BIOL 112- Chapter 26

Seed Plants

Gymnosperms

• Plants with naked seeds, partially sheltered by sporophylls

• lack flower and fruits of angiosperms

• have ovule exposed on a scale

• pollination by wind

• vascular system (tracheids)

• alternation of generations

• reduced ***

conifer life cycle (Gymnosperm)

1. female cones grow on upper branches, male on lower

2. ovule one female cone where egg forms. in male, pollen grains are located (each are haploid gametes)

3. pollen tube forms in scale of cone where the pollen grain makes its way to the pollen tube

4. diploid zygote forms and we get a seed

phyla of gymnosperms

• conifero

• cycado

• ***

Coniferophyta

• Conifers

• Most diverse gymnosperms

• Bear cones

  • Male- pollen cone

  • female- ovulate cone

• dominate high altitudes and latitudes in Northern hemisphere

• many are evergreen with needle-like leaves

• ex: pine, fir, spruce, sequoias

cycadophyta

• cycads

• fern/palm-like frond radiate from central stem

• central female and male cones

• flagellated sperm

• beetles involved in pollination of some cycads

gingkophyta

gingkos

one extant tree: ginkgo biolba

herbal medicine

with flagellated sperm

unique fan shaped leaf and veins
female sporophylls- NOT cones

male sporophylls- in strobili

gnetophyta

gnetophytes

3 genera

1. gnetum in tropics

2. welwitschia in SW africa deserts

3. ephedra in US deserts, used for herbal medicine

male and female strobili, sperm not motile

angiosperms

• most diverse

• flower

flower

structure specialized to facilitate s**exual reproduction

• success mainly due to coevolution with pollinators

• stigma is sticky

sepals

green leaf-like appendages that enclose the rest of the flower

petals

brightly colored appendages that aid in attracting pollinators****

angiosperm life cycle

MALE: microsporangia → male sporocytes (2n) → (meiosis) microspores (n) → (mitosis) pollen grains

FEMALEA: ovule → megasporangium → megasporocyte (2n) → meiosis- 4 megaspores (n) → only large megaspore survives → mitosis 3× 8 nuclei distrivuted among 7 cells of female gametophyte → 3 cells at one pole become egg and 2 synergids, last 3 become antipodal cells

center cell → 2 polar nuclei

double fertilization: 2 sperm nuclei→ 1 fuses with egg, forming zygote (2n) and the other fuses with 2 central nuclei forming endosperm ****

fruit

mature ovary of flower, thickens around seeds

• may: have additional tissues, be fleshy or be dry

protects seeds

enhances seed dispersal

phylum anthrophyta

****

Monocots

• include: orchids, palms, lilies, grasses

• 1 cotyledon

• veins usually parallel

• vascular tissue scattered

• root system fibrous (no main root)

• pollen grain with 1 opening

• floral organs in multiples of 3

• woody tissue rarely found

dicots

oaks, peas, roses, potatoes

• 2 cotyledons

• veins usually netlike

• vascular tissue usually arranged in a ring

• taproot (1 main root) usually present

• pollen grain with 3 openings

• floral organs in multiples of 4 or 5

• can be herbaceous (non wood) or woody (toughed walled xylem cells)

carnivorous plants

• pitcher plants

• sundews

• Venus flytrap

parasitic plants

usually lack chlorophyll (white colored)

photosynthesize off of another plant

seed plants

1. gymnosperms

2. angiosperms

• 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

 - Plants are a direct source of medicinal compounds

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

• perfumes

• latex rubber

• Ornamental plants

evolution and history of seed plants

• Seed plants are the Gymnosperms and Angiosperms

• Seed plants first appeared 305–465 MYA

• Angiosperms (flowering plants) are the most recently evolved plants

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

female gametophyte

• Develop within an ovule [contain the egg and endosperm-producing cell (supports the growth of the embryo)]

• Enclosed within diploid sporophyte tissue in angiosperms 

male gametophyte

• Within pollen grains (contain the sperm of the plant)

• Protected from desiccation

• Not dependent on water to reach the female organs

gametophytes + sporophytes: mosses and other nonvascular plants

gametophytes + sporophytes: ferns and other seedless vascular plants

gametophytes + sporophytes: seed plants

Reduced & Retained Gametophytes 

• Seed plants are heterosporous: 

  • megaspores (grow into female gametophytes) 

  • microspores (grow into male gametophytes) 

• Both gametophytes mature within sporangia

  • highly reduced in size   

  • protected from drying & UV

seed

Develops from fertilized ovule  

• includes: embryo, food supply, seed coat 

ovule

Ovule = integument + megasporangium + megaspore
Megaspore germinates within ovule, develops into tiny female gametophyte – produces egg which will eventually be fertilized

pollen grains

3. male gametophyte surrounded by pollen wall (partly secreted by sporophyte).

• Capable of long dispersal, tough & resistant, & sperm nuclei does not require external H₂O for fertilization

• Sporopollenin in the pollen wall protects pollen grains

pollination

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

Pollen grain germinates → Pollen tube → Sperm discharged into female gametophyte