PLANTS II
Objectives:
1. Describe the life histories of cycads, conifers and
angiosperms and indicate which is the dominant generation in each division.
2. Compare and
contrast the gametophyte of a fern, a conifer and an angiosperm.
3. Give reasons why
gymnosperms persisted, even though angiosperms became dominant.
4.
Describe the adaptations present in angiosperms but not in gymnosperms that
made angiosperms so successful.
5. List the important features that distinguish monocots
and dicots.
6. Given a plant specimen or description, place it
correctly in one of these groups: Coniferophyta, Cycadophyta, or Anthophyta.
Introduction
There
are two divisions of plants that produce seeds – Gymnosperms (naked seed) and angiosperms (hidden seed)
Gymnosperms
include the cycads which resemble palm trees but have cones (Cycadophyta.) ,Gingko
(Gingkophyta), Gnetum and its
relatives '(Gnetophyta), and the familiar conifers (Coniferophyta). Angiosperms
are placed in the division Anthophyta, which includes all flowering plants.
These plants have
solved the problem of reproducing on land by doing away with flagellated sperm
altogether. The male spores are retained within the parent plant and develop
into immature male gametophytes called pollen grains. These are resistant to
dehydration and can be spread in large numbers by the wind. Additionally, the
young sporophyte embryo does not develop into a mature sporophyte immediately
but can' survive as a dormant seed until environmental conditions are
favorable. The production of pollen and seeds allowed these plants to reproduce
in the absence of water and major reason for their success.
Gymnosperms such as conifers have continued to survive in
spite of the success of angiosperms because they are better adapted to poor,
rocky soils and extreme cold. Their
needles (evergreen leaves) allow them to carry out photosynthesis all year
round even in extreme cold conditions. Many land plants, particularly conifers,
have formed symbiotic relationships with fungi called mycorrhizae. The fungi
associate with the roots and significantly increase the surface area for
absorption of minerals from poor soils.
Angiosperms are
characterized by their flowers and their highly efficient vascular tissues. The
rapid uptake of water and minerals by the root system (below ground) and their
distribution to the shoot system (above ground)
allow an
angiosperm to maintain large leaves with broad surface areas. The higher rate
of photosynthesis carried on by these leaves allows the plant to grow much more
quickly than a gymnosperm, and it may reach reproductive maturity in a few
weeks.
Most
plant growth is indeterminate and stops only when the plant dies. Not all parts
of the plant undergo cell division, however. Only certain tissue, called
meristem, contains actively dividing cells. Meristematic tissue is found at the
tip of the shoot (the part above the ground growing upward) and the tip of the
root (the part underground growing downward). Growth occurs there due to the
actively dividing cells of the apical meristem.
Plants may survive for 1, 2, or many years. The annuals
die after a season's growth and allow their seeds to continue the species the
following spring. Biennials reproduce after two seasons and then die.
Perennials live on for many years. The body of an annual grows mainly in
length, from the tips of its shoot system and from the tips of its roots where
the actively dividing apical meristem is found. This type of growth is called
primary growth. Some annuals and most perennials also increase in size
sideways. This growth in girth by the addition of new cells is called secondary
growth and is due to lateral meristem. The stem of some perennials-the trunk of
a tree, for example-continues to increase in diameter year after year. Other
perennials, such as the chrysanthemum and bulb-forming plants, die back each
year and produce little or no secondary growth. When secondary growth occurs,
large amounts of secondary xylem called wood may be formed. This tissue gives
great strength to the stems and roots of woody plants. Plants that do not form
wood are called herbs. Secondary phloem is also produced.
Angiosperm plants
show great diversity, but they fall into two main groups: the monocots and the
dicots. These names are derived from the structure of the seed. A monocot has
one seed leaf (cotyledon), whereas a dicot has two. The characteristics of the
roots, stems, and leaves are also different. Monocots are usually herbs,
whereas dicots include both herbs and woody plants.
