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OCR Biology A Level > 3.1.3 Transport In Plants > Flashcards

3.1.3 Transport In Plants Flashcards

1
Q

Why do large multicellular plants need a transport system?

A
  • larger organisms have a smaller SA:Vol ratio
  • rate of diffusion too slow + diffusion distance too long
  • molecules and mineral ions need transporting from one part of the plant to the other
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2
Q

Why does a small SA:Vol ratio mean that large multicellular plants require a transport system?

A
  • leaves have a large SA:Vol ratio but stems, trunks + roots have a small SA:Vol
  • therefore cannot rely on diffusion across outer surface alone to supply cells with required molecules
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3
Q

Why does a larger size mean that large multicellular plants require a transport system?

A
  • some plants are tall
  • diffusion distance is too great
  • effective transport system needed to move substances up + down tip to root of leaves and stems
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4
Q

Why do larger metabolic domands mean that large multicellular plants require a transport system?

A
  • underground parts of plant don’t photosynthesise - need glucose transporting to them + remove waste
  • hormones need transporting to area of effect
  • mineral ions need transporting from root hair cells to cells of plant to make proteins
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5
Q

Where are food stores in Dicots and Monocots?

A

Dicots: Cotyledons x2
Monocots: Endosperm

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6
Q

What are the roles of the xylem and phloem

A

Xylem: Tranport water + mineral ion up the plant
Phloem: Transport sugars/sucrose up + own the plant
Both examples of mass flow

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7
Q

What is meristematic tissue and where is it found?

A

Tissue where cells are able to divide by mitosis and differentiate into other cell types - found at growing points of the plant (root tips and shoot tips)

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8
Q

Name 2 ways you could observe the position of xylem vessels in leaf stalks?

A
  • put leaf in dye or food colouring
  • cut transversely
    OR
  • cut a thin transverse cross section
  • stain or observe with microscope
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9
Q

How are the xylem and phloem positioned in a leaf?

A

As a vascular bundle - xylem on top, phloem underneath

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10
Q

What components are phloem tissue made from?

A

Companion cells + sieve tube elements

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11
Q

How are companion cells and sieve tube elements linked?

A

Via microscopic channels through their cellulose cell walls called plasmodesmata - links cytoplasm of adjacent cells

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12
Q

What are sieve tube elements?

A
  • elongated cells with little cytoplasm
  • joined end to end to form a column so solutes can be transported long distances
  • perforated so solutes can pass from cell to cell
  • few organelles + no nucleus
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13
Q

What process is the phloem used for and what does it transport?

A

Translocation - transaports assimilates (sucrose + amino acids)

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14
Q

Explain the sites found in the plant and what happens in them

A

Source site - assimilates loaded into phloem
Sink site - where assimilates are unloaded from the phloem

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15
Q

Give examples of sources and sinks

A

Sources
- green leaves
- green stems
- tubers unloading stores
- food stores in seeds when germinating

Sinks
- actively dividing meristems
- developing tubers laying down food stores
- growing roots
- developing seeds laying down food stores

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16
Q

Give evidence for the phloem being used

A
  1. Bark/ outer edge of tree removed (including phloem)
  2. This lowers water potential in bark above cut out
  3. This swells due to water moving into this area by osmosis
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17
Q

Why is starch not transported in phloem sap?

A
  • too viscous to move
  • insoluble
  • can’t enter + leave cells
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18
Q

Explain the process of how sucrose is moved from the source

A
  1. Sucrose is taken into companion cell from source using ATP
  2. Sucrose diffuses through plasmodesmata into phloem sieve tube element
  3. Sucore lowers water potential of sieve tube element
  4. Water moves in via osmosis
  5. This increases hydrostatic pressure at source
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19
Q

Explain the process of how sucrose is moved to the sink

A
  1. Sucrose leaves sieve tube element and moves into sink cell/companion cell by diffusion or active transport
  2. Loss of sucore from sieve tube element increases water potential
    3.Water moves out via osmosis
  3. This decreases hydrostatic pressure at source
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20
Q

What is mass flow?

A

Sucrose moveing from an area of high hydrostatic pressure to low hydrostatic pressure

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21
Q

Explain how assimilates are loaded into the phloem and out of it

A
  1. H+ ions are actively transported out of companion cells into source cells (creating a concentration gradient)
  2. H+ ions move back into companion cell with sucrose/amino acids into companion cell through co-transport proteins
  3. Surcose/amino acids diffuse from companion cell into sieve tube element via plasmodesmata - lowering water potential of sieve tube element
  4. Water moves into sieve tube element via osmosis creating high hydrostatic pressure
  5. Water moves from high to low hydrostatic pressure carrying sucrose/ amino acids
  6. Assimilates moves into companion + sink cell via diffusion or active transport
  7. Water leaves phloem via osmosis from high to low water potential
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22
Q

Describe and explain pieces of evidence that prove translocation in companion cells?

