Chapter 22: Introduction to Plants

1. Chapter 22: Introduction to Plants Sections 1-4

2. What is a plant? • Organisms in Kingdom Plantae are eukaryotes that have cell walls containing cellulose and carry out photosynthesis using chlorophyll a and b

3. Plant Needs • Sunlight –photosynthesis • Leaves broad and flat, arranged on stem to maximize light absorption • Gas exchange –oxygen for cellular respiration, carbon dioxide for photosynthesis • Gases exchanged with atmosphere/soil without losing too much water • Water and minerals – structures limit water loss, faster uptake of water from soil; some have specialized tissues to carry water/nutrients

4. The History and Evolution of Plants • Ancestors of land plants water-dwellers, similar to green algae • Simpler, have cell walls, identical photosynthetic pigments, similar reproductive cycles to plants • So genetically similar they should be plants • First land plants had a water problem – grew close to ground in damp places, dependent on water for life cycle • Several groups evolved – one line lead to mosses, another to ferns, cone-bearing plants and flowering plants

5. Overview of Plant Kingdom • Five major groups based on embryo formation, specialized water-conducting tissues, seeds, and flowers

6. The Plant Life Cycle • Alternation of generations – shifting between a diploid (2n) phase and a haploid (n) phase

7. The Plant Life Cycle • Multicellular diploid called sporophyte produces haploid spores by meiosis • Spores grow into multicellular haploids called gametophytes • Gametophytes produce gametes – egg and sperm • Zygote forms through fertilization, which develops into new sporophyte

8. Trends in Plant Evolution • Reduction in gametophyte size, increase in sporophyte size

9. Green Algae Characteristics • “Algae” refers to any photosynthetic eukaryote other than a land plant • Classified in group of seedless plants • Mostly aquatic (fresh and salt) or on land in damp/moist areas • Absorb moisture and nutrients directly from surroundings – no specialized tissues

10. Green Algae Life Cycle • Many alternate between haploid and diploid forms, but not necessarily with each generation • Example: Chlamydomonas • Favorable conditions – haploid cell reproduces asexually by mitosis • Unfavorable conditions – switches to sexual reproduction • Cells fuse to form zygote (sporophyte) with thick protective covering which will grow when conditions improve, divide by meiosis into 4 haploids

11. Green Algae Life Cycle

12. Multicellularity • Green algae can form colonies • Spirogyra form filaments • Volvox form colonies of up to 5000 – shows some specialization

13. Mosses and Other Bryophtyes • Mosses have protective coating that makes them resistant to drying, rhizoids to anchor them to soil and absorb water and minerals

14. Bryophytes • Group including mosses, liverworts, and hornworts • Specialized reproductive organs enclosed by nonreproductive cells • Higher degree of cell specialization • Among first land plants • Small because they do not make lignin, which is used to harden cell walls, and do not have vascular tissues

16. Bryophyte Life Cycle • Alternation of generations • Gametophyte dominant, sporophyte depends on it • Produce sperm cells with flagella for swimming so water must be present at some point in year • When a moss spore lands in a moist place, it grows into a gametophyte • Forms rhizoids that grow into ground, shoots that grow into air

17. Bryophyte Life Cycle • Gametes formed at tips of gametophyte • Eggs produced in archegonia • Sperm produced in antheridia • Egg/sperm fuse to form diploid zygote – beginning of sporophyte stage • Sporophyte grows within gametophyte – dependent • Eventually grows out of gametophyte, develops stalk ending in sporangium • Sporangium produces haploid spores by meiosis • Spores released

19. Vascular Plants • Plants growing high above ground appeared ~ 420 mya • Had vascular tissues – carry water and nutrients more efficiently than bryophytes • Vascular plants called tracheophytes because of tracheids – water-conducting cells that are hollow, tube-like, cell walls strengthened with lignin • Tracheids arranges end to end make up xylem, the tissue that carries water upwards from the roots – pits between tracheids increase water movement • Phloem is the other vascular tissue – transports solutions of nutrients and photosynthetic products

20. Seedless Vascular Plants • Three phyla, commonly known as club mosses, horsetails, and ferns (most) • Ferns have vascular tissues, strong roots, rhizomes (stems underground), fronds • Thrive with little light • Wet environments

21. Fern Life Cycle • Spores produced by the sporophyte grow into thin, heart-shaped haploid gametophytes (independent) • Sperm/eggs produced on gametophytes in antheridia and archegonia • Sperm swim to eggs – water needed • Zygote develops into a new sporophyte plant (dominant) • Haploid spores develop on the undersides of the fronds in sporangia

23. Fern Spores

24. Seed Plants • Seeds contain tiny living plant ready to sprout • Plant embryo and a food supply – diploid, early stage sporophyte • Common ancestor for all modern seed plants • Ability to survive on dry land – developed adaptations • Cones and flowers • Pollen • Seeds

25. Cones and Flowers • In seed plants, male and female gametophytes grow/mature within sporophyte – in cones or flowers • Gymnosperms (naked seeds – cone-bearing plants) bear seeds on scales of cones • Angiosperms (flowering plants) bear seeds in flowers within protective tissue

26. Pollen • Male gametophyte is contained in a pollengrain • Carried to the female reproductive structure by wind or animals • The transfer of pollen from the male reproductive structure to the female reproductive structure is called pollination

27. Seeds • After fertilization, the zygote within seed grows into a tiny plant (sporophyte embryo) • A tough seed coat surrounds and protects the embryo, keeps it from drying out • The embryo begins to grow when conditions are right • Uses nutrients from stored food supply until it can carry out photosynthesis on its own

28. Gymnosperm Life Cycle • Seeds exposed on scaled within cones • Reproduction occurs in cones produced by mature sporophyte • Pollen cones (male) produce pollen grains (male gametophyte) • One haploid nucleus within pollen grain later divides to produce 2 sperm nuclei

29. Gymnosperm Life Cycle • Seed cones (female) produce female gametophytes • Scales contain 2 ovules , where meiosis produces haploid cells that develop into female gametophytes • Each gametophyte contains multiple egg cells • In spring, pollen cones release pollen grains which are carried by wind • Female cones secrete sticky substance to trap pollen which is pulled inside the ovule • Fertilization without open water

30. Gymnosperm Life Cycle • Pollen grains landing near ovules split open, grow a structure called a pollen tube containing 2 haploid sperm nuclei • Once the pollen tube reaches the female gametophyte, one sperm nucleus disintegrates; the other fertilizes the egg • Zygote develops into embryo • Seed encases embryo, dispersed by wind

32. Flowers and Fruits • Angiosperms most abundant plants • Most recent to evolve • Develop flowers, which contain ovaries to surround and protect seeds

33. Advantages of Flowers • Flowers attract pollinators • More efficient than relying on wind • After pollination, ovary develops into a fruit, containing at least one mature embryo • Wall of fruit helps distribute seeds – animals eat, seeds go through digestive system • Increases range

34. Angiosperm Classification • Used to be classified by numbers of leaves in their embryos – cotyledons • Monocots – one cotyledon • Dicots – two cotyledons

35. Angiosperm Classification • Now, monocots single group, dicots in several

36. Characteristics of Monocots and Dicots

37. Woody and Herbaceous Plants • Differences in stems • Woodyplantsare made of cells with thick cell walls that support the plant body • Herbaceousplantshave stems that are smooth and nonwoody

38. Annuals, Biennials, and Perrenials