Transport In Plants Flashcards
Why do plants need a transport system?
Plants need a transport system because large plants have a smaller surface area to volume ratio, requiring a specialised gas exchange surface and a transport system. They also need to move water and minerals from roots to leaves and sugars from leaves to the rest of the plant.
What is the transport system in plants composed of?
The transport system in plants consists of specialised vascular tissue.
What does xylem carry?
Xylem carries water and mineral ions.
What does phloem carry?
Phloem carries sugars.
Where are xylem and phloem found?
Xylem and phloem are found in vascular bundles.
What other types of tissues are found in vascular bundles?
Vascular bundles contain other types of tissues such as collenchyma and sclerenchyma, which provide strength and help support the plant.
What is the structure of xylem and phloem in the root?
In the root, xylem and phloem are found in the endodermis and medulla.
What is the structure of xylem and phloem in the stem?
In the stem, xylem and phloem are found in the medulla, along with collenchyma and sclerenchyma.
Function of the xylem
Transports water and dissolved mineral around the plant
Structure of xylem
-walls are lignified- waterproof
-made of dead cells
-parenchyma cells acts as packing tissue to separate and support vessels
Structural ADAPTATIONS of the xylem
-Lignified makes it waterproof and gives it strength
-Bordered pits so water and minerals can move into other vessels
-Narrow tubes so water column doesn’t break
Function of phloem
-transports assimilates around plant
What is a structure and the adaptation for phloem
-Sieve tube elements- no nucleus and other organelles to free up space for mass flow
-companion cells which have mitochondria to produce atp for the active processes
-has sieve plates - which allows movement of sap from one element to the next
What is the plasmodesmata
Gap in the cell wall containing cytoplasm that connects 2 cells
What are the pathways taken by water
Apoplast
Symplast
Vacuolar
What is the apoplast pathway
Water travels through spaces in the cell wall between cells
What is the symplast pathway
Water travels through the cytoplasm
What is the vacuolar pathway
-water moves similar to symplast but also through the vacuole
What is transpiration
The evaporation of water from the leaf
How is water loss limited from transpiration
Waxy cuticle limits it
When does majority of water loss happen and why
During the day when the stomata is open
What is the pathway of water loss
-water moves into leaf by xylem and moves by osmosis to the spongy mesophyll
-it then evaporates from the cell wall
-and leaves by the stomata by diffusion
What is the importance of transpiration
-maintains cell turgidity
-keeps plant cool on a hot day
-transports minerals up the plant
How does light intensity affect transpiration
-stomata opens to allow gas exchanges higher light intensity= higher transpiration
How does temperature affect transpiration
-increases rate of evaporation form cell surface
-increases diffusion through stomata
How does humidity affect transpiration
-high humidity in air DECREASES transpiration as more moisture in air so small water potential between air outside and leaf
How does wind affect transpiration
-it carries the water vapour away
-which maintains a high water potential
Describe water movement across the root
-root hair cell increases surface area of the root
-water moves across root cortex down a water potential to the endodermis
-water travels through the apoplast pathway but is blocked by the casparian strip so has to take the symplast Pathway
What is mass flow
Water travelling upwards through the xylem
What is rhe 3 processes that help water travel up the stem
Root pressure
Transpiration pull (cohesion-tension theory)
Capillary action
Explain the process of root pressure
-pressure in the root medulla pushes water into xylem
-water moves up xylem
-this pushes water a few meters up the stem
Explain the process of the cohesion tension theory (transpiration pull)
-water is loss from top part of the plant
-so must be replaced
-water molecules stick together by cohesion
-this holds the water in a column
-when water is lost from top the whole column is pulled upwards creating tension
Why do xylem need to be lignified
To make them stronger
Because of cohesion tension colum is pulled up creating tension
Explain the process of capillary action
-adhesion makes the water molecules stick to the walls of the xylem
-so forces of attraction can pull the water up the sides of the column
What is a terrestrial plant and how do they reduce water loss
-plants that live on land
-have waxy cuticle which reduces evaporation
-stomata is closed at night - when there no light for photosynthesis to stop gas exchange
-stomata under leaves- to reduce evaporation because of direct sunlight
What is a xerophyte and give examples
A plant that is adapted to live in dry conditions
E.g cactus and marram grass
give the adaptations of marram grass
-leaf is rolled - to trap air inside making it humid to reduce water loss
-thick waxy cuticle on outer side - to reduce evaporation
-stomata in pits in lower epidermis- covered with hair to reduce air movement
-stomata on inner side of rolled leaf- protected by enclosed air space
Give adaptations of catcti
-green stem for photosynthesis
-succulents- so store water in stems
-stems are ribbed so can expand when water is available
-leaves reduced to spines which reduce surface area to reduce water loss
-roots are widespread - gets any available water from underground
What is a hydrophyte and give and example
-plant that is adapted to live in water
E.g water lily
Give adaptation of water lily
-stomata on upper side of epidermis - allows it to be exposed to air for gas exchange
-large air spaces to keep it afloat and can absorb sunlight
What is translocation and where does it occur
-movement of assimilates
-happens in phloem
What is the source
Where assimilates are produced
What is the sink
Where the assimilates are used or stored
What is the first step of translocation and explain it
Loading
- H+ ions are actively pumped out of the companion cells
- H+ ions flow back into the companion cells down the conc gradient through a co transporter protein with sucrose
-water potential is low bc sucrose conc is high
-water ,moves into companion cell
-water and sucrose them diffuse into the sieve tube through the plasmodesmata
What is the second step of translocation
-pressure flow
-since water and sucrose have moved in sieve tubes the hydrostatic pressure is increased near the source
-cells in the sink are using water and sucrose, removing them from the phloem tubes creating a low pressure at the sink
-sugars move down the phloem by mass flow
What’s the last step of translocation
Unloading
- as sucrose conc is higher in the phloem it diffuses into the respiring sink cells
-water follows by osmosis lowering through hydrostatic pressure and increasing mass flow
In some cases sucrose is actively pumped against its conc gradient into the sink
What is used to measure transpiration in plants
Potometer
Explain the investigation into transpiration
Set up pototmeter and pick 2 species to compare
Make sure shoots are cut under water
Measure the distance of the bubble moved at regular intervals
Find mean and plot it on a graph
Make sure the size of the leaf is the same for both species
Make sure temperature is the same when experiment is carried out as it can affect transpiration if not controlled, same with light intensity, keep lamp at the same distance throughout experiment
What are precautions needed for setting up the potometer
Shoot should be cut under water
No extra air bubbles
Leaf should be dry otherwise stomata is blocked
