chapter 9 - transport in plants Flashcards
what are dicotyledonous plants
flowering plants that have a pair of leaves, or cotyledons, in the embryo of the seed
what are meristem tissues
where are they found and what are they called in plants?
a layer of dividing stem cells
found between the xylem and the phloem
called the cambium/ pericycle
define collenchyma
the supporting tissue composed of elongated cells within non-lignified primary walls. filled with water which helps plant keep its shape
where is collenchyma present?
between the cortex of stem and the endoderm of its vascular bundles
define sclerenchyma
strengthening tissue in a plant, formed from cells with thickened, lignified walls
where is sclerenchyma found in plants?
in non-growing regions, usually in the bark or mature stems
define parenchyma
where is it found predominantly
cells that perform storage or secretory functions and form wood rays, typically soft and succulent,
found chiefly in the softer parts of leaves, pulp of fruits, bark and pith of stems, etc.
what is the central midrib
thick linear vein that runs along the length of the plant thallus or lamina
what is a thallus
what are plants called that have a thallus
thallus = plant body which is not properly differentiated into root, stem or leaf
- thallophytes
what is the lamina
the flat region of the leaf containing the chloroplasts, veins and stomata
what is the pith,
what is it also known as
a tissue in the stem. composed of soft spongy parenchyma cells which store & transport nutrients throughout the plant
also known as the medulla
what are ground tissues
tissues that are not considered vascular or dermal (either parenchyma, sclerenchyma or collenchyma
what is the apical stem
the main branch, in dicots, other branches stem off
where is the cortex of a plant
what is it composed of?
the outer layer of a stem or root in a vascular plant, lying below the epidermis, but outside vascular bundles.
composed of mostly large, thin-walled parenchyma cells
what is the cuticle of a plant?
what is the function of the cuticle
waterproofing layer of cutin
function: acts as a permeability barrier to prevent the evaporation of water from the outer epidermal surface
what is the epidermis
single layer of cells, transparent, secretes cutin (skin/surfaces)
what are the three passage ways of water from the root cells to the xylem
apoplast - through spaces in the cell walls and gaps between cells - does not pass through plasma membrane
once the water meets the casparian strip - it inters the cytoplasm of the endodermis and takes the symplast route
symplast - enters through plasma membrane then passes through plasmodesmata
vacuolar - enters through plasma membrane, passes through plasmodesmata AND VACUOLES
what is the difference between diffusion and mass flow as seen in the vessels
mass flow - movement of dissolved nutrients into a plant as the plant absorbs water for transpiration
diffusion - movement of nutrients in the root surface in response to a concentration gradient
why is mass flow the best way to transport around the plant?
because mass flow is faster and can move large amounts of fluid long distances
why do plants not need to transport gases such as oxygen in their transport system?
plants are not very active and their respiration rate is low - therefore demand for oxygen is low - can be met by diffusion
what is vascular tissue
tissues which carry/ transport substances
xylem and phloem
what is dermal tissue
surface/ skin tissue - outer protective layer layer
describe the structure of the xylem vessel
lignified, non-living tissue, supports plant and transports water and mineral ions from root to leaves (transpiration)
long hollow structures, cells fuse end to end
thick walled xylem parenchyma - stores food and tannin deposits
how is lignin arranged in the xylem vessels
either in spirals running around the lumen
rings between xylem parenchyma
solid tubes - with lots of small non-lignified bordered pits
describe the structure of the phloem
living tissue, transports the products of photosynthesis around the plant.
transporting vessels - sieve tube elements
non-lignified
areas between cells, walls become perforated to form sieve plates - let phloem contents pass through
mature phloem cells have no nucleus or tonoplast due to pores in walls
need companion cells to support
contains supporting tissues, including fibres and sclereids (cells with extremely thick walls)
why do sieve tube elements need companion cells
as sieve tube elements have no nucleus and less organelles
companion cells are linked to sieve tube elements by plasmodesmata.
