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Name ____________________ Period _______
Flower Lab
Introduction
There are over 200,000 species of flowers in the world. They range in size from microscopic water
blossoms to tropical flowers as large as 91 cm across! They range in shape from the familiar star to shapes
mimicking insects or birds. As varied as flowers are, they all play the same role in the angiosperm life
cycle. Flowers are the sexual reproductive parts of angiosperms! Plants reproduce sexually when some
flower parts produce pollen (male gametes) and some parts produce eggs (female gametes). Fertilized
eggs become zygotes protected by seeds, and seeds are surrounded by fruits. After the fruit ripens, the
seeds are released and the seeds may germinate into new plants.
Purpose
List, explain, and identify the structures of flowers.
Relate the structures of flowers to their role in angiosperm reproduction.
Materials
Assorted flowers, scalpel or razor blade, dissecting scope, slides, cover slips, microscope, eye dropper,
and lens paper
Procedure
There are four basic parts of a flower; sepals, petals, stamens, and pistils. Some flowers do not have all
four parts and are called incomplete. Flowers that have all four parts are called complete.
1. Obtain a flower from your teacher. What is the name of the flower you have? _______________
Record whether it is complete or incomplete. _______________
2. Examine the petals. The petals are showy, colorful, outer structures. Petals protect the inner flower
parts and attract insects and other pollinators. The sepals are leaf like parts below the petals. In most
species they are green, but may also be colored. The sepals enclose the flower when it is in a bud and
help support the flower when it opens.
3. Some flowers have both male and female reproductive organs and are known as perfect flowers.
Other flowers have only male or only female organs and they are called imperfect.
Gently pull away the petals and sepals from the flower. When removing these structures, take care not
to destroy the widened base of the flower where they are both attached. Is your flower perfect or
imperfect? _______________ How do you know?
Examine the stamen, if your flower has them, which look like stalks with swords on the ends. The
stamen is the male reproductive part of the flower. The stalk–like part is called the filament and it
supports the sword–like anther. The anther produces pollen grains, which contain sperm.
Carefully tap some pollen from the stamen onto a slide, prepare a wet mount, and examine the pollen
with the light microscope at various magnifications. Draw what you see at 100X magnification.
4. Examine the pistil, a stalk–like structure that widens at the base. This is the female reproductive
organ. The pistil is divided into three main parts from top to bottom; stigma, style and ovary. Inside
the ovary are the ovules and inside the ovules are eggs.
5. Pollen is transferred from the anther to the stigma by insects and other pollinators, which are attracted
by the petals, scent, or nectar. In flowers without petals, pollen is often transferred by wind. The
pollen grows a pollen tube which extends down the length of the style into the ovary. Sperm travel
through the pollen tube to the ovary. Only pollen from a flower of the same species will reach the
ovary.
Some flowers self–pollinate and some must cross–pollinate. Cross–pollination leads to a greater
genetic diversity in the species and is therefore advantageous for the plant species. Whether self–
pollination or cross–pollination occurs, they BOTH are sexual reproduction, since two gametes come
together to form an offspring.
6. The number of flower parts indicates whether a flower is from a monocot or a dicot. Most plant
structures of a monocot flower usually occur in multiples of three. The structures of a dicot flower
usually occur in multiples of four or five. Count the number of stamen you have and record the
number. _______ Count the number of petals you have and record the number. _______ Do these
numbers identify your flower as a monocot or dicot? _______________ If you have a flower with a
huge number of petals, what other characteristics can you use to identify the flower as a monocot or
dicot? _______________
7. Many ovaries are divided into chambers called carpels. Inside the carpels are numerous ovules, each
of which contain an egg. After the eggs are fertilized, the ovules develop into seeds.
Using a scalpel or razor blade, cut the ovary in half lengthwise from top to
bottom as shown: Examine the cut ovary under the dissecting scope
(stereoscope). Locate the carpels and the white, dot–like ovules. 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 the endosperm.
Endosperm divides and provides nourishment for developing embryo.
Since two sperm are essential in producing a seed, flowering plants have double fertilization.
8. Throw away your flower and begin answering the analysis questions below. These should be typed
(except for illustrations) for homework. Use complete sentences and thoughts!
Analysis Questions
1. Draw and label a complete, perfect flower.
2. Draw pollen at 100X magnification. Label the name of the flower from which the pollen originated.
3. Describe the functions of the following parts in your own words.
Anther, filament, ovary, style, stamen, ovule, pollen, stigma, and pistil
4. Can an imperfect flower be complete? Explain. Can an incomplete flower be perfect? Explain.
5. Many more pollen grains are produced compared to ovules. Why do plants do this?
6. Some flowers reject pollen produced by the same plant. Why do plants do this?
7. Many flowers have anthers that are lower than the stigma. How does this anatomy help to ensure
cross–pollination?
8. Is self–pollination sexual or asexual reproduction? Explain.
9. If one ovary of a flower contains 9 ovules, how many fruits will develop? How many seeds could be
produced?
10. In a paragraph, explain the relationship between flowers, fertilization, fruits, and seeds. Be sure to
explain any specific structures involved.