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Chapter 30: Plant Diversity II - Lecture Notes | BIOL 112, Study notes of Biology

Christian Brothers University (CBU)Biology

Material Type: Notes; Class: Principles of Biology II; Subject: Biology; University: Christian Brothers University; Term: Unknown 1989;

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Chapter 30 PLANT DIVERSITY II.
THE EVOLUTION OF SEED PLANTS
OVERVIEW OF SEED PLANT EVOLUTION
The most important reproductive adaptations of seed plants are:
1. Continued reduction of the gametophyte
2. Evolution of the seed.
3. Evolution of the pollen.
The reduced gametophyte can develop from spores retained within the sporangia of the
parental sporophyte.
Retaining the female gametophyte within the sporangium protects it from environmental
stresses.
The gametophyte obtains food from the sporophyte.
All seed plants have two different kinds of spores. They are heterosporous.
1. Megasporangium produces megaspores, which produces female gametophytes.
2. Microsporangium produces microspores, which produces male gametophytes.
In seed plants, the megaspores and the female gametophyte are retained on the parent
sporophyte.
Layers of sporophyte tissue envelop the megasporangium. These tissues are called
integuments.
The megasporangium, megaspore and integuments are called the ovule.
The female gametophyte develops inside the megaspore and produces one or more egg cells.
Megasporangium → megaspores → female gametophytes → egg cell.
Microsporangium → microspores → male gametophytes (pollen) → sperms.
Pollen does not need a liquid for fertilization.
Pollination is the transfer of pollen to ovules. Wind and animals carry out pollination.
Pollen grains are well protected by sporopollenin.
Sporopollenin contains only carbon, hydrogen and oxygen; it is an isoprene polymer.
The seed is a sporophyte embryo packaged along with a food supply within a protective coat.
Seeds can be very resistant and can be dispersed widely by animals and wind.
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Download Chapter 30: Plant Diversity II - Lecture Notes | BIOL 112 and more Study notes Biology in PDF only on Docsity!

Chapter 30 PLANT DIVERSITY II.

THE EVOLUTION OF SEED PLANTS

OVERVIEW OF SEED PLANT EVOLUTION

The most important reproductive adaptations of seed plants are:

  1. Continued reduction of the gametophyte
  2. Evolution of the seed.
  3. Evolution of the pollen. The reduced gametophyte can develop from spores retained within the sporangia of the parental sporophyte.  Retaining the female gametophyte within the sporangium protects it from environmental stresses.  The gametophyte obtains food from the sporophyte. All seed plants have two different kinds of spores. They are heterosporous.
  4. Megasporangium produces megaspores , which produces female gametophytes.
  5. Microsporangium produces microspores , which produces male gametophytes. In seed plants, the megaspores and the female gametophyte are retained on the parent sporophyte. Layers of sporophyte tissue envelop the megasporangium. These tissues are called integuments. The megasporangium, megaspore and integuments are called the ovule. The female gametophyte develops inside the megaspore and produces one or more egg cells. Megasporangium → megaspores → female gametophytes → egg cell. Microsporangium → microspores → male gametophytes (pollen) → sperms. Pollen does not need a liquid for fertilization. Pollination is the transfer of pollen to ovules. Wind and animals carry out pollination. Pollen grains are well protected by sporopollenin. Sporopollenin contains only carbon, hydrogen and oxygen; it is an isoprene polymer. The seed is a sporophyte embryo packaged along with a food supply within a protective coat. Seeds can be very resistant and can be dispersed widely by animals and wind.

SEED SPORE

  1. Multicellular embryo Single cell
  2. Food supplied by tissue Food only in the cell
  3. Multicellular seed coat Covering not cellular
  4. Diploid sporophyte Haploid cell
  5. Product of fertilization Product of meiosis There are two groups of seed producing plants, gymnosperms and angiosperms.  Produce seeds.  Vascular tissue: xylem for water and mineral transport and phloem for dissolved sugars.  Gametophyte is much reduced and totally dependent on the sporophyte.  Heterosporous: microspores and megaspores.

