is the transfer of pollen grains from an anther to the stigma of a flower.
Which statement is a key takeaway from this lesson?
Practice Problems
- Name the four parts of a complete flower.
- Describe the two parts of a stamen and the three parts of a pistil.
- Where are male gametes and egg cells located in a flower?
- Why can a sticky stigma be useful?
- What is the purpose of removing stamens from a young bud?
- Identify the comparison that represents natural pollination in the pea investigation.
- Explain how fruit formation provides evidence that pollen transfer occurred.
Key Takeaways
• Flowers are the reproductive organs of angiosperms. • Stamens produce pollen containing male gametes. • The pistil includes stigma, style and ovary. • Ovules inside the ovary contain egg cells. • The pea investigation connects pollen transfer with fruit formation.