Question
Label and explain the parts of a typical bisexual flower. What are the functions of each part?
Solution — Step by Step
A typical flower has four whorls arranged from outside to inside on the thalamus (the swollen end of the flower stalk):
- Calyx (outermost) — made of sepals
- Corolla — made of petals
- Androecium — male reproductive parts (stamens)
- Gynoecium (innermost) — female reproductive parts (pistil/carpels)
A flower with all four whorls is called complete. A bisexual flower has both androecium and gynoecium present.
Calyx (Sepals):
- Typically green, leaf-like structures
- Function: Protect the flower bud from mechanical damage and desiccation before it opens
- In some flowers (like petals falling off early), sepals may be colourful to attract pollinators
Corolla (Petals):
- Usually brightly coloured, often fragrant
- Function: Attract pollinators (bees, butterflies, birds) through colour and fragrance
- Shape and size of petals are adapted to specific pollinators
- In some wind-pollinated flowers (like grasses), petals are absent (apetalous)
These two whorls together are called the perianth.
Each stamen consists of:
- Filament: A stalk that holds the anther up to where pollinators can access it
- Anther: A two-lobed structure, each lobe containing two pollen sacs (microsporangia) where pollen grains are produced through meiosis
Function of androecium: Produces and releases pollen grains (the male gametophytes containing sperm cells).
A flower may have many stamens (polyandrous, like hibiscus with hundreds) or just a few (like Brassica with 6 stamens, 4 long and 2 short — tetradynamous arrangement).
Each carpel (pistil if single) has three parts:
- Stigma: The sticky tip that receives pollen grains during pollination. The stickiness enables pollen adhesion.
- Style: A neck connecting stigma to the ovary. Pollen tubes grow through the style after germination.
- Ovary: The swollen base containing one or more ovules (each with an egg cell inside). After fertilisation, the ovary becomes the fruit and each ovule becomes a seed.
Function of gynoecium: Receives pollen, facilitates fertilisation, and develops into the fruit protecting the seeds.
The gynoecium may have one carpel (monocarpellary, like mango) or many carpels fused together (syncarpous, like tomato) or many free carpels (apocarpous, like lotus).
Peduncle (Flower stalk): Supports the flower.
Thalamus: The swollen tip of the peduncle on which floral parts are arranged.
Nectaries: Glands at the base of petals or ovary that produce nectar — sweet liquid that attracts pollinators.
Bracteoles: Small leaf-like structures just below the flower, if present.
Summary table:
| Part | Whorl | Function |
|---|---|---|
| Sepal | Calyx | Protect bud |
| Petal | Corolla | Attract pollinators |
| Stamen (anther + filament) | Androecium | Produce pollen |
| Pistil (stigma + style + ovary) | Gynoecium | Receive pollen, form fruit/seed |
Why This Works
Every part of a flower is adapted toward a single goal: successful reproduction. The outer whorls (sepals, petals) are supportive — they protect the reproductive parts and attract the agents needed for pollination. The inner whorls (stamens, carpels) perform the actual reproductive function.
The distinction between the flower parts and their precise functions reflects the flower’s evolutionary success — over 350,000 species of flowering plants (angiosperms) have diversified by adapting these basic structures to different pollinators, climates, and strategies.
Alternative Method
To remember the four whorls in order (outside to inside): “Carefully Consider All Parts” → Calyx, Corolla, Androecium, Gynoecium (the last word starts with P for pistil, but the mnemonic reminds you of the four levels).
CBSE Class 6 and Class 11 both cover flower structure — at different depths. For Class 6, focus on the basic parts (petals, sepals, stamens, pistil) and their simple functions. For Class 11 (Morphology of Flowering Plants), go deeper into androecium/gynoecium morphology, placentation, and types of flowers.
Common Mistake
Students often confuse the stamen with the pistil. Stamen = male (think “stamina” — it works hard producing pollen); Pistil = female (think “pistol” — it’s the central weapon). Also, students write “pollen is produced in the ovary” — this is completely wrong. Pollen is produced in the anther (male). The ovary (female) contains ovules, which become seeds after fertilisation.