Adaptations for transport in plants Flashcards
Distribution of vascular tissue
Vascular tissue= xylem and phloem in plants, found adjacent to each other in vascular bundles- have different distributions on different parts of plant
Xylem definition
Tissue in plants conducting water and dissolved minerals upwards- in roots is star shaped
Phloem definition
Plant tissue containing drive tube elements and companion cells, translocation good sucrose and amino acids from the leaves to the rest of plant- is found in roots between groups of xylem cells
Why is structures of xylem and phloem in root useful
Resists vertical stresses (pull)- anchors plant in soil
What are vascular bundles like in stems
Vascular bundles are in ring at periphery- xylem towards centre- phloem towards outside- gives flexible support- resists bending
Vascular structure in leaves
Vascular tissue in midrib/ in a network of veins- gives flexible strength/ resistance to tearing
Xylem structure
Main cell types in xylem are vessels/ tracheids
Tracheids
Spindle shaped, water conducting cells in xylems of ferns, conifers and angiosperms (flowering plants)- not in mosses- grow shorter
Vessels
Water conducting structures in angiosperms comprising of cells fused end to end making hollow tubes with thick lignified cell walls- essentially hollowed out as empty space called lumen is left
How lignin works in vessels
Lignin is laid down in a spiral pattern- kills contents of vessels while staining red- easy to see on microscope sections
Xylem functions
Transport of water/ dissolved minerals
Provide mechanical strength and support
Why vessels are better than tracheids
Teachers cell walls contain lignin- which is hard/ strong/ waterproof- walls have gaps called pits which water travels through- tracheids are spindle shaped water takes a twisting path compared to straight path of vessels
Transport in the xylem- water uptake by roots
Water is taken up through soil through the roots- transported to the leaves- maintains turgidity/ is a reactant in photosynthesis- but lots of water is lost through stomata via transpiration- need constant replacement from soil
Transport in the xylem- water uptake by roots pt2
Region of greatest uptake= root hair cell- it’s vacuole/ cytoplasm contains concentrated solution of solutes- has lower, more negative water potential- so water passes to root cell via osmosis
Movement of water through root- apoplast
Apoplast pathway- water moves in cell walls- cellulose fibres in the cell wall are separated by spaces through which the water moves
Movement of water through root- symplast
water moves through cytoplasm/ plasmodesmata= strands of cytoplasm through pits in the cell wall- joining adjacent cells so simplest is a continual pathway across root complex
Movement of water through root- Vacuolar
Water moves from vacuole to vacuole- 2 main pathways= symplast/ apoplast- apoplast is fastest
Structure of endodermis
Water only passes into xylem via symplast/ apoplast pathways- vascular tissue at root centre is surrounded by pericycle region- this is then surrounded by single layer of cells- endodermis
Structure/ role of endodermis
Endodermis cell walls= impregnated with waxy material= suberin- forms a band on radial/ tangential walls- called casparian strip- suberin= hydrophobic- casuarina strip prevents water forming around apoplast- water and dissolved minerals apoplast contains leaves apoplast- enters cytoplasm before moving further across root
More on casparian strip
Water moves from root endodermis into xylem across endodermal cell membranes- look at diagram- 2 explanations for this
Reason for method of water movement in casparian strip
Increased hydrostatic pressure forces water into xylem- pressure increase due to- active transport of ions (especially sodium) into endoderm’s cells- reduces water potential- draws water in
Diversion of water into endoderm’s cells from app palsy pathway by casparian strip
OR
Decreased water potential in xylem below endodermal cells- draws water in across endoderm’s cell membranes- reasons for wp decrease- water being diverted into endoderm’s cells by casparian strip
Active transport of mineral salts mainly sodium ions from endodermis and pericycle into xylem
Uptake of minerals
Soil water is much more dilute than contents of root hair cells- minerals are present in low concs- so minerals are usually absorbed into cytoplasm via active transport against conc gradient
Uptake of minerals pt 2
Mineral ions can also move along a poplars pathway in solution- when they reach endodermis casparian strip prevents further movement in cell walls- mineral ions enter cytoplasm via active transport then diffuse or are actively transported into xylem
Uptake of minerals nitrogen example
Enters plant as nitrate/ ammonium ions- diffuses down conc gradient in apoplast pathway enters symplast via active transport then flows into cytoplasm through plasmodesmata- active transport allows plants to absorb ions selectively at endodermis
Movement of water roots- leaves
Water moves up potential gradient- air has low water potential, soil water is dilute- has high water potential so water mover from roots though plants to leaves to air.
