Plant KingdomPlant 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 (1st time we see this)• Eggs and sperm produced- need

water• Immature leaves are called

fiddleheads- mature leaves- fronds

FernsSorus- 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

GinkgosFigure 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

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!