Homework to be emailed to valenciabiologyhw@gmail.com
6) If you were faced with the choice of eliminating all mutualistic symbioses involving plants and other organisms (besides humans), with the goal being to preserve the most plant biomass, which of the following would you save from elimination?
7. During glacial periods in the early evolution of land plants, which of the following would have been a beneficial adaptation regarding the number of stomata per unit surface area, and what accounts for it?
Big Bend National Park in Texas is mostly Chihuahuan desert, where rainfall averages about 10 inches per year. Yet, it is not uncommon when hiking in this bone-dry desert to encounter mosses and ferns. One such plant is called "flower of stone." It is not a flowering plant, nor does it produce seeds. Under arid conditions, its leaflike structures curl up. However, when it rains, it unfurls its leaves, which form a bright green rosette on the desert floor. Consequently, it is sometimes called the "resurrection plant." At first glance, it could be a fern, a true moss, or a spike moss.
8) What feature of both true mosses and ferns makes it most surprising that they can survive for many generations in dry deserts?
9) Which of the following features is most important in order for true mosses and ferns to survive and reproduce in the desert?
10-. Which of the following characteristics is (are) possessed in common by true mosses, ferns, and spike mosses, and therefore becomes useless at helping to determine to which of these groups flower of stone belongs?
1. a sporophyte generation that is dominant
2. true leaves and roots
3. flagellated sperm
4. strobili
5. alternation of generations
11. Upon closer inspection of the leaves of flower of stone, one can observe tiny, cone-like structures. Each cone-like structure emits spores of two different sizes. Based on this information, which of the following can be properly inferred about flower of stone?
1. It is heterosporous.
2. It is a fern.
3. The cone-like structures are sori.
4. It is a lycophyte.
5. It has separate male and female gametophytes.
12) In which combination of locations would one who is searching for the gametophytes of flower of stone have the best chance of finding them?
1. moist soil
2. underground, nourished there by symbiotic fungi
3. south- or west-facing slopes
4. permanently shady places
5. far from any flower of stone sporophytes
Overview: The Greening of Earth
Looking at a lush landscape
It is difficult to imagine the land without any plants or other organisms
Land plants evolved from green algae
Researchers have identified green algae called charophyceans as the closest
relatives of land plants
Plants
Plants appeared on land about 425 million years ago, and the evolutionary
history of the plant kingdom reflects increasing adaptation to the terrestrial
environment. There are about 290,000 known plant species. (Food agriculture is
based on only about two dozen species.)
LE 29-3
LE 29-4
. The Invasion of the Land is really the Invasion of the Atmosphere!!!
The Protoplasm of Individual Plant Cells is surrounded by a Cellulose Wall.
While Cellulose is strong and prevents mechanical damage to the cell contents,
it is extremely hydrophilic and readily absorbs water.However, Cellulose easily
loses water via evaporation.
Land plants
Plants
A. General Characteristics of Plants
Plants are multicellular eukaryotes that are photosynthetic autotrophs. They
share the following characteristics with their green algal ancestors:
· Chloroplasts with the photosynthetic pigments:
chlorophyll a, chlorophyll b, and carotenoids.
· Cell walls containing cellulose.
Food reserve is starch that is stored in plastids.
Plants
As plants adapted to terrestrial life, they evolved complex bodies with cell
specialization for different functions.
· Aerial plant parts are coated with a waxy
cuticle that helps prevent desiccation.
Though gas exchange cannot occur across the waxy cuticle, CO2 and 02 can
diffuse between the leafs interior and the surrounding air through stomata,
microscopic pores on the leafs surface.
Plants
With the move from an aquatic to terrestrial environment, a new mode of
reproduction was necessary to solve two problems:
1. Gametes must be dispersed in a nonaquatic environment. Plants produce
gametes within gametangia, organs with protective jackets of sterile (nonreproductive)
cells that prevent gametes from drying out. The egg is fertilized within the
female organ.
Plants
2. Embryos must be protected against desiccation. The zygote develops into an
embryo that is retained for awhile within the female gametangia's jacket of
protective cells. Emphasizing this terrestrial adaptation, plants are often
referred to as embryophytes.
