Question
Draw a labelled diagram of a typical bisexual flower and briefly explain the function of each labelled part.
Solution — Step by Step
A typical flower has four whorls arranged from outside to inside: calyx → corolla → androecium → gynoecium. This order is critical — examiners check if your labels follow this arrangement. Think of the flower as a series of concentric rings when viewed from above.
Start your diagram with the receptacle (the swollen tip of the flower stalk/peduncle). The whorls attach to the receptacle.
Calyx (outermost whorl):
- Made of sepals — small, leaf-like structures, usually green
- Function: protect the flower bud before it opens
- Collectively called calyx; individual units are sepals
Corolla (second whorl):
- Made of petals — usually colourful and attractive
- Function: attract pollinators (insects, birds, bats) through colour, shape, and scent
The androecium is the male whorl, made of stamens. Each stamen has two parts:
- Filament — the slender stalk that holds the anther up
- Anther — the bilobed structure at the top where pollen grains are produced and stored
Function of androecium: produce male gametes (pollen grains containing the male nuclei). Label both filament and anther separately — examiners award marks for each.
The gynoecium (innermost whorl) is made of carpels (also called pistils). Each carpel has three distinct parts — label all three:
- Stigma — sticky top surface that receives pollen during pollination
- Style — elongated tube connecting stigma to ovary; pollen tube grows through it
- Ovary — the swollen base containing ovules, which develop into seeds after fertilisation
The gynoecium as a whole will develop into the fruit after fertilisation.
Label these supporting structures:
- Peduncle — the flower stalk
- Pedicel — the small stalk of an individual flower in a cluster
- Receptacle — the swollen tip where all whorls are attached
- Thalamus — another name for receptacle, sometimes used in CBSE questions
- Bracts — leaf-like structures at the base of the flower (if present)
Why This Works
The four-whorl arrangement reflects the evolutionary adaptation of flowers for sexual reproduction. The outer two whorls (calyx and corolla) are accessory whorls — they do not directly participate in reproduction but support it through protection and pollinator attraction. The inner two whorls (androecium and gynoecium) are essential whorls — they directly produce and receive gametes.
A flower with all four whorls is called complete. A flower with both androecium and gynoecium is called bisexual (or hermaphrodite). Most CBSE questions deal with complete bisexual flowers unless stated otherwise.
Alternative Method
For exam purposes, remember the parts through the acronym “CAPS + SAO”:
- Calyx (sepals), Androecium (stamens), Petals (corolla), Stigma/Style/Ovary (gynoecium/carpel parts)
For drawing, always draw a longitudinal section (LS) of the flower rather than an external view — the LS shows all internal parts clearly and is what CBSE mark schemes expect.
CBSE Class 12 Biology (Reproduction in Flowering Plants) asks 3–5 mark questions on flower structure. The 5-mark question expects both the diagram AND explanation of each part’s function. Marks are awarded separately for the diagram (2 marks) and the description (3 marks). A clean, large diagram with all 8–10 labels scores full marks on the diagram component.
Common Mistake
Students often draw petals and sepals as identical shapes and forget to differentiate them. In your diagram, draw sepals as narrower, green structures and petals as broader, coloured structures. Also, many students label “pistil” without breaking it into stigma, style, and ovary — you lose marks for not showing all three parts of the carpel.