Name:
Dissecting a Flower
SNC2D
Purpose: To become familiar with the reproductive structures of a flowering plant.
Materials:
flower, such as a lily, tulip, or gladiolus
tweezers
scalpel
hand lens
microscope
slide and cover slip
sugar solution
Procedure:
Obtain a single flower and observe its petal. Compare
your flower with the diagram at right.
There are four basic parts of a flower: the petals, sepals,
stamens, and pistils.
The petals are the showy, colourful outer structures.
They protect the inner flower parts and attract insects
and other pollinators. How many petals does your
flower have?
The sepals are the leaf-like parts below the petals. They
enclose the flower when it is a bud and help support the
flower when it opens. How many sepals does your
flower have?
The stamens are the male reproductive parts of the
flower. The stalk-like part is the filament, and it
supports the sword-like anther. The anther produces pollen grains,
which contain sperm. How many stamens does your flower have?
Examine the anther with a hand lens. Add a drop of sugar solution to a microscope slide. Place the
anther in the sugar solution and stir it around gently. Remove the anther and place a cover slip over the
solution. Observe the pollen grains remaining in the sugar solution under the microscope.
The pistil is the female reproductive part of the flower. It is a stalk-like structure that
widens at the base. At the top of the pistil is the stigma. The sticky surface of the
stigma is an adaptation for collecting pollen, transferred by the wind, insects, or other
pollinators. The pollen germinates in the stigma, developing pollen tubes that grow down the
slender style to the vase-shaped ovary. Sperm travel through the pollen tube to the ovary.
The ovaries of many flowers are divided into chambers called carpels. Inside the carpels are
numerous ovules, each of which contains an egg. After the eggs are fertilized, the ovules will
develop into seeds. Using a scalpel, cut the ovary in half crosswise. Examine the cut surface
with the hand lens. Locate the carpels and the white dot-like ovules. Draw a cross section of
the ovary in the space below, showing the number of chambers and the placement of the ovules.
Finally, in the space below, draw a complete diagram of your flower, labelling the parts as in the
diagram on the previous page.
Actually, two sperm are involved in producing a seed in a flowering plant. One sperm
fertilizes the egg, which develops into the embryo. The nucleus of the second sperm unites with
two nuclei of a cell in the middle of the ovule. This second fertilization forms a tissue called
endosperm that provides food for the developing embryo. Since two sperm are essential in
producing a seed, flowering plants are said to have double fertilization.
After fertilization, the embryo develops into a tiny plant inside the seed. The seed is a
mature ovule. As the ovules inside an ovary mature into seeds, the ovary develops into a fruit.
A fruit is a ripened ovary containing seeds.
Discussion - Please write the answers to the following questions using complete sentences.
1. Which does your flower produce in greater numbers: ovules or pollen grains? Explain why
this would be important in terms of reproductive success.
2. What are some adaptations of flower petals to help attract pollinators?
3. How is the stigma of your flower adapted to capture and hold pollen?
4. Describe where pollination and fertilization occur.
5. Explain the differences between pollination and fertilization.
6. a) In which part of the male reproductive organ are the pollen grains made?
b) In which part of the female reproductive organ are the egg cells made?
c) By which nuclear process are these gametes formed?
7. How do the sperm nuclei in a pollen grain reach the egg nucleus in an ovule?
8. a) Which part of the flower becomes the seed?
b) Which part becomes the fruit?
c) Which part of the fruit contains the embryo?