plant transport

Question 1

definition of xerophyte

Answer 1

Plant ADAPTED TO reduce water loss so it can survive in VERY ARID conditions

Question 2

Why is transpiration unavoidable during the day

Answer 2

The stomata are open for photosynthesis
Oxygen has to be removed
stomata is an easy route for water to be lost

Question 3

How do most plants reduce water lost

Answer 3

Waxy cuticle

Question 4

Xerophytes adaptations for surviving in arid conditions

Answer 4

1.Small leaves,

Question 5

How is sucrose loaded into the phloem

Answer 5

Companiion cells use ATP to actively tranport Hydrogen ions out into surrounding tissues

Diffusion gradient produced and hydrogen ions diffuse back into companion cell, through COTRANSPORTER PROTEINS

tHESE PROTEINS allow hydrogen to bring sucrose molecules into the companion cells

As concentration of sucrose builds up they diffuse into SIEVE TUBE ELEMETNS THROUGH PLASMODESMATA

Question 6

Definition of translocaion

Answer 6

The transport of assimilates throughout the plant in the phloem tissue

Question 7

Definiton of source and sink

Answer 7

Source loads sucrose into the phloem

Sink Unloads sucrose from the phloem

Question 8

WHy does the bark swell when it has been cut

Answer 8

Area above the bark acts as a sink where sugar collects, and cell division occurs

Question 9

How do we know phloem is used

Answer 9

If radioactively labelled CO2 is used in photosynthesis the labelled carbon appears in phloem

Ringing a tree to remove phloem results n sugars collecting above the ring

Aphid feeding on stem, mouthparts are taking food from phloem

Question 10

How do we know that trasnlocation is an active process

Answer 10

COmpanion cells have many mitochondria

MEtabollic poisons inhibits formation of ATP

Question 11

How do we know translocation uses this mechanism

Answer 11

pH of companion cell is higher than surrounding cells

Higher concentration of sucrose in source than sink

Question 12

Evidence against the mechanism of translocation

Answer 12

not all solutes in phloem sap flow at the same rate

role of sieve plates is unclear

Question 13

WHat is meant by active loading

Answer 13

using atp to transport sucrose

Question 14

compare translocation with transpiration

Answer 14

Translocation is an active process that loads sugars from the source to the sink
Decreasing the water potential, Water enters via osmosis and increases the hydrostatic pressure

TRANSPIRATION- driven by the evaporation of water from leaf
this reduces the hydrostatic pressue in the top of the plant, creating a pressure gradient, pulls the water up aided by cohesion

Question 15

WHy do companion cells have a higher PH compared to surrounding cells

Answer 15

Hydrogen ions pumped out of companion cells, leaves
fewer hydrogen ions
Hgher PH

Question 16

Possible function of sieve plates

Answer 16

COuld be used to block the flow of sugars if phloem is cut and sugars lost

Question 17

8 Physical and Environmental factors that affect water loss

Answer 17

Physical:
Number of leaves
Number and size of stomata
Presence of cuticle

Environmental
Light 
temperature
humidity
air movement/ wind
water availibility- little water in soil, means it can't replace water loast via evaportaation

Question 18

How can a potometer be used to measure water uptake

Answer 18

Potometer measures water uptake by a leafy shoot
water uptake is measured by the movement of the meniscus along a capillary tube
The volume = cross sectional area x distance moved

Question 19

Precaustions taken when using a potometer

Answer 19

Set up underwater, ensure no extra air bubbles get into system

Joints must be air tight and water tight

Potometer and shoot must be left to climatise before readings start

Question 20

Two adaptations of the sieve tubes that allow mass flow to occur

Answer 20

elements joined end to end to form a column

Little cytoplasm to reduce resitance to cell sap

Question 21

WHy might flower survive longer if the ends cut off immediately before put into water

Answer 21

Air in xylem

restores continuous column

Question 22

Suggest why a potmoter gives only an estimate of water uptake

Answer 22

It measure the water uptake
not all water is lost
some used for photosynthesis

Question 23

describe the role of the Casparian strip

Answer 23

Cells with a waterprood strip in the endodermis
block the apoplast pathways
force water to take a symplastic route to pass through plasma memranes, so ions entry can be controlled

Question 24

Definition of turgid and plasmolysis

Answer 24

Turgid means full of water

Plasmolysis means the cells contents have shrunk enough to pull the membrane away from the cell wall

Question 25

Describe the structure of xylem

Answer 25

Dead cells aligned end to end, with no end walls to form a continuous column

Walls are reinforced with waterpoof lignin deposits

Lignin is patterned in annual, reticulate and spiral to allow the xylem to stretch as plant grows, and allow flexibility

Tubes are narrow so water doesn’t break easily

Question 26

Desribe the strucutre of phloem

Answer 26

Sieve elements have very little cytoplasm to reduce the resistance of cell sap
Lined end to end, with cross walls, perforated by pores to allow flow of assimilates

Companion cells- large nucelus and lots of mitochondria, produce ATP for active processes
Plasmodesmata allows communication and flow of substances between cells