Plant Diversity & Evolution (Outline)

Transcription

1 Plant Diversity & Evolution (Outline) Characteristics of organisms in the Kingdom Plantae. Evolution of plants: Challenges and adaptations to living on land Highlights of plant evolution of the four groups of plants. Distinguishing features of mosses, ferns, cone-bearing, and flowering plants. Haploid and diploid cells and structures in plants: gametophyte and a sporophyte genetic content, cell division and resulting cells. Life cycle of mosses, ferns, cone-bearing, and flowering plants: Structural adaptations Alternation of haploid and diploid in early plants with that of later plants in relation to: The haploid or diploid nature of the cells making up the green leafy part of the plant. Cell division leading to the growth of the green leafy plant. Presence of male and female gametes: their names reflecting mode of dispersal for fertilization and zygote formation. Co-dependence: evolution of animal and land plants. Modern day importance of plants for human existence.

2 Last 0.5 bilion years Cenozoic Humans 0 Colonization of land Origin of solar system and Earth Animals Continental drift changes the land masses on 1 earth and 4 Proterozoic Archaean impact all forms eon eon of life: 2 3 altering habitats and triggered extinctions Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen Prokaryotes Millions of years ago Paleozoic Mesozoic Cenozoic South America Africa Eurasia India Antarctica Laurasia Figure 15.3B

3 Highlights of plant evolution Land plants Bryophytes (nonvascular plants) Seedless vascular plants Vascular plants Seed plants Liverworts Hornworts Mosses Lycophytes (club mosses and relatives) Pterophytes (ferns and relatives) Gymnosperms Angiosperms Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya)

4 Early aquatic photosynthetic organisms - Prokaryotic bacteria - Eukaryotic algae Plants and green algae share a common ancestor LM 444

5 Problems for plant life on land: 1. Water and nutrients are in the ground 2. Carbon dioxide and light are above the ground. 3. Support against the force of gravity 4. Dry conditions will dry out reproductive cells.

6 Early plants thrived on moist shorelines as multicellular eukaryotic organisms developed adaptation not present in algae Plant Reproductive structures, as in flowers, contain spores and gametes Leaf performs photosynthesis Cuticle covering leaves and stems reduces water loss; stomata in leaves allow gas exchange Stem supports plant and may perform photosynthesis Roots anchor plant; absorb water and minerals from the soil Surrounding water supports alga Whole alga performs photosynthesis; absorbs water, CO 2, and minerals from the water Holdfast anchors alga Alga Sea lettuce a multi cellular algae

7 Plants have adaptations for life on land Access to inorganic molecules by two specialized organs 1. Roots that anchoring the plant and absorb nutrients and water from ground 2. Shoots (stems and leaves) to support the leaves that access light and CO 2 for photosynthesis.

8 Some plants have vascular tissue to distribute water and nutrients from ground to leaves and sugar from leaves to the rest of plant body

9 1. Supporting the Plant Body against gravity Thickened cell walls of some plant tissue- lignin 2. Protection against dehydration of plant cells- Maintaining Moisture A waxy cuticle covers the stems and leaves of plants and helps retain water Stomata are tiny pores in leaves that allow for gas exchange 3. Protection of gametes from dehydration Many living plants produce gametes that are encased in protective structures

10 Evolution of Land Plants 1. Non-vascular plants - mosses 2. Vascular plants a. Seedless- ferns b. Seed forming Early land plants - naked seed- conifers (firs and pines) - Flowering plants- fruit bearing All have a life cycle that includes a haploid and a diploid stage.

11 Bryophytes lack vascular tissue and include mosses, hornworts, and liverworts

12 Key Haploid (n) Diploid (2n) Gametophyte plant (n) Sperm Spores (n) Gametes (n) Egg Meiosis Fertilization Zygote (2n) Sporophyte plant (2n)

13 Key Haploid (n) Diploid (2n) Gametophyte plant (n) Sperm Spores (n) Gametes (n) Egg Meiosis Fertilization Zygote (2n) Sporophyte plant (2n)

14 Life cycle of a moss Key Haploid (n) Diploid (2n) 5 Mitosis and development Gametophytes (n) Male 1 Sperm (n) (released from gametangium) Spores (n) Female 1 Egg (n) Fertilization Sporangium Stalk Sporophytes (growing Meiosis from gametophytes) 4 Sporophyte (2n) 2 Zygote (2n) 3 Mitosis and development

15 Haploid and diploid generations alternate in plant life cycles 1. The haploid gametophytes (separate male and female green leafy plants) produce gametes (eggs and sperms) by mitosis 2. The zygote develops into the diploid sporophyte (not green) on the female gametophyte plant and produces haploid spores by meiosis 3. Spores grow by mitosis into the haploid male and female gametophyte plants

