Download Ch. 20 Plant Diversity II: The Evolution of Seed Plants

Ch. 30 Plant Diversity II: The
Evolution of Seed Plants
The seed replaces the spore
Spores used for first 100 million years
of plant life on land
A seed is a resistant structure that is
multicellular and is more complex
Overview
Seed plants are vascular plants
Produce seeds
Three Important Reproductive adaptations



Advent of seed
Evolution of pollen
Reduction of Gametophyte (produce gametes)
Reduction of Gametophyte
Alteration of
generations:
2N vs. 4N life stage


Gametophyte:
haploid cell,
Sporophyte: dipliod
cell
Reproductive Adaptations
Gametophytes of seedless vascular plants
develop is soil independently
Gametophytes of seed plants are protected in
reproductive tissue of sporophyte generation
Seeds for dispersing offspring
Solution for resisting harsh climates
Sporophyte embryo w/ food supply w/I protective coat
Two types of sporangia produce 2 spores

Megasporangia: megaspores; give rise to female
gametophyte, kept w/ parent
 Integument cover megasporangium

Microsporangia: microspores; give rise to male gametophyte
Ovule: integument, megasporangium, megaspore
Pollen
Microspore develop into pollen grain
Pollination: transfer of pollen to ovule
•Two Clades of seed plants (seeds/pollen)
•Gymnosperm
•Angiosperms
Gymnosperms
Means naked seeds
Mesozoic era “age of gymnosperm”
There are four divisions



Cycad – resemble palms
Ginkgo – fanlike leaves, gold and decidous in
autumn
Gnetophyta – 3 genera not closely related
 Weltwitshcia, gnetum, gnetophyta

Conifers
Phylum Cycadophyta
Resembles palms
trees
Cycads
Phylum Ginkophyta
Fanlike leaves, deciduous,
Phylum Gnetophyta
Three Genera



Welwitschia: giant strap like leaves
Gnetum: tropical trees, vines
Ephedra: a shrub of American deserts
Conifers
Cones Latin conus, cone and ferre, to carry
Pines, firs, spruces, larches, most large trees
Most are evergreen, retain leaves for year
Needle shaped leaves, thick cuticles,
Most pulp and paper come from conifers
Largest and oldest organism on earth
Largest phylum of plants
Figure 30.8a Phylum Coniferophyta: Douglas fir
Oregon
Most used for timber
Figure 30.8b Phylum Coniferophyta: Sequoia
2500 metric tons
14 blue whales
40,000 people
Figure 30.8bx Sequoias
Figure 30.8c Phylum Coniferophyta: Cypress
Figure 30.8d Phylum Coniferophyta: Pacific yew
Source of Taxol (treatment of ovarian cancer)
Figure 30.8e Phylum Coniferophyta: Common juniper
Fleshy sporophylls cones
Figure 30.8f Phylum Coniferophyta: A pine farm
Clones from cell culture produce seedlings
Figure 30.8g Phylum Coniferophyta: Wollemia pine
Thought to be extinct till found in 1994
40 individuals, in two small groves
“Living Fossil”
Life Cycle of Pine: Step 1
•Pollen cones and Ovulate cones
•Pollen has microsporangia
•Meiosis
•Pollen grains
•Ovulate contains
•Scales each w/ 2 ovules
•Megasporangim
•Pollination
•Pollen falls on ovulate cones
•Drawn into ovule
•Pollen grain germinates forming pollen tube, digest its
way through megasporangium
•Fertilization occurs 1 year after pollination
Life Cycle Part 2
Megaspore mother
cell produces 4
megaspores, only
one survives.
Two archegonia
develop each w/ egg
Pollinization occurs
Life Cycle Part 3
•New sporophyte has
rudimentary
•Roots
•Embryonic
leaves
•Food Supply
(female
gametophyte)
•Ovule developed into
Pine seed
•Embryo (new
sporphyte)
•Three Plant
Generations:
•One Gametophyte
•Two Sporophyte
Figure 30.10 A closer look at pine cones (Pinus sp.)
Figure 30.10x1 Pine Sporangium with spores
Pollen Grain
Figure 30.10x3 Pine embryo
Angiosperms: Flowering Plants
Most diverse and widespread
Vascular seed plants producing a flower.
Most diverse and widespread

250,000 known species (720 known gymnosperms)
There are two classes of angiosperms


Monocots- lillies, orchids, yuccas, palms, and
grasses
Dicots- roses, peas, buttercups, sunflowers, oaks,
maples
Refinements of Angiosperms
Better xylem, better
tracheids.
Fiber cell for support
of tracheids.
Vessel Elements
more efficient.
Strong role in
adaptations leading
to flowers and fruits.
Flowers: reproductive organ
Reproductive structure of
angiosperm

Flower: specialized shoot w/
4 modified leaves
 Sepals: green, enclose flower
before it opens
 Petals: bright colors, Attractor,
sterile, surrounds sporophyll
(fertile)
 Stamen: produce microspore,
give rise to male gametophyte.
 Carpels: female sporophyll,
produces megaspore, give rise
to female gametophyte
Carpel Evolution: Theory
Fruit
Mature Ovary



Develops from Ovule
Protects dormant seed
Aids in dispersal
Modifications:


(flower withers, fruit develops)
Pericarp: wall of ovary, thickened wall of fruit
Pollination does not occur, no fruit develops
Figure 30.16 Fruit adaptations that enhance seed dispersal: Red berries (left),
dandelion (right)
Figure 30.16x1 Dandelion seed dispersal
Figure 30.16x2 A bird eating berries containing seeds that will be dispersed later with
the animal's feces
Fruit Classifications:
Fruits have several types



Simple Fruit: fruit from single ovary. Cherry,
soybean pod
Aggregate Fruit: single flower that has several
carpels. Blackberry.
Multiple Fruit: group of flowers clustered together.
Walls of ovaries thicken and fuse
together…..become one fruit. Pineapple

Inflorescence
Life cycle of an angiosperm
Pollen Grain
Ovule
Embryo Sac
Cross pollination: same species, different
plant


Stamen/Carpel mature at different time
Arragment prevents self pollination
Double Fertilization: 2 sperm pollinate single
ovule, triploid nucleus
Figure 30.17 The life cycle of an angiosperm
Figure 38.1 Simplified overview of angiosperm life cycle
Flowers:
Complete flowers have all four basic floral
organs
Incomplete flowers lacking one or more floral
organs
•Bisexual Flower: equipped with both stamen and carpel
•Trillium
•Unisex Flower: missing either stamen or carpel
•Monoecious: stamen and carpel are located on
same individual plant
•Dioecious: stamen and carpel located on
separate plants
Figure 38.4 The development of angiosperm gametophytes (pollen and embryo
sacs)
Figure 38.7 Genetic basis of self-incompatibility
Figure 38.9 Growth of the pollen tube and double fertilization
Figure 38.10 The development of a dicot plant embryo
Figure 38.11 Seed structure
Coevolution
Angiosperms and Animals have
influenced each other.
Mutual evolution b/w two species is
CoEvolution:


Pollinator/Plant relationships
Monkey and the Fig
Figure 30.18 Flower-pollinator relationships: Scottish broom flower and honeybee
(left), hummingbird (top right), baobab tree and bat (bottom right)
Plants and Humans
Agriculture based mostly on
angiosperms
Nonrenewable source


Space for people vr. Plants
Slash and Burn
 50 million acres of tropical rain forest cut down
per year (state of Washington)
 Source of medicine resource
Figure 30.19 Deforestation is an international practice
Figure 30.19x Deforestation
Table 30.2 A Sampling of Medicines Derived from Plants