Text Chapter 16, pp 319 - 34 Study Guide pp 190 - 98, # 4 - 60 PLANTS, AND THE MOVE ONTO LAND
Colonizing Land • Plants • Are terrestrial organisms. • Are multicellular eukaryotes that make organic molecules by photosynthesis. • Living on land poses different problems than living in water does. • Plants require structural specializations, such as roots and shoots.
Life on Land • Structures that help adapt plants to life on land include roots, shoots, leaves, and flowers. Figure 16.2
Roots both anchor plants and absorb water and minerals for the plant. Contain vascular tissue for transporting vital materials. Roots • Most plants have mycorrhizae, symbiotic fungi associated with their roots, that increase their absorption potential.
Shoots support the body of the plant and hold leaves and flowers above the soil. Also contain vascular tissue for transporting vital materials. Leaves Are the main photosynthetic organs of most plants. Have stomata for gas exchange. Also contain vascular tissue for transporting vital materials. Shoots and Leaves
Leaf Structure • Most leaves are broad and flat to maximize absorption of light for photosynthesis. • Running through the leaf are veins, tough vascular tissues which transport water in the xylem and sugars in the phloem. Figure 16.4
Flowers • Flowers are specialized leaves that contain the sexual reproductive structures in a plant. • In plants, but not algae, the zygote develops into an embryo while still contained within the female parent.
The Evolution of Plants • Molecular evidence suggests that plants evolved from green algae. • The move onto land and the spread of plants to diverse terrestrial environments were incremental. • The fossil record chronicles four major periods of plant evolution. Each period represents a major adaptational change
The first period - the origin of plants from their aquatic ancestors. This is represented by the Bryophytes, non-vascular plants, or mosses. • The second period - the diversification of vascular plants. This is represented by seedless, vascular plants, or ferns. • The third period - the origin of the seed. This is represented by gymnosperms, the naked-seed, cone-bearing plants, or evergreens. • The fourth period - the emergence of flowering plants, or angiosperms. Flowering plants are also noted by the presence of fruits, and are the most successful type of plants today.
Bryophytes • Mosses • Are the most familiar bryophytes. • Mosses display two key terrestrial adaptations: • A waxy cuticle that helps prevent dehydration • The retention of developing embryos within the mother plant’s gametangium.
Mosses have two distinct forms: • The gametophyte, which produces gametes • The sporophyte, which produces spores
The life cycle of a moss exhibits an alternation of generations.
Ferns • Ferns • Are seedless vascular plants.
Gymnosperms • The gymnosperms • Include the conifers, cone-bearing plants. • Are usually evergreens, which retain their leaves throughout the year. • A pine tree or other conifer is actually a sporophyte with tiny gametophytes living in cones.
Terrestrial Adaptations of Seed Plants • Conifers and most other gymnosperms have three terrestrial adaptations: • Further reduction of the gametophyte (to a cone) • The evolution of pollen • The advent of the seed
Angiosperms • Angiosperms supply nearly all of our food and much of our fiber for textiles. • More efficient water transport and the evolution of the flower help account for the success of the angiosperms. • The dominant stage of the angiosperms is a sporophyte with gametophytes in its flowers. • The seed being enclosed within an ovary distinguishes angiosperms from gymnosperms.
The Life Cycle of an Angiosperm Figure 16.18
A fruit • Is a ripened ovary. • Helps protect the seed and increase seed dispersal. • Is a major food source for animals.
Angiosperms and Agriculture • Angiosperms • Provide nearly all our food. • Supply fiber, medications, perfumes, and decoration. • Agriculture • Is a unique kind of evolutionary relationship between plants and animals.
Plant Diversity as a Nonrenewable Resource • The exploding human population is extinguishing plant species at an unprecedented rate. • Humans depend on plants for thousands of products including food, building materials, and medicines. • Preserving plant diversity is important to many ecosystems as well as humans.