Plant Diversity II – The Evolution of Seed Plants

1. Plant Diversity II – The Evolution of Seed Plants

2. Seeds and Pollen Grains are Key Adaptations for Life on Land • Seeds are embryos packaged with a food supply in a protective coat

3. 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

4. Heterospory: Production of two types of spores • Megaspores produce female gametophytes which produce the egg. • Microspores produce male gametophytes which contain sperm nuclei.

5. 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.

6. 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.

7. 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.

8. Germinating Seeds

9. Seed Plants are Divided into Gymnosperms and Angiosperms

10. 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.

11. Four Phyla of Gymnosperms • Cycadophyta • Ginkophyta • Gnetophyta

12. 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.

15. Reproductive Adaptations of Angiosperms Include Flowers and Fruits. • Flowering plants are in the phyla Anthophyta • 90% of all plant species are angiosperms.

16. 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.

18. 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.

22. 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.

23. 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.