transport in plants (9)

Question 1

what are dicotyledonous plants

Answer 1

these are plants that make 2 cotyledons (food stores) in their seeds.

Question 1

what are the 3 reasons for a transport system in plants/ why do multicellular plants need transport systems

Answer 1

high metabolic demands - underground parts of plant don’t photosynthesise so they need waste substances removed and o2 and glucose transported to them. mineral ions need to be transported to all cells to make proteins.
size - bigger, taller plants need efficient transport systems to move substances up and down plant.
SA - plants have a large SA: volume ratio so they cant solely rely on diffusion to supply cells w everything

Question 2

what are cotyledons

Answer 2

food stores

Question 3

what are the 2 types of dicotyledonous plants. and give an example of each

Answer 3

herbaceous - soft tissues, short life cycle (little plants)
woody - lignified tissues, long lived (trees)

Question 4

how are the xylem and phloem arranged in the stems, roots, leaves

Answer 4

vascular bundles

Question 5

where in the stem are the vascular bundles located and why are they there

Answer 5

around the edge to give support and strength

Question 6

where in the roots are the vascular bundles located

Answer 6

in the middle to help plant withstand tugging strains from the wind blowing the stem and leaves

Question 7

where are the vascular bundles in the leaves and why there

Answer 7

in the midrib of a dicot leaf. helps support structure of leaves.

Question 8

in a vascular bundle where are the phloem and xylem located

Answer 8

phloem on outside and xylem on inside

Question 9

function of xylem tissue

Answer 9

structural support and transports water + minerals up plant.

Question 10

what is the function of the spiral band of lignin in the xylem vessel

Answer 10

spiral bands allow vessels to elongate, thus allowing tissues to expand w/o breaking the vessel walls

Question 11

what is the function of the bordered pits in the vessel

Answer 11

they act as channels for the transport of h20 +minerals between the adjacent cells

Question 12

is their lignin in the phloem

Answer 12

no

Question 13

are their bordered pits in the phloem

Answer 13

no

Question 14

what is plasmodesmata

Answer 14

gaps in cell wall between companion cells + sieve tube elements

Question 15

what feature would not be found in mature xylem vessels

Answer 15

cytoplasm

Question 16

xylem vessels contain lignin carbohydrate. what is this for

Answer 16

allows water to pass into adjacent vessels

Question 17

a feature of the sieve tubes

Answer 17

contains perforated cross walls

Question 18

what roles does water have within plants

Answer 18

turgor pressure - provides a hydrostatic skeleton to support stems + leaves.
evaporation- keeps plants cool.
turgor drives cell expansion -
the force that enables plant roots to force their way thru tarmac + concrete.
transport - mineral ions + products of photosynthesis are transported in aqueous solutions
raw material - h20 is raw material for plants

Question 19

adaptations of the root hair cell

Answer 19

they are microscopic so can penetrate easily between soil and branches.
large SA: V ratio
thin surface layer for fats diffusion =osmosis
the concentration of solutes in the cytoplasm of root hair cells maintains a water potential gradient between the soil water and cell

Question 20

talk about soil water

Answer 20

has a very low concentration of dissolved minerals so has a high water potential. while RHCs have a high conc of solvents so the water potential in rhc is lower this drives more water into the RHCs by osmosis

Question 21

what is another reason for the lignin in the xylem

Answer 21

lignin reinforces the xylem so it doesn’t collapse under the transpiration pull

Question 22

how are sieve plates formed and what are they for

Answer 22

in the areas between the cells the cell walls become perforated = sieve plates.
they let the phloem contents flow through

Question 23

as large pores appear in the phloem what happens

Answer 23

the tonoplast, nucleus and other organelles break down. so mature phloem cells have no nucleus

Question 24

after the water is in the RHC how does it travel to the xylem. what are the 2 pathways water moves thru the plant to the xylem

