Transport in Plants Flashcards
what is the need for plant transport systems
- need substances from the environment to live
- need to excrete substances
- small surface area to volume ratio
- high metabolic demands
- cannot use direct diffusion
what is xylem tissue
- non-living tissue
- transport water and mineral ions
- no end walls allowing water to pass through
- walls are thickened with lignin to support xylem vessels and prevent collapsing
- water and ions move in and out of the vessels through small pits where there are no lignin
what is phloem tissue
- living tissue
- transports food in the form or organic solutes around the plant from the leaves
- sieve tube elements
- companion cells
what are sieve tube elements
- living cells that form the tube
- joined to end to end to form sieve tubes
- end walls have holes allowing solutes to pass through
what are companion cells
- carries out living function for themselves and sieve cells
- plasmodesmata
- large nucleus
- dense cytoplasm
what is the vascular bundle
- plants that have a specialised transport system
- xylem and phloem tissue
what is plasmodesmata
pores connecting cytoplasm of neighbouring cells across cell walls
what is the importance of water in a cell
- turgor pressure provides hydrostatic skeleton to support stems and leaves
- loss of water by evaporation cools the plant
- minerals and products of photosynthesis are transported
how is water moved into the root
- root hair cell
- microscopic size to penetrate easily between soil particles
- large SA:V of each hair - thin surface layer for diffusion and osmosis to take place easily
how does water move across the root
- apoplast pathway
- symplast pathway
what is the symplast pathway
- water moves through the symplast (cytoplasm) connected by plasmodesmata
what is the apoplast pathway
- water moves through cell walls and intercellular spaces
- cohesive and tension forces against the cell wall pulls the water up the plant
- continuous flow of water
how does water move into the xylem
- water moves until it reaches the casparian strip in the endodermis
Casparian strip
- band of waxy material forming a waterproof layer
- all water in the apoplast pathway is forced into the symplast pathway
how is water moved up the stem
- root pressure
- transpiration
- capillary action
what is the evidence for the role of active transport in root pressure
- affect of cyanide - stops mitochondria from working and the production of ATP - no root pressure
- root pressure increases when temperature increases
- when oxygen and respiratory substrates fall root pressure falls
what is transpiration
movement and loss of water from plants
what is the process of transpiration
- water molecules evaporate from the surface of mesophyll cells into air spaces in the leaf and move out of the stomata into the air by diffusion
- loss of water by evaporation lowers the water potential of the cell
- water moves from the xylem into the mesophyll cells via pathways
- water moves out of the xylem by osmosis
- water molecules form hydrogen bonds with carbohydrates in the xylem vessels by adhesion
- water molecules form hydrogen bonds with each other and stick by cohesion
- water is drawn up by the xylem in a continuous stream to replace the water lost by evaporation
- transpiration pull results in tension in the xylem which moves water across the roots from the soil - cohesion tension theory
what is the evidence for cohesion tension theory
- changes in tree diameters - transpiration at highest in the day so is tension in xylem vessels and tree shrinks in diameter
- broken xylem vessels - cut flower stems in water air is drawn in rather than water leaking out
how does the stomata control the transpiration rate
- low turgor pressure cell wall closes
- favourable conditions guard cells pump in solutes by active transport increasing turgor
- cellulose hoops prevent cells from swelling in width
- water becomes scarce and hormonal signals from the roots can trigger turgor loss from the guard cells which close the stomatal pore and conserve water
what are the facts affecting transpiration
Light
- low light intensity stomata are closed and high they are open (increasing diffusion of water vapour and evaporating)
- increasing light intensity increases rate of transpiration
Humidity
- high humidity lowers transpiration rate as there is a reduced water potential vapour gradient
Temperature
- increase in temperature increases kinetic energy and rate of evaporation
Air movement
- increases rate of evaporation and transpiration
what is translocation
- transport system in the phloem
- transport of organic compounds from sources to sinks
- active process that requires energy
what are sources and where are they found
- provide assimilates to the plants
- green leaves and stems
- storage organs - tubers
- food stores in seeds
what are sinks and where are they found
- use assimilates from the plant
- growing roots / actively absorbing mineral ions
- actively dividing meristems
what is the process of translocation
Phloem loading
- soluble products of photosynthesis are moved into the phloem from sources
Symplast route - passive process
- sucrose moves through cytoplasm of mesophyll cells into seive tubes by diffusion through plasmodesmata
- sucrose in sieve elements and water flows by osmosis
- creates pressure of water that moves sucrose through the phloem by mass flow
Apoplast route - active process
- sucrose travels through the cell walls and inter cellular spaces to the companion cells and sieve elements by diffusion
- in companion cells sucrose is moved into the cytoplasm
Phloem unloading
- diffusion of sucrose from the phloem to the surrounding cells
what are xerophytes
- live in a low water area
what are the adaptations of xerophytes
Thick waxy cuticle
- minimise water loss
Sunken stomata
- located in pits to reduce air movement producing still humid air that reduces water vapour
Reduced number of stomata
- reduces water loss and gas exchange
Reduced leaves
- reduces SA:V to minimise the amount of water loss
Hairy leaves
- create a microclimate of still humid air reducing water vapour and loss of water by transpiration
Succulents
- stores water when it is in plentiful supply and used later on
Root adaptations
- long deep roots to access water below the surface
what are hydrophytes
- live partially or completely submerged in water
what are the adaptations of hydrophytes
Thin / No waxy cuticle
- don’t need to conserve water
Open stomata on upper surface
- maximises gaseous exchange
- no loss of turgor - always water avaliable
- inactive guard cells
Reduced structure
- water supports the leaves and flowers
Small roots
- water diffuses directly into stems
Air Sacs
- enables leaves and flowers to float to the surface
