Transcript Plants

Plants
Evolution and Classification
• The common ancestor of plants is green algae
• Plants are all
– Eukaryotic
– Multicellular
– Photoautotrophs (use light to produce food)
– Have cellulose in their cell walls
– Absorb nutrients through their roots (a major
difference from algae)
– Reproduce with spores or seeds (a major
difference from algae)
Evolution and Classification
Order of major evolutionary advances from
algae to flowering plants
1. Spores
2. Vascular tissue
3. Seeds
4. Flowers
Evolution and Classification
• Since plants came from algae, the first giant evolutionary step was
to move onto land
– To do this, cuticles (waxy layer around leaves) had to evolve to allow
plant to prevent water loss
– Reproduction with spores over reproduction by binary fission
• Seedless
– Reproduce with spores
– Have a sexual life stage
• Sperm must have moisture to reach egg producing part of plant, so plant is
bound to moist areas
– Gametophyte is main life stage – sporophytes are temporary
structures (opposite of seed plants)
• non-vascular
– Stuck low to the ground
– Nutrients and water must reach all cells via osmosis and diffusion, so
plant must remain small, as nutrients take too long to get to outer
cells.
– Use rhizoids – root like structures
Seedless, Nonvascular Plants
Sporophyte growing from gametophyte
• Mosses
•
•
Hornworts
Liverworts
Evolution and Classification
• Next came evolution of vascular tissue
– Allowed roots to sink into ground to reach deeper
water
– Allowed plant to grow up and compete for
sunlight
– Allowed plant to have a much greater surface for
photosynthesis compared to land area taken
– Nutrients and water can travel much faster to all
parts of the plant, allowing it to grow bigger.
Seedless vascular plants
• Reproduce with spores (still need moisture for
sperm to swim from male gametophyte to female
gametophyte - egg producing part of plant)
• Can grow tall and spread leaves out
• Ferns
• Horse tails
• Club mosses
Seedless vascular plants
• ferns
Spores found
on underside of
leaves (p 660)
• horsetails
Seedless Vascular Plants
• Club mosses
• Gametophytes produce
sporophytes
Evolution and Classification
• Then came seeds!
• Soooooooooooo many ways to disseminate!
Disperse! Spread out! Scatter and otherwise
get away from the parent plant!
Seeds - dispersal
Maple seeds
come down like
little helicopters
Dandelion
seeds float
off in the
breeze
Ever had a bur stuck
in your sock?
Seeds - dispersal
By animals – carried off and
buried, or ingested and
“dropped” somewhere else
A coconut
(seed for a
palm tree)
Floating on the
currents to far
away islands
seeds
• Advantages
– Dispersal – so many ways!
– Not bound to moist ground for sperm to swim to
female gametophyte – yeah – true dry ground!
– Protected by durable seed coat that can stay
dormant for long periods
– Cotelydons provide nutrition until sporophyte
produces green parts (germination is complete)
Vascular seed plants
• Sporophyte is most prominent part of life
cycle, producing gametophytes (opposite of
seedless plants)
• Two types:
• Gymnosperms
– “naked seeds”
– Four main divisions
• Angiosperms
– Flowering plants
– Ovary grows into fruit around seeds
Gymnosperms
• ginkgos
Gymnosperms
• Gnetophytes – neato! (p 618)
Gymnosperms
• Cycads
Gymnosperms
• Conifers –
– cone bearing plants
– Pinetrees
– Leaves are long and narrow =
needles
– Adapted for cold and shaped
not to break under weight of
snow.
Gymnosperms - conifers
• The tree is the sporophyte
• The sporophyte produces the gametophytes:
– The male gametophytes produce pollen in the
spring (it’s yellow and gets on everything)
– The cones are the female gametophyte containing
the eggs, which get fertilized by pollen and grow
into seeds inside the cone.
Evolution and Classification
• Finally Flowers!
• Advantages:
– Seeds Dressed, not Naked! - surrounded by a “fruit”
– Many ways to attract pollinators
– Seeds protected (and dispersed) by fruit
Angiosperms – “fruit” aren’t just apples
and oranges.
There are sooooo many ways to disperse.
Take on many shapes and sizes
Angiosperms – attracting pollinators
•
•
•
•
Symbiosis – mutualism
Pollinators get nectar & plant gets to reproduce
Pollen is male sex cell of plant
Pollen is carried by pollinator from male
gametophyte (stamen) to female gametophyte
(pistil)
Angiosperms – attracting pollinators
Plant parts
• What are the main functions of:
• Roots?
– To take in nutrients and water
– To store energy (as starch – as in potatoes)
– To anchor the plant
• Stem?
– To transport nutrients and water around plant
– To support plant
• Leaves?
– Produce food with photosynthesis
• Flower?
– reproduction
Stems - structure
•
•
•
•
•
Vascular tissue – some transport down, some up
What goes up?
Water with dissolved nutrients from roots
What goes down?
Food made by leaves to feed rest of plant, and to
be stored in roots for winter.
• What is exception?
• Food goes up in spring – sap rises – to give energy
for leaves to grow back
Stem – transport tissue
•
•
•
•
Up vascular tissue is called
Xylem
Down is
Phloem – think phood phloes
down
botany.hawaii.edu
Leaves – structure
See text p. 644 for diagram
•
•
•
•
Main function is photosynthesis
Cells filled with chloroplasts are sandwiched between:
Top layer cuticle: prevent water loss
Bottom layer cuticle with embedded stomata
–
–
–
–
–
Stomata open to let in
CO2 (carbon dioxide), and let out
Oxygen (O2)
Stomata close at night to prevent
Loss of water vapor
• Running through all this is the vascular tissue
transporting water and nutrients in from roots (xylem),
and transporting food out (phloem).
Flowering plant life cycle
1.
2.
3.
4.
5.
6.
7.
Pollen is produced by stamen – (get it?)
Pollen lands on female pistil
Pollen travels down pollen tube – in the style
Pollen fertilizes eggs inside ovary to produce zygotes
Zygotes grow into seeds
Ovary grows into fruit around seeds
Seeds get dispersed, land and grow into new
sporophyte (main plant)
8. Sporophyte produces new gametophytes (flowers),
which produce pollen and eggs
Tropisms – see text p. 651
•
•
•
•
•
Plant responses to stimulus
Stimulus = gravity
Response:
Gravitropism –
Roots grow down and shoots grow up
Tropisms
•
•
•
•
•
Stimulus = light
Response:
Phototropism
Plants grow toward the light,
With help of auxin – a hormone that increases
growth on side of stem that’s away from light
• – get it?
Tropisms
•
•
•
•
•
Stimulus – touch
Response:
Thigmotropism
Plants grow toward touch
This is for vines that climb or use other
plants/objects to support them
Nastic Responses
see text p. 650
• Movement independent of direction of
stimulus
• Can be repeated many times
• Examples:
– Sun flowers move to always face the sun
– sunflowers move to face sun
– Venus fly traps snap shut when an insect triggers
the response