·
Understand that all vascular
plants use the same basic body structures.
·
List the three major types of
plant tissues and their functions.
·
Know the different types of
meristems and where they are located.
·
Describe the various cell
types that comprise ground tissue.
·
Understand the nature of the
cell types comprising xylem and phloem, the vascular tissue of the plant.
·
Describe the structure of the
photosynthetic organs, the leaves.
·
Understand how primary growth
differs from secondary growth in stems.
·
Know what cell types comprise
wood and bark.
· Describe the structure and function of roots.
·
Be able to characterize the
flowering plant life cycle.
·
Diagram the basic structure
of a flower and indicate the location of its four whorls.
·
Describe the steps leading to
pollination and fertilization.
·
Characterize the nature and
function of a seed.
·
Discuss the purpose and
design of fruit.
·
Describe the process of
germination.
·
Explain how the growth of the
plant body is adjusted by hormones.
· Explain how plant growth and development are related to photoperiod.
17.1
Organization of a
Vascular Plant (p. 376; Fig. 17.1)
A. Most plants possess the same fundamental architecture.
B. A vascular plant is organized along a vertical axis, with a root, and a shoot consisting of a stem and leaves.
C. Meristems are zones of undifferentiated cells whose sole purpose is to divide rapidly to increase the size of the plant.
1. At the growing tips of the plant, apical meristems are found that are responsible for the primary growth, or growth in length, of the plant.
2. Secondary growth is due to lateral meristems found around the plant periphery.
3. Two kinds of lateral meristems add to the girth of the plant: vascular cambium gives rise to secondary phloem and xylem, and cork cambium produces layers of bark on the stem and roots of the plant.
17.2
Plant Tissue Types
(p. 377; Figs. 17.2, 17.3, 17.4, 17.5, 17.6, 17.7)
A. Plant organs are composed of different types of tissues.
B. A tissue is a functional unit made up of a group of cells that work together to serve a purpose for an organism.
1. The three major types of plant tissues are ground tissue, dermal tissue, and vascular tissue.
C. Each type of tissue is composed of distinctive kinds of cells.
D. Ground Tissue
1. Ground tissue is made up of several types of cells.
2. Parenchyma cells are very common and make up the bulk of roots, leaves, and stems; they are alive at maturity and have only primary cell walls.
3. Collenchyma cells form continuous chains of cells under the epidermis of stems or leaf stalks as well as along the veins in leaves; they provide support for any plant organ that has not yet undergone secondary growth.
4. Sclerenchyma cells have thick secondary walls and are nonliving at maturity; their purpose is to lend strength to the tissues in which they are found.
5. Two types of sclerenchyma exist: fibers, long cells that form strands, and sclereids, which are often branched and variably shaped and make up the walls of the “stones” in peaches and nutshells.
E. Dermal Tissue
1. Dermal tissue is made up of numerous flattened epidermal
cells covered by a thick, waxy coat called the cuticle.
2. Guard cells are pairs of cells scattered between epidermal
cells.
3. The openings between the guard cells, called stomata, are
where gas exchange occurs between the atmosphere and the interior tissue of the
plant.
4. Trichomes are extensions of the epidermal cells that help
to regulate the heat and water balance of the leaves.
5. Some trichomes are glandular and secrete substances that
seem to deter predators.
6. Root hairs are epidermal extensions near root tips and take up water and nutrients from the soil.
F. Vascular Tissue
1.
Xylem and phloem are the two
principal types of vascular tissue of plants.
2.
Xylem conducts water in a continuous
column throughout the plant.
3.
Xylem is made up of tracheids and
vessel elements, neither of which have living cytoplasm at maturity.
4.
Tracheids are characteristic of more
primitive vascular plants, and have pits in their secondary walls through which
water flows.
5.
Vessel elements have both pits and
perforations in their end walls through which water moves.
6.
Phloem is made up of sieve-tube
members and sieve cells, both of which are alive but without nuclei at
maturity.
7.
Sieve-tube members are more
evolutionarily advanced, are found in angiosperms, and are arranged in an
end-to-end fashion, forming a sieve tube through which carbohydrates and other
nutrients may pass.
8.
Companion cells often assist
sieve-tube members.
9.
Sieve cells are more primitive, less
efficient, are found in other vascular plants, and lack companion cells.
