Plant Reproduction

1. Plant Reproduction Chapter 24

2. Chapter 24 Vocabulary 24.1 • Pollen Cone • Seed Cone • Ovule • Pollen Tube • Sepal • Petal • Stamen • Filament • Anther • Carpel • Ovary • Style • Stigma • Embryo Sac • Endosperm • Double Fertilization 24.2 • Dormancy • Germination 24.3 • Vegetative Reproduction • Stolon • Grafting • Budding

3. Reproduction with Cones & Flowers Chapter 24.1

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

5. 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).

6. Gymnosperm Life Cycle • Takes place in cones, which are produced by a mature sporophyte plant. • Pollen Cones = Male Cones • Produce Male Gametophyte = Pollen Grains • One pollen grain will divide to produce two sperm nuclei. • Seed Cones = Female Cones • 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. Female Cone Cone Anatomy Male Cone

8. Gymnosperm Life Cycle

9. Gymnosperm 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.

10. Gymnosperm Fertilization & 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.

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

12. Flowers: Sepals & 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.

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

14. Flowers: 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.

15. Angiosperm Life Cycle • 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.

16. Angiosperm Life Cycle Cont… • 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.

17. Angiosperm Life Cycle Cont… • 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.

18. Angiosperm Life Cycle

19. Angiosperm Pollination & Development • 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.

20. Seed Development & Germination Chapter 24.2

21. Essential Questions • How do seeds develop and germinate?

22. Seed & Fruit Development • After fertilization, nutrients flow into the flower tissue and support the development of the growing embryo within the seed. • As angiosperms seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds. • A fruit is a ripened ovary that contains angiosperm seeds. • It refers to any seed that is enclosed within its embryo wall. • The ovary wall may be fleshy (grapes, tomatoes, peaches) or tough (pod of a bean).

23. Seeds & Fruits Cont… • Some seeds are rigidly attached to the surface of the seed and some dry and form an aerodynamic shape like a maple seed. • Parts of the ovule toughen to form the seed coat, which is the outer layer of that protects the delicate embryo and its food supply • The ovary wall thickens and may join with other parts of the flower stem. • The structures together form a fruit that encloses the seeds.

24. Seeds & Fruits Cont…

25. Seed Dispersal • Seeds spread by animals when the seed is contained in a fruit that entices them to eat it and thus spread the seeds. • Animals include insects, birds, and mammals. • Seeds spread by animals tend to be enclosed in fleshy, nutritious fruits that provide nutrition for the animal that eats it. • Seeds pass through digestive tract and sprout in the feces of the animals. • Advantageous to plant because it helps get the seed away from the parent plant – less competition and is more efficient than seeds spread by the wind. • Seeds spread by wind and water tend to be lightweight allowing them to be carried by the air or float on the surface of water.

26. Anatomy of a Seed

27. Seed Dispersal Methods

28. Pollinators

29. Seed Dormancy • Dormancy – embryo is alive but not growing. • Length of dormancy varies by species. • Environmental factors such as temperature and moisture can cause a seed to end its dormancy and germinate. • Adaptation for plants because it allows for long-distance dispersal, temperature extremes (forest fires), etc.

30. Seed Germination • Germination - early growth stage of plant embryo. • Early seeds absorb water causing food-storage to swell, cracking open the seed coat. • The young root begins to grow and the seed leaves (cotyledon) emerges. • Monocot – one seed leaf (cotyledon). • Dicot – two seed leaves – two ways of germination.

31. Monocot vs. Dicot Germination

32. Monocot Seed Germination • Monocots grow straight up with sheath covering shoot. • One embryonic leaf. • Seed remains underground.

33. Dicot Seed Germination • Two ways dicots grow: • cotyledon emerges above the ground and protects the plant (pumpkin). • cotyledon remains underground and provides food source for growing seedling (bean).

34. Embryo Anatomy • Epicotyl - Grows into the leaves of the plant • Hypocotyl - Becomes the stem • Radicle - Becomes the root

35. Plant Propagation & Agriculture Chapter 24.3

36. Essential Questions: • What is vegetative reproduction? • Describe plant propagation.

37. Vegetative Reproduction • Vegetative reproduction: method of asexual reproduction that produces new plants from stems, plantlets, and underground stems. • Plant grows by mitosis alone – no sexual reproduction. • Enables plant to produce many offspring that are genetically identical to itself. • Plants can reproduce very quickly since it does not involve pollination or seed formation.

38. Vegetative Reproduction Cont… • Plants can also reproduce by growing horizontal stems called stolons. • Ex – Strawberry Plants • Stolons produce roots when they touch the ground. • Some plants like bamboo grow underground stems that allow plants to send up new shoots.

39. Strawberry Plant - Stolon

40. Plant Propagation • Propagation uses cuttings, grafting, or budding to make many identical copies of a plant or to produce offspring from seedless plants. • Plant hormones are often used to stimulate cuttings to grow. • Grafting and budding are used to reproduce seedless plants and woody plants that do not produce strong root systems.

41. Plant Propagation Cont… • A piece of stem is cut from the parent plant and attached to another plant. • The cut piece is called the scion and the plant to which it is attached is called the stock. • When wood stems are used as scions, the process is called grafting. • When buds are used as scions, the process is called budding. • Grafting works best when plants are dormant because wounds created can heal before new growth starts.

43. Agriculture • Agriculture is the systematic cultivation of plants. • Developed about 10,000 to 12,000 years ago. • Agriculture is the principal occupation of humans. • Most people of world depend on a few crop plants such as wheat, rice, and corn for the bulk of their food supply. • About 80% of US cropland is used to grow just four crops: corn, wheat, soybeans, and hay.