9.1-9.5 transport in plants Flashcards
(36 cards)
what is a hydrophyte?
a plant that lives on the surface or submerged in water (e.g a water lily)
what are the specialised parenchyma cells found in hydrophytes?
arenchyma
what is the purpose of parenchyma (in hydrophytes) ?
they have more air spaces which make leaves and sets more buoyant and form pathways for O2 with less resistance for tissues below water that have extremely low oxygen
What are the adaption to the leaves of xerophytes?
-thick waxy cuticle to minimise water loss
-sunken stomata located in pits to decrease air movement and make a micro-climate of humid air which decreases the water potential gradient and slows down the rate of transpiration
-less stomata
-curled or rolled leaves create a micro climate like the stomata pits
-needles instead of leaves to decrease the surface area
what is a xerophyte?
a plant that lives in an area with extremely low water availability (e.g cacti and marram grass)
adaptions for the roots of xerophyte cells?
long tap roots that go meters down into the soil or mass widespread shallow roots to absorb as much water as possible after rainfall
what are the 5 factors affecting transpiration
-light-increasing light intensity increases the volume of open stomata for photosynthesis, meaning an increase in the rate of transpiration
-temperature- increasing the temperature increases the kinetic energy of the water molecules so the evaporate faster which increases the diffusion gradient so the rate of transpiration increases
-humidity- increasing humidity decreases the water potential gradient decreasing diffusion and the rate of transpiration
-air movement- decreasing air movement leads to an accumulation of water around the stomata which decreases the diffusion gradient and therefore the rate of transpiration
-soilwater availability- less water = decrease rate of transpiration
what are the components of the xylem vessel?
-thick lignified cell wall; spirals of lignin to prevent the xylem from collapsing under the transpiration pull
-non-lignified pits ( tracheid ) that allow the continual flow of water incase of air bubbles
-xylem parenchyma between xylem vessels
-small diameter to prevent water columns breaking
-dead tissue
what does the xylem do?
transports water and minerals from the roots to the leaves and the rest of the plant
how does water move into the xylem?
-follows the symplast or apoplast pathway till it reaches the endodermis due to the casparian strip where all water goes into the symplast pathway filtering out any toxic solutes.
- water then enters the xylem using osmosis as the water potential of the xylem is a lot lower than in the endodermal cells
-minerals are pumped into the xylem via active transport which results in root pressure pushing water up the xylem
what is the casparian strip?
a band of waxy material called suberin that runs around endodermal cells forming a waterproof layer
how does water move out of the xylem into the leaves?
water diffuses into the apoplast pathway in the leaves where it moves into mesophyll cells and evaporates in the air spaces then diffuses out of the stomata. this is a turgor driven process
what is the transpiration pull?
due to cohesive and adhesive forces water is able to move upwards against gravity (cohesion tension theory)
what evidence is there on the transpiration pull?
-when a xylem is broken air is drawn in rather than water leaking out
-changes in tree diameter due to when xylem tension is at its highest during the day or its lowest at night
what are components of the phloem?
-sieve plate
-sieve tube elements
-hollow structure that is filled with phloem sap that breaks down organelle
-companion cells with lots of mitochondria to provide energy for active transport of assimilates
-companion cells linked to phloem by plasmodesmata
what does the phloem do?
it is a transport vessel for organic solutes made up of living tissue
what is translocation?
the transport of organic compounds known as assimilates from sources to sinks via phloem loading and unloading
examples of sources go organic compounds for translocation
-green leaves and stems
-food stores in seeds when they germinate
examples of sinks in translocation
-growing roots
-meristem
-developing seeds
-fruit or storage organs
what is phloem unloading?
assimilates are unloaded to any cells that they are required in via diffusion.
what are the two types of phloem loading?
active and passive
what is an example of phloem unloading?
sucrose is unloaded into the leaves and broken down into glucose. this maintains the diffusion gradient for sucrose
what is passive loading of the phloem?
sucrose moves through the cytoplasm of mesophyll cells (the symplast pathway) and into sieve tubes by diffusing across the plasmodesmata
