Seed Reproduction

1. Seed Reproduction Chapter 7: Section 3

2. Importance of Seeds & Pollen • Fruits and vegetables that we eat come from seed plants • All flowers are produced by seed plants • Most of the plants on Earth are seed plants • How do you think they became such a successful group? • Reproduction involving pollen and seeds

3. Pollen • In seed plants, some spores develop into small structures called pollen grains • Pollen grains have water resistant coverings and male gametophyte parts that produce sperm • Sperm (pollen) are carried by gravity, wind, water currents or animals • Transfer of pollen grains to female part of plant is called pollination • After pollen grain reaches female part, sperm and pollen tube are produced • Sperm moves through pollen tube then fertilization occurs

4. Seeds • After fertilization the female part of a plant can develop into a seed • Seed has embryo, stored food, & seed coat • Embryo has structures that eventually form stem, leaves, & roots • Embryo grows to a certain stage then stops until seed is planted • Stored food provides energy for plant when it begins to grow • Plants develop more rapidly from a seed than from a spore

5. Seed Plants • Two types of seed plants: • Gymnosperms • Angiosperms • One difference is the way the seeds develop! • G: Cones • A: Flowers & Fruit

6. Gymnosperms • Gymnosperm plant seeds develop into cones • Cones are reproductive structures of gymnosperms • Each gymnosperm species has a different cone • Includes pines, firs, spruces, cedars, cycads, and gingkoes

7. Cones • Pine trees are Sporophyte plants that produce male and female cones • Male and female gametophyte structures are produced in cones but you’d need a magnifying glass to see them clearly • Mature female cone has spiral of woody scales & short stem • 2 ovules are base of each scale • Pollen grains are produced in smaller male cones • Clouds of pollen released from male cones in spring

8. Gymnosperm Seeds • Pollen is carried from male cones to female cones by wind • To be useful the pollen has to be blown between the scales of a female cone • Its trapped in a sticky fluid secreted by ovule • If the pollen and female cone are same species, fertilization can occur • Crackling noise as cones release seeds • Releasing of seeds can take 2-3 years!!

9. Angiosperm Reproduction • Most of the seed plants on Earth today are angiosperms • All angiosperms have flowers • Sporophyte plant produces the flowers • Flowers are reproductive organs • Contain gametophyte structures that produce sperm or eggs

10. Flowers • Flowers are pretty and full of sweet smells • Some are drab and have no smell • Have 4 main parts: • Petals • Sepals • Stamen • Pistil

11. Flowers • Petals: colorful parts of flower • Sepals: leaf-like parts outside of petals • Stamen: male reproductive organ inside flower; also where pollen is produced • Pistil: female reproductive organ • Ovary : swollen base of pistil that contains ovules • NOT ALL PLANTS HAVE ALL 4 PARTS

12. Parts of a Flower

13. Importance of Flowers • Appearance of flowers can say a lot about a plant • Large, bright, colorful flowers attract insects & bugs • As they crawl along the flower, pollen gets all over their bodies • Insects visit more flowers and take the pollen with them

14. Angiosperm Seeds • Figure 16 on page 219 • Pollen grains reach stigma in variety of ways • Plants are pollinated when pollen reaches sticky stigma • Pollen tube grows from pollen grain down through the style, enters the ovary, and reaches an ovule • Sperm travels down the tube and fertilizes egg in ovule • Zygote forms and grows into plant embryo

15. Seed Dispersal • Plants have many ways of dispersing seeds • Gravity is how many seeds get dispersed • Wind dispersal is another way seeds move • Animals can disperse many seeds • Passed through digestive system • Carried and buried great distances • Attached to feathers, fur, or clothing • Water: raindrops knock seeds out of fruits • Float on water

16. Germination • Once the seed is dispersed, what happens next?... • Germination: Series of events that result in growth of plant from a seed • Can occur in a few days or in weeks or months • Some seeds stay in a resting stage for years • Will not occur until environmental conditions are right • Temperature, presence or absence of light, water, amount of oxygen affect germination

17. Germination • Begins when seed tissues absorb water • Seed swells and coat breaks open • Chemical reactions occur that release energy from stored food in seed • Eventually roots grow from the seed, followed by the stem and leaves • Once the plant emerges, photosynthesis can begin

18. Review Questions • Compare and contrast life cycles of gymnosperms and angiosperms. • Describe the 3 parts of a seed and their functions. • Explain the process of germination. • Walnut trees produce edible seeds with a hard outer covering. Maple trees produce seeds with wing-like edges. What type of seed dispersal applies to each type of tree? • How can animals spread pollen? • Where are the ovules found in the flower?