. Cellulose is like a sponge. If you drop a sponge in water, it saturates
instantaneously. A wet sponge readily loses water when it is placed on a dry
substrate. In order for an isolated plant cell, like a unicellular alga, to
survive, it must be in constant contact with water.
In order to withstand periodic dry spells, plant cells needed a water protective
coating.
. One of the most important plant adaptations is the Cuticle. It is a waxy
material that is secreted to the outside of the plasma membrane. It fills in the
spaces between cellulose fibrils and forms a continuous external waxy layer to
the outside of the cell wall. This makes the cell watertight!
. This cell can be called an "all purpose" cell because it Regulates its water
balance and performs Photosynthesis.
The Cuticle keeps water inside but it also prevents water uptake. The Cuticle
is usually thicker on the side of the cell facing the light. Consequently, water
could enter the bottom of the cell where the cuticle is thin and where water is
more
. abundant, and be retained within the cell by the thick cuticle on its upper
side. This could lead to the formation of colonies. The first multicellular
forms could be filaments. These might be followed by flat sheets.
The Chlorophyta (Green Algae) is algal group which probably gave rise to land
plants. The genus Coleochaete is regarded as the
Plant Evolution
Adaptations
Cuticle
alternation of generations
specialized tissues
Cuticle
Waxy coating on surfaces
resists drying out
stomata exist to allow necessary gas exchange
Morphological and Biochemical Evidence
Many characteristics of land plants
Also appear in a variety of algal clades
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*
Genetic Evidence
Comparisons of both nuclear and chloroplast genes
Point to charophyceans as the closest living relatives of land plants
Adaptations Enabling the Move to Land
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
: Land plants possess a set of derived terrestrial adaptations
Many adaptations
Emerged after land plants diverged from their charophycean relatives
Defining the Plant Kingdom
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
Derived Traits of Plants
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
Additional derived units
Such as a cuticle and secondary compounds, evolved in many plant species
The Origin and Diversification of Plants
Fossil evidence
Indicates that plants were on land at least 475 million years ago
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
Land plants can be informally grouped
Based on the presence or absence of vascular tissue
: The life cycles of mosses and other bryophytes are dominated by the
gametophyte stage
Bryophytes are represented today by three phyla of small herbaceous (nonwoody)
plants
Liverworts, phylum Hepatophyta
Hornworts, phylum Anthocerophyta
Mosses, phylum Bryophyta
Debate continues over the sequence of bryophyte evolution
Mosses are most closely related to vascular plants
Bryophyte Gametophytes
In all three bryophyte phyla
Gametophytes are larger and longer-living than sporophytes
The life cycle of a moss
Mosses
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
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
Bryophyte diversity
Ecological and Economic Importance of Mosses
Sphagnum, or peat moss
Forms extensive deposits of partially decayed organic material known as peat
Plays an important role in the Earths carbon cycle
Plants
Bryophytes are embryophytes that generally lack vascular tissue and require
environmental water to reproduce
The bryophytes include plants found in three divisions:
· Bryophyta (mosses)
· Hepatophyta (liverworts)
Anthocerophyta (hornworts)
Plants
Bryophytes have two adaptations that made the move onto land possible:
A waxy cuticle that prevents desiccation.
Plants
Gametangia that protect developing gametes.
a. Antheridium, or male gametangium, produces flagellated sperm cells.
b. Archegonium, or female gametangium, produces a single egg; fertilization
occurs within the archegonium, and the zygote develops into an embryo within the
protective jacket of the female organ (embryophyte condition).
Plants
Bryophytes are not totally free from their ancestral aquatic habitat.
They need water to reproduce. Their flagellated sperm cells must swim from the
antheridium to the archegonium to fertilize the egg.
Most have no vascular tissue to carry water from the soil to aerial plant
parts;
Plants
they imbibe water and distribute it throughout the plant by the relatively
slow processes of diffusion, capillary action, and cytoplasmic streaming.
Bryophytes lack woody tissue and cannot support tall plants on land; they may
sprawl horizontally as mats, but always have a low profile.
