Seed ReproductionChapter 7: Section 3

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

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

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

Seed Plants• Two types of seed plants:1. Gymnosperms2. Angiosperms• One difference is the way the seeds develop!– G: Cones– A: Flowers & Fruit

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

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

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!!

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

Flowers

• Flowers are pretty and full of sweet smells• Some are drab and have no smell• Have 4 main parts:1. Petals2. Sepals3. Stamen4. Pistil

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

Parts of a Flower

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

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

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

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

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

Review Questions

1. Compare and contrast life cycles of gymnosperms and angiosperms.

2. Describe the 3 parts of a seed and their functions. 3. Explain the process of germination. 4. 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?

5. How can animals spread pollen?6. Where are the ovules found in the flower?