In this exercise you will be examining representatives of
the plant divisions whose members produce seeds. Using prepared slides and, in
some cases, fresh tissue, you will learn to identify the major seed plant
divisions based on their anatomy and morphology. As you examine the slides and
plant material, attempt to identify the adaptations in the morphology and
lifecycle of gymnosperms and angiosperms that have made them so successful in a
terrestrial environment. Finally, at the end of the laboratory, you will learn
how to distinguish between the two classes of angiosperms based in their
anatomy and morphology.
Group: Vascular plants with seeds - Gymnosperms (naked
seeds)
·
Over
760 species.
·
Woody
trees, shrubs, and a few vines.
·
Usually
cones as reproductive structures.
·
Seeds
are borne exposed on scales of cones.
·
Normally
wood (xylem) lacks vessels, has only tracheids for water conduction.
Division: Cycadophyta
·
Cycads.
·
About
100 species, important phylum during the Triassic period (248 million years
ago).
·
Dioecious,
meaning that seed cones and pollen cones are on two separate plants.
·
They
are tropical and subtropical plants with trunk-like stems and compound leaves.
·
They
are popular as ornamentals.
·
Zamiapumila is the only
·
Examples:
False king sago, and coontie (Zamia pumila).
Examine the potted specimen, if
available. These palm-like plants are gymnosperms as they produce cones. In
some species, both male and female plants produce cones, while in others only
the male bears cones (the female reproductive structure is more leaf-like in
these species). Examine the cone specimens available in lab and see if you can
determine which is which.
Division:
Ginkgophyta
·
Only
1 species left, a native of
·
It
is the oldest species off living tree; the other ginkgoes went extinct 200
million years ago.
·
Deciduous
(shed leaves), with seeds completely exposed (no cone).
·
Important
medicinal plant enhancing neurological functions such as memory in geriatric
patients.
·
Seeds
are eaten in
·
Example:
Ginkgo biloba.
Division: Gnetophyta
·
About
70 species
·
Possess
more efficient water-conducting cells (vessel elements) in their xylem. The
other gymnosperms usually do not have vessels (angiosperms have these vessel
elements too). Include tropical shrubs and vines. Some found in deserts and
other dry regions.
·
Believed
to be most closely related to flowering plants
·
Examples:
Ephedra and Welwitschia.
Division: Coniferophyta (Latin Conus, cone; ferre, to carry)
·
Pines,
spruces, hemlocks, and firs
·
About
550 species.
·
Woody
trees or shrubs tha 5pROlutsecondary xylem every year (wood and bark).
·
Possess
long and narrow leaves called needles, and produce resin.
·
Usually
monoecious, meaning that seed cones and pollen cones are on the same plant.
·
Ecologically
important for providing shelter and food to animals and for preventing soil
erosion (roots), lumber, paper, and medicine (taxol).
·
Examples:
Longleaf pine, Slash pine, Sand pine, Pond pine, Bald cypress (Taxodium distichum), and Pond cypress (Taxodium acendens).
Group:
Vascular plants with seeds - Angiosperms (seeds enclosed within a fruit)
·
Over
250,000 species
·
Woody
or herbaceous.
·
Flowering
plants that produce flowers, fruits, and seeds.
·
Seeds
are enclosed within a fruit.
Division: Anthophyta
·
Largest
group of plants.
Heterosporous, bear flowers, and seeds enclosed in a
fruit.
·
Two
classes based on the seed leaf of the plant embryo, called cotyledon.
Class: Liliopsida
·
True monocot.
Class: Magnoliopsida
·
True
Dicots.
·
Example:
Slides of maize caryopsis (corn seed) showing scutellum i.e. cotyledon, coleoptile,
coleorhiza, epicotyl, and hypocotyl; endosperm, and ovary wall. Also Capsella (shepherd's purse) showing
cotyledons, epicotyl, hypocotyl, and seed coats.
In this part you will learn the
difference between monocots and dicots (examine the appropriate specimens and
slides), the basic plant anatomy, various terms for different fruits, modified
stems, and roots. You will need to be able to identify these differences.
