AP biology: 29-30 Flashcards
For more than the first 3 billion years of Earth’s history
The terrestrial surface was lifeless
Since colonizing land
Plants have diversified into roughly 290,000 living species
Researchers have identified green algae
(charophyceans) as the closest relatives of land plants
Many characteristics of land plants
Also appear in a variety of algal clades ( Kingdom Protista currently)
There are four key traits that land plants share only with charophyceans
Rose-shaped complexes for cellulose synthesis
Peroxisome enzymes
Structure of flagellated sperm
Formation of a phragmoplast
In charophyceans
A layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out
The accumulation of traits that facilitated survival on land
May have opened the way to its colonization by plants
Many adaptations
Emerged
after land plants diverged from their charophycean relatives
Systematists
Are currently debating the boundaries of the plant kingdom
Some biologists think that the plant kingdom
Should be expanded to include some or all green algae
Until this debate is resolved
This textbook retains the embryophyte definition of kingdom Plantae
Five key traits appear in nearly all land plants but are absent in the charophyceans
Apical meristems Alternation of generations Walled spores produced in sporangia Multicellular gametangia Multicellular dependent embryos
Fossilized spores and tissues
Have been extracted from 475-million-year-old rocks
Whatever the age of the first land plants
Those ancestral species gave rise to a vast diversity of modern plants
Absence of vascular tissue
Bryophyta- including mosses, liverworts and hornworts
Presence of Vascular Tissue
Pterophytes- ferns- seedless vascular
Gymnnosperms- naked seeds vascular
Angiosperms- seed and fruit producing, flowering plants
Bryophytes are represented today by three phyla of small
herbaceous (nonwoody) plants
Liverworts, phylum Hepatophyta
Hornworts, phylum Anthocerophyta
Mosses, phylum Bryophyta
In all three bryophyte phyla
Gametophytes are larger and longer-living than sporophytes
Bryophyte gametophytes
Produce flagellated sperm in antheridia
Produce ova in archegonia
Generally form ground-hugging carpets and are at most only a few cells thick
Some mosses
have
conducting tissues in the center of their “stems” and may grow vertically
Bryophyte sporophytes
Grow out of archegonia
Are the smallest and simplest of all extant plant groups
Consist of a foot, a seta, and a sporangium
Hornwort and moss sporophytes
Have stomata
Sphagnum, or “peat moss”
Forms extensive deposits of partially decayed organic material known as peat
Plays an important role in the Earth’s carbon cycle
Bryophytes and bryophyte-like plants
Were the prevalent vegetation during the first 100 million years of plant evolution
Vascular plants
Began to evolve during the Carboniferous period
These early tiny plants
Had independent, branching sporophytes
Lacked other derived traits of vascular plants
In contrast with bryophytes
Sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern
The gametophytes are tiny plants that grow on or below the soil surface
Vascular plants have two types of vascular tissue
Xylem and phloem
Xylem
Conducts most of the water and minerals
Includes dead cells called tracheids
Phloem
Distributes sugars, amino acids, and other organic products
Consists of living cells
Roots
Are organs that anchor vascular plants
Enable vascular plants to absorb water and nutrients from the soil
May have evolved from subterranean stems
Leaves
Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis
Leaves are categorized by two types
Microphylls, leaves with a single vein
Megaphylls, leaves with a highly branched vascular system
According to one model of evolution
Microphylls evolved first, as outgrowths of stems
Sporophylls
Are modified leaves with sporangia
Most seedless vascular plants
Are homosporous, producing one type of spore that develops into a bisexual gametophyte
All seed plants and some seedless vascular plants
Are heterosporous, having two types of spores that give rise to male and female gametophytes
Seedless vascular plants form two phyla
Lycophyta, including club mosses, spike mosses, and quillworts
Pterophyta, including ferns, horsetails, and whisk ferns and their relatives
Modern species of lycophytes
Are relics from a far more eminent past
Are small herbaceous plants
Ferns
Are the most diverse seedless vascular plants
The ancestors of modern lycophytes, horsetails, and ferns
Grew to great heights during the Carboniferous, forming the first forests
The growth of these early forests
May have helped produce the major global cooling that characterized the end of the Carboniferous period
Decayed and eventually became coal
Seeds changed the course of plant evolution
Enabling their bearers to become the dominant producers in most terrestrial ecosystems
In addition to seeds, the following are common to all seed plants
Reduced gametophytes
Heterospory
Ovules
Pollen
The gametophytes of seed plants
Develop within the walls of spores retained within tissues of the parent sporophyte
Seed plants evolved from plants that had megasporangia
Which produce megaspores that give rise to female gametophytes
Seed plants evolved from plants that had microsporangia
Which produce microspores that give rise to male gametophytes
An ovule consists of
A megasporangium, megaspore, and protective integuments
Microspores develop into pollen grains
Which contain the male gametophytes of plants
Pollination
Is the transfer of pollen to the part of a seed plant containing the ovules
If a pollen grain germinates
It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule
Pollen, which can be dispersed by air or animals
Eliminated the water requirement for fertilization
A seed
Develops from the whole ovule
Is a sporophyte embryo, along with its food supply, packaged in a protective coat
Among the gymnosperms are many well-known conifers
Or cone-bearing trees, including pine, fir, and redwood
The gymnosperms include four plant phyla
Cycadophyta
Gingkophyta
Gnetophyta
Coniferophyta
Fossil evidence reveals that by the late Devonian
Some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants
Gymnosperms appear early in the fossil record
And dominated the Mesozoic terrestrial ecosystems
Living seed plants
Can be divided into two groups: gymnosperms and angiosperms
Key features of the gymnosperm life cycle include
Dominance of the sporophyte generation, the pine tree
The development of seeds from fertilized ovules
The role of pollen in transferring sperm to ovules
Angiosperms
Are commonly known as flowering plants
Are seed plants that produce the reproductive structures called flowers and fruits
Are the most widespread and diverse of all plants
The key adaptations in the evolution of angiosperms
Are flowers and fruits
The flower
Is an angiosperm structure specialized for sexual reproduction
A flower is a specialized shoot with modified leaves
Sepals, which enclose the flower
Petals, which are brightly colored and attract pollinators
Stamens, which produce pollen
Carpels, which produce ovules
Fruits
Typically consist of a mature ovary
Can be carried by wind, water, or animals to new locations, enhancing seed dispersal
In the angiosperm life cycle
Double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule
One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates development of food-storing endosperm
The endosperm
Nourishes the developing embryo
Clarifying the origin and diversification of angiosperms
Poses fascinating challenges to evolutionary biologists
Angiosperms originated at least 140 million years ago
And during the late Mesozoic, the major branches of the clade diverged from their common ancestor
In hypothesizing how pollen-producing and ovule-producing structures were combined into a single flower
Scientist Michael Frohlich proposed that the ancestor of angiosperms had separate pollen-producing and ovule-producing structures
The two main groups of angiosperms
Are monocots and eudicots
Basal angiosperms
Are less derived and include the flowering plants belonging to the oldest lineages
Magnoliids
Share some traits with basal angiosperms but are more closely related to monocots and eudicots
Pollination of flowers by animals and transport of seeds by animals
Are two important relationships in terrestrial ecosystems
Humans depend on seed plants for
Food
Wood
Many medicines
Destruction of habitat
Is causing extinction of many plant species and the animal species they support
