Introduction to Plants

What is a plant? Multicelluar Photosynthetic (autotrophic), eukaryote Cells supported by cell walls made of cellulose Reproduce sexually (some are asexual) Life cycles involve alternation of generations

Life on land Challenge of the environment –Prevent water loss Challenge of Structure (hold your weight up) –Rigid structures for support –Transport water and nutrients Challenge of reproduction –Transport of sperm to eggs without water Two major groups of plants –Bryophytes (partially adapted to life on land (moss) –Tracheophytes (fully adapted to life on land)

Bryophytes Grow and reproduce only when wet Never grow more than a few centimeters tall Sphagnum (peat moss) grows almost completely submerged

Tracheophytes Still depend on water to survive BUT Have vascular tissue to transport water throughout the plant: Ferns Gymnosperms Angiosperms

Ferns Have roots, stems and leaves Life cycle requires wet conditions Rare or absent in dry terrestrial habitats Coal comes from Devonian and Carboniferous Period ferns

Gymnosperms Do not need standing water to reproduce A seed is a reproductive structure that includes a developing plant, a food reserve all enclosed in a resistant outer covering Seeds exposed to the air in cone shaped structures Conifers most common (ginkgoes are gymnosperms too) The Petrified Forest in AZ is fossilized conifer trunks

Angiosperms The flowering plants Divided in to two groups based on the food in the seed Food is called a cotyledon One cotyledon: monocot Two cotyledons: dicot Fill in the chart on page 643

Adapting to land The structures of a plant that make them successful on land are: Roots Leaves, Vascular tissue, and Stems

Roots Anchor the plant Adsorb water and nutrients

Leaves The surface area necessary for photosynthesis The bigger the leaf the more sunlight it captures BUT the more water the plant losses by evaporation Leaves of land plants are covered with a water- proof (wax) cuticle BUT wax creates another problem: CO2 and O2 need to diffuse in and out The cuticle has specialized cells that open and close for gas diffusion These are the stomata

Vascular tissue Transport water from the roots to the leaves (xylem) Transport products of photosynthesis form leaves to rest of the plant (phloem) Phloem transport can be up or down

Stems Hold the plant up to the sun Contains the vascular tissue