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

Gymnosperms 720 species “naked seed” seeds not enclosed in any structure Cones called strobili Do NOT need water for sperm to reach egg- now covered to reduce water loss Pollen- enclosed sperm

Ginkgos- Ginkgophyta 1 species alive- Ginkgo biloba flourished during age of dinosaurs Fan-shaped leaves Resistant to air-pollution, insects, disease, highly planted in cities Seeds are thick and fleshy and produced on female trees

Ginkgos Figure 9.1: Ginkgo biloba (A) typical leaf; (B) pollen-bearing strobilus; (C) paired ovules on stalk at the point of pollination. Ovules continue to develop and fertilization takes place after ovules fall to the ground.

Ginkgos

Cycads- Cycadophyta 100 species alive- also flourished with dinosaurs Male and female plants Leaves resemble a palm tree Large cones Several species facing extinction

Cycads

Gnetophyta 3 genera One or two strap-shaped leaves that split as the plant ages Ephedra- gives us the drug ephedrine

Ephedra

Conifers- Coniferophyta Pine trees Produce true cones Male cones are small, clustered and fleshy Female cones are large and become woody Leaves are needle-like

Conifers Leaves fall off all year long, but are continuously replaced- called evergreens During pollination- males release clouds of pollen that is airborne to the female cones Female cones are fertilized 1 year after pollination Germination may take another year

Conifers Sporopohyte is the dominant generation May grow for many years Some are found that were growing during the age of pharoahs

Pine Cones

Angiosperms- flowering plants Last group to evolve Largest group of plants Seeds enclosed in fruits that grow from flowers Flowers are used to attract pollinators Seeds and fruits are highly valuable

Angiosperms By this point we have the following major advntages –Cuticle- nonvascular plants –Vascular tissues- vascular seedless –Seeds- gymnosperms –Flowers- angiosperms Angiosperms are at the top of the plant evolutionary tree

Flowers Highly specialized reproductive structures Stamen- male part- anther + filament- produces pollen Pistil-female part – stigma+style+ovary+ovule- produces eggs Pollination occurs when pollen is delivered to the egg

Flowers

Angiosperm transport Roots- absorb nutrients and water and transport them up the plant Stems- support plant and transport substances up and down the plant Leaves- main photosynthetic organ, draws water up the plant from the roots

Fruits and seeds Ovary of fertilized flower will develop into a fruit Fruits contain seeds –Seeds with one half- monocots –Seeds with two halves- dicots

Plants as food How many different plants do we eat for food? Fruits – the vegetative (reproductive) part of a plant- all fruits contain seeds Vegetable- any other part of the plant- leaf, stem, root

Root Crops Rich in calories, easy to grow Potatoes, beets, radishes, carrots, cassava Grow underground

Legumes Members of the pea family Protein-rich seeds in pods Beans, peas, peanuts, soybeans, alfalfa Relationships with nitrogen-fixing bacteria that can put nitrogen back into the soil- farmers rotate crops from corn to soybeans

Cereals Grasses that produce grains (dry, edible, fruit) Each grain is actually a fruit that develops from a single flower. Each corn kernel is a single, fruit Rich in carbohydrates More than 70% of all cultivated ground is used for cereals Corn, wheat, rice= ½ human calories

Nonfood uses Rubber, latex- from rubber tree Wood-lumber, heating, furniture… Medicines- aspirin from willow trees –Digitalis- foxglove plant for heart disorders –Cancer treatments from periwinkle –Caffeine –Drugs

Nonfood uses Fibers –Paper –Cotton –Flax –Hemp

Next chapter Reproduction –Asexual –Sexual –Flowers –Cones Easy chapter!