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4.4 Bio Transport in Plants, 2 - The Uptake of Water By Plants, 1 -…
4.4 Bio Transport in Plants
2 - The Uptake of Water By Plants
water from soil
water mostly absorbed by younger roots, more root hair cells
larger SA for absorption, more contact with soil water
water uptake into roots
depends on CGs between xylem/ root/ soil
soil water --> root hair cells, down CG, osmosis
translocation of water
transpiration + transpiration stream
modelling transpiration
measuring water movements
factors affecting transpiration
root pressure
1 - Transport in Plant Tissues
Xylem
evidence of water movement in xylem
cut shoot + eosin dye tracks water movement in VBs
ringing experiments - remove bark ring, kills phloem cells, add eosin dye, water moves up
autoradiography - trace movement of water with radioactive isotopes up xylem
give plant radioactive substance, it's taken up same as non-radioactive
movement tracking methods
place plant against photographic film, produces autoradiograph - radioactivity shadows film
examine each plant area with scintillation counter - shows where radioactive substance is
water + minerals up
mostly dead cells, start as living - xylem vessels
protoxylem - first xylem, stretches/ grows. Walls aren't fully lignified.
cellulose microfibrils laid vertically in xylem vessels in stem
increased strength
withstand compression
stem ages
xylem growth stops, vessels die
walls in-between vessels break down, hollow xylem
more lignin in xylem vessel cell walls, impermeable, strong, supportive
becomes metaxylem - lignified, mature xylem vessels
most support in big plants, less in smaller
smaller supported by:
parenchyma - unspecialised plant cells, fill stems + roots, support
sclerenchyma - thick lignified walls, empty lumen, dead
collenchyma - thick cellulose, mechanical strength + support to cells
make tree trunks
cambium on outside, under bark
new vascular tissue ring formed each year, tracks tree growth
more strong/ supportive
transport water + minerals in transpiration stream - water exits xylem, into surrounding cells, through unlignified areas or holes (pits)
Phloem
transport sucrose (glucose converted after photosynthesis) + organic solutes up/ down, where growth/ storage occurs
living cells, not lignified - phloem cells
phloem sieve tubes - many cells joined together, tubes from top/ bottom of plant
sieve plates - hole-y walls between cells. phloem contents flow through holes, phloem sap fills cells, cell contents mostly break down. No nucleus.
survive due to companion cell
many mitochondria for ATP for active transport of materials into sieve plates
many plasmodesmata to sieve plates
many infoldings, increase SA for active transport/ diffusion
xylem + phloem in vascular bundles
cambium - layer of unspecialised cells, divide, differentiate into xylem/ phloem cells
3 - translocation of sucrose