Topic 16.3A · Core · Direct Paper 6 relevance
Flower Structure
This is one of the most directly examinable diagrams in the whole syllabus — Cambridge routinely hands you an unfamiliar flower and asks you to label it, draw it, or explain a structure's function from a photograph. Knowing the names isn't the mark. Knowing what each part actually does for pollen or the ovule is.
The two organ systems in a flower
An insect-pollinated flower is built around two reproductive organs, and almost every labelling error comes from mixing up a whole organ with one of its parts. The stamen is the male reproductive organ, and it is made of two parts: a filament and an anther. The carpel is the female reproductive organ, made of three parts: a stigma, a style and an ovary. Say “stamen” when you mean the whole male structure, and “anther” only for the pollen-producing part at its tip — the same discipline applies to carpel versus stigma, style or ovary.
Every structure and its function
| Structure | Function |
|---|---|
| Sepals | Protect the flower while it develops inside the bud |
| Petals | Help attract pollinating insects, often through colour, scent or nectar |
| Stamen | The male reproductive organ — filament plus anther together |
| Filament | Supports and positions the anther |
| Anther | Produces and releases pollen grains, which carry the male nucleus used in fertilisation |
| Carpel | The female reproductive organ — stigma, style and ovary together |
| Stigma | Receives pollen grains, and is typically sticky in an insect-pollinated flower |
| Style | Connects the stigma to the ovary and provides the route a pollen tube grows through |
| Ovary | Contains the ovules |
| Ovules | Contain the female nucleus involved in fertilisation |
Reading the structure as a pathway
These ten structures aren’t ten unconnected facts — they map onto one continuous pathway, and holding that pathway in mind is what actually helps on an unfamiliar diagram: pollen is made at the anther, carried or transferred to the stigma, and then grows a pollen tube down through the style until it reaches an ovule sitting inside the ovary. If you can place a labelled structure somewhere on that pathway, you can usually work out its function even if you’ve forgotten the exact word for it.
What Cambridge actually asks for
The required visual skill here is twofold: you need to be able to identify each of these ten structures on a diagram or photograph of an unfamiliar flower, and you need to be able to draw an insect-pollinated flower showing them correctly positioned relative to each other. A pollen grain carries the male nucleus — it’s imprecise to say the whole pollen grain fuses with the ovule, since only the nucleus inside it eventually does.
Where this leads next
Once you can label a flower confidently, the next question is how pollen actually gets from the anther of one flower to a stigma, and what happens biologically once it’s there — covered on pollination and fertilisation in plants.