Plants
Mosses (Division Bryophyta)
A tight pack of many moss plants forms a spongy mat that can absorb and retain
water.
Each plant grips the substratum with rhizoids, elongate cells or cellular
filaments.
Plants
·a
. Meiosis marks the start of the
Haploid Gametophyte Generation
The Meiospores are Green.
Plants
·a
Plants
·
Plants
Photosynthesis occurs mostly in the small stemlike and leaflike structures
found in upper parts of the plant; these structures are not homologous with
stems and leaves in vascular plants.
Plants
There is an alternation of haploid and diploid generations in the moss life
cycle.
The sporophyte (2n) produces haploid spores by meiosis in a sporangium; the
spores divide by mitosis to form new gametophytes.
Plants
· Contrary to the life cycles of vascular
plants, the haploid gametophyte is the dominant
generation in mosses and other bryophytes. Sporophytes are generally smaller
and depend on the gametophyte for water and nutrients.
Plants
2. Liverworts (Division Hepatophyta) Less conspicuous than mosses, liverworts:
· Sometimes have bodies divided into lobes.
·Have a life cycle similar to mosses. Their sporangia have elaters, coil-shaped
cells that spring out of the capsule and disperse spores.
Plants
Can also reproduce asexually from gemmae (small bundles of cells that can
bounce out of cups on the surface of the gametophyte when hit by rainwater).
Plants
3. Hornworts (Division Anthocerophyta)
Hornworts:
· Resemble liverworts, but sporophytes are
horn-shaped, elongated capsules that grow from the mat-like gametophyte.
Their photosynthetic cells have only one large chloroplast, unlike the many
smaller ones of other plants.
: Ferns and other seedless vascular plants formed the first forests
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
Origins and Traits of Vascular Plants
Fossils of the forerunners of vascular plants
Date back about 420 million years
These early tiny plants
Had independent, branching sporophytes
Lacked other derived traits of vascular plants
Life Cycles with Dominant Sporophytes
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
Transport in Xylem and Phloem
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
Evolution of Roots
Roots
Are organs that anchor vascular plants
Enable vascular plants to absorb water and nutrients from the soil
May have evolved from subterranean stems
Evolution of Leaves
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 and Spore Variations
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
Classification of Seedless Vascular Plants
Seedless vascular plants form two phyla
Lycophyta, including club mosses, spike mosses, and quillworts
Pterophyta, including ferns, horsetails, and whisk ferns and their relatives
Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts
Modern species of lycophytes
Are relics from a far more eminent past
Are small herbaceous plants
. The species to the right could be a candidate for soil stabilization research.
It is a complex plant which has horizontal Stolons which have Isotomous
Branching. These produce the Roots which anchor the plant to the substrate.
. While extant Lycopods are small plants with little ecological significance.
Forests of tree-sized lycopods once dominated certain habitats. The most famous
of these is Lepidodendron which reached heights up to 30 meters. They had
secondary growth. The stems were coated with leaf bases and there appeared to be
little internodal elongation.
Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives
Ferns
Are the most diverse seedless vascular plants
Ferns
The Significance of 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
Plants
A. The Earliest Vascular Plants
Oldest fossilized vascular plant is Cooksonia (late Silurian):
· Discovered in both European and North American
Silurian rocks; North America and Europe were probably connected during the late
Silurian, about 408 million years ago.
Plants
· Simple plant with dichotomous branching and
bulbous terminal sporangia on some stems.
· True roots and leaves were absent; the largest
species was about 50 cm tall.
· Grew in dense stands around marshes.
As vascular plants became more widespread, new species appeared.
Plants
Ferns and other seedless vascular plants dominated the Carboniferous "coal
forests"
The earliest vascular plants were seedless and they dominated the
Carboniferous forests. Modern flora includes four divisions of seedless vascular
plants.
Plants
A. Division Psilophyta
Psilophyta consists of only two genera: Psilotum (whiskferns) and Tmesipteris.
Whiskferns are the most well known and share the following characteristics:
· True roots and leaves are absent, subterranean
rhizomes are covered with hair-like rhizoids, and shoots have scales which lack
vascular tissue.
Plants
Dichotomous branching.
