9 plant biology Flashcards
why is palisade mesophyll located on the upper surface of the leaf
it’s the site of photosynthesis so needs to absorb light
why is spongy mesophyll on the lower surface of the mesophyll
main site of gas exchange so near stomata
why are stomata on the underside of the leaf
prevents obstruction otmaintain an open channel for gas exchange
why is the top of a leaf covered in a thick waxy cuticle
prevents water absorbtion which would affect transpiration
where are vascualr bundles located and why
located centrally to allow for optimal access by all leaf cells
label a plant from the inside out
pith
cortex
epidermis
fucntion of epidermis
waterproof, protect the stem and control gas exchange
what does the cortex and pith do
transport and storae of materials within the stem
what is the cambrium
centrally located, circular layer of undifferentiated cells responsible for lateral growth of the stem
describe the location of the xylem and phloem
xylem located to interior side of bundle and phloem on exterior
where are the vascular bundles located and why
in bundles near the outer edge of the stem to resist compression and bending
functions/adaptations of root hair cells
increase available surface area
central region called the stele and is surrounded by an endodermis with a casparian strip (controls water transport)
what does the pericycle/cambium provide
strength to the root and is also responsible for the development of lateral roots
what converts water in the leaves to vapour
light energy
where does water vapour evaporate from
from leaf to air from stomata
how is a difference in pressure created within the plant
new water absorbed from the soil by the roots, creating a difference in pressure between the leaves (low) and roots (high)
where does water flow in a plant
along pressure gradient to replace the water lost from leaves along xylem. this is called the transpiration stream
as photosynthetic gas exchange requires stomata to be open, transpiration will be affected by the level of…
photosynthesis
how does water get from the roots to the leaves
via the xylem.
function of roots
uptake of water and minerals
cross structure of leaf labelled from outside in
cuticle upper epidermis palisade cells containing chloroplasts spongy mesophyll containing air spaces and the vascular bundles lower epidermis stomata and guard cells
what does the mesophyll layer contain
palisade cells
spongy mesophyll
by what processes does water travel up the xylem
cohesion by hydrogen bonding
how does water travel from the soil into the root cells
osmosis.
due to a high solute concentration inside the cytoplasm, established by active transport of mineral ions
what transmits the pulling force from one water molecule to the next
cohesion of water molecules due to hydrogen bonding
why are cell surfaces moist
water is adhesive to the hydrophilic cellulose in the cell walls
what does water adhering to cellulose allow for
carbon dioxide to dissolve and diffuse into the cytoplasm, and excess oxygen to dissolve out
what is the symplast pathway
osmosis via centre of cells
what is the apoplast pathway
diffuses along cell wall boundaries
what contains the casparian strip
endodermis
apoplast pathway
Involves the cell walls (spaces between cellulose fibres allow water to pass easily)
Water diffuses from the soil to the endodermis where the waterproof Casparian strip prevents further progress through the apoplast pathway
At the Casparian strip water must pass through the selective membrane (by osmosis down a water potential gradient) into the symplast pathway if it is to get into the xylem vessels. This prevents harmful molecules such as toxins or viruses entering the xylem vessels and being transported around the plant because the membrane would not let these molecules past.
symplast pathway
Involves the cytoplasm and vacuoles.
To move into the symplast pathway water must pass through a membrane by osmosis due to a lower water potential in the cytoplasm than the soil water. Water potential in the root hair cells is reduced by the active transport of mineral ions into them from the soil
In the symplast pathway water diffuses along a water potential through pores between cells of the cortex called plasmodesmata
what is the transport system called which moves substances around the plant in special tissue
vascular tissue
what does the xylem transport
water and soluble minerals upwards
what does the phloem transport
transports sugars upwards and downwards
what cells are around the vascular bundle
the endodermis
what is inside the endodermis
a layer of meristem cells called the pericycle
where are the vascular bundles found
near the outer edge of the stem.
xylem inside
phloem outside
what is in between the xylem and phloem vessels
the cambium
LABEL PAGE ON ONENOTE CALLED
- XYLEM AND PHLOEM NTOES
what do the fibres in the xylem do
support the plant and living parenchyma cells
what do xylem walls have
lignin
what does lignin do
make the xylem cell walls waterproog and this causes the cells to die, so their contents and end walls decompose laving a hollow tube of dead cells. the lignin strengthens the tube and prevents the vessel from collapsing
adv of the xylem vessels being narrow
water column doesnt break easily, and capillary action can be effecive
what does lignin being depositied in spiral circles or broken rings allow
the xylem to stretch as the plant grows and enables the stem or branch to bend
what does the phloem consist of
sieve tube elements and companion cells
why are seive tube cells not cells
dont have much cytoplasm and no nucleus
why is sucrose used instead of glucose
glucose would all be respired if that is waht the plant stored
what is the sucrose dissolved in
water to form sap
how does sap flow through the phloem
it contains cross walls at intervals, perforated by many pores to allow the sap to flow. hence the cross walls are called sieve plates and the tubes sieve tubes.
describe companion cells
small cells with large nucleus and dense cytoplasm. large numbers of mitochonfria.
