Download Chapter 10: Terrestial Plants

Chapter 10. Terrestrial Plants
Evolutionary Challenge Facing The Emergence of Terrestrial Plants
In order for plants to survive and reproduce outside the aquatic or marine
environment, several challenges needed to be overcome. Plants must now:
1) hold themselves up to the sun
2) obtain sufficient water and nutrients
3) transport and distribute water and dissolved minerals
4) transport food products to different parts of the organism
5) prevent desiccation - excessive water loss through evaporation
6) maintain proper gas exchange (CO2 in and O2 out) with surrounding air
7) increase the chance of fertilization
8) protect gametes and zygote
9) withstand extreme environmental changes
Adaptations:
1) Roots – anchorage and absorption of water and nutrients
2) Stems – hold leaves toward sun to maximize photosynthesis
3) Leaves – specialized structures to maximize photosynthesis
4) Cuticle – a waxy ‘seal coat’ covering which retains water within the plant
5) Stomata – special openings in the leaves which can be controlled to allow
gas exchange yet retain moisture at the same time.
6) *Xylem – dead tube-like cells which act like ‘straws’ to transport water up
the stem.
7) *Phloem – living cells to distribute sugars through the plant.
*together xylem and phloem are called the vascular system.
Terrestrial plants are divided into four categories as outlined in the following
table:
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Terrestrial Plants
NonVascular
Lack xylem/phloem
Bryophyta
Mosses
Vascular
Liverworts
Hornworts
Tracheophyta
Seeds
Naked seeds
Gymnosperms
Coniferous Trees
Cone bearing plants
Seedless
Protected Seeds
Angiosperms
Flowered Trees and Plants
Spores Only
Pterophyta
Ferns
Non – Vascular Plants: Bryophyta
Mosses
Reproduction:
Has alternation of generations dominated by the short, green
gametophyte. Has male antheridium and female archegonium. Sperm is
released from antheridium in the presence of moisture and travels to the
archegonium.
Thin sporophyte grows out of the gametophyte once zygote has been
produced, and produces a diploid sporangium. Spores later released and
germinate to form haploid protonema –(similar to filamentous green
algae) which develops into new gametophyte. (See Figure 10.5)
Asexual reproduction via fragmentation and gemmae
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Absorption/Anchorage:
Rhizoids – primitive root-like structures which have limited ability to
absorb water or anchor plant.
Transport:
Leaves are only one cell thick so most transport is by diffusion from cell to
cell with some exchange with the environment directly through leaf cells.
Some transport occurs through unspecialized vertically elongated cells in
the stem.
Vascular Plants (Tracheophyta)
Further divided into two groups: spore bearing or seed bearing.
•
Spore bearing – Pterophyta. E.g. Ferns
•
Seed bearing – naked seeds: Gymnospermae e.g. cone plants (conifers)
- protected seeds: Angiospermae e.g. flowering plants
Spore Plants - Ferns
Reproduction:
Has alternation of generations dominated by the tall, green sporophyte
which produces haploid sori on the underside of the leaf (frond). Spores
from the sori germinate into a small, inconspicuous gametophyte
(prothallus) which has male and female parts. Sperm is released from
male part in the presence of moisture and travels to the female part.
Fertilzation leads to production of the sporophyte. (See Figure 10.7)
Absorption/Anchorage:
Has a rhizome and adventitious roots
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Transport:
Well developed vascular system with upright leaves.
Seed Plants – Gymnosperms
Reproduction:
Has alternation of generations dominated by the tall, green sporophyte
(tree) which produces small haploid gametophytes which are made up of
the female egg cell inside the cone and the male pollen grains (also in
cones). (See Figure 10.10)
Absorption/Anchorage:
Has true roots which tend to be surface oriented
Transport:
Well developed vascular system with upright leaves.
Anti-desiccation:
Thick waxy cuticle. Thin, needle like leaves.
Seed Plants – Angiosperms
Reproduction:
Has alternation of generations dominated by the tall, green sporophyte
(tree) which produces small haploid gametophytes which are made up of
the female ovule inside flower ovary and the male pollen grains produced
by the flower’s anther. (See Figures 10.12, 10.13) Egg is completely
surrounded by ovary which develops into a protective fruit.
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Absorption/Anchorage:
Has true roots which tend to be surface oriented
Transport:
Well developed vascular system with upright leaves.
Anti-desiccation:
Thick waxy cuticle. Broad, veined leaves.
A word on Seed Dispersal
a) Wind
•
Wings
•
Parachutes
•
Fluff
b) Water
•
Floatable due to trapped air (coconut)
•
Waxy coating. Germination begins when coat wears out.
c) Animals
•
Ingest fruit/nut. Seed excreted later.
•
Hooks and burrs.
•
Mud encased
•
Store caches
d) Explosive triggers
•
Some plants have triggers that eject seeds at great distances once a
mechanism is activated. Commonly the mechanism is triggered by the
drying out of part of the seed storage container.
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A word on Monocots and Dicots
Angiosperms are further divided into two classes depending on the number of
seed storage leaves that the sporophyte produces. Monocots have one leaf while
dicots have two. In addition to this all monocots share other similarities. Dicots
also have common traits as well. See Figure 10.17.
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