· The gametophytes are subterranean and lack chlorophyll,
depending on symbiotic soil fungi for food.
· Flagellated sperm swim through the soil from
antheridia to the archegonium of the gametophyte.
The sporophyte emerges from the gametophyte, which then dies.
Plants
. B. Division Lycophyta (Lycopods)
The Division Lycophyta include the club mosses and ground pines.
· Survived through the Devonian period and
dominated land during the Carboniferous Period (340-280 million years ago).
Some are temperate, low-growing plants with rhizomes and true leaves.
Plants
· Some species of Lycopodium are
epiphytes, plants that use another organism as a substratum but are not
parasites. The sporangia of Lycopodium are borne on sporophylls, leaves
specialized for reproduction. In some, sporophylls are clustered at branch tips
into club-shaped strobili - hence the name club moss.
Plants
Spores develop into inconspicuous gametophytes. The non-photosynthetic
gametophytes are nurtured by symbiotic fungi.
Most are homosporous (making only one type of spore which develops into a
bisexual gametophyte).
Plants
Genus Selaginella is heterosporous, having megaspores which develop into
gametophytes bearing archegonia, and microspores which develop into gametophytes
with antheridia. The gametophytes are unisexual, either male or female.
Plants
C. Division Sphenophyta (Horsetails)
The division Sphenophyta includes the horsetails; it survived through the
Devonian and reached its zenith during the Carboniferous period.
Plants
The only existing genus is Equisetum, which:
· Lives in damp locations and has
flagellated sperm.
· Is homosporous.
· Has a conspicuous sporophyte generation.
Has photosynthetic, free-living gametophytes (not dependent on the sporophyte
for food).
Plants
Division Pterophyta (Ferns)
Appearing in the Devonian, ferns radiated into diverse species that coexisted
with tree lycopods and horsetails in the great Carboniferous forests.
Most diverse in the tropics, ferns are the most well represented seedless
plants in modern floras; there are more than 12,000 existing species of ferns.
Plants
· Fern leaves are generally much larger than those of lycopods and probably
evolved in a different way.
Lycopods have microphylls, small leaves that probably evolved as emergences
from the stem that contained a single strand of vascular tissue.
Ferns have megaphylls, leaves with a branched system of veins. Megaphylls
probably evolved from webbing formed between separate branches growing close
together.
Plants
Most ferns have fronds, compound leaves that are divided into several
leaflets.
· The emerging frond is coiled into a
fiddlehead that unfurls as it grows.
Leaves may sprout directly from a prostrate stem (bracken and sword ferns) or
from upright stems many meters tall (tropical tree ferns).
Plants
Ferns are homosporous and the conspicuous leafy fern plant is the sporophyte.
Specialized sporophylls bear sporangia on their undersides; many ferns have
sporangia arranged in clusters called sori and are equipped with springlike
devices that catapult spores into the air, where they can be blown by the wind
far from their origin.
Plants
The spore is the dispersal stage.
The free-living gametophyte is small and fragile, requiring a moist habitat.
· Water is necessary for fertilization, since flagellated sperm
cells must swim from the antheridium to the archegonium, where fertilization
takes place.
The sporophyte embryo develops protected within the archegonium.
129Ferns are seedless vascular plants
130Spore production by ferns
131Standard fern gametophyte
Plants
E. The Coal Forests
During the Carboniferous period, much of the land was covered in shallow seas
and swamps.
· Organic rubble of the plants above
accumulated as peat.
When later covered by the sea and sediments, heat and pressure transformed the
peat into coal.
Enough for now!
Sponge Activity-What did you learn today?
1`. In seedless plants, a fertilized egg will develop into _____. (Concept
29.2)
2. The diploid generation of the plant life cycle always produces_____.
(Concept 29.2)
3Most bryophytes, such as mosses, differ from all other plants in that they
_____. (Concept 29.3
4. In contrast to bryophytes, in vascular plants the dominant stage of the
life cycle is the _____. (Concept 29.4)
5. During the Carboniferous period, forests consisting mainly of ____ produced
vast quantities of organic matter, which was buried and later became coal.
(Concept 29.4)