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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.

Vascular Seed Plants (Spermatophytes): The

Angiosperms

Angiosperms – Phylum Anthophyta, the flowering plants - ~250,000 species

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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Figure 2. Structure of a flowering plant.

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

the petals help attract animals that pollinate the

flowers. The petals collectively form the flower's corolla.

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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.

• 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.

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Figure 4. Angiosperm Life cycle.

Figure 5. Stages of microsporogenesis and

microgametogenesis in pollen.

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.

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 6. Stages of megasporogenesis and megagametogenesis in

the embryo sac of an ovary.

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Figure 7. Seed structure of a dicot and a monocot.

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.

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

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.

Figure 8. Diagrams of fruit and their originating flowers.

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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