17.3
Leaves (p. 380;
Figs. 17.8, 17.9, 17.10)
A. Leaves are the major light-capturing organs of plants and are structurally very diverse.
B. Leaves grow by means of marginal meristems which cease to function once the leaf blade is fully expanded.
C. Most leaves have a slender petiole, which may be accompanied by stipules.
17.4
Stems (p. 382;
Figs. 17.11, 17.12, 17.13, 17.14)
A. The stem is the part of the plant that serves as a framework for positioning the leaves.
B. Primary Growth
1. The points where leaves arise along stems are called nodes.
2. As the leaves grow larger, a small bud forms in the axil
near the point from which the leaf arises from the stem.
3. Whether or not this bud develops depends on hormonal
signals from the terminal bud of the shoot.
4. During primary growth, vascular tissue forms a cylinder
close to the periphery of the stem in dicots, and is scattered throughout the
stem in bundles in monocots.
5. When only primary growth has occurred, the center of the stem contains pith, and outside the pith is the cortex.
C. Secondary Growth
1. The vascular cambium initiates secondary growth in stems.
2. The vascular cambium develops from parenchyma cells that lie between the primary xylem and primary phloem.
3. Cells that divide on the bark side become secondary phloem, while those that divide more toward the center become secondary xylem.
4. While secondary growth is occurring, a second kind of secondary cambium, the cork cambium, develops in the outer layers of the stem.
5. The cells forming to the outside of the cork cambium are waterproof, densely packed cork cells that are nonliving at maturity.
6. The term bark refers to any tissues of the stem outside the vascular cambium.
7. Inside the vascular cambium is the secondary xylem, which is commonly referred to as wood.
8. Rings are formed in wood when a spurt of growth occurs during the growing season, producing a light-colored area, followed by a period of slower or no growth in which the cells are darker in color.
17.5
Roots (p. 384;
Figs. 17.15, 17.16, 17.17)
A. Roots are organized in a manner similar to stems except that dicot roots contain no pith; instead, a central column of xylem can be found with rays radiating outward.
B. Roots have a pericycle, a layer of thick-walled cells around the outer boundary of the vascular tissue.
C. Lateral roots arise from the pericycle.
D. Just outside the pericycle lies the endodermis, a layer of tissue that regulates the flow of water between the outer portion of the root and its vascular tissue.
E. A thickened, waxy band, the Casparian strip, surrounds the endodermis.
F. Distal to the apical meristem of the root is the root cap, a layer of undifferentiated cells that protects the apical meristem as the root pushes its way downward.
G. Extensions of epidermal cells, called root hairs, are responsible for the absorption of water and nutrients from the soil.
H. The tissue associated with the cork cambium is called the
periderm.
·
root (p. 376)
·
stem (p. 376)
·
leaves (p. 376)
·
meristems (p. 376)
Plant meristems are made up of cells whose function is to divide.
·
vascular cambium (p.
376)
·
ground tissue (p. 377)
·
dermal tissue (p. 377)
·
stomata (p. 378)
“Stoma” is singular, “stomata” is plural.
·
xylem (p. 378)
·
phloem (p. 378)
·
mesophyll (p. 381)
Mesophyll means “middle leaf”.
·
wood (p. 383)
·
Casparian strip (p.
384)
·
root hairs (p. 384)
18 Plant Reproduction and Growth
18.1The Angiosperm
Flower (p. 396; Fig. 18.1)
A. Angiosperm life cycles involve alternation of generations, with the sporophyte as the dominant generation and the gametophyte developing within the confines of the sporophyte.
B. Both microgametophytes (male gametophytes) and megagametophytes (female gametophytes) are housed within the same structure, the flower.
C. Flower production is seasonal and not a permanent feature of the mature sporophyte.
D. Pollen grains are the male gametophytes while embryo sacs are the female gametophytes.
E. Structure of the Flower
1. Flowers are arranged in whorls.
2. The outermost whorl, the calyx, is made up of the protective sepals.
3. The second whorl is the petals, which collectively are called the corolla, and functions to attract pollinators.
4. The third whorl is the male androecium, made up of stamens and anthers; pollen grains develop within the anthers.
5. The innermost whorl is the female gynoecium made up of carpels; each carpel is composed of a stigma that collects pollen, a style, and an ovary that houses the ovules in which embryo sacs develop.
18.2Angiosperm
Reproduction (p. 397; Figs. 18.2, 18.3, 18.4)
A. Pollen Formation
1. Pollen grains develop from microspores that form in the pollen sacs.
2. Within the pollen sacs, the microspore mother cells undergo meiosis to form microspores; microspores undergo mitosis to form pollen grains.