Complete
the following exercises and answer the accompanying questions:
1. Draw a diagram illustrating the anatomy of a
typical flower. Identify and label the following structures:
a. pedicel
b. receptacle
c. sepals
d.
petals
e. stamen, including the filament and anther
f. pistil (carpel) containing the stigma, style and ovary
g. ovule
2. Draw a diagram outlining the life cycle of a typical angiosperm. Indicate
which structures are diploid and haploid.
Examine
the cones available in the lab and identify the staminate and ovulate
cones. Draw a diagram of the pine life
cycle, indicating which structures are haploid and which are diploid. Examine
prepared slides (if
available) of conifer pollen, evergreen leaves (needles)
and cones. Draw diagrams of your observations and use these to answer the
following questions:
1. You may have noticed that the pollen of conifers
appears to be winged. What is the function of the wings on the pollen grain?
2. What are the advantages of the pollen grain over the
flagellated sperm?
3. Which part of the pine life cycle represents the
sporophyte?
4. Which part
of the pine life cycle represents the microgametophyte and the macrogametophyte
generations and where are they located?
5. What is the advantage of
evergreen leaves?
6. Why are evergreen leaves
usually needle-like or covered with a thick protective cuticle?
3. Complete the following table that
compares the class Monocotyledonae (monocot) and the class Dicotyledonae
(dicot). Examine the available angiosperm specimens and classify each as either
a monocot or a dicot.
Feature |
Monocotyledonae |
Dicotyledonae |
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Number of cotyledons |
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Multiples of flower parts |
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Vein pattern in leaves |
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Arrangement of vascular bundles |
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Type of root system |
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Examples |
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4.
Angiosperm stems (the ascending portion of the plant) not only produce and
support leaves and flowers, and transport water and nutrients, but can be
modified or a number of specializations.
The table below lists five of the most common stem modifications. Define each of these modified stems and give
at least one example of each.
Stem Modification |
Definition/description |
Example |
Tuber |
|
|
Rhizome |
|
|
Tendril |
|
|
Bulb |
|
|
Corm |
|
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5. Seed dispersal in angiosperms is accomplished by the use of fruits. Ten different types of fruit are recognized by plant biologists and descriptions of each type are included in the table below. Using these descriptions, examine the examples of angiosperm fruits provided and list it in the table in the box next to the correct description. (Hint: Not all fruit types may be present, some may be used more than once)
Category |
Fruit Type |
Description |
Example |
|
Simple
fruits |
|
|
|
|
Dry fruits (at maturity) |
Achene |
Ovary wall and seed coat are fused, one seed |
|
|
|
Nut |
Ovary wall hard or woody but can be separated from
seed, one seed |
|
|
|
Capsule |
Ovary has several cavities in cross-section, several to many seeds |
|
|
|
Legume |
Ovary has .one cavity that opens along both sides, many seeds |
|
|
|
Follicle |
Ovary has one cavity that opens along one side, many
seeds |
|
|
Fleshy fruits |
Drupe |
Ovary with one seed surrounded by very hard- seed,
outer covering of seed formed from inner ovary
wall |
|
|
|
|
Mature ovary,tissue soft and fleshy,
surrounding flower tissue does not develop into fruit, many seeds |
|
|
|
Pome |
Fleshy fruit develops in part from surrounding flower
tissue (base of sepals and petals), ovary wall forms "core" around
seeds, many seeds |
|
|
Compound fruits |
|
|
|
|
more than one ovary |
Multiple fruit |
Fruit formed from ovaries of many flowers |
|
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|
Aggregate fruit |
Fruit formed several ovaries in one flower |
|
6. Identify the function of each of the following
structures found in seed plants.
Consider their function in the land environment.
a. pollen grain
b. microsporangium
c. flower
d. carpel
e. seed
f. fruit
g.
endosperm
7. As a way of summarizing what you
have learned about land plants in the last two weeks, complete the following
table that compares the important characteristics of land plants.
Features |
Moss |
Fern |
Conifer |
Flowering Plant |
|
Dominant
generation |
|
|
|
|
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Vascular tissue (+/-) |
|
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Seed (+/-) |
|
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Fruit (+/-) |
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Water required for fertilization |
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Pollen grain +/- |
|
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Homosporous or heterosporous |
|
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Examples |
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