Download
1 / 177
1.85k likes | 2.35k Views
PLANT DIVERSITY. LAND PLANTS EVOLVED FROM GREEN ALGAE. The Origin of Plants from Algae The closest modern relatives of the ancestors of plants are the green algae, charophytes. Today this species is found around the edges of ponds and lakes.
E N D
LAND PLANTS EVOLVED FROM GREEN ALGAE • The Origin of Plants from Algae • The closest modern relatives of the ancestors of plants are the green algae, charophytes. • Today this species is found around the edges of ponds and lakes. • The theory is that some ancient charophytes might have lived in similar locations that dried out and adapted to the new conditions as plants.
LAND PLANTS EVOLVED FROM GREEN ALGAE • The oldest plant fossil is approximately 475 million years ago. • Modern plants have since diversified and is now a multicellular autotroph in which the embryo develops within the female parent. • Challenges of Life on Land • The differences between plants and charophytes are related to living on land and amount to four challenges.
LAND PLANTS EVOLVED FROM GREEN ALGAE • Obtaining Resources From Two Places at Once • Aquatic organisms and algae get their resources from the surrounding water. • Land plants (photosynthetic) get their resources from air and soil. • Light and carbon dioxide are available above ground. • Water and mineral nutrients are found in the soil. • Shoots and roots allow access to these two environments.
ALGAE vs. PLANTSalgae are simple and unspecialized possessing a holdfast that serves as an anchor, while plants have specialized tissues that perform specific tasks. Plants have a root system that holds it in place and extracts mineral and nutrients from the soil. Algae take up minerals and nutrients directly from the water via diffusion. Algae lack specific reproductive structure while plants have stamens and carpels. Both have photosynthetic properties.
LAND PLANTS EVOLVED FROM GREEN ALGAE • The plant’s roots absorb water, minerals, and nutrients from the soil. • Plant shoots bear leaves above ground which use the sun as energy for photosynthesis. • Most plants have a vascular system that transports the minerals, nutrients, and water between the roots and shoots and leaves. • Staying “Afloat” in Air • Sea weed or kelp (both algae) stay upright because of the buoyancy of the water.
LAND PLANTS EVOLVED FROM GREEN ALGAE • Plants stay upright because of the strong support system they have. • This terrestrial adaptation includes the chemical lignin, which hardens the plants’ cell walls. • Maintaining Moisture • Even though the plant is on soil and exposed to dry air, its cellular processes take place in an aqueous environment. • Plants possess the ability to maintain a watery internal environment. • Examples are the waxy surfaces of a cactus or apple.
LAND PLANTS EVOLVED FROM GREEN ALGAE • A waxy cuticle coats the leaves and other above ground parts, helping maintain water internally. • One negative of this is the slowing down of the exchange of CO₂ and O₂. • The result, therefore, is the exchange of gasses through the stomata, which are microscopic pores in a leaf’s surface. • Two surrounding cells regulate the stoma’s opening and closing., opening only when necessary to prevent evaporation.
LAND PLANTS EVOLVED FROM GREEN ALGAE • An Overview of Plant Diversity • There are four major periods of plant evolution. • The first dealt with the origin of plants from charophytes, their aquatic algal ancestors. • The bryophytes were the first to diversify. • These are the mosses. • These plants don’t have seeds and lack lignin-hardened material. • Vascular plants marked the second period of plant evolution and saw the development of vascular
LAND PLANTS EVOLVED FROM GREEN ALGAE tissue with lignin-hardened vascular tissue that transport water and nutrients. • The third period included the origin of the seed. • Seeds are embryos within a seed coat that also contains a store of food. • Seeds allow for the spread of plants to diverse areas without allowing the embryo to dry out. • Early seed plants included gymnosperms (Gr. for naked seed) that have seeds that develop without being enclosed within a chamber on specialized leaves. • Conifers that produce cones are examples of these. • The fourth period of plant evolution began with flowering plants, or angiosperms.
LAND PLANTS EVOLVED FROM GREEN ALGAE • In angiosperms, the seed develops within a protective organ, the ovary, contrasting with the gymnosperm’s naked seeds. • Alternation of Generations • Plant generations alternate between diploid (2n) and haploid (n) forms. • Recall that diploids have two sets of chromosomes, one from each parent. • Haploids have one set as a result of meiosis. • In the plant life cycle, the haploid and diploid forms are distinct, multicellular generations.
LAND PLANTS EVOLVED FROM GREEN ALGAE • Animals have a unicellular haploid stage, a single sperm or egg cell. • The haploid generation of plants produces gametes called gametophytes. • The diploid generation produces spores called sporophytes. • In the plant’s life cycle, each generation takes turns giving rise to the other. • The alternation between the haploid and diploid forms is called the alternation of generations.
LAND PLANTS EVOLVED FROM GREEN ALGAES • Spores differ from gametes in two ways. • Spores can develop into new organisms without fusing with another cell. • Gametes must fuse together to produce a zygote. • Spores of some plants have tough coats that enable them to resist harsh environments and lay dormant. • Gametes cannot tolerate harsh environments and lay dormant. • Alternation of generations occurs only in life cycles of plants and certain algae.
REVIEW: CONCEPT CHECK 19.1, page 424 • Name the group of algae most closely related to plants. What is a major difference between plants and algae? • Make a table listing the four major challenges to plants living on land. In the second column, list at least one plant adaptation for each challenge. • List the four main groups of plants and describe two characteristics of each. • List the difference between the sporophyte and gametophyte plant generations.
POLLEN AND SEEDS EVOLVED IN GYMNOSPERMS • Gymnosperm Adaptations • Gymnosperms have adapted with a smaller gametophyte, pollen, and seeds for survival on land. • Gymnosperms are plants that bear seeds that are not enclosed in an ovary (naked). • Here the diploid sporophyte generation is more highly developed than the haploid generation.