A
  • companion cells become negatively charged compared to surroundings - H+ ions move out of companion cells
  • pH changes don’t occur in companion cells treated with cyanide, which stops aerobic respiration - H+ ions can only move out of companion cells by active transport, which requires ATP
  • scientists see mitochondria, plasmodesmata and intrinsic proteins in the cell surface membrane - mitochondria for ATP production, plasmodesmata for assimilate diffusion and proteins for movement of H+ ions + sucrose/ amino acids
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23
Q

Why does translocation require ATP and how do we know it does?

A

Assimilates move 100,000x faster in phloem faster than with just diffusion - companion cells have many mitochondria to make ATP - if aerobic respiration stops so does translocation

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24
Q

What are xylem vessels and what do they transport?

A
  • Dead hollow cells with lignified cell walls + no organelles
  • joined end to end with no end walls forming a continuous tube
  • transports water + minerals
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25
Q

Explain key aspects of how aphids and phloem are linked

A
  • aphids pierce plant tissue with mouth parts/stylet to reach the phloem
  • if aphid is removed from stylet, sap continues flowing due to pressure from phloem contents
  • used to measure flow rate and concentration of sucrose at different parts of the plant
  • shows pressure + flow rate is lower closer to sink than source - concentration of sucrose is higher near the source
26
Q

What does lignin to do the vessels?

A
  • strengthens + thickens the xylem wall to prevent collapse when water is under tension
  • waterproofs the wall to reduce lateral loss of water through the wall
  • allows for adhesion of water molecules, increasing capillarity
  • in spiral pattern to allow vessel to stretch, preventing stem breaking
27
Q

What do pits in the walls do?

A
  • allow water to move between vessels
  • allow water to bypass a blockage/ air lock
  • allows water to be supplied to other tissues or plant parts
28
Q

Why do plants require water?

A
  • raw material in photosynthesis
  • mineral ions + products of photosynthesis transported in aqueous solution
  • loss of water by evaporation cools plant
  • hydrostatic pressure (turgor pressure) in plants supports stems + leaves and stops wilting
29
Q

What is transpiration?

A

Evaporation of water and loss of water vapour from aerial parts of a plant via the stomata

30
Q

What is the transpiration stream?

A

The movement of water up xylem vessels from roots to leaves and then to air surrounding the leaves

31
Q

Explain how tension is created in the transpiration stream

A
  1. Water enters xylem by osmosis into roots - caused by active transport of ions into root cells + xylem, causing high hydrostatic pressure at bottom of xylem
  2. Transpiration from leaf mesophyll cells through stomata creates low hydrostatic pressure at the top of the xylem
  3. Water under tension: cohesion between water molecules + adhesion of water molecules to xylem walls
32
Q

Name parts of the leaf

A
  • waxy cuticle
  • upper epidermis
  • palisade mesophyll
  • spongy mesophyll
  • lower epidermis
  • stomata
  • guard cell
  • phloem
    -xylem
33
Q

What is the function of guard cells?

A
  • open stomata for gas exchange
  • CO2 enters here for photosynthesis to make sugars
  • water vapour is lost here when opened
34
Q

Explain the structure of the upper and lower epidermis

A

Upper epidermis
- few stomata in upper epidermis
- thick waxy cuticle - reduces evaporation of water + loss of water vapour

Lower epidermis
- large air spaces for CO2 diffusion - large SA for evaporation

35
Q

What 3 processes are involved in transpiration and why?

A
  • evaporation of water from surface of mesophyll into air spaces
  • diffusion of water vapour through stomata into air
  • osmosis from xylem to mesophyll cells of leaf
36
Q

Summarise the transpiration pull

A
  • pulling of a constrant stream of water up the xylem
  • water molecules held together by cohesion
  • result of evaporation of water from mesophyll cells in the leaf
  • a passive process
  • negative force created at top of xylem
37
Q

List parts of the root structure

A
  • root hairs
  • epidermis
  • cortex
  • phloem
  • xylem
  • endodermis with casparian strip
38
Q

How is a root hair cell specialised for taking in water + mineral ions?

A
  • cells have extended hairs - increase SA to absorb water by osmosis + mineral ions by active transport
  • thin cell wall for short pathway
  • many mitochondria for ATP for active transport
39
Q

What are the:
- Apoplastic pathway
- Symplastic pathway
- Vacuolar pathway
- Casparian strip?

A

Apoplastic pathway: Water moves through the cellulose cell walls and between cells
Symplastic pathway: Water moves by osmosis through cytoplasm
Vacuolar pathway: Uses cytoplasm + vacuoles
Casparian strip: Waxy waterproof layer, forces water from apoplastic pathway into symplastic pathway

40
Q

What is the advantage of plants having a casparian strip?

A
  • forces water + dissolved ions to travel across cell surface membrane, which is selectivley permeable
  • stops toxic solutes from soil reaching xylem + other tissues (no transport proteins for toxic molecules)
41
Q

How do water + minerals enter the xylem from soil with low mineral ion concentration

A
  • can’t enter root via diffusion - use active transport using ATP from respiration in mitochondria
  • water moves into roots due to higher ψ in soil
  • mineral ions actively transported into xylem
  • creates ψ gradient for water to move into xylem
  • water creates high hydrostatic pressure in lower xylem
42
Q

How does transpiration create mass flow

A
  • creates low hydrostatic pressure
  • water under tension moves from low to high hydrostatic pressure
  • helped by adhesion + cohesion
43
Q

What is cohesion-tension theory and how do air bubbles disrupt this?

