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Biology A1 OCR A > Transport in Plants > Flashcards

Transport in Plants Flashcards

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1
Q

Why do plants need a transport system(3points)

A
  • Large multicellular organism,small SA:V so can’t rely on diffusion to transport nutrients
  • Size-Plants are very large.transport system needed for movement roots to leaves

Metabolic demand-glucose made in leaves and transported to parts of plant that don’t photosynthesise

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2
Q

explain how the placement of vascular bundles in roots is advantageous for the plant.

A

vascular bundles in center.

gives support to plant and helps withstand tugging strains when stem and leaves are blown in the wind

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3
Q

explain how the placement of vascular bundles in stems is advantageous for the plant.

A

vascular bundles on the edge.

gives support

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4
Q

explain how the placement of vascular bundles in leaves is advantageous for the plant.

A

vascular bundles in the midrib of leaf.

heps support structure of leaf.small vein branch from a vascular bundles spreading across leaf.for transport and support.

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5
Q

Describe the structure of xylem

A

xylems are very long,tube-like structures formed from dead cells and joined end to end.The cell walls are lignified and contain bordered pits,allowing water to pass through.

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6
Q

explain the function of 2 other tissues associated with xylem in herbaceous dicots

A

xylem parenchyma- packed around xylem tissue and stores food and contains tannin deposits.

Tannins-bitter chemicals which protects against predators (plant responses)

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7
Q

Describe the structure of xylem and how it relates to its function

A

function:transport of water and mineral ions

long, tube-like structures formed from
dead cells and joined end to end- efficient transpiration if alive cells they would’ve absorbed h20 2 survive

The cell walls are lignified(in spirals/solid tubes)- support 2 withstand tension

contain bordered pits- allowing water to pass through.

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8
Q

describe the structure of phloem and how it relates to its function

A

Function:Transport of sucrose and amino acids

Main transport system are sieve-tube elements which are made up of living cells joined end to end to form a long hollow tube.this hollow tube is perforated to form sieve plates.

Linked to sieve-tube are companion cells-life support system.Carry out all reactions for sieve-tube.

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9
Q

what is translocation?

A

-Transport of assimilates (eg. sucrose) through the phloem.

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10
Q

Describe active loading in translocation

A
  • ATP used to actively transport H+ out of companion cells, sets up a conc. gradient
  • H+ and sucrose binds to co-transporter in companion cell membrane , sucrose moved against its conc. gradient.
  • sucrose transported into sieve tubes same way
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11
Q

Describe what happens at source- mass flow hypothesis

A
  1. source
    - sucrose moved into phloem from companion cells.
    - this lowers ψ so H2O moves in by osmosis.
    - this H2O increases hydrostatic pressure in sieve tube.
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12
Q

Describe what happens at sink- mass flow hypothesis

A
  • solutes diffuse into cells down a conc. gradient as they being used up immediately.
  • this decreases solute conc. in phloem so H2O moves out via osmosis.
  • reducing pressure
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13
Q

How is the flow of assimilates maintainou=5ed?

A
  • pressure gradient from source to sink
  • This gradient pushes solutes along the sieve tubes towards the sink.
  • The higher the conc. of sucrose at source,the higher the rate of translocation.
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14
Q

where are the main sinks in a plant

A
  • roots-growing
  • meristems-dividing
  • developing seeds,fruits/storage organs
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15
Q

Where are the sources in plants

A
  • green leaves
  • storage organs eg tuers tap roots that are unloading
  • food stores in seeds when germinate
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16
Q

what is transpiration

A

loss of water vapour / evaporation of water ;

from, aerial parts of plant / leaves / stomata

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17
Q

how is gas exchange linked to water loss

A
  • When stomata open to allow CO2 in and O2 out water vapour diffuses out the leaves down a concentration gradient.
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18
Q

what are factors affecting transpiration

A
  • light intensity
  • temperature
  • humidity
  • wind
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19
Q

How does wind affect transpiration

A
  • increases rate of transpi…

- air movement blows away water vapour away from stomata. Increasing the ψ gradient.

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20
Q

How does humidity affect transpiration

A

lower humidity=faster transpi..

-less water molecules in air so H2O diffuses out down ψ gradient.

-

21
Q

How does temp affect transpiration

A
  • High temp= faster transpi….

- high temp increases kinetic e of H2O molecules so more transpi..

22
Q

How does temp affect humidity and ψ

A

increase temp. increases conc. of H2O vapour air can hold before it become saturated

-decreases relative humidity and ψ

23
Q

How does light intensity affect rate of transpiration?

A

increases light intensity= faster transpiration

24
Q

what is the transpiration stream?

A

movement of water from roots to leaves

25
Q

what are the 3 mechanism of transpiration stream (cohesion-tension theory)

A
  • tension
  • cohesion
  • adhesion
26
Q

Explain the cohesion tension theory

A
  1. evaporation at top of plant
  2. creates tension in xylem,pulling water up to leaves
  3. water molecules are cohesive due to HB so whole column of H2O moves up
  4. water enters the stem through root cortex cells.
27
Q

How is water able to move up against gravity?

A

adhesion

H2O molecules form HB bonds w xylem walls so entire columns of water able to move up

28
Q

What are xerophytes?

