adaptions for transport: PLANTS (C3) Flashcards
Equation for photosynthesis
CO2 + H2O ———> c6 h12 o6 + O2
Two transport systems in plants and what they transport
XYLEM tissue: water and mineral ions available only in the soil
PHLOEM tissue: photosynthates - glucose produced during photosynthesis used to make sucrose and amino acids
*xylem and phloem are vascular tissues
Arrangement of vascular tissue in the leaf (TS)
VASCULAR BUNDLE arranged as a VEIN or MIDRIB
Arrangement of vascular tissue in the stem (TS)
VASCULAR BUNDLES arranged around the PERIPHERY of the stem
Arrangement of vascular tissue in the root (TS)
Vascular tissue arranged in the CENTRE OF THE ROOT and together with the endodermis and the pericycle is called the STELE
*no vascular bundles in the root
Explain the uptake of water and mineral ions by the root
- mineral ions such as nitrates are ACTIVELY TRANSPORTED from the soil into the root hair cells (O2 enters the roots from the soil used in aerobic respiration, providing ATP for AT)
- this LOWERS the water potential INSIDE the root hair cell
- WATER enters the root via OSMOSIS down a water potential gradient
- water and dissolved min ions then travel through the root cells of the CORTEX to the ENDODERMIS and down a water potential gradient
Issue of a plant being in water logged conditions
waterlogged soils lack oxygen (less aerobic resp.) and so plants struggle with uptake of ions due to lack of ATP for active transport
Transport of water across the root routes
- symplast
- apoplast
- vacuolar
Apoplast pathway
Water is taken up by the root hair cell and moves across the roots cortex by cohesion via CELL WALLS
Symplast pathway
Water moves from the CYTOPLASM of one cell to the next by osmosis via PLASMODESMATA
Vacuolar pathway
Water can move via the CYTOPLASM and VACUOLES
What is the feature does the endodermis cell in the root have?
Contains a CASPARIAN STRIP
- made of a waxy substance called SUBERIN which is IMPERMEABLE to water molecules and mineral ions
Movement of water and mineral ions in apoplast and symplast pathway when at the endodermis cell
- at the endodermis water and mineral ions am from the apoplast pathway are FORCED into the symplast pathway due to the impermeable CASPARIAN strip
- therefore the only way the water and mineral ions can pass through the endodermis to the pericycle into the xylem by the SYMPLAST pathway
- giving the plant greater CONTROL over which ions enter the xylem and transported to the rest of the plant (preventing toxic ions from entering)
Transpiration definition
Transportation is the evaporation of water from INSIDE the leaves, through the STOMATA and into the ATMOSPHERE
*this gives rise to the transpiration stream
Movement of water from root to leaf
- water is absorbed by the ROOT HAIR cells
- water moves through the root tissue, into the XYLEM and is transported up the xylem in the plant stem to the leaf
- water is transported by osmosis from the xylem in the leaf to the cells of the SPONGY MESOPHYLL, where is evaporates from the surface of the cells into AIR SPACES
- water VAPOUR then DIFFUSES from the air spaces out of the leaf through the STOMATA down a water potential gradient
Cohesion definition
water molecules are attracted to EACH OTHER by HYDROGEN BONDS
Adhesion definition
water molecules are attracted to the HYDROPHILIC LINING of the LIGNIGIED xylem vessel WALLS
What is the cohesion-tension theory? (transpiration pull)
- as water vapor diffuses out of the STOMATA of the leaf by TRANSPIRATION, water molecules are DRAWN UP from behind to REPLACE those lost
- water molecules are draw ACROSS the leaf and UP the xylem due to COHESION between water molecules from HYDROGEN BONDS and ADHESION between water molecules and the xylem vessel walls
- this UPWARD MOVEMENT of water creates TENSION on the xylem vessel walls
Processes that help water move up the xylem to the leaves (1 main, 2 that help a little)
- COHESIO-TENSION THEORY (transpiration pull)
- CAPILLARITY
- ROOT PRESSURE
Explain capillarity
the forces of ADHESION and COHESION allow water molecules to RISE UP NARROW tubes for a SHORT distance
*only useful in small plants
Explain root pressure
when water moves from the ENDODERMAL cells of the root and into the XYLEM by osmosis this generates HYDROSTATIC PRESSURE and FORCES water a small distance up the xylem
*has more effect in small plants
Environmental factors affecting
transpiration (4 - which increase and decrease?)
*increasing water potential gradient between water vapor in the leaf and atmosphere increases rate of transpiration
R of T increased by…
- light intensity
- temperature
- wind speed
R of T decreased by…
- humidity
Affect on rate of transpiration: temperature
- RISE in temp, increases KE of water molecules
- increases rate of evaporation and diffusion into atmosphere
e.g water potential is LOWER in atmosphere of HIGHER TEMPERATURES (dryer) which INCREASES water potential gradient
Affect on rate of transpiration: air movement
- STILL air results in a layer of water vapor around the stomata of a leaf (DIFFUSION SHELL) this REDUCES wp gradient between inside and outside of the leaf
- air movement BLOWS away the diffusion shell so increases GRADIENT and R of T
Affect on rate of transpiration: humidity
- MORE water vapor in the ATMOSPHERE so wp gradient DECREASES
- leaf remains more SATURATED with water
e.g rainforest
Affect on rate of transpiration: light intensity
- LIGHT causes STOMATA to OPEN to allow gas exchange for photosynthesis
- increasing water movement out of the stomata
*limiting factor = number of stomata
What does a potometer measure?
the RATE of UPTAKE of water by the SHOOT which INDICATES the rate of transpiration
*the assumption is made that the rate of evaporation from the leaf is equal to the rate of uptake
Potometer method
- cut a leafy shoot UNDER WATER to prevent entry of air bubbles into the xylem vessels (these would BREAK hydrogen bonds, affecting cohesion)
- immerse the potometer completely under water and ASSEMBLE it (to prevent any air bubbles entering)
- fit leafy shoot and SEAL all joints with PETROLEUM jelly (so apparatus is air tight)
- PAT the leaves DRY (otherwise wp gradient will be reduced affecting results)
- OPEN TAP to introduce ONE air bubble in the CAPILLARY tube
- measure DISTANCE air bubble moves along SCALE in a SPESIFIC TIME (repeat 3x and calculate a mean)
Calculation of volume of water in capillary tube
V = pi x r2 x L
r = radius of internal capillary tube L = distance moved by bubble
Xylem tissue components: vessels
- MAIN cells that conduct water
- continuous column of DEAD CELLS arranged END to END , forming LONG, HOLLOW tubes
- walls THICKENED with LIGNIN, IMPERMEABLE to water to help water moving upwards in a unbroken stream and SUPPORTS plant from collapsing
Xylem tissue components: pits in vessels and tracheids
*both have pits in side walls
VESSELS:
- allow movement of water between adjacent vessels
TRACHEIDS:
- involved in movement of water to nearby living tissue
