Exercise A Flower Structure

Flowers arc modified branches bearing four sets of floral organs. The tloral organs arc sepals, petals, stamens, and carpels. These four flower parts are in whorls on the receptacle, the expanded top of the flower stalk, or pedicel (fig. 6.1).

The sepals are the outermost floral organs. They are leaflike structures that cover the unopened flower bud. In most flowers, the sepals arc green and photosynthetic. The petals make lip the next whorl of flower parts. Petals are often brighdy colored and conspicuous; their function is to attract animal pollinators.

The male and female structures arc usually located in the center of the flower. The stamens are the male structures, and each stamen consists of an anther supported on a stalk, called the filament. The anther consists of four chambers, where meiosis occurs and where pollen develops. Each pollen grain is a male gametophvtc and is capable of producing sperm during the growth of the pollen tube just prior to fertilization.

The female structures are carpels, which are located in the middle of the flower. Flowers can have from one to many carpels. When there is only one carpel present, it is called a simple pistil. When a flower has many carpcis, they may either be fused together to form one compound pistil or remain as many separate simple pistils. Carpels, whether single or fused, consist of three parts: the stigma, the style, and the ovary. The stigma, which is at the tip of the carpel, receives pollen on its sticky, feathery, or hairy surfacc. One to man\ ovules develop within the ovary at the base of the carpel. The style connects the Stigma to the ovary.

The ovule includes the female gametophvtc, and when mature it contains an egg that can be fertilized by sperm from the pollen. Following fertilization, die ovary becomes the fruit and cach fertilized ovule becomes a seed (fig. 6.2). An ovary can have one ovule las in a peach or plum) or thousands of ovules (as in a watermelon or pumpkin). The resulting fruits can have one to thousands of seeds.

Monocots generally have floral organs in 3s or multiples of 3, whereas dicots have floral organs in 4s or 5s or

Structure Flower And Fruit

Carpel

Pollen chamber

Anther

Filament

Sepal Pedice'

FIGURE 6.1 PARTS OF A FLOWER. (LEFT) CROSS SECTION OF ANANTHER. (RIGHT) LONGITUDINAL SECTION OF A PISTIL.

multiples of 4 or 5. For example, a lily, which is a mono-cot, has 3 sepals, 3 petals, 6 stamens, and a 3-part ovary formed from the fusion of 3 carpels. The flower of a wild geranium, a dicot, consists of 5 sepals, 5 petals, 10 stamens, and 5 fused carpels with separate stigmas.

Flowers that contain all four floral organs arc known as complete and perfect flowers; however, the basic flower structure is frequently modified. In some flowers, one or more flower parts are missing: such flowers arc incomplete, incomplete flowers that lack cither carpels or stamens are also called imperfect. If carpels arc missing, the flower is staminate (male); and if stamens are lacking, the flower is carpellatc or pistillate (female).

Although many flowers develop individually on a stalk, other flowers are grouped into a cluster called an inflorescence. Many times what looks like a single flower at first glance, such as a sunflower or a daisy, is actually an inflorescence. Another example is dogwood; the small flowers are in a cluster and surrounded by showy pink or wrhitc bracts (leaflike structures that often look like petals).

Pollination is the t ransfer of pollen from the anther to the stigma. In a flower that is sclf-pollinatcd, the trans fer occurs within a single flower. By contrast, cross-pol lination involves the transfer of pollen from one plant to another. A variety of animals, including insects, birds, and even mammals, serve as agents to transfer pollen for many flowers; wind carries the pollen for other plants. Animal-pollinated plants usually have large, showy flowers. The petals arc brightly colored, and essential oils impart scents ro attract the pollinator. These flowers often produce nectar, which is a reward for the animal. Pollen in the flowers is usually large, heavy, and sticky. By contrast, wind pollinated flowers tend to be small and inconspicuous. They are often formed in an inflorescence and lack petals. Wind-pollinated flowers produce copious amounts of small, lightweight pollen.

