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Plant Transport
Systems
Honors Biology
Chapter 7
p. 185-191
Plant Life on Land
• 430 million years ago plants
adapted to life on land.
• First plant adaptations to land were
a thick waxy cuticle to prevent
water loss and protection for
gametes and embryos.
• Vascular and Nonvascular Plants
– Vascular plants- have vessels to
transfer water and nutrients
– Non Vascular Plants- mosses
bryophytes, etc. (moist environments)
Vascular Plants
• Vascular Plants have specialized
leaves and stems to get CO2 and light
from above ground.
• Vascular Plants have underground root
system to absorb water and minerals
from ground.
– Some roots have root hairs to increase
water absorption.
• Lignin- hard material in the cell walls
of vascular plants that allows plants
and trees to stand upright.
Lignin
Xylem
• Carry water and nutrients from
roots to rest of plant.
• Tracheids- pointed ends and thick
walls with pits that connect them
to cells.
• Vessel elements- wider, shorter,
thinner walled, and less tapered
Cohesion-Tension Theory
• Water moves up the xylem of a vascular
plant due to root pressure,
transpiration, and the adhesive and
cohesive properties of water.
• Pressure exerted by the roots forces
water up the xylem.
• Cohesion- the property of water
molecules to stick together (water
molecules hydrogen bond to other water
molecules)
• Adhesion- the property of water to stick
to other charged molecules.
Cohesion-Tension Theory
• Due to cohesion of water and the
adhesion of water to charged groups on
the surface of the tracheid and vessel
cells, water will rise in the xylem
through capillary action.
• Transpiration- Leaves lose water by
evaporation through their leaves
• Transpiration cause an area of
tension(low pressure)
• As water molecules transpire through
the stomates of leaves the cohesion of
water will pull on other water molecules
that will pull water up the xylem of the
entire plant.
Cohesion-Tension Theory
Animations
• http://bcs.whfreeman.com/thelife
wire/content/chp36/36020.html
• http://academic.kellogg.cc.mi.us/
herbrandsonc/bio111/animations
/0031.swf
Phloem
• Sugar and other organic materials must
move to all parts of the plant.
• Phloem- living cells that transport
sugars and amino acids to different
parts of the plant.
• These substance can move up or down
the plant through the phloem.
• Holes called sieve tubes transport
materials between phloem cells.
Phloem
Pressure Flow Hypothesis
• Materials from phloem move from
source to sink cells.
– Source cells can be- cotyledons and
endosperm during germination,
leaves during spring and summer,
storage roots during spring.
– Sink cells are any cell that uses water
and sugars, food storage areas, and
growing leaf buds, root tips, flowers,
fruits, and seeds.
Pressure Flow Hypothesis
• Sucrose is actively transported into a
source cell.
• Water will flow into the source cell by
osmosis which increases the turgor
pressure.
• This increased pressure will push sucrose
molecules through the sieve tubes to
other phloem cells towards sink cells.
• At the sink cells, sucrose and amino acids
will be actively transported to other cells
to be used or stored
• Water will flow out of the sink cells by
osmosis
Pressure-Flow Theory
• http://bcs.whfreeman.com/th
elifewire/content/chp36/3602
0.html
• http://bcs.whfreeman.com/th
elifewire/content/chp36/3602
0.html