3 mechanisms movement of water from roots- leaves -1
1) Cohesion tension- in transpiration water goes out of leaves via stomata to atmosphere- draws water across leaf cells in apoplast , symplast/ vacuoles pathways from the xylem. As water molecules leave xylem cells in leaf they pull up other water molecules behind them in xylem- (cohesion)- continuous pull causes tension in water column.
3 mechanisms movement of water from roots- leaves -2
Capillarity- movement of water up narrow tubes- in this case= xylem by capillary action- cohesion between water molecules generates surface tension, this combined with their attraction to walls of xylem vessels (adhesion) draws water up- capillarity only operates over short distances up to 1m- only makes small contributions to plans over a few cm tall- effective in moss
3 mechanisms movement of water from roots- leaves -3
short distances in living plants- result of moving water up from endodermal cells into xylem pushing water already there further up- caused by osmotic movement of water down water potential gradient across root into base of xylem.
Definitions- movement of water from roots to leaves- pt 1
Cohesion- Attraction of water molecules to each other- seen as hydrogen bonds- resulting from dipole structure of water molecule
Adhesion- attraction between water molecules and hydrophilic molecules in cell walls of xylem
Definitions- movement of water from roots to leaves- pt 2
Cohesion tension theory- Theory of mechanism which water moves up xylem as result of cohesion/ adhesion of water molecules and tension of waters column- all resulting in water’s dipole structure
Capillarity- The movement of water- up narrow tubes by capillary action
Root pressure- Upward force of water in roots derived from osmotic movement of water in root system
Transpiration
The evaporation of water from the leaves/ other above ground parts of the plant, our through stomata into atmosphere- around 99% of water absorbed by plant- lost to transpiration- need to balance water uptake w/ loss- if only small volume lost ok- if excessive- turgid lost after wilting- dies
Stomata- transpiration
Stomata must be open during day for gas exchange - results in water loss - plants have adaptations
Factors affecting transpiration rate
Genetic factors- distribution/ size of stomata
Environmental factors
Temperature- temp increase lowers water potential of the atmosphere- increases kinetic energy of water molecules accelerating their rate of evaporation from walls of mesophyll cells and if stomata are open- speeds rate of diffusion into atmosphere- higher temp- water diffuses quicker from leaf- lowers water potential around leaf
Factors affecting transpiration rate pt 2
Humidity- air inside leaf is saturated with water vapour- relative humidity= 100%- humidity of atmosphere around leaf varies but never greater than 100%- water potential gradient between leaf and atmosphere- when stomata open vapour diffuses down diffusion gradient out of leaf- in still air- layer of saturated air accumulates around leaf- water vapour gradually diffuses away- leaves concentretic rings- water vapour diffuses down relative humidity gradient (also water potential gradient) away from leaf
Factors affecting transpiration rate pt 3 air speed
Surrounding air blows humid humid air at leaf’s surface- water potential gradient between inside/ outside of leaf increases- water diffuses out via stomata quicker- faster air- faster concentric ‘diffusion’ shells get blown away
Light intensity- stomata open wider as light intensity increases- increases transpiration rate- stomata open widest in middle of day
Environmental factors interact
More water lost on dry, windy day than humid still day- because walls of spongy mesophyll are saturated w/ water- evaporated moves down water potential gradient out of leaf to atmosphere which has lower humidity- as wind reduced saturation layer thickness around leaf
Potometer exp
Sometimes called transpirometer- device that indirectly measures rate of water loss during transpiration by measuring water uptake- since most water uptake up by leafy shoot is lost during transpiration- look at diagram-217
Adaptations to flowering plants to differing water availability- definitions
Mesophyte- Land plant adapted to neither wet or dry environments
Xerophyte- land plant adapted to environments with little water
Hydrophyte- Plant adapted to living in aquatic environment
Mesophytes
Are most plants in temperate regions. Have adequate water supply despite losing lots of water- replaced by uptake from soil-so don’t need methods of conservation- too much water loss- wilts- stomata close- leaf SA for absorbing light reduced- less efficient photosynthesis- grow best in drained soils/ moderately dry air
