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Enlarged: How do Plants Make Seeds and Fruit?

based on 4 ratings
Author: Janice VanCleave

Problem

How do plants make seeds and fruit?

Materials

  • 2 sheets of white typing paper
  • pen
  • scissors
  • transparent tape
  • ruler
  • manila file folder

Procedure

  1. On one sheet of typing paper, draw and label a flower pistil as shown in the first diagram.
  2. Cut out the section of the pistil indicated by the dotted line in the diagram.
  3. Enlarged

  4. Tape the second sheet of typing paper behind the first sheet. As shown in the second diagram, do not place tape directly above or below the pistil.
  5. Drawing on the second sheet of paper within the cutout section of the first sheet, use the diagram to draw and label the inner parts of the pistil.
  6. Enlarged

  7. Cut a 4-by-10-inch (10-by-25-cm) strip from the file folder. Insert the strip between the two sheets of paper in the untaped area so that the strip covers the drawing in the cutout.
  8. Slowly pull the paper strip down.

Results

As you pull the paper strip down, the pollen tubes appear to grow, and one tube reaches the lower part of the pistil.

Why?

The pistil (the female reproductive organ inside a flower of an angiosperm) has three basic parts: the stigma, the style, and the ovary. The stigma is the sticky top that holds pollen grains that land on it. The style is a tube-like structure that supports the stigma and connects it with the rounded base of the pistil, called the ovary.

Inside the ovary are seed-like parts called ovules, which contain eggs. The ovules ripen into seeds as a result of fertilization of the eggs by sperm. Sperm are contained in pollen grains. Pollination occurs when the pollen grains from the stamen land on the stigma.

After pollination, the pollen grains begin to grow a long tube down the style toward the eggs. Each tube, called a pollen tube, contains two sperm. The tube enters the ovule through a hole in the ovule wall called the micropyle. As soon as the tube comes in contact with the egg, the two sperm are released. One sperm fertilizes the egg, producing a zygote (a fertilized egg) that develops into an embryo (an organism in its earliest stages of development). The other sperm combines with a special cell to form the endosperm (the nourishing tissue for the developing embryo).

Enlarged

After fertilization, the sepals, petals, and stamens wither and the ovary and ovules develop. The ovules develop into the seeds of the plant, each of which contains an embryo and a stored food supply. In flowering plants, the seed is enclosed in a fruit (enlarged ovary). In many plants the receptacle (the top of the flower stem supporting the reproductive organs) also enlarges and becomes part of the fruit.

Let's Explore

Use a biology book and information in chapter 6, "Bloomers," to find out about the other parts of a flower. Draw the rest of the flower around the pistil on the model of the pistil from the original experiment. Label each part. Science Fair Hint: Display the model as part of your project and use it when giving an oral presentation.

Show Time!

  1. Observe the outside of the apple and find the stem and the dried stamens opposite the stem. Ask an adult to cut an apple in half from the stamens to the stem. Make and display a diagram similar to the one shown, comparing the fruit parts to the flower parts.
  2. Enlarged

  3. Fruits help to scatter seeds as well as protect them. Some fruits, such as beggar-ticks, have stickers or spines on them. These stickers catch on clothes or the fur of animals, which carries the fruit with its seeds away from the parent plant. The process by which seeds are scattered is called seed dispersal. Find out more about seed dispersal. How are seeds of fleshy fruits, such as apples or berries, dispersed? Prepare a seed dispersal display with examples of seeds for each type of dispersal.
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