Chapter 26 : The Seed Plants: Gymnosperms & Angiosperms

Describe the evolutionary history of seed plants for each era. How did the climate change throughout this?

Describe the Female gametophyte in seed plants and its structure. What function to these structures serve?

• The egg

• Endosperm-producing cell (supports the growth of the embryo)

• Embryo – produced from the diploid zygote, grows into the sporophyte when seed germinates

• Seed - offers the embryo protection, nourishment, and a mechanism to maintain dormancy, allow plants to disperse the next generation through both space and time

Describe the Male gametophyte in seed plants

• Pollen grains (contain the sperm of the plant)

• Protected from dessication

• Not dependent on water to reach the female organs

How do the Gametophyte and Sporophyte differ in mosses and other nonvascular plants compared to ferns and other seedless vascular plants?

• Mosses and other nonvascular plants

  • Gametophyte: Dominant

  • Sporophyte: Reduced, dependent on gametophyte for nutrition

• Ferns and other seedless vascular plants

  • Gametophyte: Reduces, independent (photosynthetic and free-living)

  • Sporophyte: Dominant

Describe the gametophyte and sporophyte of seed plants. What do they look like in Gymnosperms and Angiosperms?

• Gametophyte: reduces( usually microscopic), dependent on surrounding sporophyte tissue for nutrition

• Sporophyte: Dominant

What does it mean for seed plants to be heterosporous? Describe heterosporous spore production.

• Seed plants are heterosporous:

  • megaspores (grow into female gametophytes)

  • microspores (grow into male gametophytes)

• Heterosporous spore production

  • Megasporangium in megasporophyll → Mgeaspore → Female gametophyte → Eggs

  • Microsporangium in microsporophyll → Microspore → Male gametophyte → Sperm

Where do both gametophytes mature and why?

• Both gametophytes mature within sporangia

  • highly reduced in size

    • protected from drying & UV

What structures is the ovule composed of and how does the Megaspore eventually produce an egg?

• Ovule = integument + megasporangium + megaspore

• Megaspore germinates within ovule, develops into tiny female gametophyte – produces egg which will eventually be fertilized

Where does the seed develop from. What is included in the seed?

• Develops from fertilized ovule

• includes: embryo, food supply, seed coat

What are pollen grains? What in the pollen wall protects the pollen grains?

• Pollen grains: male gametophyte surrounded by pollen wall (partly secreted by sporophyte)

  • Capable of long dispersal, tough & resistant

• Sporopollenin in the pollen wall protects pollen grains

True or false: The sperm nuclei in the pollen grain requires external H2O for fertilization.

FALSE. It does not require external H2O.

What are the 3 steps of fertilization in pollen grains? Define pollination.

1. Pollen grain germinates

2. Pollen tube

3. Sperm discharged into female gametophyte

Pollination: transfer of a pollen to a part of the seed plant that contains the ovule

Describe Gymnosperms: What do they look like, how do they pollinate, what does their life cycle look like, and what cell they have in their xylem

• ‘Naked’ seeds (partially sheltered by sporophylls)

• Separate male and female gametes

• Pollination by wind

• Tracheids: long, tube-shaped cells in the xylem of vascular plants that transport water and minerals and provide structural support

• Life cycle involves alternation of generations

Describe the gametophytes and sporophytes of Gymnosperms, heterosporous/homosporous, and their reproductive organs

• Reduced male and female gametophytes

• Dominant sporophyte

• All are heterosporous

• Male and female reproductive organs can form in cones or strobili

• Monoecious (has both male and female reproductive organs on the same individual) or Dioecious(has male and female reproductive organs on separate individuals)

What is the life cycle of a Conifer? (gymnosperm)

Describe differences between Gymnosperms and Angiosperms. Give 3 examples for Gymnosperms and 1 for Angiosperms.

• Gymnosperms

  • Non flowering

  • naked seed

  • EX: Conifers, cycads, Ginkgos

• Angiosperms

  • Flowering

  • Covered seed

  • EX: all flowering plants

What are the Five Phyla of Extant Seed Plants. Which ones are Gymnosperms and which ones are Angiosperms?

