Chapter 24 Reproduction of Seed Plants

1. Chapter 24Reproduction of Seed Plants 24.1 Reproduction with Cones and Flowers

2. Essential Questions • What are the reproductive structures of gymnosperms and angiosperms? • How does pollination differ between angiosperms and gymnosperms?

3. Alternation of Generations • All plants have a life cycle in which a diploid sporophyte generation alternates with a haploid gametophyte generation • Gametophyte plants produce male and female gametes • When the gametes join, they form a zygote that begins the next sporophyte generation • In seed plants the diploid sporophyte is the recognizable plant. • The gametophyte is hidden inside of the cones (gymnosperms) and flowers (angiosperms).

4. Figure 24-4

5. Figure 24-1

6. Life Cycle of Gymnosperms • Takes place in cones, which are produced by a mature sporophyte plant. • Pollen cones are male cones and produce male gametophytes, which are called pollen grains. • One pollen grain will divide to produce two sperm nuclei. • Seed cones are female and produce female gametophytes. • Ovules in which the female gametophyte develops are found near the base of each scale. • When mature, the ovules contain a few large egg cells, each ready for fertilization by the sperm nuclei.

7. Male and Female Pine Cones Male Cone Female Cone

8. Pollination • The gymnosperm life cycle takes two years to complete. • The cycle begins in the spring as the male cones release enormous numbers of pollen grains. • The wind carries the pollen to the female cones and are caught in a sticky secretion called the pollination drop.

9. Fertilization and Development • If a pollen grain lands near an ovule, the grain splits open and begins to grow a pollen tube, which contains two haploid sperm. • Once the pollen tube reaches the female gametophyte, one sperm disintegrates and the other fertilizes the egg contained within the female gametophyte. • More than one egg cell can be fertilized but only one embryo will develop. • Fertilization produces a diploid zygote– the new sporophyte plant.

10. Structure of Flowers • Flowers are reproductive organs that are composed of four kinds of specialized leaves: sepals, petals, stamens, and carpels.

11. Sepals and Petals • Outermost circle of floral parts contains the sepals, which are green and resemble leaves. • Sepals enclose the bud before it opens and protects the flower while it is developing. • Petals are found just inside the sepals and are often brightly colored to attract insects and other pollinators to the flower. • Sepals and petals are sometimes called sterile leaves because they do not produce reproductive cells.

12. Stamens • Stamen is the male part and produces the haploid male gametophyte • consists of an anther and a filament • filament is a long, thin stalk that supports the anther • anther is an oval sac found at tip of filament and is where meiosis takes place, producing make gametophytes i.e. pollen grains

13. Carpels • Carpel is the female part and produces the haploid female gametophyte • innermost flower parts, also called pistils • Each carpel has a base that forms an ovary containing ovules that produce female gametophytes • A narrow stalk called the style attaches the ovary to the stigma • Stigma is a sticky portion on the end of the style where pollen grains land

14. Life Cycle of Angiosperms • Begins when mature sporophyte produces flowers • Each flower contains anthers and an ovary • Inside anthers, each cell undergoes meiosis and produces four haploid spore cells • Each of these cells becomes a pollen grain with a thickened cell wall to protect it when it is released from the anther • Nucleus undergoes one mitotic division to produce two haploid nuclei

15. Cont’d • Ovary contain the ovules in which female gametophyte develops • A single diploid cell goes through meiosis to produce four haploid cells, three of which disintegrate • Remaining cell undergoes mitosis to produce eight nuclei • Eight nuclei and surrounding membrane are called embryo sac

16. Cont’d • Embryo sac is contained within ovule and is the female gametophyte • The egg nucleus, near the base of the gametophyte, is the gamete and will become the zygote if fertilization takes place • The zygote grows into a new sporophyte plant also called a seedling.

17. Figure 24-7

18. Pollination • Once gametophytes have developed inside the flower, pollination takes place. • Most gymnosperms and some angiosperms are wind pollinated • Most angiosperms are pollinated by animals • Animals are mainly insects, birds, and bats that carry pollen from one flower to another • Insect pollination is more efficient than wind pollination