16 MOSSES Mosses have a dominant green gametophyte A mat of moss is mostly two separate haploid gametophyte plants: female plants produce eggs male plants produce swimming sperm The zygote develops on the female green gametophyte into the smaller diploid sporophyte

17 Ferns are seedless vascular plants with flagellated sperm (water-dependent for sexual reproduction)

18 FERNS Ferns, like most plants, have a dominant sporophyte Sperm, produced by the male gametophyte swim to the protected egg in the female gametophyte Sporophyte depends on the gametophyte only very early Mature sporophyte is independent of gametophyte Both the gametophyte and the mature sporophyte are green and free living

19 Life cycle of a fern Key Haploid (n) Diploid (2n) 5 Mitosis and development Meiosis Spores (n) 1 Gametophyte (n) (underside) Egg (n) Sperm (n) (released from male gametangium) Female gametangium (n) Fertilization 4 Clusters of sporangia Mature sporophyte (independent of gametophyte) New sporophyte (2n) growing out of gametophyte 3 2 Zygote (2n) Mitosis and development

20 Seedless plants dominated vast coal forests Ferns and other seedless plants once dominated ancient forests their remains formed coal

21 Seed plants - Have pollen grains instead of flagellated sperm - Protect their embryos in seeds Cone-bearing Flowering plants

22 Cone-bearing plants Gymnosperms Conifers -naked seed plants (example: pine) Gingkos Cycads A pine tree is a sporophyte (diploid) with tiny gametophytes (haploid) in its cones A male gamete is a pollen grain (does not swim) fertilizes an ovule in the female gametophyte The zygote develops into a sporophyte embryo and becomes a seed, with stored food and a protective coat

23 Life cycle of a pine tree 1 Female cone bears ovules. Pollen grains (male gametophytes) (n) Meiosis Ovule 4 A haploid spore cell in Scale ovule develops into female gametophyte, which makes eggs. Meiosis Sporangium (2n) Spore mother cell (2n) Integument Eggs (n) 3 Pollination Sperm (n) Male gametophyte (pollen grain) Female gametophyte (n) 5 Fertilization Male gametophyte (pollen) grows tube to egg and makes and releases sperm. 2 Sporangia in male cone produce spores by meiosis; spores develop into pollen grains. Mature sporophyte Seed coat Key Haploid (n) Diploid (2n) 7 Embryo (2n) Food supply Seed germinates, and embryo grows into seedling. Seed 6 Zygote develops into embryo, and ovule becomes seed. Zygote (2n)

24 Dispersal of pollen and fertilized naked seeds depends on wind Both pollen and seeds of gymnosperms have wing-like structures and can be airborne

25 Flowering plants Angiosperms The angiosperm plant is a sporophyte with gametophytes in its flowers The flower is the centerpiece of reproduction A male gamete is a pollen grain (does not swim) fertilizes an ovule in the female gametophyte The flower is modified into a fruit once fertilization takes place, with the zygote developing into a sporophyte embryo and becomes a seed, with stored food and a protective coat

26 Flowers usually consist of: sepals, petals, stamens (which produce pollen), and carpels (which produce eggs) Anther Stamen Filament Stigma Style Ovary Carpel Petal Sepal Receptacle Ovule

27 Stigma Anther Life cycle of an angiosperm 1 Haploid spores in anthers develop into pollen grains: male gametophytes. Pollen grains (n) 3 Pollination and Meiosis growth of pollen tube Stigma 2 Haploid spore in each ovule develops into female gametophyte, Pollen grain which produces egg. Pollen tube Meiosis Egg (n) Sporophyte (2n) Ovule Ovary Ovule 7 Seed germinates, and embryo Seeds grows into plant. Sperm 6 Fruit (mature ovary) Key Haploid (n) 5 Seed Diploid (2n) Food supply Seed coat Embryo (2n) Fertilization 4 Zygote (2n)

28 Angiosperms evolved in the presence of insects and other animals 1. Pollen has no wing-like structures. Depend on insects and birds for pollination. 2. Seeds don t have wing-like structure. Depend in addition on dispersal by animals either physically or by eating fruits and dispersing their seeds over long distance with their feces. 3. Interactions with animals have profoundly influenced flowering plant evolution, a major source of food for animals

29 Animals also aid plants in pollination

30 The structure of a fruit reflects its function in seed dispersal fruits are adaptations for seed dispersal

31 Angiosperms provide 1. food produced by agriculture 2. important medicinal products

32 Some plants in these forests contain chemicals that have medicinal uses