• Gymnosperms:

  • Coniferophyta

  • Cycadophyta

  • Gnetophyta

  • Ginkophyta

• Angiosperms:

  • Anthophyta

Describe the Phylum Coniferophyta: common name, female and male structures, environment, appearance, 4 examples

• “conifers”

• Most diverse gymnosperms today

  • “cone-bearers”

    • male pollen cone (sperm not motile)

    • female ovulate cone

• dominate high altitudes & latitudes in N. Hemisphere

• most are evergreen with needle-like leaves

• EX: pine, fir, spruce, sequoias

Describe Phylum Cycadophyta (cycads): appearance, female and male structures, pollination method

• fern-like or palm-like fronds radiate from central stem

• central female & male cones

• with flagellated sperm

• beetles are involved in pollination of some cycads

Describe the Phylum Ginkgophyta - ginkgos: appearance, what are they used in, what structure does the sperm have, male and female structures, one example

• unique fan-shaped leaf & veins

• herbal medicine

• with flagellated sperm

• female sporophylls, not cones

• male sporophylls, in strobili

• one extant tree: Ginkgo biloba

Describe the Phylum Gnetophyta: gnetophytes: what are the 3 distinct genera, male and female structures, 1 example

• 3 distinct genera:

  1. Gnetum in tropics

  2. Welwitschia in SW Africa deserts

  3. Ephedra in U.S. deserts

• male & female strobili; sperm not motile

• Ephedra - herbal medicine (Ephedrine)

What are the two key innovations of Angiosperms?

flowers & fruits

What is the purpose of the flower in Angiosperms? Why is it a successful innovation? Define each structure in the flower: sepals, petals, stamen, filament, anther, carpel, stigma, style, ovary, ovules

• Sepals – green leaf-like appendages that enclose the rest of the flower

• Petals – brightly colored appendages that aid in attracting pollinators

• Stamen:

  • Filament – stalk that holds up pollen-producing sac

  • Anther – terminal sac that produces pollen

• Carpel (aka “pistil”):

  • Stigma – sticky tip of carpel that receives pollen

  • Style – long tube leading from stigma to ovary

  • Ovary – structure at base of the carpel that produces ovules

  • Ovules - develop into seeds if fertilized

Fill in the blank

Describe the Life cycle of Angiosperms: from Microsporangia to Pollen grains, From Ovule to 2 polar nuclei

• Microsporangia → Male sporocytes (2n) -(meiosis)→ Microspores (n) -(mitosis)→ Pollen grains

  • Pollen grains: 1 generative cell, 1 tube cell

• Ovule → Megasporangium → Megasporocyte (2n) -(meiosis)→ 4 Megaspores (n) → Only large megaspore survives -(mitosis x3)→ 8 nuclei distributed among 7 cells of female gametophyte → 3 cells at one pole become egg and 2 synergids (remaining 3 cells become antipodal cells) → Center cell → 2 polar nuclei

How does double fertilization happen in angiosperms?

• double fertilization with 2 sperm nuclei:

  • one fuses with egg, forming zygote(2n)

  • one fuses with 2* central nuclei (polar nuclei), forming endosperm (3n*) food supply in seed

What is a fruit and what is its purpose in Angiosperms? Give 5 examples.

• Fruit - mature ovary of a flower, thickens around seeds

  • may include some additional tissues as well

  • may be fleshy or dry

  • protects seeds

  • main function is enhancing seed dispersal

  • EX: Tomato, Ruby grapefruit, Nectarine, Milkweed, Hazelnut

What are the two big groups of angiosperms? What are some examples from each group?

• The 2 big groups of angiosperms are the Monocots (~60,000 spp.) & the Eudicots ( ~ 175,000 spp.)

  • Monocots include orchids, palms, lilies, grasses…

  • Dicots include… lots! (oaks, peas, roses, potatoes, etc.)

Describe the differences between Monocots and Eudicots in the following structures: tissue, embryos, leaf venation, stems, roots, pollen, flowers

• Tissue

  • Monocots: True woody tissue is rarely found

  • Eudicots: can be herbaceous (non woody) or produce woody tissues – tough walled xylem cells

• Embryos

  • Monocot: One cotyledon

  • Eudicot: Two cotyledons

• Leaf venation

  • Monocot: Veins usually parallel

  • Eudicot: Veins usually netlike

• Stems

  • Monocot: Vascular tissue scattered

  • Eudicot: Vascular tissue usually arranged in a ring

• Roots

  • Monocot: Root system usually fibrous (no main root)

  • Eudicot: Taproot (main root) usually present

• Pollen

  • Monocot: Pollen grain with one opening

  • Eudicot: Pollen grain with three openings

• Flowers

  • Monocot: Floral organs usually in multiples of three

  • Eudicot: Floral organs usually in multiples of four or five

How do humans use seed plants?

• Almost all food & beverages & spices

  • (80% calories globally!)

• Wood products, including paper

• Fuel

• Fiber for clothing, rope

  • cotton, linen, jute, hemp

• Secondary compounds:

  • countless drugs & medicines

    • In the United States, about 25% of prescription drugs contain an active ingredient from plants

  • perfumes

  • latex rubber

• Ornamental plants