GYMNOSPERMS

There are about 720 species found in all terrestrial habitats grouped into four divisions (phyla). They have great economic importance: lumber, paper, and chemicals. By the late Devonian period (~375 million years ago) some plants had begun to acquire some adaptations that characterize seed plants. The first fossils of seed bearing plants appeared in the Carboniferous, some 360 million years ago. The Permian was warmer and drier and the gymnosperm began to diversify because they were better adapted than Lycopods to this type of climate. Gymnosperms dominated the landscape during the Mesozoic era, which began about 250 million years ago. The Mesozoic ended 65 million years ago and the Cenozoic began. A great extinction took place at the end of the Mesozoic, which included the elimination of the dinosaurs. The Cenozoic is dominated by flowering plants but gymnosperms remain an important component of the flora. CHARACTERISTICS OF GYMNOSPERMS

 Stamens consist of a filament and an anther.  Carpels are also referred to as pistils. They consist of an ovary, a style and a stigma. Flowers may be borne singly or in clusters called inflorescence. Flower parts are considered modified leaves. III. DOUBLE FERTILIZATION. It is characteristic of flowering plants. Double fertilization results in the formation of a diploid zygote and a triploid endosperm. The female gametophyte or embryo sac has an egg nucleus and two polar nuclei. One sperm fertilizes the egg nucleus and forms the zygote, 2n. Another sperm joins the two polar nuclei forming the triploid (3n) nutritive tissue called the endosperm. IV. FRUIT CLASSIFICATION. A fruit is a mature ovary. Accessory fruits include other parts in addition to the ovaries, e.g. strawberry, apple, and pear. Simple fruits develop from a single carpel or several united carpels. Aggregate fruits are produced from separate carpels in one gynoecium, e.g. blackberries, magnolia.  The individual parts of the aggregate fruit are known as fruitlets. Multiple fruits consist of several female structures and accessory flower parts that become fused into one fruit, e.g. pineapple, Osage orange. See the angiosperm life cycle on page 600. V. EVOLUTION OF ANGIOSPERMS Angiosperms evolved some 145 million years ago during the early Cretaceous (Mesozoic) or possibly in the late Jurassic. Angiosperm began to dominate the landscape at the end of the Mesozoic and they form now the dominant plant form. There are different opinions about the origin of the angiosperms and their flower.

MONOCOTS have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the embryo. Venation is usually parallel (there are exceptions). Their vascular bundles are scattered throughout the ground tissue. The root system is fibrous. DICOTS have floral parts in multiples of four or five, and their seeds contain two cotyledons. The cotyledons usually absorb the food from the endosperm first, and then provide the food for the embryo. Venation is netted. The vascular bundles in the stem cross-section are arranged in circles (rings). They usually have a taproot system for at leas part of their life. Current research supports the hypothesis that monocots are monophyletic and form a single clade. The dicots, however, appear to be a polyphyletic grouping. Most of the dicots belong to the eudicots. Three lineages of the remaining dicots form what is called the basal angiosperms because they include what are considered to be the oldest lineages. Another group is called the magnoliids. VI. COEVOLUTION OF FLOWERING PLANTS AND ANIMALS. Coevolution is the process by which two or more species act as selective forces on one another and each undergoes evolutionary change. The earliest seed-bearing plants were pollinated. Pollen became a source of food for insects and those flowers that could better attract insects were visited more often thus increasing the chances of passing those characters to the next generation. Any mutation that made those visits more frequent offered a selective advantage. Bisexual flowers have the advantage that visiting insects can pick up pollen from the anthers and deliver pollen from a neighboring plant at the same time. In the early part of the Tertiary, 40 - 60 million years ago, specialized groups of flower-visiting insects became more diverse.