gymnosperms “naked seeds” i can: describe the characteristics of gymnosperms do now: list two...

GYMNOSPERMS

“Naked Seeds”

I can: Describe the characteristics of gymnosperms

• Do Now: List two similarities and two differences between mosses and ferns:

• HW: Check webpage for worksheet

2

Gymnosperms: General Characteristics

Vascular

Alternation of generations– Dominant sporophyte – Reduced, dependent gametophyte

Produce uncovered seedsPollen-

4 main groups of Gymnosperms

Cycads

Gingko

Conifers

Gnetophytes

Cycads

• Only 100 living species

• Cones

Strobilus of a “female” cycad

Ginkgos

One surviving species, Ginkgo biloba

Deciduous: lose their leaves during the winter

Seeds are completely exposed

Gnetophytes

• Cone clusters resemble flower clusters

• Parts of life cycle more like angiosperms– Welwitschia –

grows in Namib desert (So. Africa).

– Live up to 2000 years

Conifers

• Widest known, largest number of living species

• Woody trees or shrubs

• Most are evergreen – Keep their leaves all year-round

• Bear seeds on exposed cone scales

• Most produce woody cones

I can: describe the characteristics of gymnosperms

• Do Now: Give three characteristics of gymnosperms.

The Importance of Pollen and Seeds

• Oak, maple, and other shade trees are seed plants.

• All flowers are produced by seed plants. In fact, most of the plants on Earth are seed plants.

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• How do you think they became such a successful group? Reproduction that involves pollen and seeds is part of the answer.

Pollen• In seed plants, some

spores develop into small structures called pollen grains.

• A pollen grain has a water-resistant covering and contains gametophyte parts that can produce the sperm.

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Pollen

• The sperm of seed plants are carried as part of the pollen grain by gravity, wind, water currents, or animals.

• The transfer of pollen grains to the female part of the plant is called pollination.

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Pollen

• After the pollen grain reaches the female part of a plant, sperm and a pollen tube are produced.

• The sperm moves through the pollen tube, then fertilization can occur.

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Seeds• A seed consists of

an embryo, stored food, and a protective seed coat.

• The embryo has structures that eventually will produce the plant’s stem, leaves, and roots.

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Seeds

• The stored food provides energy that is needed when the plant embryo begins to grow into a plant.

• A new plant can develop more rapidly from a seed than from a spore.

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Gymnosperm Reproduction

• Cones are the reproductive structures of gymnosperms.

• Each gymnosperm species has a different cone.

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• The pine is a familiar gymnosperm.

Cones

• A pine tree is a sporophyte plant that produces male cones and female cones.

• Male and female gametophyte structures are produced in the cones but you’d need a magnifying lens to see these structures clearly.

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Cones

• A mature female cone consists of a spiral of woody scales on a short stem. At the base of each scale are two ovules.

• The egg is produced in the ovule.

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• Pollen grains are produced in the smaller male cones.

Pine Cones

• Woody scales of a “pine cone” are the parts where megaspores formed and developed into female gametophytes

• Male cones, where microspores and pollen are produced, are not woody

Pine Cones

Gymnosperm Seeds

• Pollen is carried from male cones to female cones by the wind.

• To be useful, the pollen has to be blown between the scales of a female cone.

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• If the pollen grain and the female cone are the same species, fertilization and the formation of a seed can take place.

Gymnosperm Seeds

• It can take a long time for seeds to be released from a female pine cone.

• From the moment a pollen grain falls on the female cone until the seeds are released, can take two or three years.

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The Life CycleOf a

Gymnosperm