companion cells are very active cells that function as a life support system for the sieve tubes which lost their normal cell functions
how are the vascular bundles arranged in cross sections of
stems
roots
leaves
stem = xylem and phloem are near the outside to provide scaffolding - reduces bending
root = xylem and phloem are in the centre to provide support for the root as it pushes into the soil
leaf = midrib of a dicot leaf is the main vein carrying the vascular tissue
what properties do sieve tube elements have
very little cytoplasm
no nucleus
no vacuole
DO have mitochondria and RER
lined end to end to form tubes with cross wall intervals - sieve plates - have pores to allow flow of water and solutes
what are the properties of the companion cells in the phloem
large nucleus
dense cytoplasm
lots of mitochondria
carry out metabolic processes for sieve tube elements
describe the process of pressure potential
as the cell fills up, the water exerts turgor pressure on the cell wall, which is known as pressure potential
as the pressure increases, it reduces the intake of water
how does water enter the root in terms of water potential
mineral ions (nitrates etc) are actively transported into the root hair cell
this lowers the water potential of the cytoplasm
water enters the cell via osmosis
why are xylem cells lignified in a specific way
to strengthen the xylem to withstand pressure created by the flow of water
with gaps - non-lignified pits allowing for lateral movement of water and minerals between xylem vessels
compare sclerenchyma fibres to xylem vessels
sclerenchyma vessels consist of dead cells like xylem
they are lignified like xylem but do not have pits
true or false - the phloem and xylem have no support function in the plant
false
the phloem has no support function but the xylem has lignin which provides support for the plant
what is the pericycle and where is it found
a layer of meristem cells inside the endodermis that remain able to divide
define endodermis
an inner layer of cells in the cortex of a root and of some stems, surrounding a vascular bundle, adjacent to the pericycle
how is the endodermis adapted to regulate water flow into the plant
cell walls of the endodermis are impregnated with hydrophobic substances (casparian strip) to restrict apoplastic flow o water to the inside
how does light intensity affect transpiration
light intensity - increasing light, increases number of open stomata and increases the rate of water vapour diffusing out and therefore increasing transpiration
what factors affect transpiration
light intensity
humidity
temperature
wind speed/ air movement
soil-water availability
how does humidity affect transpiration
high humidity lowers rate of transpiration because of the reduced water vapour potential gradient between the inside of the leaf and the outside air. lower humidity increases the rate by increasing the potential gradient
how does temperature affect transpiration
increase in temperature increases transpiration rate because
1. increases kinetic energy of the water molecules, increasing rate of evaporation from spongy mesophyll cells into the air spaces of the leaf
- increases concentration of water vapour that the external air can hold before it becomes saturated (decreases relative humidity and its water potential)
both factors increase diffusion gradient between the air inside and outside the leaf
how does wind speed/ air movement affect transpiration
still air around the leaf diffuses the concentration gradient by trapping water vapour that diffuses out of the leaf.
high windspeed will increase transpiration by increasing the concentration gradient
how does soil-water availability affect transpiration
if it is very dry in the soil, the plant will be under water stress and lose less water, decreasing transpiration rate
why is water key to both structure and metabolism of plants
- turgor pressure (or hydrostatic pressure) as a result of osmosis in plant cells provide a hydrostatic skeleton to support stems and leaves
- turgor also drives cell expansion - force enables plant roots to force their way through tarmac and concrete
- the loss of water by evaporation keeps plants cool
- mineral ions and the products of photosynthesis are transported in aqueous solutions
- water is a raw material for photosynthesis
At what point does the apoplast pathway join the symplast pathway
When the water reaches the casparian strip
define translocation
the movement of assimilates (products of photosynthesis) around the plant
what are the main sources and sinks in plants (translocation)
sources (produces the assimilates)
- green leaves and green stems
- storage organs such as tubers and tap roots that are unloading their stores at the beginning of a new growth period
- food stores in seeds when they germinate
sinks (recipients of assimilates)
- roots that are growing and/or actively absorbing mineral ions
- meristems that are actively dividing
- parts of the plant that are laying down food stores, such as developing seeds, fruits or storage organs
describe the passive way of phloem loading
- passive symplast route - assimilates move through the cytoplasm of mesophyll cells and into sieve tube through diffusion through plasmodesmata. sucrose ends up in the sieve tube elements and water follows via osmosis, creates a pressure of water that moves the sucrose through phloem by mass flow.
describe the active way of phloem loading
apoplast route
hydrogen ions are actively pumped out of phloem (via proton pump protein) into the companion cells then into the surrounding tissue using ATP
hydrogen ions return to the phloem via diffusion due to concentration gradient. return via hydrogen ion, sucrose cotransporter protein, bringing sucrose molecules with it into the phloem. increasing sucrose concentration in the phloem
the increase in sucrose concentration, means water moves by osmosis, creating a build up of turgor pressure due to rigid cell walls.