POLLEN AND SEEDS EVOLVED IN GYMNOSPERMS • Pine trees are sporophytes in which tiny gametophytes live in cones. • Pollen is a second adaptation of seed plants to dry land. • Pollen is male gametophytes that contain cells that develop into sperm. • Wind carries the pollen in many plants, including the conifer. • Evolution has allowed plants on dry land to
POLLEN AND SEEDS EVOLVED IN GYMNOSPERMS • develop pollen so that sperm can reach eggs (female cone in the case of conifers) without swimming through water. • Seeds are plant embryos surrounded by a protective coat that includes a food supply within its confines. • In the pine tree’s cones, there are many spore sacs, thousands of haploid spores that develop into pollen grains (male gametophytes).
POLLEN AND SEEDS EVOLVED IN GYMNOSPERMS • The female gametophytes develop in the ovules. • Within each of the two ovules on each scale of the female cones, a large spore cell undergoes meiosis and produces four haploid cells. • One of these will survive and grow into the female gametophyte. • The pollen will travel from tree to tree by the wind.
POLLEN AND SEEDS EVOLVED IN GYMNOSPERMS • If a pollen grain reaches the female cone, sperm cells mature and fertilize egg cells within the female gametophyte. • More often than not, both eggs in the ovule will be fertilized but only one develops into an embryo. • The embryo is then the new sporophyte plant. • The Diversity of Gymnosperms • Four gymnosperm phyla exist today.
POLLEN AND SEEDS EVOLVED IN GYMNOSPERMS • Ginkgos • Date back to dinosaur era • Tolerates city pollution well • Gnetophytes • Usually located in desert locale • Cycads • Sago palms • Conifers • Evergreens like spruce, pine, firs, juniper, cedar, redwoods • Leaves replace only when old ones die.
REVIEW: CONCEPT CHECK 19.4, page 433 • Name three adaptations of gymnosperms and the advantages they provide. • Make a table listing the four different gymnosperm groups and a beneficial use or fact about each one.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • Angiosperm Adaptations • These were the last major group of plants to evolve. • Angiosperms are flowering plants where the reproductive structures are flowers, not cones like the gymnosperms. • The gametophytes develop within the flowers of the sporophyte. • The flower is specialized to function in reproduction and is unique to angiosperms.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • Flowers are structured to attract insects and other animals to transfer pollen from one flower to the next. • The following contribute to the interactions between angiosperms and the animal pollinators: • Variety of flower • Shape of flower • Odor • Texture • Color
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • Grasses, an angiosperm, are wind pollinated but have flowers which are smaller and less of an attraction than those pollinated by animals. • The stamen is the male reproductive organ of a flower. • This consists of a filament on which the anther, which produces the pollen or male gametophyte, sits. • The carpel is the female reproductive organ and is composed of the stigma, style, and ovary.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • Within the ovary, ovules or female gametophytes (embryo sacs) develop. • Referring to the slides with the stages of the life cycle of an angiosperm, the following is a description. • During reproduction, the pollen lands on the sticky stigma. • A tube then grows from each pollen grain down the style toward an ovule in the ovary.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • Two sperm cells in the pollen are released into the female gametophyte. • One sperm fertilizes an egg cell, producing a zygote, which then develops into an embryo. • The second sperm cell fuses with nuclei in the larger center cell of the female gametophyte, which then develops into a nutrient-storing tissue called endosperm. • This endosperm nourishes the embryo as it grows. • This is “double fertilization” and simultaneously produces the zygote and endosperm.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • The seed then develops from this whole ovule, containing the zygote and endosperm. • Some flowers contain many ovules and can produce many seeds. • This development of seeds within ovaries is in contrast to the gymnosperm's “naked” seed development. • As the seeds develop from the ovules, the ovary wall thickens and forms a fruit the surrounds the seeds. • A fruit is the ripened ovary of a flower. • Fruits provide protection and a means of dispersal of the seeds.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • The Diversity of Angiosperms • Biologists, at one time, divided angiosperms into monocots and dicots. • These differ in the structure of the leaves, flowers, seeds, roots, and vascular tissue • Recent advances have added information to expand the cladogram. • Some flowering plants descended from ancestors that evolved earlier than the oldest known monocot or dicot.
FLOWERS AND FRUITS EVOLVED IN ANGIOSPERMS • Human Dependence on Angiosperms • All fruit and most vegetables are angiosperms that provide the food that supports life. • Corn, rice, wheat, and other grains are fruits of grasses. • Angiosperms provide furniture, medicines, perfumes, decorations, and cotton fiber.
REVIEW: CONCEPT CHECK 19.5, page 437 • Define and give examples of a fruit and a flower. • Name three examples of monocots and three examples of dicots. • Make a list of benefits angiosperms offer humans. • Explain what is meant by the term double fertilization.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE TO ANGIOSPERM SUCCESS • Flowers and Reproduction • Most flowers share the same basic pattern. • Flowers are specialized shoots found only in angiosperms the usually consist of four different rings of modified leaves: sepals, petals, stamens and carpels. • The sepals cover and protect the flower bud before it opens. • The next ring is the petals, which are colorful, and in some cases, have markings to direct the insect toward the reproductive parts.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE TO ANGIOSPERM SUCCESS • The stamens and carpels, the reproductive parts, are closest to the center of the flower. • Most flowers have multiple stamens and one carpel. • Some plants, like wild roses, have more than one carpel. • The male gametophytes are produce within the stamens. • The stamen is composed of the filament and the anther. • In the anther, meiosis produces spores that become pollen, the male haploid gametophytes.
