Transport in Plants

Question 1

Why do larger plant organisms NEED a transport system?

Answer 1

1. Increased diffusion distances
   Low SA:V ratio
   Higher metabolic demands
2. all WILL mean that transport system will allow all respiring cells with demand for oxygen and nutrients producing more waste, to supply nutrients!

Question 2

why is mass flow important in plant transport?

Answer 2

1. Mass transport systems help to:
   Bring substances quickly from one exchange site to another / Maintain the diffusion gradients at exchange sites fluid surroundings / Ensures effective cell activity within a suitable metabolic range
2. Plants have evolved two separate mass transport systems: PHLOEM and XYLEM

Question 3

Where and WHY is xylem found in plants?

Answer 3

1. Xylem tissue is found vascular bundles in tissue!
2. Vascular tissue that carries dissolved minerals and water up the plant, provides structural support via lignin and source of food storage

ROOTS = the vascular bundle is found in centre core of this is xylem tissue. (star shape)

STEM = the vascular bundles are located around the outside and the xylem tissue is found on the inside (closest to stem center) to help support the plant (dotted ring shape)

LEAVES = the vascular bundles form the midrib and therefore spread from the centre of the leaf in a line. The xylem tissue is found on the upper side (closest to the upper epidermis) (bird-wing shape)

Question 4

Where and WHY is phloem found in plants?

Answer 4

1. Phloem tissue is found vascular bundles in tissue!
2. transports organic compounds, sucrose, from the leaves to roots. The transport of these compounds can occur up and down the plant
   ROOTS = vascular bundle is found in the centre and on the edges of the centre core is the phloem tissue (star core)

STEM = vascular bundles are located around the outside, the phloem tissue is found on the outer edge (closest to the epidermis) (dotted ring shape)

LEAVES = vascular bundles form the midrib spread from the leaf centre. The phloem tissue is found on the lower side of the bundles (closest to the lower epidermis) (bird-wing shape)

Question 5

2 main types of PLANT TISSUE!

Answer 5

1. Collenchyma = supporting tissue of living, elongated cells with thickened, iregular cell walls
2. Sclerenchyma = more thicker and lignified than collenchyma, supporting tissue in more WOODY plants

Question 6

Adaptaions of Xylem Vessles?

Answer 6

1. lignified cell walls = strength to withstand hydrostatic pressure, impermeable to water
2. no end wall/plates = ALLOWS MASS FROW OF WATER AND MINERAL IONS TO BE COHESIVE AND ADHESIVE TO EACH OTHER!
3. dead cells = no interference with osmosis and mass flow in xylem
4. non-lignified bordered pits = allows lateral water flow, in case of air bubbles to form!

Question 7

Adaptaions of Phloem Vessles?

Answer 7

1. Sieve tube elements = no nucleus. very little cytoplasm, ending sieve plates&raquo_space; allows cell sap movements via mass flow, keeps lumen open, callose booster
2. companion cells = between sieve tubes, dense cytoplasm and large nucleus, carries out areobic respiration, provides ATP to sieve elements, loading sucrose via gaps of plasmodesmata for substance flow

Question 8

what are assimilates?

Answer 8

substances that WILL be incorperated into biological tissue (e.g. sucrose)

Question 9

3 main pathways of water movement in PLANT

Answer 9

1. apoplast = passes between gaps in cell walls and cells edges, no plasma membrane whatsoever
2. symplast = enters via plasma membreane, through to cytoplasm
3. vacuolar = like symplast, but will ASLO travel through via large vacuoles in cells

Question 10

WHAT and WHY is the Casparian Strip used?

Answer 10

1. forms an IMPERMEABLE barrier for water travelling via apoplast pathway
2. HENCE, forces water to travel via symplast, increasing root pressure and control over mineral ion distribution to xylem…

Question 11

main PURPOSES of 3 main pathways of water movement in PLANT

Answer 11

1. apoplast = water does not pass through membranes&raquo_space; dissolved mineral ions/salts carried&raquo_space; DIFFUSION due to NOT CROSSING PP MEMBRANE
2. symplast = enters via plasmodesmata&raquo_space; OSMOSIS due to PASSING OF PP MEMBRANES!
3. vacuolar = water not confined to cytoplasm, but also vacoles too, faster than symplastic pathway!

