Sexual Reproduction in Flowering Plants
Flower Anatomy detail http://www.enchantedlearning.com/subjects/plants/printouts/floweranatomy.shtml
Pollination occurs when pollen grains land on the sticky surface of the stigma and are trapped there. The pollen grain germinates and a pollen tube emerges from the grain. It releases special enzymes that digest a cell the wall on the surface of the stigma. The pollen tube grows down through the style to the ovary and enters the ovule, making a continuous passageway for the two sperm nuclei to enter the ovum. Fertilization occurs when the sperm nuclei join the egg nuclei.
The fertilized egg becomes an embryo. The wall of the ovule thickens and forms a seed, thus enclosing and protecting the embryo. The ovary wall also thickens and develops into a fruit. In some plants such as apples, the ovary walls become fleshy and contain stored sugars and starches. In other plants such as walnuts, the ovary walls become dry and hard.
1. Separate the last page of this lab to make the Observations Chart accessible.
2. Obtain a single flower and observe its parts carefully. Flower parts are
arranged in a circular pattern. Each circle is called a whorl. The whorls are
attached at the enlarged receptacle located at the base of the flower.
Please read this overview before you begin your flower dissection:
As you examine your flower, you will be carefully removing parts beginning
with the outer whorl and working your way in towards the pistil. You will
arrange each whorl in a circle on the plain paper, beginning with the sepals as
the largest outermost circle. As you proceed with your dissection, you will
carefully tape each whorl of flower parts into position and label them (please
use pencil!). As each whorl is observed and removed, you will complete the
appropriate information in the Observations column of the chart. Use the
information in the handout to complete the Function column of the chart.
3. The sepals form the outermost whorl of the flower. The sepals are leaf-like
structures that are usually green in color. Sometimes, the sepals are the
same color as the petals, or appear to be another set of petals of a different
color. The function of the sepals is to protect the inner part of the flower
before it blossoms. Gently remove the sepals, tape them into position onto
the paper, and label them. On the chart, record the following observations:
a) How many sepals does your flower have?
b) Describe the appearance of the sepals (color, markings, etc.).
4. The petals are found directly under the sepals. The color and odor of the
petals help to attract birds and insects to the flower for pollination. Gently
remove the petals, tape them into position onto the paper, and label them.
On the chart, record the following observations:
a) How many petals does your flower have?
b) Describe the appearance of the petals (color, markings, etc.).
5. The stalk-like structures inside the petals are the stamens, the male
reproductive organs. Depending on the species, the stamens may be
attached to the receptacle, to the petals, or to the pistil. The enlarged portion
at the top of the stamen is the anther. Inside the anther are pollen sacs,
which produce pollen grains. When the pollen grains mature, the pollen
sacs split open, releasing the dust like pollen grains. The filament is the thin
structure that supports the anther. Gently remove the stamens, tape them
into position onto the paper, and label them. On the chart, record the
a) How many stamens does your flower have?
b) To which structure(s) were the filaments attached?
c) Have the pollen sacs opened? How can you tell?
d) If pollen grains are visible, describe their appearance.
6. The central structure of the flower is
the female reproductive organ, the pistil. The top of the pistil
is the stigma. When mature
the stigma is enlarged, and its surface is moist
and sticky. The style is the
middle portion of the pistil. It
sigma. Some flowers lack a
style. The ovary is the
a) What color is the pistil?
b) Describe the appearance of the stigma. Is the stigma mature? How can you tell?
c) How long is the style (in mm)?
d) Describe the appearance of the ovary.
e) How many locules does the ovary contain?
f) Approximately how many ovules are contained in one locule?
7. Check your flower parts sheet and your chart for the following:
· All flower parts are correctly taped in place.
· All flower parts are labeled correctly (in pencil).
· The pistil is drawn on the paper (in pencil).
· Your name(s) and class period are written on the paper.
· The Observations column of your chart is completed.
Discussion - Please write the answers to the following questions in your lab databook using complete sentences.
4. Describe where pollination and fertilization occur.
5. Explain the differences between pollination and fertilization.
b) In which part of the female reproductive organ are the egg cells made? c) By which nuclear process are these gametes formed?
b) Which part becomes the fruit?
c) Which part of the fruit contains the embryo?
Check your chart to be sure that the function column is complete. Then summarize the information presented in this lab by creating a brief outline and writing it in your lab databook. Your outline should include information about types of flower parts, male and female structures, pollination, fertilization, and development of seed and fruit. Use the Introduction as your guide!
Name _____________________________ Tape Your Flower Parts here.
Name _____________________________ Complete this table as you do the lab.
|Flower parts fun: Biodiversity and Conservation, University of Western Cape|