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I. The flower: site of sexual reproduction

A. Flowering plants are known as angiosperms

B. Flower development initiates the sexual reproduction cycle in all flowering plants

C. The complete sexual cycle involves production of special reproductive cells following meiosis; pollination;  fertilization; seed and fruit development; seed and fruit dissemination; seed germination

II. Parts of a Complete Flower and Their Functions

A. A typical flower is composed of 4 whorls of modified leaves: sepals, petals, stamens and carpels

1. Sepals: generally green and enclose other floral parts in the bud; collectively called the calyx

2. Petals: usually conspicuous, colored and attractive; collectively called the corolla

3. Stamens: form the whorl just inside the corolla; composed of filament and anther; the whorl of stamens is called the androecium

4. the gynoecium is the female part of the flower and is composed of one or more carpels; sometimes one carpel or group of fused carpels is called a pistil

5. The term perianth is applied to the calyx and corolla collectively

B. The Male Organs of the Flower are the Androecium

1. The anther is made up of four elongate lobes called pollen sacs

a. Each pollen sac contains dividing cells called microsporocytes

b. Each microsporocyte divides by meiosis to form 4 microspores

c. The nucleus of each microspore divides by mitosis to form a two celled pollen grain which contains a tube cell and a smaller generative cell

d. the role of this 2 celled, haploid male gametophyte is to produce sperm cells for fertilization

e. after pollen grains mature, the anther wall splits open and pollen is shed

f. pollination transfers pollen to stigmas of flowers

g. pollen grain then germinates to form a pollen tube that grows toward the ovary

h. pollen tube secretes enzymes that partially break down transmitting tissue cells, making it easier for pollen tubes to grow

C. The female organs of the flower are the Gynoecium

1. in its simplest from, the gynoecium is a single folded carpel or simple pistil

2. a fused group of carpels is called a compound pistil

3. the ovary is a hollow structure with one to several chambers, the locales

4. the placenta is the tissue within the ovary to which an ovule is attached

5. the manner in which the placenta are distributed in the ovary is the placentation

a. three types of placentation are axile, parietal, and central

6. the stalk emanating from the ovary is the style with the stigma at its tip

a. often the stigma is covered with hair and sticky fluid

7. within the ovary is the ovule that eventually becomes the seed

a. a mature ovule is covered with two outer protective layers, the integuments; a small opening the micropyle is left where the integuments fail to fuse

8. within the ovule, one of the dividing cells, the megasporocyte, enlarges

a. the megasporocyte is embedded in a tissue called the nucellus

D. The embryo sac is the female gametophyte plant

1. meiosis of the megasporocyte produces four (n) megaspores

2. the 3 megaspore nearest the micropyle disintegrates and disappear

3. the megaspore farthest from the micropyle enlarges and develops into a mature embryo sac that contains (after 3 meiotic divisions) eight nuclei

1. at the end of the process, an egg cell and two synergid cells are positioned at the micropylar end of the embryo sac (all 3 are often referred to as the egg apparatus)

b. two polar nuclei have migrated to the center of the large central cell.

c. three nuclei at the opposite end of the micropyle are antipodal cells

4. the embryo sac is the female gametophyte, a haploid or n plant

E. Double fertilization produces an embryo and the endosperm

1. the pollen tube, produced by the germinating pollen grain, grows through the stigma and style and enters the ovary

2. synergids may release chemicals that direct the pollen growth tube

3. double fertilization

a. the sperm and egg nuclei fuse to form a 2n zygote

b. the other sperm nucleus fuses with the polar nuclei of the central cell to from a primary endosperm nucleus (Divides to later become endosperm, a food reserve in the seed

III. Apical meristems: sites of flower development

A. sometime during the growing season, signals trigger transformation of the shoot apex into a floral apex

1. bracts form first followed by floral organs in whorls or spirals

B. the development of an inflorescence follows the same sequence

C. flowers vary in their architecture

1. A complete flower has all four sets of floral leaves; an incomplete flower lacks one or more of the four sets

2. unisexual flowers are either staminate or pistillate and are imperfect

3. bisexual flowers are perfect

4. a plant bearing both staminate and pistillate flowers is nomoecious; a dioecious plant bears either staminate of pistillate flowers but not both

5. flowers may have regular symmetry (radial) or irregular symmetry (bilateral)

6. the parts of a flower may be free or united; union of flower parts from 2 different whorls is adnation

7. the ovary position differs among flowers; superior or inferior

8. in a flower with an inferior ovary, the lower portions calyx, corolla and androecium- have fused to form a tube, the hypanthium, which is also fused to the ovary

D. often flowers occur in clusters, or inflorescences

1. an inflorescence is a flowering branch

2. types of inflorescences are: raceme, panicle, spike, catkin, umbel, head and cyme

a. short branches from the main axis of the inflorescence, each of which terminates in a flower are called pedicels

 

Lesson Objectives/Homework questions Ch. 13

1. What is the function of a flower and what major group of plants produces flowers?
2. What stages does the complete sexual cycle of a plant include?
3. What are the 4 whorls of organs that compose the perianth, the androecium and gynoecium? These organs are modified from what normal plant parts? Describe the function of each whorl.
4. Describe how pollen forms in a pollen grain, and draw and label important structures and their roles in this process.
5. Differentiate between pollination and fertilization.
6. Distinguish between a compound and simple pistil; and between an ovule and an ovary.
7. Define the following, and draw and label them so you understand the structure of the gynoecium: micropyle, integuments of ovule, megasporocyte, nucellus, megaspores.
8. Describe or draw how the egg and synergids, as well as the polar nuclei are positioned within the embryo sac. (Where did the embryo sac come from?)
9. Describe what happens in double fertilization.
10. Describe or draw and label examples of the following: perfect and imperfect flowers, bisexual and unisexual flowers, monoecious and dioecious plants, regular and irregular flowers, free and united floral parts, adnation, flowers with superior and inferior ovaries,

13.  Describe the parts of a complete flower and give functions of each.

14.  Know terminology associated with floral anatomy.

15.  Describe the function of male and female gametophyte in flowering plants and their cycles.

16.  Describe the double fertilization that is unique to flowering plants at the level of detail reviewed in class.

17.  Define the terms associated with variations in floral morphology (e.g. ovary position, incomplete vs. complete flowers, perfect vs. imperfect flowers, regular or irregular symmetry, adnation vs free, fused whorls.

18.  Define inflorescence and describe variations in handout from lab.

19.  Compare and contrast llthe reproductive strategies of self and cross pollination

20.  Describe pollination vectors and be able to describe some specific examples from the video we saw in class.