Answer 24

apoplast + symplast pathways

Question 25

explain symplast pathway

Answer 25

symplast is the continuous cytoplasm of the living plant cells that is connected thru the plasmodesmata - by osmosis. the RHC has a higher water potential than the next cell along cos pf water diffusing in from the soil making the cytoplasm more dilute, so water moves from the RHC into the next cell by osmosis. this process repeats cell to cell until the water has reached the xylem. as water leaves a RHC the water potential of cytoplasm drops again, this maintains a a steep water potential gradient

Question 26

explain apoplast pathway

Answer 26

this is the movement of water through cell walls + intercellular spaces. water fills the spaces between the open network of fibres in the cellulose cell wall. as water molecules move into the apoplast more are pulled behind due to cohesive forces between the water molecules. the pull from water moving up into the xylem and from the cohesive forces creates a tension that makes a continuous flow of water through the xylem w little resistance

Question 27

describe pathway of water after reaching the root

Answer 27

the water moves across the route via symplast or apoplast pathway until it reaches endodermis. the water runs around the apoplast strip, the apoplast strip is made of suberin so the water is forced into the cytoplasm (symplast pathway). to get into cytoplasm the water crosses the selectively permeable cell surface membranes. the endodermal cells move mineral ions into the xylem by active transport, this lowers the water potential of the xylem , lower than of the endodermal cells. creates root pressure. this increases the rate of water moving into the xylem by osmosis down a conc gradient from the endodermis down the symplast pathway

Question 28

what is the endodermis

Answer 28

a layer of cells that surrounds xylem + phloem

Question 29

what is suberin and what does it prevent

Answer 29

a strip of waxy material that runs around each of the endodermal cells - the apoplast strip. it prevents the movement of water thru the cell walls (apoplast pathway)

Question 30

1st evidence for active transport

Answer 30

poisons (cyanide) affect the mitochondria, so the root pressure disappears. root pressure needs energy, mitochondria produce ATP . no ATP no energy.

Question 31

2nd evidence for active transport

Answer 31

root pressure increases with a rise in temp, this suggest chemical reactions are involved cos increasing temp increase chemical reactions (partucles move faster and collide more often, so chemcal reaction rate increases)

Question 32

3rd evidence for active transport

Answer 32

if levels of oxygen or respiratory substrate fall root pressure falls. oxygen is needed for respiration

Question 33

4th evidence for active transport

Answer 33

root pressure and transpiration are independent of eo - when water transpiration is low xylem sap can still be seen exuded from the tips of leaves.

Question 34

what is ttranspiration

Answer 34

loss of water. when the stomata open for gas exchange, water moves out of the leaf by diffusion

Question 35

why does stomata close at night (dont forget some stomata stay open allthetime)

Answer 35

reduces water loss. no photosynthesis at night so demand for o2 is low

Question 36

what do guard cells do

Answer 36

when conditions are optimal they pump in solutes by active transport which increases the turgor.

Question 37

2 features of guard cells

Answer 37

guard cells have cellulose rings around them, so they cannot swell but can lengthen. inner wall not as flexible so the cells curve becoming bean shaped, creating a pore.

Question 38

when water is scarce what happens with the guard cells

Answer 38

a hormonal signal is sent from the roots and trigger turgor loss in the guard cells thus closing the stomata

Question 39

what are the 5 stages of the transpiration stream

Answer 39

1 - water enters root by osmosis 2 - water transported up xylem up to leaves 3 - water moves by osmosis and diffusion across membranes along the apoplast pathway from the xylem 4 - water evaporates from freely permeable cellulose cell walls of the mesophyll cells into the air spaces 5 - water vapour moves out of the leaves thru the stomata down a concentration gradient/diffusion gradient

Question 40

what is cohesion tension theory

Answer 40

driving force for water movement up from the roots to the leaves

Question 41

adhesion + cohesion = ?

Answer 41

water exhibiting capillary action, the process by whuch h20 can rise up a narrow tube agianst gravity

Question 42

what is the transpiration pull

Answer 42

where water is drawn up xylem in a continuos stream to replace h20 lost by evaporation

Question 43

evidence for cohesion tension theory

Answer 43

changes in tree diameter - when transpiration as at its height during the day tension in xylem is at a highso the tree shrinks in diameter. at night are the lowest rates of transpiration so diameter increases. breaking a xylem vessel - cut a flower stem, put in water and air will be drawn into the xylem rather than water as the continuous stream of water molecules held tg by cohesive forces has been broken

Question 44

limitations to transpiration?