Materials Needed for Exercise A

Dissecting microscope and compound microscope

Four different flowers. Select from those provided by the instructor.

Prepared slide of Lilium (lily) anther Prepared slide of Lilium (lily) ovary Razor blades, single-edged or scalpel and dissecting needles

Procedure for Exercise A

1. Examine the flowers available in lab. You should be able to determine whether you are looking at a single flower or an inflorescence. You should also be able to identify sepals, petals, stamens, and carpels. Which flowers are incomplete? Which are imperfect: Based

Ovule

Microspore Mother Cell

say ii wuh rowhks 73

Mature sporophyte

Ovary

^ Ovule

/ Megaspore / mother cell

Meiosis

Young sporophyte

Germination

Anlhor

Integuments

Micropyie

Microspore mother cells

PoJ'en chamber with microspores

Three ^ megaspore: degenerate

Ovary develops into fruit: ovule de/stops mto seed

Zygote develops ! into embryo

Tetrad

Each microspore matures into a poflen grain

Embryo

Pollen grain

Endosperm forms when the two polar nucia and one sperm unite

On the stigma. the pollen germinates and produces two sperm

Tube nucleus

- Generative nucleus

Antipodats ft>!ien tube

The eight nuclei are produced by three successive divisions of the megaspore nucleus. They become rearranged ¡n what «s now called the embryo sac, or female gametophyle.

Potar nuclei

Polar nuclei

Fertilization

Synergids

Ruination

FIGURE 6.2 REPRODUCTION IN AN ANGIOSPERM

on the structures you see, predict whether each flower is wind pollinated or animal pollinated. Fill in your answers in worksheet 6-1 at the end of this laboratory topic.

  1. Remove the sepals and petals, and placc the remainder of the flower on the stage of the dissecting microscope. How is the stigma adapted to catch pollen? Using the scalpel or razor blade, cut open the ovary of a flower. How many carpels are visible? Can you find the ovules inside?
  2. Examine the slide of Lilium (lily) ovary with the compound microscopc. These slides show nearly mature ovules. There are two or three sections of ovaries on each slide, with several ovules visible in each ovary. When mature, the ovules contain 8 cells (8 nuclei). One of the 8 is the egg. It may not be possible to actually find an ovule showing all 8 cells. Typically, only a part of the ovule is found in a section, so that only 2, 3, or 4 cclls arc visible. Locate the ovules on the slide and try to identify the egg.
  3. Examine the slides of Lilium (lily) anthers. These slides are cut across the anthers and show the mature or nearly mature pollen grains. When the pollen is mature, the anthers split open and release the pollen. There are two different slides available in lab—one showing the closcd anthers and the other showing the open anthers. Examine both.

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Responses

  • Quartilla
    How can one determine a monocot flower from a dicot flower by simply loking at its floral parts?
    8 years ago
  • LUKAS
    How to prepare lily anther in slide?
    8 years ago
  • lavinia
    How many carpels does lily flower have?
    8 years ago
  • edda
    How many ovules develop in a lily carpel?
    8 years ago
  • REIMA
    What are examples of stigma & style of carpel?
    7 years ago
  • ensio kemppi
    How many ovules develops in a stargazer lily carpel?
    6 years ago
  • Tanja Laine
    How many lily flower have ovules?
    2 years ago
  • Lena
    Are flower ovules visible?
    2 years ago
  • quintilio
    How many carpels are present in lillies?
    1 year ago
  • Lily
    How many carpels does a peruvian leave contain?
    1 year ago
  • quadrato
    How many carpels do roseaceae have?
    11 months ago
  • TANJA
    How many chambers are in a lily ovary?
    10 months ago
  • Rebecca
    How many stigma does a lilium have?
    10 months ago
  • michelle
    What are the functions of stamens and carpels?
    8 months ago
  • lily
    How many stigma do lilies have?
    2 months ago
  • john
    How many ovules in one locule in lilly?
    1 month ago
  • hannes koivu
    How to tell how many lolecules are in the overy of a flower?
    17 days ago

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