Question 12

Define Xerophyte and Hydrophyte and Succulent

Answer 12

1. x = plant adapted for living with VERY little watered conditions (dry)
2. h = adapted for living with HIGHLY watered , very wet conditions
3. s = plants storing a lot water in stems, becoming very fleshy and swollen! (cacti, aloe vera!)

Question 13

Describe Xerophyte adaptations!

Answer 13

1. Longitudnal rolling > reduces SA exposed to wind!
2. thick waxy cuticle > reduces water evaporation from cells
3. stomata in pits, folded in leaf > created pits of of water vapour build-up, reducing water conc grad and evaporation
4. low stomata density > reduces water evaporation from cells

Question 14

Describe succulent adaptations!

Answer 14

1. Spine leaves > reduced SA of leaves significantly, less water loss via transpiration
2. Green stem > allows photosynthesis to occur, without normall leaves..
3. Long, very wide roots > able to reach water deeb inground…

Question 15

Describe Hydrophytes adaptations!

Answer 15

1. Large air spaces in leaf > keeps leaves afloat, allows to absorb sunlight + O2 rapid diffusion to roots for aerobic respiration!
2. upper epidermis stomata > allows for gas exchange to still occur

Question 16

What are Hydathodes?

Answer 16

1. specialised structures on plant leaf tips, releases water droplets
2. helps drives the transpiration stream during high humidity (abnormally high water potential!)

Question 17

What are Epiphytes?

Answer 17

1. plants that grow on OTHER plants (parasite-like, climbs upwards)….

Question 18

define “Source to Sink”, and its interchangeable nature!

Answer 18

1. the movement of substances from part where assimilates are LOADED to transport system, to part where assimilates are removed from system!
2. SUMMER = leaves produce sugars to be transported [source], as roos, recieve sugars to convert to storage STARCH[sink]!
3. SPRING = Leaves need sugars tom aid re-growth[source], as starch from roots are converted into sugars![sink]

Question 19

Hiw does transpiration stream draw water molecules?

Answer 19

1. Via strong COHESION with hydrogen bonds to water molecules, and ADHESION with sides of xylem vessels!

Question 20

define TRANSLOCATION

Answer 20

transportation of assimilates in phloem vessels, from source to sink via mass flow!!!

Question 21

define TRANSPIRATION

Answer 21

LOSS OF WATER VAPOUR from upper part of plant, at leaves, into the atmosphere

Question 22

Steps of TRANSLOACATION MECHANISM

Answer 22

1. H+ ions are actively transported from companion cells via ATP to surrounding outer leaf tissue, creating a H+ ion diffusion gradient!
2. H+ ions and sucrose will diffuse back through leaf tissue to companion cells, via cotransporter protiens
3. High sucrose conc in companion cells causes sucrose to diffuse along conc grad into sieve tube elements, via plasmodesmata

all under ACTIVE LOADING

Question 23

How is movement of sucrose controlled along phloem?

Answer 23

1. moves via MASS FLOW!
2. caused by DIFFERENCES IN HYDROSTATIC PRESSURE at 2 ends of tube, causing a pressure gradient…
3. water enters the tube elements at the SOURCE, increasing hydrostatic pressue, leaves tube elements at SINK =hence assimilates move from SOURCE to SINK

Question 24

How does movement of sucrose affect water potential?

Answer 24

1. sucrose, beign actively loaded at SOURCE, will REDUCE WATER POTENTIAL of sieve tube elements at place
2. water will FOLLOW VIA OSMOSIS, increasing water potential AFTER LOADING OF SUCROSE
3. sucrose will move from higher to lower hydrostatic pressue , ALWAYS!!
4. as sucrose reaches SINK, sucrose diffuses into nearby cells, increases water potential
5. HENCE, water will FOLLOW AGAIN AFTER SUCROSE, osmosis to cells, reduces hydrostatic pressure again……/