3.3 transport in plants

Question 1

what is meristem

Answer 1

a layer of dividing cells

Question 2

what is the function of the phloem

Answer 2

transports dissolved assimilates up or down

Question 3

what is vascular tissue

Answer 3

cells specialised for transporting fluids by mass flow

Question 4

what is the function of the xylem

Answer 4

transports water and minerals upwards

Question 5

why do plants need a transport system

Answer 5

larger plants have a smaller surface area to volume ratio therefore, they need to have a specialised exchange surfaces and a transport system

Question 6

what do plants need to move via the transport system?

Answer 6

wat er and minerals from the roots to the leaves
sugar from the leaves to the rest of the plant

Question 7

what are dicotyledonous plants

Answer 7

those that have two seed leaves and a branching pattern of veins in the leaf

Question 8

describe the structure of xylem and phloem in the young root

Answer 8

it is found at the centre of the young root and there is a central core of xylem, and the phloem is found between the arms of the x-shaped xylem tissue

Question 9

how is the structure of the xylem and phloem in the young root adapted for its function

Answer 9

the x-shaped arrangement provides strength to withstand the pulling forces to which roots are exposed to

Question 10

describe the structure of phloem and xylem in the stem

Answer 10

the vascular bundles are found near the outer edge of the stem.
The xylem is found towards the inside of the vascular bundle and the phloem towards the outside and in between there is a layer of cambium which is a layer of meristem cells that divide to produce new phloem and xylem

Question 11

describe the structure of xylem and phloem in the leaf

Answer 11

the vascular bundles form the midrib and veins of the leaf, within each vein the xylem is located on top of the phloem

Question 12

describe the development of xylem vessels

Answer 12

as they develop lignin impregnates the walls of the cells making the walls waterproof. This end walls and contents of the cell decays leaving a long column of dead cells

Question 13

describe the structure and function of lignin in the xylem vessels

Answer 13

the lignin thickening may form spiral or reticulate patterns in the cell wall which prevents the vessel from being too rigid allows flexibility to the branch

Question 14

describe bordered pits

Answer 14

this is where lignification is not complete, and gaps are left in the cell wall. They are aligned which allows water to leave one vessel and pass onto the next.

Question 15

what are the adaptations of xylem to its function?

Answer 15

continuous column
the tubes are narrow so that the water column doesn’t break easily, and capillary action can be effective
bordered pits allow water to move
patterns of lignin deposits allow the xylem to stretch as the plant grows and enables the stem or branch to bend
the flow of water is not impeded because there are no cross walls or cell contents

Question 16

describe the structure of the phloem

Answer 16

phloem tissue consists of sieve tubes made up of sieve elements and companion cells

Question 17

describe tsieve tube elements

Answer 17

they are lined up end to end to form sieve tubes

they contain no nucleus and very little cytoplasm leaving space form mass flow of sap to occur and at the ends of the sieve tube elements are perforated cross walls called sieve plates

Question 18

describe companion cells

Answer 18

in between the sieve tubes are small cells each with a large nucleus and dense cytoplasm
They also have numerous mitochondria to produce the ATP needed for active processes

Question 19

what is the function of the companion cells

Answer 19

the companion cells carry out the metabolic processes needed to load assimilates actively into the sieve tubes

Question 20

define plasmodesmata

Answer 20

gaps in the cell wall containing cytoplasm that connects two cells

Question 21

what are the different pathways water can take through a plant

Answer 21

the apoplast pathway
symplast pathway
vacuolar pathway

Question 22

describe the apoplast pathway

Answer 22

water passes through spaces in the cell walls and between cells and doesn’t pass through any plasma membranes so therefore it moves by mass flow rather than osmosis

Question 23

describe the symplast pathway

Answer 23

water enters the cell cytoplasm and passes through plasmodesmata from one cell to the next

Question 24

describe the vacuolar pathway

Answer 24

similar to the symplast pathway but the water is able to enter and leave the vacuoles

Question 25

define water potential

Answer 25

the tendency of water molecules to move from one place to another

Question 26

define osmosis

Answer 26

the movement of water from a region of high water potential to an area of low water potential across a partially permeable membrane

Question 27

what is the endodermis

Answer 27

a layer of cells surrounding the medulla and xylem and it contains granules of starch

Question 28

what is the role of the endodermis

Answer 28

it contains the Casparian strip which blocks the apoplast pathway between the cortex and the medulla ensuring that water and dissolved mineral ions have to pass into the cell cytoplasm through the plasma membranes

