Adaptations for transport in plants

Question 1

Distribution of vascular tissue

Answer 1

Vascular tissue= xylem and phloem in plants, found adjacent to each other in vascular bundles- have different distributions on different parts of plant

Question 2

Xylem definition

Answer 2

Tissue in plants conducting water and dissolved minerals upwards- in roots is star shaped

Question 3

Phloem definition

Answer 3

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

Question 4

Why is structures of xylem and phloem in root useful

Answer 4

Resists vertical stresses (pull)- anchors plant in soil

Question 5

What are vascular bundles like in stems

Answer 5

Vascular bundles are in ring at periphery- xylem towards centre- phloem towards outside- gives flexible support- resists bending

Question 6

Vascular structure in leaves

Answer 6

Vascular tissue in midrib/ in a network of veins- gives flexible strength/ resistance to tearing

Question 7

Xylem structure

Answer 7

Main cell types in xylem are vessels/ tracheids

Question 8

Tracheids

Answer 8

Spindle shaped, water conducting cells in xylems of ferns, conifers and angiosperms (flowering plants)- not in mosses- grow shorter

Question 9

Vessels

Answer 9

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

Question 10

How lignin works in vessels

Answer 10

Lignin is laid down in a spiral pattern- kills contents of vessels while staining red- easy to see on microscope sections

Question 11

Xylem functions

Answer 11

Transport of water/ dissolved minerals
Provide mechanical strength and support

Question 12

Why vessels are better than tracheids

Answer 12

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

Question 13

Transport in the xylem- water uptake by roots

Answer 13

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

Question 14

Transport in the xylem- water uptake by roots pt2

Answer 14

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

Question 15

Movement of water through root- apoplast

Answer 15

Apoplast pathway- water moves in cell walls- cellulose fibres in the cell wall are separated by spaces through which the water moves

Question 16

Movement of water through root- symplast

Answer 16

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

Question 17

Movement of water through root- Vacuolar

Answer 17

Water moves from vacuole to vacuole- 2 main pathways= symplast/ apoplast- apoplast is fastest

Question 18

Structure of endodermis

Answer 18

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

Question 19

Structure/ role of endodermis

Answer 19

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

Question 20

More on casparian strip

Answer 20

Water moves from root endodermis into xylem across endodermal cell membranes- look at diagram- 2 explanations for this

Question 21

Reason for method of water movement in casparian strip

Answer 21

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

Question 22

Uptake of minerals

Answer 22

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

Question 23

Uptake of minerals pt 2

Answer 23

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

Question 24

Uptake of minerals nitrogen example

Answer 24

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

Question 25

Movement of water roots- leaves

Answer 25

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.

Question 26

3 mechanisms movement of water from roots- leaves -1

Answer 26

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.

Question 27

3 mechanisms movement of water from roots- leaves -2

Answer 27

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

Question 28

3 mechanisms movement of water from roots- leaves -3

Answer 28

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.

Question 29

Definitions- movement of water from roots to leaves- pt 1

Answer 29

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

Question 30

Definitions- movement of water from roots to leaves- pt 2

Answer 30

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

Question 31

Transpiration

Answer 31

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

Question 32

Stomata- transpiration

Answer 32

Stomata must be open during day for gas exchange - results in water loss - plants have adaptations

Question 33

Factors affecting transpiration rate

Answer 33

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

Question 34

Factors affecting transpiration rate pt 2

Answer 34

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

Question 35

Factors affecting transpiration rate pt 3 air speed

Answer 35

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

Question 36

Environmental factors interact

Answer 36

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

Question 37

Potometer exp

Answer 37

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

Question 38

Adaptations to flowering plants to differing water availability- definitions

Answer 38

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

Question 39

Mesophytes

Answer 39

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