BIOL-1507EL Study Guide - Final Guide: Apoplast, Polychaete, Cellular Respiration
27 Jun 2018
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Biology Exam Review
Transports in Plants
-Physical forces drive the transport of
materials in plants over a range of
distances
-Short distance transport is bringing
substances from cell to cell (in all tissues
and organs)
-Such as bringing sugars from a
photosynthetic leaf cells into the sieve
tube of the phloem
-As well as long distance transport within
xylem and phloem along the whole plant
-Things involved in transports are:
-A selective permeability of membrane
-Passive transport
-Active transport
-One important active transport in plant cells
is the proton pump, which hydrolyzes ATP (to ADP) and uses it to release energy to
pump hydrogen ions (H+) out of the cell
-This is because the proton pump moves the positive charge H+ out of the cell, which
makes a membrane potential as there inside of the cell becomes negative with
relation to the outside
-The membrane potential helps to drive K+ into the cell because the K+ will be
attracted to the more negative region of the cell, this is a passive transport
Routes of Transport
-First Route
-Substance move out of one cell, across the cell wall, and into the neighbouring cell
-The thin transmembrane route requires repeated
exists, as it exits one cell and enters the next
-Second Route
-Through the symplast, the continuation of cytosol
within a plant tissue requires the crossing of the
plasma membrane after entering a cell
-Solutes exit one cell and then move from cell to cell via
the plasmodesmata
-Third Route
-Through the appals, there is lateral transport that
occurs within a plant tissue or organ
-The extracellular pathways consist of cell walls and
extracellular spaces, through which water and solutes
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can move freely from one location to another
-The water and minerals that move to the endodermis cannot continue into the stele
via apoplectic root due to the presence of the endodermal casparian strips
-Only minerals that are already in the symplast can detour around the casparian
strips
-Once water reaches the xylem in the stele, the water enters the xylem cells, and
the minerals and water move through the apoplast route
Root Pressure
-When transpiration is very low (like at night), the root cells secrete ions into the xylem
-Due to the endoderms, ions will not leak out of the xylem making the water potential
of the xylem more negative and therefore water will move into the xylem by osmosis
-This will create root pressure, and will force both water and dissolved ions up through
the xylem
-Root pressure guttation: the exudation of water droplets
-Transpiration: the loos of water vapour by any part of the plant body
Surface Tension
-Surface tension is caused by the cohesiveness of water molecules, due to the
molecular structure of water molecules
-Each water molecule tends to form hydrogen bonds with four other molecules, and
each bond is fragile and short lived, but the sum of all of the bonds hold water
together with tremendous strength
-Adhesion: the holding together of unlike substances
-Cohesion: the holding together of like substances
-Cohesion - Adhesion tension mechanism
-When the cells of a leaf lose water, their ions and molecules become more
concentrated as the water potential of the cells becomes more negative
-Due to the intercellular spaces, this potential moves from one cell to another until it
is transmitted to the contents of the xylem, which will build up there
-Due to the cohesiveness of water, this tension is transmitted all the way down the
stem to the roots once the water potential of the roots becomes more negative,
which will increase their ability to extract water from the soil
-The stoma
-Each stoma is surrounded by a pair of guard cells, that are
held by subsidiary cells
-They will control the diameter of the stoma by changing
shape
-When they take water in by osmosis, they become more
turgid and swell, increasing the gap between the cell
-When they lose water and become more flaccid, they sag
together and close the space between them
-These changes result primarily from the absorption and
loss of potassium ions (K+)
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-This occurs from from the movement of the guard cells paralleling the flow of K+
ions in and out of the cell
-In general stomata will be open during the day and close at night, but there are 3
factors that can trigger the opening and closing:
-1) The accumulations of K+ ions
-2) Opens when there is a depletion of CO2 in the air spaces in the leaf, during
photosynthesis
-3) Even in a dark spaces, the stomata will have daily rhythms of opening and
closing (known as a circadian rhythm) with cycle intervals about 24 hours
Xerophyte Adaptations That Reduce Transpiration
-Many xerophytes have small thick leaves, that reducing transpiration by reducing
surface area
-Presence of a thick cuticle giving the leaves a leathery consistency
-Other adaptations found in CAM plants (crassulaceans acid metabolism), plants
which open their stomata during the night and closing during the day
Translocation and the Phloem
-Imbibition (drinking up)
-Mass flows in the same overall movement of water it occurs in response to
differences in the potential of water
-Movement of Substances in the Phloem (Loading and unloading of assimilates)
-The pressure flow mechanisms
-According to the pressure flow hypothesis, the assimilates move through the
sieve tube along concentration gradients, between the sources (place where
food substances are available for transport) and the sinks (the sites that make
use of food substances, like growing cells or regions of storage)
-The pressure flow mechanisms operates as follows
-Sugar manufactured in the mesophyll cell in the leaf, is actively secreted into
the sieve tube of the vein, by neighbouring parenchyma cells such as a
companion cell
-This decreases the water potential in the sieve tubes, and causes water to
move from the xylem, into the sieve tube, the sugar is carried passively to the
root tip, where the sugar is removed from the sieve tube cell, by energy
-This results in increased water potential into the sieve tube cell and eventually
movement of water out of the tube cell at the sink cells
-Note that the role of the sieve tubes is a relatively passive one, as energy is
expended at the source and the sink.
Plant Hormones
-Plants often respond to external and internal stimuli, with changes in their growth
patterns
Document Summary
Physical forces drive the transport of materials in plants over a range of distances. Short distance transport is bringing substances from cell to cell (in all tissues and organs) Such as bringing sugars from a photosynthetic leaf cells into the sieve tube of the phloem. As well as long distance transport within xylem and phloem along the whole plant. One important active transport in plant cells is the proton pump, which hydrolyzes atp (to adp) and uses it to release energy to pump hydrogen ions (h+) out of the cell. This is because the proton pump moves the positive charge h+ out of the cell, which makes a membrane potential as there inside of the cell becomes negative with relation to the outside. The membrane potential helps to drive k+ into the cell because the k+ will be attracted to the more negative region of the cell, this is a passive transport.
