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How Did Plants Originate?
First land plants appeared 500 mya Resembled present day mosses Released nitric acids on rock surfaces
which created soil Likely colonies of protists adapted to
dry environment…but how?
Links Between Algae and Plants
Both have protective cell walls Both contain chlorophyll used in
photosynthesis Both store food in the form of starches
Plants Must Adapt To Live On Land
1. Absorb nutrients from surroundings2. Prevent desiccation3. Reproduce without the aid of water
If plants adapt to these strategies, they can evolve on land
Why would a plant “want” to move onto the land?
A. Preventing Water Loss Cuticle: waxy coating that prevents
tissues from drying out Stomata-openings in the cuticle that
allow gas exchange to take place and also regulate water loss
Prevent Desiccation? Desiccation= Drying Out As plants evolved further away from water,
they needed to evolve a waterproof structure/coating (cuticle)
But, this structure needs pores (stomata) WHY? Think about what the plant needs for
photosynthesis… CARBON DIOXIDE!
C. Stabilization and Nutrient Absorption(Accomplished with roots and
mycorrihizea) Roots-organ that is used to reach and
transport water and minerals, anchor plants and store food
Earliest roots are rhizoids Fossils show fungi “helped” plants
before roots evolved
The Root Main function = absorb water Functional Part = root hair Structure from outside in:
– Epidermis with root hair= protection– Cortex=support/storage– Vascular Bundle: Phloem, Vascular Cambium*,
Xylem
*Vascular Cam: growth of new vascular tissue
D. Transportation System
Stem- Transport of water, food, and
minerals Support of plant Storage of materials
Structures of the Stem Epidermis (bark or green)=protection Cork cambium =new growth of bark/
epidermis Cortex = thick layer, sometimes contains
chloroplasts, mostly for support Vascular Bundle = contain transport tissues
towards the middle of the stem Xylem = transports water and minerals
(generally in the middle)
More Structures Phloem = transports sugars to all cells,
located outside the xylem Vascular cambium = separates the X
and P, contains new cells for vascular growth
Pith = central portion of stem of tree, for storage
E. Reproduce Without Water
Spores/Cones/Seed-protective coat which prevents a developing embryo from drying out
Advent of pollen and seeds make it possible to reproduce far away from water
Pollen = plant sperm, light weight and won’t dry out, carried via wind, water, animal, etc