Download Principles of Biology Lake Tahoe Community College

Botany - Bio 201
Spring 2008
Lake Tahoe Community College
Instructor: Ralph Sinibaldi
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Chapter 13 - The Flower and Sexual Reproduction
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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
a. 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 th main axis of the inflorescence, each of which terminates in a flower
are called pedicels
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Chapter 14 - Seeds and Fruits
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I. Seeds: Dormant embryos
A. Seed and fruit are the most important source of food for people and other animals
1. Rice, corn and barley feed the majority of people in the world
2. 1500’s, Doctrine of Signatures illustrated early importance of seeds and fruits
3. Seeds are mature; seeds are packaged in fruits
B. The seed is a mature ovule
1. Following fertilization, the zygote develops intoan embryo, the primary endosperm nucleus develops
into the endoperm, and theinteguments of the ovule develop into the seed coat
2. For a short time after fertilization, the zygote divides frequently while the primary endosperm nucleus
divides rapidly to form the endosperm (nutrient-rich storage tissue to feed the germiniating seed)
3. after endosperm development, the zygote nucleus divides to form a filament of cells
4. the cell farthest from the micropyle divvides to produce the proembryo
5. the cell closest to the miropyle elongates tand divides to produce the suspensor, which supports the
embryo in the endosperm
6. further divisions produce the globular stage and finally, a heart shaped stage, after the 2 cotyledons
have developed in dicots; the embryo develops a radicle at one end and a shoot tip at the other.
7. there are many variations in embryo development, particularly between monocots and dicots
8. during embryo development, the nucellus, endosperm, and enteguments undergo characteristic
changes typical of their plant group
9. the integuments becomehard, protective seed coats
C. Seed structures vary
1. externally the commmon bean has a hilum, micropyle and a raphe
a. the hilum is a large oval scar left when the seed breaks away from its placental connection,
the funiculus
b. the micropyle is a small opening in the seed coat, at one end of the hilum
c. the raphe is a ridge at the end of the hilum opposite the micropyle
d. bean embryo consists of two fleshy cotyledons and the embryo axis
1. the embryonic root or radicle is at one end and th eenbryonic shoot or epicotyl is at
the other end; they hypocotyl is just below the cotyledons
2. Castor bean has an external structure, the caruncle
a. the hilum and micropyle are covered by the caruncle
b. the raphe runs the full length of the seed coat
c. the caruncle functions in absorbing water for germination
d. the embryo is embedded in the massive endosperm
3. Grasses have a seed that is actually a fruit, the caryopsis or grain
a. starchy endosperm constitutes the bulk of th ecaryopsis; it is surrounded y a layer of cells,
the aleurone layer
b. the grass embryo has an axis with a shoot apex and a root apex; the shoot apex, with
rudimentary leaves, is ensheatherd by a coleoptile and the radicle is surrounded by the
coleorhiza
c. a large part of the embryo is shield-shaped cotyledon, the scutellum
4. Milling to make white rice removes most of th enutrients; the milled material, bran, is now a popular
food
5. popcorn is a grass fruit; it pops when heated because steam builds up in the grain
6. The seed coat of onion encloses only a small amount of endosperm; the embryo is simple with a
prominent radicle and single cotyledon; the shoot apex appears as a notch; the embryo is coiled with the
radicle pointing toward the micropyle
II. Germination
A. the first step in embryo growth begins with imbibation, a critical step
1. Enzymes are tehn activated and rapidly released to digest stored food
2. the first indicator of germination is radicle swelling and growth to burst the seed coat; the radicle
grows downward
B. Germination process differs among plants
1. beans have an epigeal germination; the straightening of the hypocotyl raises the cotyledons and
shoot apex toward the light
2. peas have hypogeal germination; when th eepicotyl straightens, the cotyledons remain below ground,
and only the apex and first leaves are raised upward
3. castor beans have epigeal germination
4. in onion, a sharply bent, tubular cotyledon breaks soil surface and slowly straightens; the cotyledon
base encloses the shoot apex; the first leaf emerges through a small opening at the base of the
cotyeldon
5. in grasses, the shoot and root are enveloped by the coleoptile and coleorhiza; the primary root
pushes through the coleorhiza; adventitious roots arise from lower stem nodes; the coleoptile
elongates and emerges above ground; at this time, the uppermost leaf pushes its way through the
coleptile and begins Ps
C. Germination may be delayed by dormancy
1. seeds can remain viable for remarkably long periods
2. dormancy, the inability to germinate because of of reduced physiological acitvity
a. factors breaking dormancy are light, scarring, cold treatment, heat, fire
D. Dey to Fruits: a dichotomous key to identify different fruit types
III. Fruits: ripened ovaries
A. Fruits protect seeds, aid in their dispersal, and may be a factor in timing germination
1. in everyday use, the word fruit refers to a juicy and edible structure; howvever, many structures that
are commonly called vegetables may be fruits
B. The nature of the ovary determines the structure of the fruit
1. the 3 layered fruit wall is called the pericarp
