Transcript INTRODUCTION TO PLANTS

INTRODUCTION TO
PLANTS
Plants evolved in
terrestrial
environments from a
green algae
ancestor which itself
was presumably
adapted to very
shallow waters, ones
prone to drying.
Things in common:
A. Both have chlorophylls A & B and carotenoids
B. Both use starch as their primary carbohydrate food
reserve. And both deposit it in the chloroplasts, not the
cytoplasm as in other algal groups
Chlorophyll a is a
green pigment that
absorbs red and blueviolet light.
Chlorophyll b absorbs
wavelengths in the blue
and red-orange parts of
the spectrum.
All photoautotrophs contain carotenoids, which absorb
blue-violet and blue-green wavelengths that are missed
by the chlorophylls. They reflect wavelengths which are
red, orange, and yellow.
C. Cellulose is the principle component
of the cell walls in plants. Likewise
many green algae
D. All true plants are oogamous. Some green
algae are also oogamous.
- one gamete is large and non-motile; one gamete is
small and motile
E. All true plants have an alternation of
generations. So do many green algae-
Why move onto the land?
• Abundant and more consistent
light for photosynthesis
• More plentiful and freely
circulating CO2
• lack of competition from other
organisms
• More surface area on leaves
exposed to sun!
Plant terrestrial adaptations
"Living on land poses very different problems from
living in the water. As plants have adapted to the
terrestrial environment, complex bodies with
extensive specialization of cells for different
functions have evolved."
These innovations
include
Waxy cuticle
Stomata
Vascular
tissue
Woody tissue
(lignin)
Pollen
Seeds
Development of the
sporophyte as the dominant
generation
Flowers AND
Fruit
Challenges during Algae-to-Plant Transition
Algae:
Minerals absorbed from
water
Water from water
Sunlight received within
water
Weight supported by water
Sperm swim through water
Spores swim through water
Plants:
Minerals / nutrients from soil
Water from soil (susceptibility
to desiccation)
Sunlight received above soil
(products require transport
within plant)
Weight not supported by air
(requires internal supporting
structure) air is less dense!
Less water for sperm to swim
through
Less water for spores to swim
through
Lets imagine the first "plant" as an algae with
most of its thallus "rooted" in the water, but with
a portion lifted slightly above the water, or
extending slightly past the shoreline, in a effort
to better compete against its fellow algae found
only at and below the water line
Such an alga might not initially require a waxy cuticle
(since water would always be available from the
portion of the organism found below the water line),
but might have given those individuals who first
displayed such a cuticle above the water line less
of a requirement for water. Thus the alga could
move beyond the water therefore allowing slightly
greater height and extension out over the shore
Once a waxy cuticle was in place, diffusion of gasses
could limit overall plant height (or spreading beyond the
water), thereby selecting for small holes (stomata) in the
waxy cuticle
In an effort to better control moisture retention, it
would be beneficial for the organism to
selectively open and close the holes
Such a algae could be essentially preadapted at this
point to existing in the presence of less water, e.g.,
periodic desiccation due to fluctuating water levels
At some point during the above
sequence we essentially have seen
the transition from status as a green
alga to that of a moss
WAXY CUTICLE
• The transition from a watery environment to a terrestrial one
most obviously involves an exposure to air
• Air is drying (unless relative humidity is 100%
• The cuticle prevents dessication
•Stomata (singular, stoma)
• The trouble with a waxy cuticle is that along with
waterproofing comes air-proofing
• Thus, the waxy cuticle prevents the diffusion of
O2 and CO2 into and out of the plant, interfering
with carbon fixing as well as cellular respiration
• The innovation that solved this dilemma were
small, opening and closing holes, called stomata,
through which gasses can diffuse into and out of
the plant
Embryophyte
• A new mode of reproduction was needed
to solve the land issue
– Nonaquatic environment – gametes produced
in gametangia - - – Eggs fertilized with in female organ
– Embryo retained in female
ALTERNATION OF GENERATIONS
• Haploid gametophyte produces and alternates
with diploid sporophyte.
• Sporophyte the produces gametophytes.
These two types of
plants are
HETEROMORPHIC
meaning they differ
in structure.
http://www.nova.edu/ocean/biol1060/plants.html
GAMETOPHYTE
Produces sperm and egg
(hence, gamet-o-phyte)
SPOROPHTYE
Produces
spores (hence
spor-o-phyte)
it is larger and
more noticeable
in all but
bryophytes!
SPOROPHYTE grows
from GAMETOPHYTE!
4 major periods of plant evolution
1. Origin from aquatic ancestors (algae)
called charophytes
•
•
•
425 mya - Silurian period
Cuticle
Vascular tissue
2.Ferns – seedless
• 400 mya Devonian
3.Origin of Seed
• 360 mya end of Devonian
1.Gymnosperm – naked seed
2. Seed embryo packed w/ food and
resistant coat
4. Flower plants with ovaries
• 130 mya cretaceous
1. Angiosperm – angio means container
TAXONOMY
Based on vascular vs.
nonvascular
Divison Bryophyta –
mosses,
• nonvascular
2. Embryophytes
that generally lack
vascular tissue and
require water for
reproduction
2 adaptations made land
possible
1. Waxy cuticle
2. Gametangia – protect developing gametes
a. Antheridium – male gametangium
b. Archegonium – produces single egg
•Bryophytes are not free from aquatic habitat
•Bryophytes lack woody tissue, thus
•Gametophyte is dominant
PTEROPHYTA
• Carboniferous period
forests loaded w/
ferns
• Ferns have fronds
which is a compound
leaf
• Fiddlehead uncurls as
leaf grows
Seed plants:
• Coniferophyta (GYMNOSPERMS)
– Earlier Fossil Record than Angiosperms
– LACK enclosed chambers where seeds
develop
• Adaptations:
– Leaves
– cuticle
• Male
• female
Seed plants:
• Anthophyta
– Used insects for
pollination,
– Specialized
vascular tissue
• Monocotyledone
http://waynesword.palomar.edu/termfl2.htm
DICOT –
VASCULAR
TISSUE IN AN “X”
Draw these on your notes sheet
SHALLOW WATER FIRST!
A. Charophytes –
B. Drying –
C. Preadaptations for land:
- waxy cuticle
- protection of gametes
- protection of developing embryos
D. Thus land-life possible:
-
Sunlight unfiltered by water and algae
Soil rich in minerals
Absence of terrestrial herbivores
III. Vascular Tissue Breakthrough
• We talked about these on Tuesday!
IV flower structure!
A. Gametophytes retained in moist reproductive
tissue of sporophyte generation
B. POLLINATION – no longer need water for
fertilization
C. Seed replaces spore
Use your book or the computer to label/define the flower parts! These are
REALLY important!
Problems with pollination and/or fertilization can cause fruit
disorders such as "cat facing." If pollen is not evenly
distributed on the stigma, all the ovules are not fertilized,
preventing sections of the new fruit from developing
Aggregate fruit
Multiple fruit -
• Look this last part up! How did animals
and angiosperms coevolve?