transport in plants

Question 1

why do multicellular plants need transport systems?

Answer 1

big, high metabolic rate, low SA:VOL ratio so they need this to move substances to and from individual cells quickly

Question 2

what does the xylem tissue transport?

Answer 2

water and mineral ions in solution, move up the plant from the roots to the leaves

Question 3

what does the phloem tissue transport?

Answer 3

sugars both up and down the plant

Question 4

how are xylem vessels adapted for transporting water and mineral ions?

Answer 4

long tube like structures

no end walls water passes easily

dead cells so no cytoplasm

walls thickened with woody substance called lignin which supports the vessel and stops it from collapsing inwards

Question 5

how are phloem tissues adapted for transporting solutes

Answer 5

sieve tube elements - living cells joined end to end to form sieve tubes, no nucleus

companion cells- for each sieve tube element as the lack of nucleus and other organelles means they cant survive on their own. they provide energy for active transport of solutes

Question 6

where does water enter a plant?

Answer 6

through its root hair cells

Question 7

what is the symplast pathway?

Answer 7

goes through the living parts of the cell, the cytoplasm.

Question 8

what is the apoplast pathway?

Answer 8

goes through the non living parts of the cell, cell walls. mass flow (high hydrostatic pressure to low hydrostatic pressure)

Question 9

how does adhesion help move water through a plant?

Answer 9

water molecules are attracted to the walls of the xylem vessels, this helps water to rise up through the xylem vessels

Question 10

how does tension and cohesion help move water through a plant?

Answer 10

water evaporates from leaves at the top of the xylem (transpiration)

this creates a tension (suction) which pulls more water into the leaf

water molecules are cohesive (stick together), so when some are pulled into the leaf others follow. this means a whole column of water in the xylem from the leaves down to the roots, moves upwards

water enters the stem through the root cortex cells

Question 11

what is transpiration?

Answer 11

its the evaporation of water from a plants surface, the leaves

Question 12

what is transpiration a result of?

Answer 12

gas exchange

plant opens stomata to let CO2 in for photosynthesis, this lets water out at the same time as higher conc inside than out

Question 13

what are 4 main factors that affect transpiration rate?

Answer 13

light (stomata opens when it gets light)

temperature (warmer water molecules have more energy so evaporate from cells inside leaf faster)

humidity (the lower the humidity , faster rate. air around plant dry, water potential gradient increased between leaf and air )

wind ( windier, the faster rate as lots of air movement blows away water molecules from around the stomata which increases the water potential gradient

Question 14

what is used to estimate transpiration rate?

Answer 14

potometer

Question 15

where are xerophytic plants adapted to live in?

Answer 15

in dry climates

Question 16

what are 2 examples xerophytes

Answer 16

cacti and marram grass

Question 17

how is marram grass adapted to live in dry climates and reduce water loss?

Answer 17

has stomata sunken in pits so sheltered from the wind reducing transpiration rate

layers of hairs on epidermis which traps moist air round the stomata reducing transpiration rate

in windy and hot condition, it rolls up its leaves reducing exposed surface area and trapping moist air

Question 18

how is cacti adapted to live in dry climates and reduce water loss?

Answer 18

thick waxy layer on the epidermis, reducing water loss by evaporation as the layer is water proof (marram grass also)

spines instead of leaves to reduce surface area for water loss

close their stomata at hottest times of day when transpiration rates are the highest

Question 19

where are hydrophytes plants adapted to live in?

Answer 19

water

Question 20

what is an example of hydrophilic (hydrophytes) plants?

Answer 20

water lilies’

Question 21

how are hydrophytes adapted to live in water and cope with low oxygen levels ?

Answer 21

air spaces - help the plants float, can act as a store for oxygen

stomata - usually only present on the upper surface of floating leaves helping to maximise gas exchange

have flexible leaves and stems. these plants are supported by water around them so dont need rigid stems for support, flexibility helps prevent damage by water currents.

Question 22

what is translocation?

Answer 22

it is the movement of dissolved substances/assimilates (sucrose, amino acids) to where they are needed in a plant - source to sink

Question 23

what is the mass flow hypothesis?

Answer 23

active transport is used to actively load the solutes into the sieve tubes of the phloem at the source (leaves)

this lowers the water potential inside the sieve tube so water moves in via osmosis from xylem and companion cells

this creates a high pressure inside the sieve tubes at the source end of the phloem

at the sink end, solutes are removed from the phloem to be used up. this increases water potential inside the sieve tubes so water leaves via osmosis.

this lowers the pressure inside the sieve tubes

the result is a pressure gradient from the source to the sink end. the gradient pushes solutes along the sieve tubes to where they are needed

Question 24

what is a SOURCE?

Answer 24

where the substance is made

Question 25

what is a SINK?

Answer 25

where its used up

Question 26

describe the process of active loading?

Answer 26

in companion cell, ATP is used to transport hydrogen ions out of cell into surrounding tissue cells

a concentration gradient is set up more H+ outside than in companion cell

an H+ ion binds to co transporter protein in companion cell membrane and re enters the cell.

a sucrose molecule binds to the co transport protein at the same time. the movement of the H+ ion is used to move sucrose molecule into cell against its conc gradient.

sucrose molecules are then transported out of companion cells and into sieve tubes by the same process