Transcript Transport in Plants

Transport in Plants
Cambridge Biology
Think about this…
• How do animals transport fluids throughout
the body?
• How do plants transport fluids?
• Do plants have blood?
• Do plant fluids contain cells?
• Do plant fluids transport Oxygen?
• Do plants pump their fluids?
Plant Transport Systems
• Xylem: vessels that carry water and inorganic
ions from the roots to the leaves
• Phloem: sieve tubes that carry products of
photosynthesis from the leaves to the roots
(and other parts of the plant)
Why Do Plants Need Water?
• Helps keep cells turgid
– So soft parts (leaves and petals) keep their shape
• Important for Photosynthesis
• Water is a solvent: substances can be
dissolved in water and move in and out of
cells
The Pathway of Water
• Starts in the soil.
• Enters root hairs on the plant’s root.
• Travels to the center of the root, into the
xylem vessels.
• Travels through the xylem up to the leaves
• Evaporates out of leaves through stomata.
– Called Transpiration
• This whole thing is the Transpiration Stream!
Transpiration Stream
Root Hairs
Why do plants need root hairs?
• To increase the surface
area of the root!
• This helps the root draw
in more water.
• Each root hair is part of
a single cell. Root hairs
get destroyed after a
day and get replaced by
more root hairs at the
tip of the root.
How Does Water Enter the Root?
• Root hairs grow into the soil, which also
contains water.
• Water moves into root hairs through osmosis.
– BUT WHY?
• Osmosis is the net diffusion of water
molecules from a region of high water
potential to a region of low water potential
through a partially permeable membrane.
Water Potential
• A measure of the osmotic pressure of water to
move through a permeable membrane.
• Dilute solutions have a higher WP than
concentrated ones.
• Water always flows “down the concentration
gradient.”
What does WP mean for Plants?
• There are sugars and salts in the cytoplasm of
the root hair cell, but NOT in the water in the
soil.
• Soil water has a higher water potential than
the plant cell’s cytoplasm.
• So water moves from the soil and into the root
hairs!
Root Anatomy
• Water has to cross the outer cortex of the root
and enter the xylem vessels in the middle.
• The cortex is made of regular plant cells.
• Water can easily move through these cells.
Root Cross Section
Xylem Vessels
• Xylem vessels = long, hollow, dead cells that
form a continuous tube.
• Small holes called pits are on the sides of the
tube.
– This is how water from the root hairs gets in!
Xylem Vessels
So…
• We know how the water got into the roots…
• But how does the water keep going up the
roots and through the stem??
Transpiration
• The evaporation of water through the plant
stomata and into the air.
• Plant cell walls under the leaves are always
wet, so they are always transpiring.
Stomata
Stomata
So What?
• If water vapor is always transpiring out of the
leaves, then where is all that water coming
from?
• How do you suck water through a straw?
Transpiration Stream
Don’t forget about the Phloem!
Phloem Tubes
• Also called sieve tubes.
• Run alongside xylem vessels.
• Together  vascular bundles or veins
What is Phloem For?
• Transports the products of photosynthesis
from the leaves to the roots.
– Because P’sis does NOT occur in the roots!
• “Products” = glucose (= energy)
• Glucose is made in the leaves (during P’sis)
but converted into Sucrose to be carried by
Phloem
Translocation
• Translocation = the transport of substances in
the phloem tubes
• NOT the same thing as transpiration!
• Amino acids are also carried in phloem, so
they are “translocated” along with sucrose.
Contact vs. Systemic Pesticides
• Which has a better chance of reaching and
killing all the pests on the plant? Why?
• If you had to eat an orange from a tree treated
with pesticides, which type would you rather
it be? Why?
Pesticides
• Pesticides = chemicals that kill pests
– Such as insects + fungi
• Contact Pesticides
– Must be sprayed directly onto pest
• Systemic Pesticides
– Absorbed by plant and travel through phloem
tubes to all parts of the plant
Contact vs. Systemic