Ch. 22: Plant Growth, Reproduction & Response

Ch. 22: Plant Growth, Reproduction & Response

generally reproduce sexually, though many can also reproduce asexually. Some have lost ability to reproduce sexually. All plant lifecycles involve alternation of generations.

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 s female reproductive structures.

Bryophytes Alternation of generations (Fig. 13.7, p. 337): Haploid (n) gamete-producing phase (gametophyte)) alternates with diploid (2n) spore-producing producing phase (sporophyte( sporophyte). All sexually-reproducing plants exhibit this life cycle.

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.

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.

Bryophytes

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).

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

Vascular Divided into two groups: 1. Those that produce spores (not seeds) Includes club mosses, horsetails, ferns. Like bryophytes, these need water for fertilization to occur. 2. Those that produce seeds

Non Seed-producing Vascular Spots on underside of fern fronds = sori: reproductive structures where haploid spores are produced. 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.

Non Seed-producing Vascular

Seed-producing Vascular Those that produce seeds: 1. Gymnosperms/conifers (naked seeds in cones): includes pines, firs, spruces, ginkgos, cycads. a. Coniferophyta: cone-bearing; bearing; pines, firs, spruces. b. Ginkgophyta: : ginkgos c. Cycadophyta: : cycads 2. Angiosperms/flowering plants (phylum Anthophyta): seeds enclosed in fruit

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. Fig.).

Ch. 22: Sexual Reproduction in

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.

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.

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.

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: a. Tube cell b. Sperm cell that divides to produce two haploid sperm nuclei

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.

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.

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. Fig. 22.7, p. 671). Fertilization occurs when one sperm nucleus fuses with the egg. Pollination Fertilization

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.

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.

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 s waste products.

Yucca and Pronuba Moth

Composite flowers:

Composite Flowers Family Compositae:

Composite Flowers

Angiosperms are found in widely different environments. Several adaptations have contributed to their success. 1. Dominant diploid stage in the life cycle allows for the development of complex structures. 2. Evolution of pollen allows for transfer of sperm from plant to plant without need for water. 3. Evolution of the seed protects the dormant embryo and provides food and protection for the young plant. 4. A variety of adaptations that promote pollen and seed dispersal.