How Many Seeds Do Different Types of Fruit Produce?
Do you like your strawberry jelly with or without the seeds? Are you glad to have a seed-free watermelon, or do you enjoy spitting the seeds into the garden? You might not like finding seeds in your fruit, but fruit is a plant's tool for dispersing seeds to create offspring. In this activity you will investigate how many seeds can be dispersed for each type of fruit. Based on the number of seeds they produce, how productive do you think some of your favorite fruits are?
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
BackgroundMany plants grow fruit to enclose and protect their seeds, which need to spread out to grow new plants. Animals love to eat sweet, juicy fruit. This approach would seem like a poor way for plants to protect their seeds, so why would making fruit that is tasty be beneficial? When an animal eats fruit the fleshy part is digested. The seeds, however, pass without harm through the digestive system and are spread by the animal when it excretes (poops). In this way, they are deposited farther from the original plant (along with a little bit of fresh fertilizer) and can grow into a new plant. This is called seed dispersal, and it is just one strategy that plants use to spread seeds over a wide area and make more plants.
You might think that all fruit-bearing plants would pack as many seeds as possible into each fruit to maximize the number of new plants that will grow. But, in fact, different plants have different strategies for seed production and dispersal. Some fruits produce many, many seeds to make sure that at least some will grow, even if most fail. Other fruits put all of their resources into producing and protecting one very large seed.
Extra: Try this activity again but use multiple fruit of each type, such as multiple peppers, tomatoes, cucumbers and squash. Does the same type of fruit always hold a similar number of seeds, or does the amount vary a lot?
Extra: Is fruit size related to seed quantity? Repeat this activity but this time use a ruler to measure each fruit before you count their seeds to see if larger fruits tend to produce more seeds than smaller ones. (You can also use a scale to weigh each fruit as an alternative way to measure fruit size.) Do larger fruits make more seeds?
Extra: Are seedless fruit varieties really seedless? Dissect several different varieties of seedless fruits and look for seeds. Are "seedless" fruit varieties completely seedless, or simply have fewer seeds than normal? What is the decreased seed productivity of seedless varieties compared with normal varieties on a fruit-to-fruit comparison basis?
Observations and Results
Did some types of fruit clearly have more seeds than others? Did the cucumbers, squash, tomato and pepper have a lot of seeds, easily over 100 each? Did the apple only have a few seeds, no more than 10?
Fruits are divided into three general groups, with the "simple fruits" group making up the majority we encounter. They're formed from one ovary in one of the plant's flowers. As the ovary turns into fruit, different ovary parts become different fruit parts; when fertilized, small structures called ovules become the fruit's seeds—and more fertilized ovules means more seeds! The other two fruit groups are more complex. In "aggregate fruit"—such as raspberries—multiple ovaries fuse on a single flower. In the third group, called "multiple fruit," many ovaries and flowers unite. A pineapple is a good example of a "multiple fruit."
Cucumbers, melons and squash are simple fruits (they are part of a fruit type called pepo, which are berries) with a firm rind and softer, watery interior. And, as you probably saw, these fruits make many seeds! A zucchini or cucumber can easily have a couple hundred neatly patterned seeds.
Tomatoes, grapes, kiwifruit and peppers are also simple fruits (technically true berries) with fleshier walls and usually very fluid insides—think of how watery a ripe tomato is! Some, like tomatoes and peppers, can have a couple hundred seeds, whereas others, like kiwifruit, can have several hundred! Citrus fruits are berries (a type called hesperidium), too, with leathery rinds and usually only a few seeds.
Similarly, apples and pears also only have a few seeds (10 at most) but are not berries—they belong to a different fruit type, known as pomes, which have some fruit flesh not made from the flower's ovary, but rather from plant tissue near the ovary, which is the same for strawberries.
More to Explore
Plant Structures: Fruit from Colorado State University Extension
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Plants, fruits, seeds, flowers, biology
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