Transcript INTRODUCTION TO PLANTS

Adaptations of Land Plant
• Offspring develop from multicellular
embryos that remain attached to the
“mother” plant for protection and
nourishment.
• Vascular tissue is present in all but the
bryophytes ( some of these have some
type of transport vessels but lack TRUE
roots, stems and leaves.
There are four main groups of
land plants
• Bryotphytes – mosses
• Pteriodophytes – ferns
• Gymnosperm – conifers
• Angiosperms – flowering plants
Charophyceans are the green
algae most closely related to land
plants
• Charophyceans are
the green algae most
closely related to
land plants
Features that distinguish land
plants.
• Plasma membranes containing rosette
cellulose – synthesizing proteins
• Peroxisomes – help maximize the loss of
organic products due to photorespiration.
• Flagellated sperm are similar
• Cell division – formation of phragmoplast
Five Characteristics Unique to
Land Plants
• Apical meristem – localized regions of
active cell division in roots and shoots
• Embryophtes – multicellular dependent
embryos
• Alternation of Generations
• Walled spores produced in sporangia
• Multicellular reproductive structures –
antheridia and archegonia
What Is a Plant?
• Multicellular eukaryotes that are
photosynthetic autotrophs
• Cell walls made of cellulose
• Store surplus carbohydrates as starch
• Mostly terrestrial
Terrestrial Adaptations Are
Complimented by Chemical Adaptations
• Secondary products
– Synthesized by side branches of main
metabolic pathway
– Many protect the plant against excessive
damage by herbivores
– Examples
• Cuticle
• Lignin
• Sporopollenin
Reproduction
• Plants produce their gametes within
GAMETANGIA
• Zygote develops into an embryo within a
jacket of protective cells
• Embryophytes – a key adaptation to the
success of plants on land
ALTERNATION OF GENERATIONS
• Occurs in life cycle of all plants
• One generation is a multicellular haploid
condition and the next is a multicellular
diploid condition
Obstacles Plants Overcome
• Absorb Minerals
• Conserve Water
– Cuticle
– Stomata
– Guard Cells
• Reproduce on Land
A Vascular System Enables
Plants to Thrive on Land
• Most plants need a
“plumbing” system to
transport water,
minerals and
nutrients. This
system is known as
the VASCULAR
SYSTEM.
•Plants are monophylogenetic
Key to Modern Plant
Diversity
• There are four main periods of plant
evolution. Each period was an
adaptative radiation that follow the
evolution of structures that open the new
opportunities on land.
• The first terrestrial adaptations included
spores toughened by sporopollenin and
jacketed in gametangia that protect the
gametes.
• The second major period was plant
diversification in the Devonian period –
earliest vascular plants lacking seeds
• The third major period of evolution was
the origin of the seed.
• The fourth was the emergence of
flowering plants.
Bryophytes
– the Liverworts
• Simplest of plants (gametophytes are dominate
• Flat leafy body lacking cuticle, stomata, roots, stems or
leaves
– the Hornworts
• Dominate gametophyte and have stomata
– the Mosses
• Small, most have simple vascular tissue
• Sporophyte with slender stalk and spore capsule
• “leafy” green gametophyte that lacks roots, stems and leaves
Bryophyta
liverwort
Sphagnum moss
moss
hornwort
Nonvascular, no true leaves roots and stems,
root-like structures call rhizoids anchor plant
to the soil, pioneer plants, gametophyte is the
dominate generation
Moss genertations
Phylum Pterophyta
• Ferns are very divserse
• Largest ferns are 82 feet
tall with fronds 16 feet
long
• Leaves are called fronds
• A fiddlehead is a tightly
coiled new leaf
• Underground stem called
a rhizome
• In vascular plants the branched
sporophyte is dominant and is independent
of the parent gametophyte.
• The first vascular plants, pteridophytes,
were seedless.
• Vascular plants built on the tissue-producing
meristems, gametangia, embryos and
sporophytes, stomata, cuticles, and
sproropollenin-walled spores that they
inherited from mosslike ancestors.
Pteridophytes provide clues
to the evolution of roots and
leaves
• Most pteridophytes have true roots with
lignified vascular tissue.
• These roots appear to have evolved from
the lowermost, subterranean portions of
stems of ancient vascular plants.
– It is still uncertain if the roots of seed plants
arose independently or are homologous to
pteridophyte roots.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The seedless vascular plants, the
pteridophytes consists of two modern phyla:
– phylum Lycophyta - lycophytes
– phylum Pterophyta - ferns, whisk ferns, and
horsetails
• These phyla probably
evolved from different
ancestors among the
early vascular plants.
Fig. 29.21
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Ferns also demonstrate a key variation
among vascular plants: the distinction
between homosporous and heterosporous
plants.
• A homosporous sporophyte produces a
single type of spore.
– This spore develops into a bisexual gametophyte
with both archegonia (female sex organs) and
antheridia (male sex organs).
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
A sporophyte-dominant life cycle
evolved in seedless vascular
plants
• From the early vascular plants to the modern
vascular plants, the sporophyte generation is
the larger and more complex plant.
– For example, the leafy fern plants that you are
familiar with are sporophytes.
– The gametophytes are tiny plants that grow on or
just below the soil surface.
– This reduction in the size of the gametophytes is
even more extreme in seed plants.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 29.23
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Ferns first appeared in the Devonian and
have radiated extensively until there are over
12,000 species today.
– Ferns are most diverse in the tropics but are also
found in temperate forests and even arid habitats.
• Ferns often have horizontal rhizomes from
which grow large megaphyllous leaves with
an extensively branched vascular system.
– Fern leaves or fronds
may be divided into
many leaflets.
Fig. 29.21d
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• A heterosporous sporophyte produces two
kinds of spores.
– Megaspores develop into females
gametophytes.
– Microspores develop into male gametophytes.
• Regardless of origin, the flagellated sperm
cells of ferns, other seedless vascular plants,
and even some seed plants must swim in a
film of water to reach eggs.
• Because of this, seedless vascular plants are
most common in relatively damp habitats.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Coal powered the Industrial Revolution but
has been partially replaced by oil and gas in
more recent times.
– Today, as nonrenewable oil and gas supplies are
depleted, some politicians have advocated are
resurgence in coal use.
– However, burning more coal will contribute to the
buildup of carbon dioxide and other “greenhouse
gases” that contribute to global warming.
– Energy conservation and the development of
alternative energy sources seem more prudent.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Ferns produce clusters of sporangia, called
sori, on the back of green leaves
(sporophylls) or on special, non-green leaves.
– Sori can be arranged in various patterns that are
useful in fern identification.
– Most fern sporangia have springlike devices that
catapult spores several meters from the parent
plant.
– Spores can be carried great distances by the wind.
Fig. 29.24a, b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings