Transport in Plants Flashcards
Describe the process of active loading in translocation
Hydrogen ions are pumped out of companion cells
This increases the concentration of hydrogen ions outside of the cell
Hydrogen ions re-enter companion cells and sucrose moves with them down the concentration gradient by facilitated diffusion via a cotransport protein
Sucrose then diffuses into the drive tube element via plasmodesmata
Water loss from the leaf is replaced via the _________ and __________ pathways down the ________ ____________ gradient from the ______
This causes low __________ pressure in the top of the xylem creating a pressure gradient
This causes water to move from higher to lower pressure, so it is pulled up under ________ by _____ _____ and _________ between water molecules creating a ________of water molecules
Apoplast Symplast Water potential Xylem Hydrostatic Tension Mass flow Cohesion Column
What is capillary action?
Water moving up small tube (xylem) against gravity due to cohesion and adhesion between water molecules
In what way does water move up the xylem?
Mass flow
state 3 reasons why transport systems are needed in multicellular plants?
their size
metabollic rate
low SA:V
what is the structure of xylem?
xylem vessels joined end to end
no end walls so form a long hollow tube
walls are thickened with lignin to suppot and stop collapsing
water and ions move out of vessels through bordered pits where there is no lignin
what is the structure of phloem?
seive tube elements joined end to end
sieve plates between
seive tube element have no nucleus few organelles and very thin cytoplasm. cytoplasm of adjacent cells connected by holes in sieve plates
companion cell for each sieve tube element so they can survive without nucleus
how do you dissect plant stems?
use a scalpel to cut cross section of stem (longitudinal or transvese) as thinly as possible.
place cut section in water until use
transfer each section to a dish containing a stain - toluidine blue and leave for a min to stain lignin in xylem blue/green
rinse of section and mount onto slide
how is the vascular system of a plant arranged in the roots?
xylem is located in the centre surrounded by phloem to help the plant withstand tugging strains as the plant is blown in the wind
how is the vascular system of a plant arranged in the stem?
vascular bundles are located around the edge ( with xylem on central side and cambium in the middle)
gives the plant strength and support
how is the vascular system of a plant arranged in the leaves?
vascular bundles arranged in veins with xylem above the phloem. this gives leaves structure and support
state 4 factors that affect the rate of transpiration?
light
light is needed for respiration photosynthesis so stomata open when its light to allow gas exchange increasing the rate of transpiration
humidity
humidity reduces the waterpotential gradient between the leaf and the surrounding atmosphere reducing the rate of transpirstion
temperature
increases the kinetic energy of water molecules so increase rate of transpiration
air movement
maintains the waterpotential gradient between the leaf and surrounding atmosphere so increases the rate of transpiration
how can you measure the rate of transpiration?
using a potometer - measure the rate of air bubble movement.
what are 2 examples of xerophytes?
cacti and marram grass
what are 4 adaptions of maram grass?
sunken stomata
creates a microclimate of still humid air that reduces water potential gradient
hairs on epidermis
roll leaves in the wind
thick waxy cuticle
what are 4 adaptions of cacti?
thick waxy cuticle
spines instead of leaves to reduce SA:V
cacti close their stomata
specialised parenchyma tissue to store water
give an example of a hydrophyte
water lilly
what are some adaptations of hydrophytes such as waer lillies?
thin or no waxy cuticle
stomata permanently open of upper surface
lots of stomata on upper surface
reduced structure in plants (water supports it)
wide flat leaves
small roots
air sacs
what is the sugar molecules most commonly translocated?
sucrose
Describe and explain how transpiration contributes to the mechanism of water transport
up the stem.
idea of :
1 water loss (from leaf) is replaced ;
2 via, apoplast / symplast / vacuolar, pathways ;
3 down water potential gradient / AW ;
4 (lost water replaced) by water from the xylem ;
In the xylem:
5 (loss of water) causes, low / negative, (hydrostatic)
pressure (at top / in leaf)
OR
creates pressure gradient ;
idea of :
6 water moves, from higher pressure to lower pressure /
down pressure gradient ;
7 under tension / pulled up / drawn up ;
8 by mass flow ;
9 cohesion / attraction, between water molecules ;
idea of :
10 column / stream / chain, of water (molecules) ;
Describe three steps a student should take when setting up the potometer to ensure that the
apparatus works correctly.
ensure shoot is healthy
assemble aparatus/cut shoot under water
cut last 2-3 cm off at an angle
make sure aparatus is water tight
leaves dry
why is it beneficial for the carbohydrate to be transferred throughout the plant in the form of sucrose?https://www.brainscape.com/packs
sucrose is soluble so can be transported in the sap
sucrose is metabolically inactive so not used during transport
explain with an example how some parts of the plant can act as both a source and a sink?
certain parts can store and then release carbohydrates when needed
fir example leaves act as a sink or source at different times of the year