the water carrying the assimilates moves into the tubes of sieve tube elements reducing the pressure in companion cells, and moves up or down the plant by mass flow to areas of lower pressure (the sinks)
how does the phloem unload the assimilates
the assimilates are unloaded from the phloem at any point into cells that need it due to the concentration gradient (high in the phloem and low in the sinks)
the loss of solutes leads to a high water potential in the phloem so some of the water moves out into the surrounding cells via osmosis.
some water that carried the solutes to the sink is drawn into the transpiration stream in the xylem
in a root tissue plan, what is the name of the xylem, phloem and cambium in the centre
the stele
define xerophyte
a plant which needs very little water - lives in dry areas/ deserts
what adaptations do xerophytes have to reduce water loss
- thick waxy cuticle - less water vapour on stomata comes into contact with air
- sunken stomata - reduces air movement producing microclimate of humid, still air
- reduced number of stomata - also reduced gas exchange capabilities
- reduced leaves and leaf surface area - reduced SA:VOL ratio
- hairy leaves - create microclimate of still, humid air - reduces water potential gradient
- curled leaves - confines the stomata in a microenvironment of still humid air and reduces contact with air movement
- succulents - thick water storage unit - used in times of drought
- dense spongy mesophyll - less air gaps reduces water sitting on lip of guard cell
- long, thin, deep roots - find water deep underground and also anchors the plant
define hydrophyte
a plant which grows only on or in water
what adaptations do hydrophytes have to avoid water logging
- very thin or no waxy cuticle - do not need to reduce transpiration
- many and always-open stomata - maximises gas exchange
- stomata on the top of the leaf - if it were underneath stomata would be underwater and therefore no gas exchange
- reduced structure in the plant - water supports the leaves and flowers so no need for supporting features
- wide, flat leaves - increase surface area to volume ratio - absorb as much light and exchange as much gas as possible
- small roots - water can diffuse directly into the stem and leaf tissue without need for uptake by roots
- large stem surface area under water - maximises area for photosynthesis and for oxygen to diffuse into submerged plants
- air sacs - enable leaves to float to the water surface
- aerenchyma - specialised parenchyma (packing) tissue forms in the leaves, stems and roots. many large air spaces - make leaves more buoyant, forming low-resistance internal pathway for the movement of substances such as oxygen to tissues below the water.
describe the route of water from the soil to the xylem
actively transported from the soil to the root hair cells
then through the cortex
then meeting the casparian strip
then passes through the endodermis to the xylem
define aerial parts of plants
the parts above the ground
what type of plant is adapted to reduce water loss from the leaves and how does it do it?
deciduous plants - loose leaves in the winter when less water available and temperature is low
define arid conditions
what type of plants are adapted to live in these conditions
very dry conditions with little rain
xerophytes
how does having hairs on the surface reduce water loss in plants
trap a layer of saturated water vapour - water potential gradient reduced
how does the rolling of leaves reduce water loss
air saturated with water vapour is trapped in the leaf
stomata in sunken pits surrounded by leaf hairs to stop water vapour escaping
waxy cuticle on the outside so stomata are on the inside
define succulent
which types of plants are succulent
have a thickened fleshy storage of water - retains water in arid conditions
many xerophytes eg. cacti are succulents
how are guard cells adapted to perform their role
unevenly thickened cell wall
able to change shape/ bend
transport proteins / ion pumps in plasma membrane
presence of chloroplasts to provide ATP/ energy
where in the leaf can water be lost from
stoma, epidermis / cuticle
what is the difference between transpiration and transpiration stream
transpiration is when water molecules evaporate from the mesophyll cells in the leaf before diffusing out of the leaf through the stomata.
transpiration stream is the movement of water molecules up the xylem caused by the cohesion of water molecules due to their polarity and hydrogen bonding
describe and explain how water is moved up the xylem to the leaves in plants
water moves into xylem DOWN a concentration gradient
root pressure / high hydrostatic pressure at the bottom of xylem
transpiration/ water vapour loss at leaves
creating low hydrostatic pressure at top #
water under tension pulled up in continuous column - cohesion theory due to hydrogen bonding
adhesion of water molecules to xylem - due to polarity
water moves up xylem via mass flow
from higher hydrostatic pressure to lower hydrostatic pressure down hydrostatic pressure gradient
define transpiration
evaporation/ loss of water vapour
from aerial parts of a plant/ leaf
via stomata
