Ch. 22: Plant Growth, Reproduction & Response

1. Ch. 22: Plant Growth, Reproduction & Response

2. Ch. 22: Sexual Reproduction in Plants • Plants generally reproduce sexually, though many can also reproduce asexually. • Some have lost ability to reproduce sexually. • All plant lifecycles involve alternation of generations.

3. Ch. 22: Sexual Reproduction in Plants Simple plants (Bryophytes, e.g. mosses, hornworts, liverworts): • Most of life = haploid (Fig. 12.9, p. 326). • Require moist environment for reproduction, as sperm must swim through wet soil to reach plant’s female reproductive structures.

4. Bryophytes Alternation of generations(Fig. 22.1, p. 664): • Haploid (n) gamete-producing phase (gametophyte) alternates with diploid (2n) spore-producing phase (sporophyte). • All sexually-reproducing plants exhibit this life cycle.

5. Bryophytes Gametophyte: haploid individual that produces gametes; either male or female • Male gametophyte produces sperm that swim to egg (produced in female gametophyte). • Fertilization occurs in female gametophyte; diploid zygote is produced  embryo. • Developing embryo grows into stalklike sporophyte. • Some spp.: both eggs and sperm produced on same gametophyte.

6. Bryophytes Sporophyte: diploid individual that results from fertilization of gametes; produces haploid spores. • Spores transported to favorable location; germinate; develop by mitosis into haploid gametophyte plants. • Cycle repeats.

7. Bryophytes

8. Bryophytes • Bryophytes are relative newcomers among plant taxa (Earliest bryophyte fossils = 350 MYO). • Are apparently not the ancestors of vascular plants (which were around 50 – 100 MY earlier than bryophytes, according to the fossil record).

9. Ch. 22: Sexual Reproduction in Plants Vascular Plants: • More complex • Contain vascular tissue (specialized cells joined into tubes for the transport of water and minerals).

10. Vascular Plants Divided into two groups: • Those that produce spores (not seeds) • Includes club mosses, horsetails, ferns. • Like bryophytes, these need water for fertilization to occur. • Those that produce seeds

11. Non Seed-producing Vascular Plants • Spots on underside of fern fronds = sori: reproductive structures where haploid spores are produced (Fig. 22.3, p. 666). • Spores fall to ground and grow into haploid plants that produce male and female gametes. • Sperm require water to swim to the female ova. • Fertilization  zygote  develops into new diploid fern.

12. Non Seed-producing Vascular Plants

13. Seed-producing Vascular Plants Those that produce seeds: • Gymnosperms/conifers (naked seeds in cones): includes pines, firs, spruces, ginkgos, cycads (Fig. 22.4, p. 667). • Coniferophyta: “cone-bearing;” pines, firs, spruces. • Ginkgophyta: ginkgos • Cycadophyta: cycads • Angiosperms/flowering plants (phylum Anthophyta): seeds enclosed in fruit

14. Ch. 22: Sexual Reproduction in Plants Complex plants: • Adapted to wider variety of habitats. • Dominant portion of lifecycle is large diploid plant. • Haploid stage is small tissue in reproductive organs, where the ova are protected (Fig. 22.7, p. 671).

15. Ch. 22: Sexual Reproduction in Plants

16. Ch. 22: Sexual Reproduction in Plants

17. Ch. 22: Sexual Reproduction in Plants • Sperm need not swim through wet soil, as wind or symbiotic animals like bees, bats, butterflies, even humans can carry sperm to female organs. • Pollen: tough, protective package which carries sperm.

18. Ch. 22: Sexual Reproduction in Plants Angiosperms (flowering plants; Fig. 22.5 p. 668): • Most successful group of plants. • Haploid cells in flowers produce gametes. • Individual flowers may produce sperm, ova, or both.

19. Ch. 22: Sexual Reproduction in Plants

20. Ch. 22: Sexual Reproduction in Plants ♀ flower: • Carpel (AKA pistil): hollow structure made of modified leaves fused edge to edge (Fig. 22.7, p. 671). • Ovary is located at base of this structure. • Inside ovary are ovules. Ova develop inside ovules. • Within each ovule a specialized cell undergoes meiosis  four haploid cells. • Three of these cells disintegrate; fourth divides by mitosis  seven cells. • One of these seven cells will become the ovum; another (a large cell containing two nuclei) is the polar body.

21. Ch. 22: Sexual Reproduction in Plants ♂ flower: • Stamen is made up of the anther and the filament. • Anther: enlarged tip of the stamen in a flower, inside which pollen grains containing sperm form. • Cells in the anther undergo meiosis  four haploid cells (Fig. 22.7, p. 671). • Each haploid cell divides by mitosis to form a pollen grain containing: • Tube cell • Sperm cell that divides to produce two haploid sperm nuclei

22. Ch. 22: Sexual Reproduction in Plants Fertilization: • Anthers shed pollen which may be carried by wind (e.g. pines), or by insects, bats, or other animals (e.g. flowering plants) to carpel of the same or different plants. • Pollination: transfer of pollen from anther to carpel.

23. Ch. 22: Sexual Reproduction in Plants • Cross-pollination (pollination between two different plants of the same sp.) increases genetic variation by combining chromosomes of two parents. • Many complex mechanisms for pollination have evolved. • Some insects and plants are completely dependent upon one another that they cannot reproduce without the other, e.g. yucca and Pronuba moth.

24. Ch. 22: Sexual Reproduction in Plants Double Fertilization: • When pollen lands on tip of stigma (carpel), the pollen grain germinates and forms a pollen tube that grows toward the ovule, carrying the sperm nuclei (Fig. 22.7, p. 671). • Fertilization occurs when one sperm nucleus fuses with the egg. Pollination ≠ Fertilization

25. Ch. 22: Sexual Reproduction in Plants • This  diploid zygote that divides mitotically  embryo. • Second sperm nucleus fuses with the polar body (w/2 nuclei)  triploid (3n) cell that will  the endosperm.

26. Ch. 22: Sexual Reproduction in Plants

27. Ch. 22: Sexual Reproduction in Plants • Ovule becomes the seed, which is a protective coat around the embryo and endosperm • Auxin, a compound produced by the seeds that stimulates the ovary to enlarge and develop into a fruit.

28. Ch. 22: Sexual Reproduction in Plants Seeds spread in many ways: • Drift along ocean current • Carried by wind, e.g. wind- blown pollen of pine trees. • Some, e.g. cockleburs, stick to animal fur. • Many seeds are eaten by an animal, transported great distances, then pooped out in a new environment – an environment that is automatically fertilized by the animal’s waste products.

29. Ch. 22: Sexual Reproduction in Plants Yucca and Pronuba Moth

30. Ch. 22: Sexual Reproduction in Plants Composite flowers:

31. Composite Flowers Family Compositae:

32. Composite Flowers

33. Ch. 22: Sexual Reproduction in Plants Angiosperms are found in widely different environments. • Several adaptations have contributed to their success. • Dominant diploid stage in the life cycle  allows for the development of complex structures. • Evolution of pollen  allows for transfer of sperm from plant to plant without need for water. • Evolution of the seed  protects the dormant embryo and provides food and protection for the young plant. • A variety of adaptations that promote pollen and seed dispersal.