18-1
Flower Structure
~ Flowers are the reproductive structures of angiosperms.
’Angiosperms could not reproduce without the seeds developed in
the flowers. Flowers come in many colors and shapes and range in
¯ size from microscopic to about a meter in diameter. They have a
number of parts: the sepals and petals are on the outside; the
inside has the pistil, composed of the stigma, style, and ovary, and
¯ the stamen, composed of the filament and anther. The pistil Is the
flower’s female reproductive system and the stamen is the flower’s
male reproductive system. Many flowers lack one or more of these
structures. You will study a tobacco flower because it has all the
flower parts.
OBJECTIVES
Observe a tobacco [lower macroscopically and
identib! its reproductive structures.
Observe microscopically certain parts of a flnwer.
.....
¯ ~dentify the functions of flower parts.
o Diflerentiate between monocot and dicot flowers.
I ATEPdALS
":!ill tobacco flower
microscope sfldes (2)
water
dropper
single-edged razor blade
coverslips (2)
microscope
hand lens (or stereomlcroscope)
colored pencils (red, b~ue, green)
PROCEDURE
Part A. Macroscopic Exa~nat~o~
The outside of a tobacco flower has two parts.
Sepals are green, leaflike parts at the base of
the flower. Tobacco has a calyx of f~ve fused
sepals. It may be difficult to see each sepal.
Sepals protect the young flower.
Petals are the brightly colored parts of a ¯
flower. Tobacco has a corolla of five fused
petals. Counting may be difficult. Petals protect
the flower parts Ins~de. The~r colors may als~
attract insect~.
NOTE: If using p~ese~ed flowers, the
of petals a~d sepals may ha~e faded.
Ident~ the sepals an~ petals [a F~gure
Remove the petals from your flower by gently
pu]l~ng the~ ofL Tw~ different types ~f parts
should now be seen: the p~st~l and the stamens~
Sta~e~ are sta]k]ike structures. Each
~t~en ~s co~posed o~ two parts: the
and the an~ez~ The filament ~s the stalk. The
anther produces pollen gra~n~.
Figure
Identify a stamen, fi]araent, and anther
F~gure i.
Using a scalpel or single-edged razor blade,
carefully remove the pistil. Cut the ovary in
half at its widest pa~ as shown in Figure 3.
~U’~ON: ~B~ careful when handling sharp ¯
instruments. Always cut in a direction away
from your hands and body. Observe the
.inside of the ovary. Note the number and
arran~ament of the ovary chambers. The
white, oval obiects inside the chambers are
the ovules, or eggs.
In the appropriate place in Observations,
sketch a cross section of the ovary showing
the number and arrangement of the
chambers. Label the ovules, ovary walls,
and chambers. Set the pistil aside for use
in Part C.
Cuing
Stem attachment
point
Pa~ C. Ths Gamstes o~ a Flower
L With a iorceps, remove an ovule irora the dissected ovary. Place the ovule in a drop of water
in the center of a clean glass slide and add a coverslip. Observe the ovule under the low-power
objective of a microscope. In the appropriate place in Observations, sketch the ovule as seen
through the microscope. Record the magntfication of the microscope.
Gently brush an anther from one of the stamens across the stigma of the pistil. With a hand
lens, look for pollen grains that may have stuck to the stigma.
Gently touch the point of a dissecting needle to one of the anthers. Transfer some pollen
, grains to a drop of water in the center of a clean glass slide. Add a coverslip. Examine the
pollen grains under the high-power Objective of a microscop~. CALrrION: When switching to the
high-power objective, always look at the objective from the side of the microscope so that the
objective does not hit or damage the slide. The pollen grains may appear to be moving. This is
due to the movement of water under the coverslip.
the appropriate place in Observations, sketch several pollen grains as seen through the
microscope. Record the magnification of the raicroscope.
Obs~rv~tions
Data Tabla
Flower Name
Number of ~epala Color of Sepals Number of Petals Color of Petals
Flower Stamen
Reproductive Structures of a Flower
Stamen q-Anther ~
Anther --
-Pistil
/
Flower Ovary C~oss Section
Ovary wall ~..
0(:~ r:els) ~ Chambers
~
Filament
ANALY$ $
1. How many stamens arc present in tobacco flowers?
2. How many pistils ~re present in tobacco flowers?
:~. How does the number of stamens compare with the number of petals and sepals in tobacco flnwers?
4. About how many pollen cells are present in each anther? (Make a reasonable estimate.)
5, How many ovaries are present in tobacco flowers?,
i
6. About how many ovules are present in tobacco flowers? (Make a reasonable estimate.)
7. a. Are there more pollen ceils produced by one anther than ovules produced by one ovary?
h, Give a possible explanation for your answer.
Give the functions of the following flower parts.
P~t~
Anther
Ov~e
S~y~e
C~s$
Magnification
Da~e .....
Magnification