Adaptations of Land Plant Offspring develop from multicellular embryos that remain attached to the...

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.


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).


• 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



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.


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.


• 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.


• 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

Adaptations of Land Plant Offspring develop from multicellular embryos that remain attached to the...

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