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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 Terrestrial Adaptations Are Complimented by Chemical AdaptationsComplimented 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 monophylogeneticPlants 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
Nonvascular, no true leaves roots and stems, root-like structures call rhizoids anchor plant to the soil, pioneer plants, gametophyte is the dominate generation
liverwortliverwort Sphagnum mossSphagnum moss
hornworthornwort
mossmoss
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.
• 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.
Pteridophytes provide clues to the evolution of roots and leaves
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.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 29.21
• 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
• 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.
A sporophyte-dominant life cycle evolved in seedless vascular plants
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 29.23
• 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.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 29.21d
• 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.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 29.24a, b