Class Notes-10-19-09
Transport in xylem and Phloem
Two types of vascular tissue
Xylem- conducts most of the water and minerals and includes dead cells called tracheids, act as
pipes
Phloem- consists of living cells and distributes sugars, amino acids, and other organic products
Evolution of Roots
Anchor vascular plants
Enable absorption of water and nutrients from soil
May have evolved from subterranean stems
Evolution of Leaves
Increase the surface area of vascular plants, increase photosynthesis
Vascular Tissue
Allowed plants to grow taller
Allowed for the formation of branches
Sporophylls and Spore Variations
Sporophylls are modified leaves with sporangia
Most seedless vascular plants are homosporous, produce one type of spore that develops into a
bisexual gametophyte
All see plants and some seedless vascular plants are heterosporous, having two types of sports
that are male and female gametophytes
Seedless Vascular Plant Classification
Phylum Lycophyta
Club mosses, spike mosses, and quillworts
Phylum Pterophyta
Ferns, horsetails, whisk ferns
Phylum Lycophyta
Giant lycophyta thrived for millions of years in moist swamps
Surviving spieces are small herbaceous plants
Phylum Pterophyta
Ferns are diverse, with more than 12,000 species
Most diverse in tropics but also thrive in temperate forests
Some species are adapted to arid climates
The Significance of Seedless Vascular Plants
Ancestors of modern lycophytes, horsetails and ferns grew to great heights during the
Carboniferous, first forests
Forests may have helped produce the global cooling at end of Carboniferous Period
Undecayed plants of Carboniferous forests became coal
Modern peatlands also sequester atmospheric carbon
Destruction of peatlands adds to global warming
The Evolution of Seed Plants
Spore and Seed: Differences
Spore
Single celled, embryonic gametophyte (n)
Result of mitosis (after meiosis), 4 spore lines
Gametophytes are fragile, microspores must swim to megaspore, requires water
Seed
Embryonic sporophyte, multicellular, differentiated
Result of fertilization (2n), each is unique
Sporophytes often more resistant to desiccation
Seed Plant Modification
Dominant sporophyte generation
Reduction of gametophytes to single cells
Gametophytes develop within the walls of spores retained within parent sporophyte
Gametophyte is protected from desiccation
Drawback- microspore (pollen) must have a vector
Heterospory
Produce both megaspore and microspore on same plant
Megaspores give rise to female gametophyte (ovule)
Ovule consists of megasporangium, megaspore, protective integuments
Micropsores give rise to male gametophytes (pollen)
Microspores develop into pollen grains
Pollination
Transfer of pollen to ovules
Can be dispersed by air or animals, eliminate water requirement
Upon germination, it grows a pollen tube with two sperm nuclei
Evolutionary Advantage of Seeds
Seed develops from the whole ovule
Seed is a sporophyte embryo and food supply in protective coat
Gymnosperms
“Naked” seeds, born in cones
Four Phyla:
Cycadophyta- cycads or tree ferns
Gingkophyta- one living species: gingko biloba
Gnetophyta- specialized for desert living
Coniferophyta- conifers: pine, firs, redwood
Gymnosperm Evolution
Progymnosperms in Devnian Period
True gymnosperms in early carboniferous
Dominated Mesozoic terrestrial ecosystems
Life Cycle of a Pine- Key Features
Dominance of sporophyte generation
Seeds develop from fertilized ovules
Transfer of sperm to ovules by pollen
Angiosperms- flowers and fruits
Have reproductive structures- flowers and fruits
A single phylum- anthophyta
The most widespread and diverse of all plants
Flowers
Structures specialized for sexual reproduction
Has up to 4 types of modified leaves
Sepals (calyx)- encloses the flower
Petals (corolla)- brightly colored and attract pollinators
Stamens (androecium)- produce pollen
Carpels (gynoecium)- produce ovules
Fruits
A fruit consists of a mature ovary but can also include other flower parts
Protect seeds and aids in dispersal
Mature fruits can be either fleshy or dry
Dispersal
Various fruits adaptations help disperse seeds
Seeds can be carried by wind, water, or animals to new locations
The Angiosperm Life Cycle
Double Fertilization- two sperm nuclei
One sperm fertilizes the egg (2n)
Other combines with two nuclei to produce endosperm (3n)
Endosperm nourishes the developing embryo
Angiosperm Evolution
Originated at least 140 million years ago
During the Cretaceous, major branches diverged
Primitive fossils of angiosperms display derived and primitive traits
Monocots
vs
Dicots
One cotyledon
two cotyledons
Parallel veins
netted veins
Scattered vascular bundles
vascular bundles in rings
Fibrous root structure
branching roots with taproot
Flower parts are 3s
flower parts in 4s or 5s
Pollen with 1 pore
pollen with 3 pores