Each botanical fruit develops from a flower, and contains the next generation of the plant. Dissect a few fruits to understand the structures they share, and their role in plant reproduction.
- Assortment of botanical fruits (for example: apples, berries, figs, plums, corn, fava or green beans, pea pods, cucumbers, peppers, pomegranates)
- Cutting board
- Hand lens or dissecting microscope
- Paper and pencil for drawing and recording
- Optional: Flower (preferably a simple flower like a gladiola or Alstromeria, not shown)
Examine your assortment of fruits. Some might not seem like fruits to you, but many things we commonly call vegetables are defined by botanists as fruits.
What do your fruits have in common? Do you notice any similarities among the structures on the outsides of the fruits? Draw or describe these structures.
Cut each fruit in half (or for beans or corn, open up the pod or ear) and examine its insides with a hand lens. Do you notice similar structures inside the different fruits? What kinds of symmetry can you find in these structures? Try cutting a half in half again to get a closer look. Count or estimate how many seeds your fruit has. Draw or describe what you notice.
If you have a flower, carefully examine its structures. Cut the flower in half lengthwise (or do a complete dissection, as described in the Flower Dissection Science Snack). Do you notice any similarities between the structures of the flower and those of the fruit?
Some of your fruits may have structures left over from their past lives as flowers. For example, pea pods, peppers (first photo below), and other fruits retain the stem and sepals—the leaflike structures surrounding the flower’s petals. If you look closely at some fruits, you can often find the remnants of the flower’s sex organs. The multiple dried filaments on the bottom of an apple or the top of a pomegranate or strawberry (second photo below) are former stamens, the structures that carry pollen. The single filament at the bottom of a pepper or a pea pod, and the filaments on every bump of a raspberry (third photo below), are former stigmas, structures connected to the ovary. (Click on photos to enlarge.)
The shape of a fruit and the arrangement of its seeds can give you clues about the structure of the flower it came from. For example, a fruit with radial symmetry and radially arranged seeds, like an orange or an apple, grew from radially symmetrical flowers. And a fruit with many seeds came from a flower with many ovules.
Some fruits retain even more dramatic forms of their flowery past: corn, for example, contains long strands of silk. Each kernel of corn is a former ovule attached to its own strand of silk. When corn is fertilized, pollen containing the sperm cells lands on the tip of each silk strand, then travels down the silk to fertilize the ovule inside the husk. And the “baby corn” you buy in the grocery store are unfertilized ovules.
Although dissecting fruits alone is a valuable exercise, connecting the structures found in fruits to those found in flowers can help students to better understand the reproductive cycles of plants and the diverse adaptations that have made flowering plants so successful. By dissecting many types of fruit, students notice that seeds are the common structures. The fruit dissection can be followed by dissecting a seed to observe the baby plant inside.
If it’s possible to get extra fruits for your class, students can cut the same type of fruit in different directions. For example, an apple can be cut through the equator and through the stem and the bottom. This makes it easier for students to visualize the internal structures.
Providing too much vocabulary in the introduction to this activity typically interferes with students’ ability to make their own observations. Before giving them terms for botanical structures, let students notice and use their own language to describe what they see, and let them reason about the connections between the structures they notice.
Drawing can help focus their observations. Ask students to notice and draw the structures outside and inside the fruits, and the similarities between fruit structures and flower structures. Ask them how they would argue from this evidence that fruits are related to flowers.
It’s often difficult to distinguish between the remnants of stamens and stigmas on the outsides of fruits. Ask your students to reason based on their observations—they might notice that stamens are more numerous than stigmas, for example, or notice the presence of dried anthers, the pollen-containing structures of a stamen.