OCR A-level Biology- transport in plants

where are the vascular bundles in the stem and why

around the edges to provide strength and support

where are the vascular bundles in the root and why

in the middle to help withstand environmental factors like wind

where are the vascular bundles in the leaf

the vascular bundle is in the middle to help support the structure of the leaf

where is the xylem in the stem of a plant

facing inwards towards the middle

where is the phloem in a plant stem

facing outwards towards the epidermis

where is the xylem in a plant root

in the middle of the vascular bundle

where is the phloem in a plant root

on the outside surrounding the xylem

where is the xylem in a plant leaf

on the outside of the vascular bundle nearest the upper epidermis

where is the phloem in the root of a plant

on the inside of the vascular bundle nearest the lower epidermis

where is sclerenchyma tissue found in the stem of plants

on top of the vascular bundles nearest the epidermis

what is the role of collenchyma in the stem of a plant

to provide additional cellulose to strengthen the cornering tissue

what separates the xylem and phloem in vascular bundles in the stem

the cambium

what is the role of parenchyma cells in the stem

they’re highly metabolically active packing cells

what is hydrostatic pressure

the pressure exerted by a fluid onto the walls around it

what are some adaptations of a root hair cell

thin cell wall/cytoplasm/high surface area to volume ratio/large surface area/cell extension

how does water move through the symplast pathway

water moves through the plasmodesmata of neighbouring cells by osmosis

how does water move through the apoplast pathway

water moves through intracellular air spaces and dead cells by diffusion

what is the casparian strip

a layer of suberin that repels water forcing it into the symplast pathway

why is the casparian strip useful

it allows the control of substances preventing toxic substances harming the plant

what is evidence that the transport of water is active

poisons that prevent the production of ATP cause root pressure to decrease/root pressure increases with temperature increases/root pressure decreases with temperature decreases/if oxygen levels decrease root pressure decreases

what state are the guard cells in when the stomata are open

turgid

what state are the guard cells in when the stomata are closed

flaccid

what effect does high stomatal density have on transpiration

high stomatal density increases transpiration

what effect does high light intensity have on transpiration

high light intensity increases transpiration

what effect does high humidity have on transpiration

high humidity decreases transpiration

what effect does high wind have on transpiration

high wind levels increases transpiration

what effect does high temperature have on transpiration

high temperature increases transpiration

how does water move out of the guard cells

it diffuses down the water potential gradient

how does water move into the mesophyll layer

water is pulled out of the xylem vessel elements down the water potential gradient into adjacent cells

how does water move up the xylem vessels

by cohesion/tension/adhesion/cohesion-tension theory/transpiration pull what

what type of process is the opening of the guard cell and why

an active process moves water into the guard cell against the concentration gradient

what is a device used to measure the rate of water uptake in a plant

a potometer

what is the function and adaptations of xylem fibres

they’re highly lignified to provide structural support to the xylem

what are the adaptations of xylem vessel elements

thick lignified walls prevent the collapse of the xylem due to negative pressure potentials/thick cellulose cell wall increases adhesion/contain xylem pits allowing water to move laterally and avoid air bubbles/has a narrow lumen increasing turgor pressure/no end walls to impede mass flow

what are the phloem sieve tube elements function and adaptations

they’re the main site of translocation/cytoplasm pushed against the cell walls to limit impedement to mass flow/contain sieve plates that allow assimilates to pass through/contain plasmodesmata that allows the diffusion of sucrose into the phloem from companion cells

what is the function and adaptations of the companion cells

aid the active loading of sucrose/have many mitochondria to release energy to be used in the active process/have extrusive RER allowing protein synthesis to occur and process/package the assimilates/have a nucleus allowing the DNA of assimilates to be stored

what are adaptations of xerophytes

reduced leaves/reduced surface area to volume ratio/sunken stomata/thick waxy cuticle/leaf loss/specialised parenchyma to retain water

what is a xerophyte

a plant adapted to live in environments with very little water

what is a hydrophyte

a plant adapted to live in environments with lots of water

what are adaptations of hydrophytes

many open stomata/guard cells always open/not many strong structures/flexibility/aerenchyma providing buoyancy/short small roots/wide flat leaves/large surface area/chloroplast all over/even distribution of chloroplast/no waxy cuticle

what areas of the plant act as sources of sucrose

leaves/food stores/actively photosynthesising tissue

what areas of the plant act as a store of sucrose

meristematic tissue/growing roots/actively growing cells

how is sucrose loaded into a companion cell

a proton pump within a companion cell uses ATP to actively pump H+ ions against the concentration gradient, building a chemiosmotic gradient, cotransporters move the H+ ion and a sucrose molecule along the concentration gradient through facilitated diffusion, sucrose then needs to move into the phloem by diffusion through the plasmodesmata, more sucrose lowers the water potential, water moves into the phloem from surrounding cells by osmosis , high water potential increases turgor pressure allowing sucrose to be removed, increasing the water potential allowing water to move out by osmosis, decreased turgor pressure allows sucrose to move down the turgor pressure gradient by mass flow