Download Vascular Seed Plants (Spermatophytes): The Angiosperms

Vascular Seed Plants (Spermatophytes): The
Angiosperms
Angiosperms – Phylum Anthophyta, the flowering plants - ~250,000 species
Figure 1. Examples of angiosperms, the flowering plants. The first photos shows a monocot, the second photo shows a
dicot, and the third photo shows bee pollination. Pollination is a unique strategy to unite sperm and egg.
Objectives
1. Survey vascular seed plants with flowers and fruits
2. Understand a sporophyte dominated life cycle
3. Identify angiosperm monocots and dicots.
Most land plants (and several aquatic ones) are angiosperms. This group includes such obviously
flowering plants as lilies, along with less obvious ones such as grasses. You may have noticed already
that reproductive mechanisms can have an enormous impact on where and how various groups of
plants live (that’s why we don’t live in a world dominated by ferns). Flowering plants show an
amazing variety in terms of two key reproductive events: getting sperm and egg together
(pollination) and dispersing seeds by using fruits. These reproductive tricks help explain why, out of
about 300,000 known species of plants on earth, 250,000 of them are angiosperms.
Angiosperms are flowering plants. They have seeds and pollen like gymnosperms, but they also have
flowers and fruits.
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Key differences between angiosperms and gymnosperms:
• Angiosperms have flowers. Flowers help ensure that sperm and egg come together.
In gymnosperms, pollen grains are dispersed by the wind, but the angiosperms display an extremely
wide range of tricks for getting animals such as bees to carry pollen from one flower to another. Some
angiosperms, such as grasses, are wind-pollinated.
• Angiosperms have fruits. Fruits help ensure that seeds disperse to new locations and have an
opportunity at survival. As with flowers, many fruits have features that result in animals carrying the
seeds around.
Flowers help the sperm and eggs of plants fuse together. The sperm comes from the pollen, and
the flowers of many plants function to lure animals (bees, for example) to carry pollen from one
flower to another. Flowers are mostly sporophyte (2n) tissue of the parent plant, but they contain the
tiny haploid gametophytes of the next generation. Many flowers make both male gametophytes
(pollen) and female gametophytes (embryo sacs).
Anatomy
Flowers have four basic types of organs:
• Sepals. These are usually green leafy
petals
forming
an
outer
whorl
around the flower. Collectively, the
part of the flower made of sepals is
called the calyx.
• Petals. Often brightly colored and
elaborately shaped, in many species
Figure 2. Structure of a flowering plant.
the petals help attract animals that pollinate the
flowers. The petals collectively form the flower's corolla.
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• Stamens. Male gametophytes (pollen grains) develop in the stamens. Each stamen has an anther
where pollen forms and a filament that supports the anther.
• Carpels. Female gametophytes (embryo sacs) develop in the carpels. A carpel consists of an
ovary (holds the ovules, in which the embryo sacs develop), a stigma (receives pollen), and a style
(supports the stigma).
 The flower is attached to the plant's stem by a petiole. The tip of the petiole may be swollen to form
a receptacle on which the above described flower parts attach.
•
In some angiosperms, the flowers grow in a dense cluster called an inflorescence. Some flowers
may be missing some parts – they may not have sepals, or they may have only carpels or only stamens.
Some flowers may have duplicate parts – for example, many cultivated flowers have been bred to
produce extra whorls of petals. As you might guess, flowers are found only in flowering plants.
Characteristics of the Two Classes of Angiosperms
A monocot refers to monocotyledons. A cotyledon is an embryonic leaf. Therefore, when monocots
germinate, there is one leaf breaking through the soil surface. Dicots or eudicots are dicotyledons.
These angiosperms have two embryonic leaves when they germinate.
Figure 3. Characteristics and examples of the two classes of
angiosperms. Yucca, Yucca filamentosa is a monocot and Ocotillo,
Fouquieria splendens is a dicot. Both angiosperms are found in the
Chihuahuan Desert.
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Fertilization in angiosperms
Fertilization occurs when two haploid gametes fuse together to make a new diploid individual.