A

plants adapted to live in dry climates

29
Q

what are hydrophytes

A

plants adapted to live in aquatic habitats

30
Q

How are cacti adapted

A

-thick waxy layer,waterproof-reduces H2O loss by evapo..

  • spines instead of leaves-reduces S.A
  • closed stomata on hot days
31
Q

How are marram grass adapted

A
  • stomata in sunken pit so sheltered from wind
  • layer of hair on epidermis-traps moist air in stomata reduces ψ gradient between plant and air
  • in hot/windy plant rolls leaves trapping moist air & ↓ S.A
  • thick waxy layer ↓ water loss.
32
Q

How are water lilies adapted

A
  • large air spaces in tissues allowing it to float increasing light received.
  • stomata only present at upper surface maximizing gas exchange
  • wide flat leaves capturing a lot of light.
33
Q

draw symplast pathway

A

soil–> root hair cell –> cortex—>endodermis cell layers –>xylem vessels

34
Q

Outline symplast pathway.

A

goes through living part of cell-cytoplasm which is connected by plasmodesmata

-via osmosis

35
Q

describe the water potential in symplast pathway

A

root hair
-high ψ and cytoplasm is dilute due to water diffusing in.

-H2O moves by osmosis to next cell along(which has a lower ψ)
and so on until xylem is reached.

-steep ψ gradient is maintained when all H2O leaves root hair

36
Q

what is meant by apoplast

A

cell walls and intercellular spaces.

37
Q

Outline the apoplast pathway.

A
  • H2O goes through non-living parts of cell
  • cell walls v absorbent so h2o diffuses through
  • h2o carries solutes + move from areas ↑ hydrostatic pressure to areas w ↓ hydrostatic pressure
38
Q

Outline the pathway of water to xylem

A

H2O moves across root hair cells via apoplast route.

  • it diffuses through cell walls and passes through spaces between them
  • at casparian strip(band of waxy waterproof layer ) H2O forced into cell membrane & takes the symplast pathway
39
Q

State the different layers of a pant leading to xylem.

A

root hair cells–> cortex–>endodermis–> xylem

40
Q

Why is the casparian strip advantageous?

A

because due to casparian strip water is forced to go through cell membrane which is selectively-permeable
excluding potential toxic solutes

41
Q

describe the uptake of water from endodermis to xylem

include ψ

A

xylem has a ↑er conc. of solute than endodermis. as solutes are actively transported in.

∴ xylem has a lower ψ than endodermis

this increases rate of water osmosing in.

42
Q

What is the function of a potometer

A

to measure the rate of water uptake of a plant

thus the rate of transpiration

43
Q

Draw out the equipment for potometer and label.

A

kerboodle pg204.

44
Q

Explain the method of estimating transpiration streams(potometer)

A
  1. Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to
    increase the surface area available for water uptake.

2.Assemble the potometer in water and insert the shoot under water, again to prevent air
from entering

  1. Remove the apparatus from the water but keep the end of the capillary tube
    submerged in a beaker of water.
  2. Check the apparatus is watertight and airtight, using screws or petroleum jelly.
  3. Dry the leaves
  4. Allow time for the plant to acclimatise and then shut the tap.
  5. Remove the end of the capillary tube from the beaker of water until one air bubble has
    formed, then put the end of the tube back into water.
  6. Record the starting position of the air bubble.
  7. Start a stopwatch and record the distance moved by the bubble at regular time
    intervals, e.g. every 30 mins.
  8. Calculate the rate of air bubble movement by dividing the distance travelled by time.
    This is an estimate of the transpiration rate.
45
Q

How would you ensure valid data is collected in potometer practical

A

Control Variables:
temp. humidity, light, wind movement, surface area of leaves

How to control them:
Temp=
Light Intensity= changing distance between lamp+poto
Wind speed= fan near poto w diff. speeds
Humidity=wrapping plastic bag around plant

46
Q

How is rate of transpiration/uptake calculated

A

=distance travelled by air bubble/ Time taken

47
Q

Limitations of potometer practical?

A

Not all the water taken up by the plant is used for transpiration– for example some is
used in cells to maintain turgidity.
● Some water is used in photosynthesis
● The plant is dying once you cut off its roots – it may take up less water as it begins to
die.

48
Q

Method of plant stem dissection

A

1.use scalpel/razor blade to cut a cross section of stem (transverse/longitudinal) on a white tile

Cut sections as thin as possible.Use tweezers to hold stem down while cutting.

  1. Use tweezers to gently place cut sections in water(h2o is in watch glass).Keep them there until use.stops them from drying out
  2. Add drop of h2o to microscope slide,add the plant section and carefully add 1/2 drops of stain e.g toluidine blue O(TBO)
  3. Carefully add cover at an angle,u have created a wet mount
  4. View specimen under light microscope and draw labelled diagram of what you observed.
49
Q

what colours do phloem,xylem and parenchyma stain when using toluidine blue O

A

non-lignified tissue : pink/purple
lignified tissue : green/blue

Phloem – red
Xylem – green/blue-green
Parenchyma – red-purple

Biology A1 OCR A (8 decks)

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