3.1.3 - transport in plants

Question 1

why do plants need transport systems?

Answer 1

metabolic demands - the underground parts of the plant need oxygen and glucose transported to them
size - some are very large
surface area to volume ratio - cannot rely on diffusion alone

Question 2

cotyledons

Answer 2

organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates

Question 3

dicotyledon

Answer 3

a plant that has two seed leaves or cotyledons

Question 4

vascular bundle

Answer 4

plant stem structure that contains xylem and phloem tissue

Question 5

xylem and phloem in the stem

Answer 5

xylem and phloem arranged into vascular bundles with cambium
xylem on inside, phloem on outside

Question 6

xylem and phloem in the roots

Answer 6

vascular bundles are in the middle to help the plant withstand the tugging strains from wind
cross shaped xylem, and phloem around the xylem

Question 7

xylem and phloem in the leaves

Answer 7

xylem on top, phloem on the bottom

Question 8

structure of xylem

Answer 8

long continuous hollow tube
narrow lumen
wall made out of lignin (strong, waterproof and adhesive)
wall contains pits/pores, so water and minerals can leave

Question 9

structure of the phloem

Answer 9

companion cells (lots of mitochondria for ATP for active loading)
sieve tube elements (little cell contents for ease of flow)
sieve plates (connect the elements together to allow for ease of flow)

Question 10

purpose of water in plants

Answer 10

turgor pressure provides support
turgor drives cell expansion
loss of water means plants keep cool
mineral ions transported
raw material for photosynthesis

Question 11

symplast pathway

Answer 11

water moves continuously through the cytoplasm of cells (connected through the plasmodesmata)

Question 12

apoplast pathway

Answer 12

route through the cell walls and intercellular spaces or plants

Question 13

Casparian strip

Answer 13

a water impermeable ring of wax in endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls

Question 14

effect of Casparian strip

Answer 14

water can not carry on in the apoplast pathway so it is forced into the cytoplasm of the cell, joining the symplast pathway

Question 15

significance of the Casparian strip

Answer 15

water now has to pass through the selectively permeable cell membranes, excluding any potentially toxic solutes in the soi; water from reaching living tissues

Question 16

root pressure

Answer 16

the upward push of xylem sap in the vascular tissue of roots

Question 17

evidence for the role of active transport in root pressure

Answer 17

• if cyanide (affects mitochondria) is applied, root pressure disappears
• increases with higher temps, decreases with lower temps
• if oxygen falls, root pressure falls

Question 18

transpiration

Answer 18

evaporation of water from the leaves of a plant, an inevitable consequence of gaseous exchange

Question 19

transpiration stream

Answer 19

movement of water up through the xylem from the roots to the leaves

Question 20

process of the transpiration stream

Answer 20

water molecules evaporate from the surface of mesophyll cells into air spaces in the leaf and move out of the stomata into surrounding air by diffusion
this lowers wp, so water moves in by osmosis
repeated across the leaf to the xylem, water moves out of xylem by osmosis into cells of the leaf
adhesion and cohesion cause capillary action and water is moved up.

Question 21

capillary action

Answer 21

combind force of attraction among the water molecules and with the molecules of surrounding materials, causing water to rise up against the force of gravity.

Question 22

cohesion-tension theory

Answer 22

the mechanism of water movement from roots to the leaves due tovwater cohesion and water tension

Question 23

evidence for cohesion tension theory

Answer 23

changes in the diameter of trees - diameter grows at night when there is less transpiration
air is drawn into xylem when its broken

Question 24

how stomata control the rate of transpiration

Answer 24

when turgor is low, the guard cells close
when the environmental conditions are favourable, guard cells pump in solutes by active transport, increasing the turgor - guard cells become shaped and open pore

Question 25

how light affects transpiration

Answer 25

light is needed for photosynthesis, so stomata will be open in the day more light, more stomata open, increasing the evaporation from the surfaces of leaves - more transpiration

Question 26

how humidity affects transpiration

Answer 26

if the air outside the leaf is humid, the concentration between water vapour inside and outside the leaf is less steep so there is less transpiration

Question 27

how temperature affects the rate of transpiration

Answer 27

increase in temperature increases the kinetic energy and there fore increases the rate of evaporation

Question 28

how air movement affects the rate of transpiration

Answer 28

blows away the layer of humid air surface, increasing gradient, meaning more diffusion (more transpiration)

Question 29

soil water availability and transpiration

Answer 29

if dry plant is under water stress so transpiration is reduced

Question 30

source (plant)

Answer 30

where assimilates like sucrose are loaded in to e.g green leaves and stems, storage organs etc

Question 31

sink (plant)

Answer 31

where assimilates like sucrose are loaded out of e.g roots that are growing and actively absorbing mineral ions, meristems taht are dividing.

Question 32

translocation

Answer 32

movement of carbohydrate through a phloem from a source to a sink

Question 33

assimilates

Answer 33

products of photosynthesis that are transported around a plant

Question 34

how assimilates are loaded into the phloem

Answer 34

- H+ ions are pumped out of companion cells, using AT - this creates are diffusion gradient - therefore h+ ions are diffused back in, with a co transporter - sucrose is also transported in with this co transport protein

Question 35

structure of companion cells

Answer 35

many infoldings in their cell membranes to give an increased surface area for the active transport of sucrose in the cell cytoplasm lots of mitochondria to supply ATP

Question 36

phloem unloading at sinks

Answer 36

diffusion of the sucrose from the phloem into surrounding cells, the sucrose rapidly moves on into other cells by diffision or is converted into another substance loss of solutes from the phloem leads to a rise in the wp of the phloem, causing water to move out by osmosis

Question 37

evidence for translocation

Answer 37

advances in microscopyt allow us to see adaptations of CC if mitochondria are poisoned, translocation stops flow of sugar in phloem is 1000 times s=faster than diffusion alone, suggesting active process

Question 38

use of aphids with translocation

Answer 38

can demonstrate the translocation of organic solutes in the phloem. it has been shown that there is a positive pressure in the phloem that forced sap out the stylet

Question 39

xerophytes

Answer 39

plants with adaptations that allow them to survive in dry habitats

Question 40

examples of xerophytes

Answer 40

marram grass and cacti

Question 41

how waxy cuticle conserves water

Answer 41

minimises water loss due to the waterproof nature of the waxy cuticle

Question 42

sunken stomata

Answer 42

reduces water loss as the water has to travek a longer distance before it reaches the outside of the leaf

Question 43

reduced number of stomata

Answer 43

reduces transpiration rate and alos their gas exchange capabilities

Question 44

reduced leaves

Answer 44

reducing the total number of leaves and size of leaves will reduce the surface area available for water loss

Question 45

hairy leaves

Answer 45

create a microclimate of still humid air, reducing transpiration

Question 46

succulents

Answer 46

store water in a specialised parencyma tissue in their stems and toots which are used up in times of drought

Question 47

hydrophytes

Answer 47

plants taht have special adaptations to allow them to live in areas often saturated by water

Question 48

examples of hydrophytes

Answer 48

water lillies and water cross

Question 49

aerenchyma

Answer 49

a soft plant tissue containing air spaces found especially in many aquatic plants

Question 50

adaptations of hydrophytes

Answer 50

very thin or no waxy cuticle lots of stomata that are always open wide flat leaves air sacs small roots