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Explore the crucial adaptations that led to the success of seed plants, from seed production to pollen grains, enhancing reproductive fitness and enabling diverse plant species. Discover the features of gymnosperms and angiosperms, with a focus on their reproductive structures and dispersal methods.
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Seeds and Pollen Grains are Key Adaptations for Life on Land • Seeds are embryos packaged with a food supply in a protective coat
Adaptations that led to success of seed plants • Reduced Gametophyte: • Gametes mostly microscopic • Dependent on the sporophyte for food and protection • Protects anteridia and achegonia, increasing reproductive success
Heterospory: Production of two types of spores • Megaspores produce female gametophytes which produce the egg. • Microspores produce male gametophytes which contain sperm nuclei.
Ovules and Production of Eggs • Megasporangium, megaspore, and the protective tissue around them make up the ovule. • Ovule increases protection of the egg and the developing zygote. • Increases reproductive fitness.
Pollen and the Production of Sperm • A Pollen grain is a male gametophyte. • It contains two sperm nuclei. • Has a waterproof coating, allowing for transfer by the wind. • Water no longer required for sperm transfer.
Seeds • Have many advantages over spores. • Multicellular and many layered • Can provide more protection for devloping embryo • Have a supply of stored energy which allows the seed to wait for good germination conditions. • Stored energy is used for early growth of embryo.
Gymnosperms have “naked” seeds typically on cones • “Naked Seeds” means seeds are not enclosed in ovaries. • Seeds are exposed on modified leaves that form cones • Angiosperms (flowering plants) have seeds enclosed in fruits. • Gymnosperms do not have fruits.
Four Phyla of Gymnosperms • Cycadophyta • Ginkophyta • Gnetophyta
Coniferophyta: • Largest group of gymnosperms • Most are evergreen • Make up large forests in Northern hemisphere at high latitudes and altitude. • Includes the pines, firs, spruces, and redwoods.
Reproductive Adaptations of Angiosperms Include Flowers and Fruits. • Flowering plants are in the phyla Anthophyta • 90% of all plant species are angiosperms.
Major Reproductive Adaptation of Angiosperms is the Flower • Flower consists of four floral organs: • Sepals - protect the flower before emergence • Petals - attract pollinators • Stamens - male reproductive structure produces microspores in the anthers that develop into pollen grains. • Carpels - the female reproductive structure produces megaspores and their products: female gametophytes with eggs.
Fruits • Fruits are mature ovaries. • Seeds develop from fertilized ovules. • The wall of the ovary thickens to become the fruit. • Fruits help disperse the seeds of angiosperms.
Angiosperms are divided into Moncots and Eudicots (dicots) • Monocots have: • One cotyledon in the seed • Parallel leaf veination • Flowering parts in multiples of threes • Vascular bundles are scattered through out the stem.
Dicots have: • Two cotyledons in the seed • Net leaf veination • Flowering parts in multiples of fours or fives. • Vascular bundles are found around edge of stem.
