Transport In Plants Flashcards
Location of xylem/phloem in the ROOT , STEM and LEAF?
ROOT: vascular bundle in centre
xylem is in centre core of bundle/ phloem on edges of centre core
- to withstand pulling strains when plants transport water upwards/grows
STEM : vascular bundle on outside
- xylem on the inside and phloem on outside- support that reduces bending
LEAF : xylem/phloem form network of veins- support
- xylem found on upper side of vascular bundles
- phloem found on lower side of vascular bundles
Function/structure of phloem tissue?
Transport organic compounds ,like sucrose, from source to the sink
CONTAINS:
Phloem fibres
Phloem parenchyma
Sieve tube elements
Companion cells
Function/structure of xylem tissue?
- vascular tissue that transports dissolved minerals/water around plant
Structural support/food storage
Structure:
Tracheids- long narrow cells with pits (allow lateral movement of water )
Vessel elements- large with thickened (strength) cell walls/no end plates (allow mass flow of water as cohesive/adhesive forces not disrupted)
Xylem parenchyma / Sclerenchyma cells
Made up of dead cells- does disrupt mass flow of water
Small diameter of vessels - prevent water column from breaking /assist capillary action
lignified/cellulose cell wall
What are sieve tube elements in phloem tissues ?
Structure and function?
Living cells - form tube for transporting solutes through plant
- joined end to end to form sieve tubes
Sieve plates with sieve pores (on end walls) - allows continuous movement of compounds
No nucleus, few organelles - maximise space for translocation
Thin cytoplasm - reduce friction to facilitate movement of compounds
cellulose cell wall - strengthen wall to withstand hydrostatic pressures that move assimilates
Companion cells structure and function ?
Each sieve tube elements have companion cells associated with it
- control metabolism of their sieve tube member / involved in loading/unloading sugars into phloem
nucleus /organelles present - provide metabolic suppport to sieve element
Transport proteins- moves substance into/out sieve tube element
Mitochondria- provide ATP for active transport of substance into/out companion cells
Plasmodesmata - links sieve tube elements , so substance can move from companion cells into sieve elements
REQUIRED PRACTICAL: dissecting plant stems
- Use scalpel to cut cross section of stem (transverse or longitudinal) as thin as possible
- Use tweezers to put cut sections in water - prevent drying out
- Transfer each section to dish containing a stain (toluidine blue O)/ leave for a minute
Stains lignin in xylem vessel walls blue-green - Rinse in water/mount onto slide
How does water move through roots into xylem?
Apoplast pathway: goes through non living parts of cells (cell walls)
- water can diffuse through cell walls
When water reaches the endodermis cells in root , path is blocked by waxy strip in cell walls ,CASPARIAN STRIP - must take symplast pathway
- useful bc can control which substances can get to xylem/generate root pressure , as membrane is partially permeable
Symplast pathway : goes through living parts of cells - cytoplasm/plasmodesmata
Cytoplasm of neighbouring cells connected by plasmodesmata (channels in cell walls)
- water moves by osmosis into cells (across cell walls)
- slower than Apoplast pathway
Which transport pathway is more common in plants and why?
Apoplast pathway
- provide least resistance
What is the transpiration stream ?
Movement of water from roots to the leaves
- water evaporates from leaves through stomata - transpiration
- creates tension ,so pulls more water into leaf cells/ moves through Apoplastic (cell wall) or symplastic pathway (cytoplasm)
- water lost by transpiration lowers WP in the air spaces surrounding the mesophyll cells
- water evaporates from mesophyll cell wall into air spaces - cause TRANSPIRATION PULL
Water moves through mesophyll cell wall - water moves out of xylem, through non lignified areas (PIT), into mesophyll cells BY OSMOSIS
- causes water to move up the xylem vessels (due to the cohesive and adhesive properties of the water)
- adhesion allows water to move by CAPILLARY ACTION
This movement is called transpiration stream
What is transpiration ?
Water leaves xylem through NON LIGNIFIED AREA /moves into leaf cells by the APOPLAST PATHWAY
- water evaporates from cell walls into air spaces
- when stomata open , water diffuses out of leaf into surrounding air (down water potential gradient)
- loss of water = transpiration
What are four factors effecting transpiration rate?
LIGHT: stomata are open when light , for photosynthesis - co2 can diffuse into leaf to produce glucose
- faster transpiration rate, bc water is lost
TEMPERATURE : water molecules have more KE, so evaporate from cells FASTER /creates steeper water potential gradient for faster diffusion
HUMIDITY : when air is saturated with water vapour, water potential grad is decreased , so REDUCED RATE OF TRANSPIRATION
WIND : windier it is , faster transpiration rate
- blows away water molecules from leaf surface , around stomata , maintaining steep water potential grad
- as water may accumulate on surface of leaf —> create local area of humidity = lower conc grad
REQUIRED PRACTICAL : investigating rate of transpiration using potometer
- Cut a shoot at a slant (INCREASE SA) , underwater to prevent air entering xylem
- Assemble potometer in water /insert shoot underwater , so no air can enter xylem
- Remove apparatus from water/but keep end of capillary tube submerged in water - make sure apparatus is AIRTIGHT/WATERTIGHT
- Dry the leaves of shoot - moisture present could effect rate of transpiration
- Remove a capillary tube from beaker of water to allow single air bubble to form/place back in water
- Record starting position of air bubble
- Start stopwatch and record distancemoved by bubble per (minute/hour) - rate of bubble movement = rate of transpiration
- Can repeat with different conditions (temp,light, humidity and wind)
Xerophytes: what are they/adaptations?
Plants that are adapted to dry/arid conditions
E.g cacti and marram grass
Sunken stomata - slows transpiration , bc sheltered from wind , so decreased water potential gradient
- also traps moist air to area of water loss - reduce diff gradient
Hairs on epidermis - traps moist air around stomata , reducing WP grad - slow transpiration rate
Leaves curled/needle or spine like - reduced transpiration due to less SA
Thick /waxy layer on epidermis - reduce water loss by evaporation
Reduced no. Stomata - less water loss
Hydrophytes : adaptations /what are they?
Plants adapted to living in freshwater - face challenge of low CO2 level in day/O2 at night
AIR SPACES in tissues - help plant float /act as store of oxygen for respiration
STOMATA ON UPPER SURFACE of floating leaves - maximise gas exchange
FLEXIBLE LEAVES /STEMS- prevent damage from water currents
What is translocation ?
Transport of assimilates from source to source to sink - requires ATP
Source eg:
leaves/stem
Storage organs
Sink eg: meristems
Growing roots
Storage organs