Answer 44

in high intensity light, rate of photosynthesis is fast so stomata must beopen to supply the co2 but then the plant will lose alot of water, in some case too much water is lost water availability is often limited

Question 45

we measure transpiration with a ...

Answer 45

potometer

Question 46

rate of water uptake calculation (potometer experiment)

Answer 46

rate of water uptake = distance moved by air bubble/time taken for air bubble to move that distance

Question 47

for the potometer experiment where should the stem be cut

Answer 47

underwater so no air bubbles go into the stem

Question 48

a control of this experiment?

Answer 48

all joints must be sealed w waterproof jelly to ensure any water loss measured is as a result of transpiration from the stem/leaves

Question 49

5 factors affecting transpiration?

Answer 49

light, humidity, temp, air movement, soil water availability

Question 50

how does light affect transpiration

Answer 50

increased light intensity=increase photosynthesis. increased light intensity= more stomata open for gas exchange, this increases the rate of water vapour diffusing out + therefore increasing the evaporation from the surfaces of the leaf

Question 51

how does humidity affect transpiration

Answer 51

high humidity lowers rate of transpiration cos of reduced water vapour potential gradient between the inside of the leaf + outside air. dry air has opposite effect + increases rate of transpiration.

Question 52

how does temperature affect transpiration

Answer 52

increase temp increases KE of water molecules, so increases rate of evaporation from spongy mesophyll cells into air spaces of the leaf. higher temp increases conc of water vapour that the external air can hold before becoming saturated (so decreases its relative humidty and its water potential)

Question 53

how does air movement affect transpiration

Answer 53

each leaf has a layer of still air around it trapped and little hairs on the leaf to decrease air movement close to the leaf. water vapor that diffuses out of the leaf accumulates here, so the water potential around the stomata increases in turn reducing the diffusion gradient. lomg period of still air will reduce transpiration

Question 54

hoe does soil water availability affect transpiration

Answer 54

if soil is dry the plant will be under water stress and so raate of evaporation will be reduced

Question 55

when diffusion gradient is increased what else increases

Answer 55

rate of transpiration

Question 56

what is translocation

Answer 56

the transport of organic compounds ususally in the form of sucrose (produced in leaves in paliisade mesophyll))

Question 57

why is sucrose transported instead of glucose

Answer 57

increases energy storage. its an efficient energy transfer

Question 58

transport occurs from a source to a sink, true or false

Answer 58

true

Question 59

what is a source

Answer 59

regions of plant that produce assimilates by photosynthesis or form storage materials (leaves)

Question 60

what is a sink

Answer 60

regions of a plant that require assimilates to supply their metabolic needs (roots, fruits)

Question 61

what is the phloem loading

Answer 61

the movement of sucrose into the phloem to be transported. its an active process, requires ATP

Question 62

what are the 2 main ways that sucrose is loaded

Answer 62

symplast and apoplast route

Question 63

how are companion cells adapted for this loading

Answer 63

- many infoldings - many mitochondria see kerboodle for further detail

Question 64

what is phloem unloading

Answer 64

kerboodle pg 209

Question 65

evidence for mass flow in phloem

Answer 65

kerboodle pg 209 for further detail phloem sap can be exuded from hole usig aphids. flow of sugars 10000x faster than if just diffusion was responsible if mitochondria of companion clells are poisones w cyanide translocation stops microoscopy allows us to see adaptations of the companion cells

Question 66

what is apoplast route

Answer 66

kerboodle pg 208

Question 67

2 adaptations of sieve tubes that enable mass flow

Answer 67

theyre stacked and their end walls (sieve plates) have lrg pores thru which their cytoplasm can flow

Question 68

how are assimilates loaded into the phloem