Chapter 30 Plants Part 2

Biology, 7th Edition (Book & CD-ROM)

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Chapter 30 Plant Diversity II The Evolution of Plant Seeds I. Ganetophytes are protected in ovules and pollen grains A. Advantages of Reduced Gametophytes 1. Gametophytes are microscopic 2. The gametophytes develop from spores that are in the sporangia of the parents a. Protects female gametophytes 3. Moist tissues shield gametophytes from drought or UV radiation 4. Dependent gametophytes obtain nutrients from the sporophyte B. Heterospory 1. Megasporangia in megasporophylls produce megaspores that give rise to female gametophytes a. Only one functional megaspore is produced 2. Microsporangia in microsporophylls produce microspores that give rise to male gametophytes a. Vast numbers of microspores produced C. Ovules and Production of Eggs 1. Seed plants retain the megaspore within the parent sporophyte a. Integument (layers of sporophyte tissue) envelop to protect the megasporangium i Gymnosperm megaspores only have one integument ii Angiosperms usually have two integuments 2. Megasporangium + megaspore + integument = ovule a. In each ovule one female gametophyte develops and produces egg cell(s) D. Pollen and Production of Sperm 1. Microspores develop into pollen grain a. Contain male gametophyte of seed plants 2. Protected by the polymer sporopollenin 3. Methods of Travel a. Wind b. When an animal visits to feed on plant 4. When the pollen grain germinates it discharges two sperm into the female gametophyte within the ovule 5. Female gametophyte never leaves sporophyte ovule, and male gametophytes can travel long distances E. Evolutionary Advantage of Seeds 1. Seed = embryo + food supply + protective coat (integuments) 2. Able to resist harsh environments\ 3. Disperse offspring in a wider area 4. Seeds may remain dormant for a long long time until situation is stable for them to germinate II. Gymnosperms (naked seeds) A. Cycadophyta 1. Second largest group of gymnosperms 2. Have large cones and palm-like leaves 1
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3. 130 species as of today B. Ginkgophyta 1. Only one living species left: Ginkgo biloba 2. Fan-like leaves which turn gold in autumn 3. Popular ornamental tree 4. Female trees SMELL because of seeds C. Gnetophyta 1. Gnetum a. 35 species of tropical shrubs, trees, and vines b. Native to Africa and Asia c. Leaves look like those of flowering plants, seeds look like fruits 2. Ephedra a. 40 species b. Inhabit arid region world wide c. Have medicinal uses 3. Welwitchia a. One species left: Welwitchia mirabilis b. Lives in the deserts of southwest Africa D. Coniferophyta 1. 600 species 2. Most keep leaves through the year
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Chapter 30 Plants Part 2 - Chapter 30 Plant Diversity II...

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