Plant Kingdom

Plants on land Plants are the most dominant group or organisms on Earth by weight Very diverse 2mm across to 100m tall Most are photosynthetic but some are parasitic

Beginnings Photosynthetic algae must remain in water for several reasons Cannot prevent water loss out of water Sex cells must swim in water for fertilization Cannot obtain nutrients from land

Moving on to land In order to take over land plants must be able to do three things –Absorb nutrients from land –Prevent themselves from drying out –Reproduce without water

Preventing water loss First plants live at edge of water and absorb water Waxy, watertight covering called a CUTICLE- prevents water loss but also prevents gas exchange STOMATA- small pores that allow gas exchange. Bordered on each side by GUARD CELLS- these control the opening and closing

Reproducing on land Sperm and egg must be able to move without water In most plants sperm are enclosed in pollen and eggs enclosed in other structures- cone or flower Pollen permits the efficient spread of sperm

Absorbing nutrients Early plants cannot absorb nutrients but fungi can. This leads to the establishment of mycorrhizae 80% of all plants still have this relationship Eventually roots form

Vascular Tissues, seeds, flowers One of the most important changes- allows water and materials to move throughout the plant First plants could only absorb through osmosis and diffusion- very inefficient

Vascular Tissues Made of xylem and phloem Xylem moves water and nutrients from roots UP to leaves Phloem moves sugars and organic nutrients up or down the plant depending on needs.

Seeds Next important adaptation Seeds contain the EMBRYO of a plant- several advantages –Protection- seed coat prevents drying –Nourishment – stored nutrients- endosperm –Dispersal- spread very efficiently –Delayed growth- seeds can remain dormant and wait until things are right

Flowers Last adaptation to evolve Reproductive structures More efficient because they use direct pollination through animals, insects, etc… Wind is inefficient

Life cycles Plants have two phases in their life cycle – Alternation of Generations Sporophyte stage- diploid stage (2n)-produces spores Gametophyte stage- haploid stage (n)- produces gametes Dominant stage varies according to group of plants

Vascular plant sporophyte

Moving onto land The first adaptation towards life on land is to conserve water loss First land plants resemble algae- store starch, similar pigments, cellulose, similar mitosis First group to make the move are the Bryophytes

Bryophytes Oldest plants ~400 million years old Autotrophic, multicellular eukaryotes 18,600 species Mosses, Liverworts, Hornworts

Bryophytes Nonvascular- cannot transport water or nutrients or starch No true leaves, roots, stems- Small <20 cm 3 features of land plants –Cuticle –Cellular jacket around gametes –Large gametophytes separate from sporophyte

Mosses 10, 000 species Grow in moist areas- water still needed for sperm to move to egg Peat moss- used for fuel Rhizoids- root-like structures used for attachment to soil

Mosses

Hornworts

Liverworts

Bryophytes life cycle

Seedless Vascular plants Next group to evolve further features for life on land Xylem and Phloem- move water and sugars throughout the plant 13, 000 species True roots, leaves, stems- rhizomes NO SEEDS but use SPORES Large sporophyte

Seedless vascular 4 major divisions Pterophyta- ferns Psilotophyta- whisk ferns Lycophyta- club mosses Sphenophyta- horsetails

Lycophyta 1,100 species Club mosses- still need the water to reproduce Commonly called “mini pines” Cone-like structures called a strobilus contain spore producing leaves

Club Mosses

Psilotophyta Whisk ferns- not true ferns Rhizomes- short branched, horizontal absorptive stems that grow underground Reduced leaves Photosynthetic branches

Whisk Ferns

Sphenophyta Horsetails ~25 species Thrive in streambank muds, vacant lots, roadsides, disrupted habitats Vegetative photosynthetic stems Spores give rise to gametophytes Rhizomes silica containing stems- scouring rushes

Horsetails

Pterophyta Ferns- 12,000 species Largest and most diverse group Mostly tropical 1 cm across to 25 m tall Vascularized rhizomes give rise to roots and leaves Sporangia on leaves release spores

Ferns Stomata in leaves Life cycle dominated by sporpohyte (1 st time we see this) Eggs and sperm produced- need water Immature leaves are called fiddleheads- mature leaves- fronds

Ferns Sorus- clusters of sporangia- spore producing tissue

Fern life cycle

Tree fern

Seed-Bearing Plants Gymnosperms- nonflowering –4 divisions Cycads Ginkgos Conifers Gnetophytes Angiosperms –flowering –2 subdivisions Dicots monocots