Flowering plants have a complex process called double fertilization.
The essence of double fertilization is that
two sperm come from a single pollen grain.
One sperm fertilizes the egg, and the other
joins with the two haploid polar nuclei of
the female gametophyte, creating a triploid
(3N) nucleus. This triploid cell then develops
into the endosperm, the part of the seed that
provides
nutrition
for
the
developing
embryo.
Figure 4. Angiosperm Life cycle.
Study the angiosperm life cycle diagram in Figure 4. Compare and contrast this with the other life
cycle diagrams. Remember these terms about the life cycle diagram: fertilization, mitosis, meiosis,
haploid, diploid, gametophyte, sporophyte, spore, sperm, and egg.
Figure 5. Stages of microsporogenesis and
microgametogenesis in pollen.
Figure 6. Stages of megasporogenesis and megagametogenesis in
the embryo sac of an ovary.
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Seeds
Seeds are one of the key evolutionary innovations helping plants
survive on dry land. A seed contains an embryo (the new generation
sporophyte), a seed coat that protects it from the outside world, and
triploid (3n) endosperm that provides nutrition for the growing
embryo. The structure of the seed differs between dicots and
monocots. In dicots like bean plants, the two cotyledons of the dicot
absorb the endosperm before germination. In monocots like corn,
the endosperm is located next to the single cotyledon.
Figure 7. Seed structure of a dicot and a monocot.
Fruits
A fruit is a mature ovary. All fruit contain seed(s). A fruit may be dry or fleshy. Plants have two key
points in their life cycle where dispersal to a new environment can happen. The first is the pollen,
which can be carried great distances by wind or animals. The second is dispersal of the seeds. After
fertilization, a flower turns into a fruit. Many angiosperms have fruits that encourage animals to eat
the fruit (which is made from tissue of the parent sporophyte); the animals may digest the fruit but
not the seeds, eventually depositing the seeds in a new location.
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Legume Fruit
Berry Fruit
Aggregate Fruit
Pome Fruit
Figure 8. Diagrams of fruit and their originating flowers.
Angiosperm Survey
1. Observe the whole angiosperm leaves. Like the pine needle, this is a complex structure
compared to the “leaves” of a moss.
2. Observe the live flowers. You should be able to find the same parts in the live flowers. You’ll have
to dissect them to see what’s inside. Note that in the carpels, you may find gametophyte and
sporophyte tissues together.
3. View the model of a flower. Make sure that you are familiar with all flower structures.
4. Observe the various whole specimens of seeds. Identify the embryo, the endosperm, and the
parental tissues.
5. Observe the various whole specimens of fruits. Identify the carpels, the seeds, and the
parental tissues.
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Angiosperm Slides
1. Observe the prepared slides of lily flowers.
2. Observe the prepared slide of the Lilium ovaries and anthers. Relate the features of the slides
to the life cycle diagram. Ovaries make the eggs, and anthers make the pollen. Which parts are
haploid, and which parts are diploid? Where would meiosis occur? Where would fertilization
occur? Again, look for the features that distinguish angiosperms from the other groups. We'll
look at the details of these features in a later lab.
3. Observe the fresh pollen of lilies. Take some pollen and place on a microscope slide with a
little water and a cover slip. Compare this to the pine pollen.
Worksheet for Angiosperm Lab
Sources
1. Lab content http://faculty.deanza.edu/heyerbruce/bio6a
2. Figure 1 www.web.gcaz.edu , www.wisegeek.org , www.en.wikipedia.org
3. Figure 2 www.extension.org
4. Figure 3 www.lifeofplant.blogspot.com , www.enwikipedia.org , www.desertmuseum.org
5. Figure 4 www.ck12.org
6. Figure 5 www2.le.ac.uk
7. Figure 6 www.nickrentlab.siu.edu
8. Figure 7 www.plantphys.info
9. Figure 8 www.en.wikipedia.org , www.extension.umn.edu ,
www.buncombemastergardener.org , www.eky.edu , www.ext.colostate.edu
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