A

As water is removed from xylem, more water molecules are pulled up to replace them (tension)
- hydrogen bonds allow adhesion between water molecules and cell wall + cohesion between water molecules
- air bubbles cause blockage in xylem + break cohesion - no continous flow

44
Q

How air bubbles be avoided when preparing flowers?

A

Cut flowers under water, so that air doesn’t flow in, stopping blockage of xylem and allowing continous flow

45
Q

Give evidence for cohesion-tension theory

A
  • during day, transpiration rate is highest so tension in xylem is high - this draws tissue in so tree shrinks in diameter (opposite at night)
  • when a flower stem is cut air is drawn in
  • if air is pulled in, plant can no longer move water up stem as continuous stream is broken
46
Q

Give evidence for active transport being involved in root pressure

A
  • if cyanide is applied to root hair cells, root pressure disappears - cyanide stops ATP production so AT stops
  • root pressure increases with increased temperature - chemical reactions speed up with increased temp
  • if oxygen levels falls, root pressure decreases - oxygen needed for respiration to produce ATP for AT
47
Q

What is a potometer used for and how is it set up?

A

Used to estimate rate of transpiration
- take healthy leaf shoot and cut stem at angle underwater
- keep leaves dry
- assemble potometer underwater to remove air bubbles
- ensure is air + water tight with no bubbles

48
Q

How would you ensure that only the original air bubble stays in the capillary tube and no new air bubbles enter when using a potometer?

A
  • cut stem + set up apparatus underwater
  • seal all joints before you begin
  • place opem end of apparatus in water
  • dop not allow air bubble to move too far and enter xylem so it can be used for measurements
  • keep shoot supported to avoide breaking seal + column of water in xylem
49
Q

Why does a potometer only give an estimate of transpiration rate?

A

Only measures water uptake, however the water could be used for many other things apart from transpiration. Water may also be made in plant, which could be used in transpration and not recorded

50
Q

Why should at least 3 readings be taken when using a potometer?

A
  • remove anomalous results
  • increase confidence in results
  • to produce a mean
51
Q

How are plants designed to prevent water loss?

A
  • waxy cuticle
  • stomata on underside of leaf
  • somata closed at night
  • deciduous plants lose leaves in winter
52
Q

What is different about CAM plants compared to normal plants?

A

Close their stomata during the day when transpiration rate would be highest - instread open at night so CO2 can enter and used for photosynthesis in day

53
Q

What are xerophytes and give examples

A

Plants with structural and physiological adaptations that enable them to survive in hot, dry conditions e.g. conifers, cacti, marram grass

54
Q

List and explain adaptations of xerophytes to prevent water vapour loss

A
  • hairy leaves: traps water vapour so decreases water vapour potential gradient steepness
  • sunken stomata in pits: traps water vapour so decreases water vapour potential gradient steepness
  • rolled leaves: reduces surface area + traps water vapour so decreases water vapour potential gradient steepness
  • high solute concentration in cells: maintains low ψ in cell so water stays inside
  • thicker waxy cuticle: waterproof/impermeable to water, reducing evaporation
  • small leaves/ needles: reduces SA for evaporation
  • fewer stomata: reduced diffusion of water vapour
  • can close stomata in day: reduced diffusion of water vapour
  • morew stomata on leaf underside: less exposure to sun, so cooler - reduces diffusion of water vapour
  • more densely packed spongy mesophyll: reduces SA for evaporation
55
Q

How can leaf density be determind for the underside of a leaf?

A
  • using a microscope + graticule
  • count number of hairs in given area
  • repeat measurements on the same leaf
  • divide by area used to calculate density
  • calculate a mean
56
Q

When selecting leaves from trees, what factors should be considered to ensure a valid sampling method

A
  • sane age of tree
  • same size leaves
  • record results same time of day/year
  • leaves selected from same height
57
Q

What are hydrophytes and give examples

A

Plants that live in water and need adaptations to survive growing in water/soil saturated with water e.g. water lilies + water cress

58
Q

List and explain adaptations of hydrophytes

A
  • many stomata on upper leaf that are always open: maximise gas exchange + contact with air
  • very thin or no waxy cuticle: no need to reduce transpiration + conserve water
  • wide falt leaves: maximise light capture
  • small roots: water moves directly into stem + leaves
  • air sacs: to allow plant to float on water
59
Q

Give key aspects of aerenchyma

A
  • specialised parenchyma (packing tissue)
  • forms in leaves, stems + roots
  • makes leaves + stems more bouyant
  • internal pathway for movement of oxygen to tissues in water
  • found in rice plants, allowing methane to escape to atmosphere (greenhouse efffect)
60
Q

Give key aspects of Pneumatophores

A
  • aerial roots grow upwards into the air
  • have many lenticals to allow air into plant
  • found in mangrove swamps where roots can become waterlogged

OCR Biology A Level (11 decks)

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