what do companion cells do
carry out the metabolic processes using atp energy, such as loading the sucrose in the tubes
what is translocation
movement of organic compounds from sources to sinks
what is the source
where the organic compounds are synthesised (photosyntehtic tissue like leaves)
what is the sink
where the compounds are delivered to for use or storage (roots, fruit, seeds, tubers)
what are sugars principally transported as
sucrose (disaccharide) as it is soluble but metabolically inert
why do sieve elements have thick and rigid cell walls
to withstand the hydrostatic pressures which facilitate flow
how do companion cells increase SA:vol
infolding plasma membrane for more material exchange
where are transport proteins in the companion cells
in the plasma membrane
why can sieve elements not sustain independendent metabolic activiy without the support of a companion cell
sieve element cells have no nuclei and fewer organelles to maximise flow rate
what are plasmodesmata
narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them
what do plasmodesmata mediate
symplastic exchange of metabolites
which of the plant vessels ahve larger cavities
xylem
monocotyledon
flowering plant with an embryo that bears a single cotyledon (seed leaf)
dicotyledon
flowering plant with an embryo that bears two cotyledons (seed leaves)
differences in monocotyledons and dicotyledons in xylem and phloem arrangement in roots
in monocotyledons, the stele is large and vessels form a large circle around the central pith
xylem more internal, phloem more external.
in dicotyledons, the stele is very small and the xylem is located centrally with the phloem surrounding it. xylems may form x like shape, while phloem situated in surrounding gaps
where are monocotyledons in stems
vascular bundles found in a scattered arrangement throughout the stem
where are dicotyledons in stems
arranged in a circle around the centre of the stem (pith). phloem and xylem separated by the cambium
how are organic compounds actively loaded into phloem sieve tubes by companion cells
materials can pass into the sieve tube via interconnecting plasmodesmata (symplastic loading)
alternatively materials can be pumped across the intervening cell wall by membrane proteins (apoplastic loading)
describe the active transport process of glucose entering phloem sieve tubes
Hydrogen ions (H+) are actively transported out of phloem cells by proton pumps (involves the hydrolysis of ATP)
The concentration of hydrogen ions consequently builds up outside of the cell, creating a proton gradient
Hydrogen ions passively diffuse back into the phloem cell via a co-transport protein, which requires sucrose movement
This results in a build up of sucrose within the phloem sieve tube for subsequent transport from the source
incompressibility of water allows transport along…
hydrostatic pressure gradients
what makes sap solution hypertonic in the source
active transport of solutes into the phloem by companion cells
what does increase in hydrostatic pressure cause
forces the phloem sap to move towards areas of lower pressure (mass flow) so the phloem transports solutes away from the source and towards the sink
at the sink, how does the sap solution become hypotonic
solutes within the phloem unloaded by companion cells and transported into sinks (roots, fruits, seeds etc)
as the sink sap is hypotonic, what happens
the water is drawn out of the phloem and into the xylem by osmosis, so hydrostatic pressure at the sink is always lower than hydrostatic pressure at the source, so phloem sap should move from the source towards the sink
xerophytes
plants that hae adapted to live in conditions where liquid water is difficult to obtain.
adaptations of xerophytes
thick/waxy cuticle on leaf or stem fewer stomata stomata in sunken pits fine hairs along underside of leaf CAM physiology reduced air spaces in leaf mesophyll few/small leaves curled or rolled leaves water storage tissue deep highly branched roots
adaptation of thick waxy cuticle
Reduces non-stomatal transpiration rate because the cuticle is hydrophobic and creates a barrier to prevent water loss.
adaptation of fewer stomata
Reduces transpiration rate by having fewer openings in the leaf.
adaptation of stomata in sunken pits
Reduces transpiration rate by allowing moisture (humidity) to build up near stomata.
adaptation of fine hairs along underside of leaf
Reduces transpiration rate by retaining a layer of moisture near the stomata.
adaptation of CAM physiology
Reduces transpiration rate enormously because stomata close during the day. Stomata open at night to collect and store carbon dioxide, when darkness and cooler temperatures reduce evaporation. During the day, pre-collected carbon dioxide allows photosynthesis to occur without water loss.
adaptation of reeduced air spaces in leaf mesophyll
Reduces transpiration rate due to reduced surface area for evaporation.
adaptation of few small elaves
Reduces transpiration rate because there is reduced surface area for light to strike and water to evaporate.
adaptation of curled or rolled leaves
Reduces transpiration rate because there is reduced surface area for water loss and there can be production of humid areas by the stomata.
adaptation of water storage tissue
Increased water storage when water is available. Succulent plants have tissues in stems or leaves adapted to store large amounts of water; other plants store water in tubers.
adaptation of deep highly branced roots
Increased ability to take up water because deep roots may reach a lower water table beyond the dry soil. Branched roots provide increased surface area for water absorption.
halophytes
plants that have adapted to grow in areas with high salinity, such as along an ocean shoreline or in certain swamps and marshes
adaptations of halophytes
salt storage in vacuoles high conc of organic solutes salt storage glands in leaf leaf abscission for some leaves selectively permeable membrane in root cells xerophytic adaptations
adaptation of salt storage in vacuoles
Compartmentalises salt in vacuoles, thus protecting cellular organelles and enzymes from damage by high salt concentration.
adaptation of high conc of organic solutes
Increases osmolarity by having a high concentration of sugars and other solutes, thus water can still enter by osmosis.
adaptation of salt storage glands in leaf
Accumulates salt in a limited area by filling the salt glands until they release salt crystals onto the leaf surface where they will fall off or be dissolved in rain.
