Packet #68 Chapter #29

Introduction There 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 Plants Plants 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 Plants Embryophytes (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 Evidence Below 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 Evidence Additionally, there are key nuclear genes, which result in the production RNA, that are used to help make cytoskeleton proteins. Homologous chloroplasts Algal 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 Land Charophyceans 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 II The colonization of land by plants required the evolution of many anatomical, physiological and reproductive adaptations

Adaptations III Waxy Cuticle Used to protect against water loss Prevents desiccation (drying up) of plant tissues Stomata Allows gas exchange needed for photosynthesis Multicellular gametangia have (sterile) nonreproductive cells as well as gametes The fertilized egg develops into a multicellular embryo within the female gametangium.

Adaptations Plant life cycle alternates between haploid and diploid generations (alternation of generation)

Adaptations Plant Life Cycle The haploid portion is the gametophyte generation Produces haploid gametes via mitosis Within antheridia Male parts Within archegonia Female parts Gametes fuse to form the diploid zygote of the sporophyte generation

Adaptations Plant Life Cycle The diploid portion is the sporophyte generation Zygote develops within the archegonium Zygote produces haploid spores via meiosis Spores divide via mitosis and develop into the gametophyte generation

Adaptations Plant 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 VI Production 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 Adaptations Mosses 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.