B. Egg Formation
1. Eggs develop in the ovules of the angiosperm flower; within each ovule is a megaspore mother cell.
2. Each megaspore mother cell undergoes meiosis to produce four haploid megaspores, only one of which survives.
3. The lone megaspore undergoes mitotic divisions and produces 8 haploid nuclei; one will function as the egg nuclei and two are polar nuclei.
C. Pollination
1. Pollination is the process by which pollen arrives at the stigma.
2. Pollinators include various insects or birds that are attracted to the flowers by scents and colors, and are often rewarded for their efforts by sugary nectar.
3. Coevolution of flowers and pollinators can be seen in a wide variety of plants and animals.
4. Wind-pollinated flowers are not fragrant or colorful, and typically produce very large amounts of pollen to ensure that at least some of it arrives at the female stigma.
D. Fertilization
1. In angiosperms, fertilization occurs in a unique process called double fertilization.
2. Once pollen grains reach the stigma, a pollen tube grows down through the style until it reaches the ovule.
3. One of the cells of the pollen within the pollen tube becomes two sperm cells; one of the sperm cells unites with the egg cell to produce the zygote, and the other sperm cell fuses with two polar nuclei that were produced during meiosis of the egg cell.
4. The two polar nuclei and the sperm cell fuse and divide rapidly, becoming nutritious endosperm.
18.3Seeds (p.
399; Fig. 18.5)
A. The entire series of events that occur between fertilization and maturity is called development.
B. In many plants, embryo development is arrested soon after apical meristems and the first leaves (cotyledons) are differentiated.
C. The integuments surrounding the embryo develop into an impervious seed coat that protects the embryo throughout its period of dormancy.
D. Resumption of metabolic activity within the seed leads to germination.
18.4Fruit (p.
400; Fig. 18.6)
A. In some plants, the ovary surrounding the ovule develops into fruit.
B. Fruits appear to have evolved to help in seed dispersal, since animals eat the fruit and defecate or drop the seeds at some distance away from the parent plant.
18.5Germination
(p. 401; Fig. 18.7)
A. When the time is right for the embryo to resume its growth, the seed coat absorbs water, and the embryo becomes metabolically active once again.
B. Oxygen is needed during germination for most seeds, although some seem able to germinate in anoxic conditions.
18.6Photoperiodism
and Dormancy (p. 408; Figs. 18.16, 18.17)
A. Plants respond to environmental stimuli in a variety of ways.
B. Photoperiodism
1. Plants also respond to patterns of light and dark as the seasons progress, a phenomenon referred to as photoperiodism.
2. Day length cues plants to flower.
3. Some plants flower when days are shorter, others as the days become longer.
4. Still other plants are day-neutral and produce flowers when conditions are favorable, regardless of day length.
C. The Chemical Basis of Photoperiodism
1. One class of chemicals, the phytochromes, are pigment molecules that influence flowering in plants.
D. Dormancy
1. When environmental conditions are unfavorable to growth, the capacity to become dormant is critical to the survival of certain plants.
2. Annual plants overwinter as seeds.
·
calyx (p. 396) The
outermost whorl of a flower is composed of the sepals, collectively called the
calyx.
·
corolla (p. 396) The
second whorl of a flower is made up of the petals, collectively called the
corolla.
·
androecium (p. 396)
All of the stamens of the flower are the third, or male, whorl, called the
androecium.
·
anther (p. 396) The
portion of the stamens housing microsporangia (pollen sacs), within which
microspores develop into pollen grains.
·
gynoecium (p. 396) The
female, or innermost whorl of the flower, is made up of the carpel with its
stigma, style, and ovary.
·
ovules (p. 396) Within
the ovules, megasporangia produce haploid megaspores which develop into embryo
sacs containing the eggs.
·
pollination (p. 397)
Pollination is the process by which pollen is placed on the stigma. It may
arrive there by wind or by animals, unless it is self-pollinated.
·
double fertilization
(p. 398) Double fertilization involves two sperms cells, one of which
fertilizes the egg cell, and the other of which fuses with the two haploid
polar nuclei to become triploid endosperm.
·
germination (p. 399)
This is the resumption of metabolic activities in the seed, often in response
to water.
·
phototropism (p. 404)
a phenomenon in which plants bend toward the light