Life Science: Session 4
Fruit and Dispersal
What is dispersal?
After pollination and fertilization have occurred, the next events in a flowering plant’s life cycle involve the development of the offspring, which starts out as an embryo within a seed, which develops in the ovary. If this stage is successful, the next crucial event is dispersal of the seed to a suitable environment for it to germinate, grow, and develop into a reproductive adult. Seeds have a few different ways of being dispersed: expulsion, wind, water, and animals. In flowering plants, the mature ovary — or fruit — has evolved adaptations that increase the success of dispersal.
What do fruit reveal about the way they are dispersed?
Fruits can be classified into one of two broad groups: dry or fleshy. Dry fruits include grains (rice, corn, wheat, etc.) dandelions, sunflower seeds, nuts (acorns, peanuts, hickory nuts, etc.), and legumes (peas, beans, etc.). Fleshy fruits include berries, citrus fruits (oranges, lemons, etc.), drupes (peaches, cherries, etc.), pomes (apples, pears, etc.) and many more. Many produce items we call vegetables — like tomatoes and squash — are actually fleshy fruits.
In general, dry fruits are adapted for dispersal by expulsion, wind, and by attaching to the fur or feathers of animals. A mature pea pod, for example, dries to the point where it pops open, releasing the seeds. The “wings” of maple seeds or the “parachutes” of dandelions carry them in the wind away from the parent plant. People and pets may even have carried seeds away from plants that bear fruit as burrs.
Fleshy fruits tend to be adapted for dispersal by animals, who are attracted to them as food. Perhaps one of the most common means of dispersal is via fruit, which is ingested by animals and distributed in their wastes. There is a large range in size of seeds, which corresponds to the size of the animal that eats them. For example, berries have relatively small seeds and small fruit. Squirrels and birds often disperse these seeds. Conversely, avocados and peaches are quite large and have very large seeds. These large fruits are eaten by larger mammals. Finally, some fleshy fruits, such as coconuts, are adapted to float in water.
The next time you’re at a supermarket, take a look in the produce section and identify all of the fruits. What can they tell you about the way they are dispersed?
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