Packet #68Chapter #29

IntroductionThere are more than

290,000 species of plants that inhabit the earth.

How, and why, based on the theory of evolution, did plants venture out of the sea and onto dry land?Some answers lay with

the charophyceans Green algae

Information About PlantsPlants are multicellular, eukaryotic

photoautotrophs.The cells, that make up plants, have cell walls

that are composed of cellulose.The pigment chlorophyll may be found in two

forms a & b

“Evolutionist Thoughts”

Diversion of Algae and Land PlantsEmbryophytes

(plants with embryos) is the traditional scheme and is mostly associated with Kingdom Plante.

It is thought that plants evolved from green algae.Charophyceans

Morphological & Biochemical EvidenceBelow are four traits that “suggest” an evolutionary

relationship between charophyceans and land plants Homologous peroxisomes

Both groups contain enzymes that minimize the loss of organic products due to photorespiration

Formation of phragomoplast Synthesis of cell plates during cell division involves the formation of

phragomoplast Homologous Sperm

Many plants (gymnosperms) have flagellated sperm that match charophycean sperm

Homologous cellulose cell walls Cell walls of both land plants and charophyceans contain 20-26%

cellulose

Genetic EvidenceAdditionally, there are key nuclear genes,

which result in the production RNA, that are used to help make cytoskeleton proteins.

Homologous chloroplastsAlgal plastids, of green algae and algal groups

such as euglenoids, are similar to those found in land plants

Chloroplast DNA found in charophyceans, green algae, is most closely related to that found in land plants.

Adaptations Enabling the Move to LandCharophyceans have

a layer of a durable polymer called sporopollenin.Prevents exposed

zygotes from drying out.

May be the precursor to the tough sporopollenin walls that encase plant spores.

Adaptations IIThe colonization of land by plants required

the evolution of many anatomical, physiological and reproductive adaptations

Adaptations IIIWaxy Cuticle

Used to protect against water lossPrevents desiccation (drying up) of plant

tissuesStomata

Allows gas exchange needed for photosynthesisMulticellular gametangia have (sterile)

nonreproductive cells as well as gametesThe fertilized egg develops into a multicellular

embryo within the female gametangium.

AdaptationsPlant life cycle alternates between haploid

and diploid generations (alternation of generation)

AdaptationsPlant Life CycleThe haploid portion is

the gametophyte generationProduces haploid

gametes via mitosis Within antheridia

Male parts Within archegonia

Female parts

Gametes fuse to form the diploid zygote of the sporophyte generation

AdaptationsPlant Life CycleThe diploid portion is

the sporophyte generationZygote develops

within the archegonium

Zygote produces haploid spores via meiosis

Spores divide via mitosis and develop into the gametophyte generation

AdaptationsPlant Life Cycle (Extras)All plants produce spores via meiosis ONLY

as opposed to algae and fungi which produce spores via meiosis or mitosis

In “lower plants,” the gametophyte generation is the dominant stage

In “higher plants,” the sporophyte generation is the dominant stage

Adaptations VIProduction of Secondary Compounds

Plants produce many unique compounds, such as terpenes, alkaloids and tannins, as byproducts of primary metabolic pathways.

The compounds, byproducts, may have bitter tastes, strong odors or toxic effects and help plant defend itself against herbivores.

Later AdaptationsMosses and ferns, although adapted to life on

land, have motile sperm cells that require water as a transport medium for fertilization.

Ferns, and vascular plants, that “evolved” at a later time, have xylem, to conduct water, and phloem, to conduct dissolved sugar.