Flower Structure 18-1

~ 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 ¯ ~dentify the functions of flower parts. identib! its reproductive structures. o Diflerentiate between monocot and dicot flowers. Observe microscopically certain parts of a flnwer.

..... I ATEPdALS ":!ill tobacco flower dropper microscope microscope sfldes (2) single-edged razor blade hand lens (or stereomlcroscope) water coverslips (2) colored pencils (red, b~ue, green) PROCEDURE Part A. Macroscopic Exa~nat~o~ Figure 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 Identify a stamen, fi]araent, and anther anther produces pollen gra~n~. 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 Cuing 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 Stem attachment the number and arrangement of the point chambers. Label the ovules, ovary walls, and chambers. Set the pistil aside for use in Part C.

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

Reproductive Structures of a Flower Flower Stamen

Stamen q-Anther ~

Anther --

Filament -Pistil ~ /

Flower Ovary C~oss Section

Ovary wall ~..

0(:~ r:els) ~ Chambers 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~ S~y~e

Anther

Ov~e C~s$ Da~e .....

Magnification Magnification