a. beginning outermost, the layers are exocarp, mesocarp and endocarp
b. tissues other than ovary wall may form part of a fruit; they are accessory
C. Fruits may be simple or compound
1. simple fruits are derived from a single ovary; they may be dry or fleshy; the ovary may be
composed of one or more carpels; may be dehiscent or indehiscent
2. Compound fruits are composed of more than one fruit
a. aggregate fruits are derived from many separate ovaries of a single flower, all attached to a
single receptacle (strawberry)
b. multiple fruits, such as pineapple, are the enlarged ovaries of several fowers grown more or
less together into a single mass
3. Simple fruits are derived from a single ovary
a. pericarp dry and dehiscent
1. legume or pod: arises from a single carpel, splits along two sides; pea family
2. follicle: develops from a single carpel, opens along only one side; magnolia
3. silique: derived from a superior ovary with two locules and when dry, the pericarp
separates into three portions; mustard family
b. pericarp dry and indehiscent
1. achene: a dry, one seeded fruit; the pericarp is easily separated from the seed coat;
sunflower, usually called seeds
2. caryopsis or grain: dry, one-seeded pericarp and seed coat are firmly united all the
way around the embryo; grass family
3. samara: havie an outgrowth of theovary wall that is winglike; one seeded in elm, two
seeded in maple
4. schizocarp: consists of two carpels that split at maturity into two one-seeded,
indehiscent halves; carrot family
5. nut: one-seeded, indehiscent dry fruit with a hard or stony pericarp; chestnut,
walnut, acorn
c. pericarp fleshy - popular for eating and animals disperse seeds
1. drupes - from a single carpel, usually one-seeded, hard endocarp with fleshy
mesocarp and thin exocarp: cherry, almond, peach, apricot
2. berries - from a compound ovary, many seeds embedded in pericarp flesh;
tomatoes, lemons, cucumbers
a. hesperidium, a type of berry: leathery rind is exocarp and mesocarp with
thick, juicy pulp endocarp segments; lemons, oranges, grapefruits, limes
b. pepo: outer wall is receptacle tissue that surrounds and is fused with the
exocarp; the flesh is principally mesocarp and endocarp; watermelons,
cucumbers, squash
c. pome: derived from a flower with an inferior ovary with the flesh being an
enlarged hypanthium and the core from the ovary; apples and pears
4. compound fruits develop from several ovaries
a. aggregate fruit: formed from numerous carpels of one individual flower; raspberry,
strawberry, blackberry
b. multiple fruit: formed from individual ovaries of several clumped flowers: pineapple, fig
5. Not all fruits have seeds
a. parthenocarpic fruits develop without fertilization and lack seeds
IV. Adaptations for seed dispersal
A. role of ripe fruit is to aid in dispersal of seeds, deter inappropriate seed dispersing animals from taking fruit or
seed, and to protect seeds from herbivores who consume seeds but do not disperse them
B. dispersal may be wind, water, animals
1. winged and plumed fruits are common adaptations for wind dispersal; seeds may be dispersed by a
violent deshiscence (explosion) of th e pericarp; sedge seeds float as do coconut fruits
2. animal vectors include ants, birds, bats, rodents, fish, ruminants, and primates; elaiosomes
harvested by ants, allows seeds to germinate
C. some plants have evolved antiherbivore techniques
1. antiherbivore techniques include reducing the time or fruit availability, making the fruit or seed coat
physically hard, and making the fruit or endosperm chemically repellent
a. mast years are years of heavy fruit and seed production
b. many fruits are rich in secondary compounds that are negative and toxic
c. plant- herbivore interactions/coevolution
D. Distant dispersal of seeds is not a universal aim
1. self-planting near the parent as in some grasses; peanuts bury their fruit
2. sea rocket has a bipartite fruit; one-half dislodges, one-half remains with the parent
3. plant species of isolated islands often exhibit a loss of dispersal mechanisms
Chapter 14 - Study Questions
1. What part of a flower is a seed, and what is its role in the next generation.
2. Describe the two major variations in seed structure, monocot and dicot.
3. Distinguish between epigeal and hypogeal germination.
4. Describe the state of seed dormancy.
5. What part of a flower is a fruit?
6. Describe the layers of the fruit wall.
7. Describe simple, aggregate and multiple fruits and cite common examples of each.
8. What are the various types of simple fruits, and give common examples of each.
9. Describe various adaptations for seed dispersal.
10. Describe the importance of coevolution in seeds and their dispersers. Describe common examples.
Chapter 13 - Study Questions
1. Describe the parts of a complete flower and give functions of each.
2. Know terminology associated with floral anatomy.
3. Describe the function of male and female gametophyte in flowering plants and their cycles.
4. Describe the double fertilization that is unique to flowering plants at the level of detail reviewed in class.
5. 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.
6. Define inflorescence and describe variations in handout from lab.
7. Compare and contrast llthe reproductive strategies of self and cross pollination
8. Describe pollination vectors and be able to describe some specific examples from the video we saw in class.
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. Explain how each happens.
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,
11. Draw each of the following: raceme, panicle, spike, catkin, umbel, head and cyme
12. Define or draw and label a pedicel and a hypanthium.