Question 29

how does the endodermis block the apoplast pathway

Answer 29

the plasma membranes contain transporter proteins which actively pump mineral ions from the cytoplasm of the cortex cells into the medulla and xylem this makes the water potential of the medulla and xylem more negative so that water moves from the cortex cells into the medulla and xylem by osmosis

Question 30

define transpiration

Answer 30

the loss of water vapour from the upper parts of the plants

Question 31

describe the typical pathway of water leaving the leaf

Answer 31

water enters the leaf through the xylem and moves by osmosis into the spongy mesophyll

water evaporates from the cell walls of the spongy mesophyll

water vapour moves by diffusion out of the leaf through the open stomata

this relies on a steep water vapour potential gradient

Question 32

what is the importance of transpiration

Answer 32

transports useful mineral ions up the plant

maintains cell turgidity

supplies water for growth

cools the plant

Question 33

what environmental factors affect transpiration rates

Answer 33

light intensity
temperature
relative humidity
air movement
water availability

Question 34

how does light intensity affect transpiration rates

Answer 34

in light stomata open to allow gaseous exchange for photosynthesis so a larger light intensity increases the transpiration rate

Question 35

how does temperature affect transpiration rate

Answer 35

a higher temperature will increase the rate because
it will increase the rate of evaporation from the cell surfaces so water potential in the leaf rises
increases the rate of diffusion because the water molecules have more kinetic energy
decreases relative water vapour potential in the air allowing more rapid diffusion out of the leaf

Question 36

how does humidity affect transpiration rate

Answer 36

this will lower transpiration rates because there will be a smaller water vapour potential gradient between the air spaces in the leaves and the outside

Question 37

how does air movement affect transpiration rate

Answer 37

wind will carry away water vapour that just diffused out of the leaf maintaining a steep water vapour potential gradient

Question 38

how does water availability affect transpiration rate

Answer 38

if there is little water int the soil then the plant cannot replace the water that it had lost then the stomata close and the leaves wilt

Question 39

how does water move up the stem

Answer 39

mass flow

Question 40

what is root pressure

Answer 40

the action of the endodermis moving minerals into the medulla and xylem causes pressure in the roots to build up and forces water into the xylem

Question 41

what is transpiration pull

Answer 41

the loss of water from by evaporation from the leaves must be replaced by the water coming up the xylem

water molecules are attracted to each other by forces of cohesion which are strong enough to hold the molecules together in a long chain or column. So as molecules are lost from the top of the column the whole column is pulled up as a chain

Question 42

what is capillary action

Answer 42

adhesion forces attract water molecules to the sides of the xylem vessels and as xylem vessels are very narrow adhesion forces can pull water up the sides of the vessel

Question 43

define translocation

Answer 43

the transport of assimilates throughout a plant

Question 44

describe active loading during translocation

Answer 44

H+ ions are actively pumped out of the companion cell using energy from ATP

this creates a higher concentration of H+ ions outside of the companion cell - this causes facilitated diffusion back into the companion cell of H+ ions that carry sucrose through cotransport proteins in the plasma membrane

increased concentration of sucrose in companion cell causes it to diffuse through the plasmodesmata into the sieve tube elements

Question 45

what causes the movement of sucrose

Answer 45

sucrose moves through mass flow

the flow is caused by a difference in hydrostatic pressure

when sucrose is actively loaded into the sieve tube element, and this reduces water potential, causing water to follow in by osmosis increasing the hydrostatic pressure

sap then moves down from the source to the sink - high hydrostatic pressure to low hydrostatic pressure- and sucrose is then removed from the sieve tube increasing its water potential and water follows out reducing hydrostatic pressure

Question 46

what is a source in translocation

Answer 46

sucrose entering the sieve tube e.g. the roots

Question 47

what is a sink in translocation

Answer 47

anywhere that removes sucrose from the phloem sieve tubes which could be used for respiration

Question 48

what is a hydrophyte

Answer 48

a plant adapted to living in water or where the ground is very wet

Question 49

what is a xerophyte

Answer 49

plant adapted to living in dry conditions

Question 50

how do most terrestrial plants reduce their water loss

Answer 50

waxy cuticle
stomata on under face of leaf
stomata close at night
deciduous plants lose their leaves in winter

Question 51

what are some adaptations of xerophytes such as marram grass

Answer 51

leaf is rolled longitudinally so that air is trapped inside
thick waxy cuticle on the outer side of the rolled leaf
stomata are on inside of the rolled leaf (lower epidermis)
dense spongy mesophyll with few air spaces
widespread roots

Question 52

what are some adaptations of halophytes

Answer 52

many large air spaces in the leaf to keep them afloat
stomata are on upper epidermis so that they are exposed to air to allow gaseous exchange
leaf stem has many large air spaces for buoyancy