9 - transport in plants Flashcards

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1
Q

What are reasons for the need of plant transport systems?

A

METABOLIC DEMAND - Green parts of plant photosynthesis and make their own glucose, however internal and underground plants don’t and need glucose transported to them - Mineral ions must be transported from roots to rest of plants to make proteins for enzymes and cell structure - Hormones must be transported - Waste cell metabolism products must be removed SIZE - Large perennial plants need effective transport systems to move substances up and down plant (roots to leaves) SA:V RATIO - Leaves have large SA:V, but stems trunks/roots make plants overall ratio small.

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2
Q

What are herbaceous dicots?

A

Soft tissue plants with short life span (leaves and stems that die down at the end of growing season)

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3
Q

Define vascular system.

A

Series of transport vessels that run through leaves, roots and stem of a dicot plant.

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4
Q

Define vascular bundle.

A

The vascular system of herbaceous dicots comprising of xylem and phloems.

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5
Q

label the structure of the stem

A

Parenchyma - In the middle, packing and supporting tissue Phloem vessel on outside - for translocation
Xylem vessel on inside - for transpiration
Vascular cambium - new xylem and phloem cells divide from it.
In a stem the vascular bundles around the edge provide structural support.

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6
Q

label the structure of a root (dicot)

A

Root hair on the outside protruding
From root hair
Exodermis, epidermis, cortex, endodermis Phloem as 4 dots Xylem as a cross

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7
Q

label the structure of a leaf (dicot)

A

Midrib of the leaf gives structural support as it is the main vein carrying the vascular tissue through the organ

Xylem and phloem

Palisade mesophyll - main photosynthetic tissue

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8
Q

What is the function and structure of a xylem?

A

End walls removed forming a long tube
No cytoplasm or organelles - non-living tissue
Cell walls lignified (impregnated with lignin)
Makes wall waterproof and prevents xylem collapsing
Spiral, annular (ring-like) and reticulate (mesh-like) thickening to strengthen walls and prevent collapsing
Bordered pits to allow lateral water flow between xylem vessels
E.g. if the xylem has an obstruction, water can still flow but in another xylem vessel

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9
Q

What is the function of a phloem vessel and what are its components?

A

Transports assimilates actively by mass flow - involves 2 cells
Sieve Tube Elements (STE) - long sieve tubes transporting assimilates
Companion Cells - supports metabolic function of STE, also involved in actively loading the phloem

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10
Q

What are the adaptations of the sieve tube element?

A

Few organelles and no nucleus - long hollow tubular structure
Has end walls with sieve plates (perforated walls)
Thin layer of cytoplasm
Not lignified as the cell is not under tension

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11
Q

What are the adaptations of companion cells?

A

ste = sieve tube element

Closely linked to STE
Connected to STE by plasmodesmata
microscopic channels of cytoplasm through cellulose cell walls linking cytoplasm to adjacent cells
Dense cytoplasm with many mitochondria and a large nucleus
Mitochondria gives energy to move sucrose into STE

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12
Q

What are the roles of water in plants?

A

Turgor pressure (hydrostatic) as a result of osmosis in plant cells, gives a hydrostatic skeleton - supports stem and leaves.
Loss of water by transpiration keeps plants cool
Water is a transport medium for mineral ions and assimilates
Water is a raw material for photosynthesis.

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13
Q

What is the role and what are the adaptations of a root hair cell?

A

Exchange surface where water is taken into plant
Long thin extension from root hair cell is root hair
Adaptations

Small size - can penetrate soil particles
Each hair has a large SA:V ratio
Each hair has a thin surface layer to reduce diffusion and osmosis distance to quicken the process
Solute concentration in root hair cell cytoplasm maintains water potential gradient between soil and cell.

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14
Q

What is the symplast pathway?

A

Symplast - continous cytoplasm of living plant cells that are connected through plasmodesmata
Water moves by osmosis down the water potential gradient from cell to cell, starting at the root hair cell until the xylem

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15
Q

What is the apoplast pathway?

A

Apoplast - cell wall and extracellular spaces of the cell

Carries water through cell wall and between cells
Water does not enter the cytoplasm or pass the plasma membranes

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16
Q

Describe the movement of water into the xylem.

A

After water move by symplast and apoplast it reaches the endodermis (layer of cells surrounding xylem and phloem
Casparian Strip
Band of waxy material (suberin) that surrounds endodermal cells forming a water proof layer.
It stops water from entering via the apoplast pathway, it is forced into the symplast pathway
For water to enter the symplast pathway from apoplast, it must pass the selectively permeable membrane which stops toxic solutes from entering from the soil as there are no carrier proteins to admit them

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17
Q

After entering the xylem does the water stay in the symplast pathway?

A

No it re-uses the apoplast pathway

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18
Q

What is root pressure?

A

Root endodermis uses metabolic energy to pump mineral ions into root medulla
Reducing water potential in medulla and xylem to lower than the cortex, so water moves across the endodermis into the xylem
Water cannot move back to the cortex as it is blocked by the Casparian Strip, creating pressure in the cortex pushing water up the xylem

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19
Q

Define transpiration.

A

Loss of water vapour from the upper segments of the plant (mainly leaves)
Occurs through evaporation from leaf surface and through stomata

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20
Q

What are the components of the transpiration stream?

A

Transpiration stream: movement of water from roots to leaves

Capillary action
Transpiration pull

21
Q

What are the stages of transpiration?

A

Water moves by osmosis from the xylem to mesophyll cell in the leaf
Water evaporates from the surfaces of the spongy mesophyll into air spaces
Water vapour diffuses out of the leaf from the air spaces through the stomata down the conc. gradient
The stomata remain open during the day to allow for gas exchange enabling photosynthesis
Since the stomata are open, water vapour is lost so transpiration is a consequence of gaseous exchange

22
Q

What is capillary action?

A

Water rising through narrow tubing against gravity

Needs cohesion + adhesion

Adhesion: Formation of H-bonds between water molecules and carbs in xylem walls

Cohesion: Formation of H-bonds between water molecules

23
Q

What is the transpiration pull?

A

Water moving out of xylem creating a pull to replace loss of water vapour from the leaves
Since water is cohesive it moves as on body under tension, which pulls the water up the stem
known as cohesion-tension theory

24
Q

Show evidence for cohesion tension theory.

A

Change in tree diameter - rate of transpiration is highest during the day, xylem vessel tension is highest - tree diameter shrinks

At night transpiration rate is low and the tension on xylem is low, increasing tree diameter

Xylem vessel damage - air is drawn into xylem, plant can’t transpire, continuous water stream is broken

25
Q

What happens when stomata are flaccid?

A

Turgor pressure is low (guard cells are flaccid)

Pore closes

26
Q

What happens when stomata are turgid?

A

When conditions are favourable guard cells actively pump solutes in increasing turgor
Cellulose hoop stop cells from swelling widthways and they extend lengthways
Inner cell wall less flexible than outer making a bean shape
If water becomes scare - hormonal signals from roots trigger guard cell water loss closing the aperture.

27
Q

What are factors affecting transpiration?

A

Light intensity - light needed for photosynthesis - stoma open, at night, no photosynthesis, stoma close
Relative humidity - amount of water vapour in air
High humidity = low rate of transpiration due to decreased water vapour gradient vice versa
Temperature - increases evaporation so there will be a higher water potential in leaf
Temp rise - also increases amount of water external air can hold before saturation, decreasing humidity and increasing water vapour gradient
Air movement - if there is more wind this blows water vapour (trapped in the hairs at the surface of the leaf) increasing the water vapour gradient
Soil-water availability - if there is not enough water in soil, plant will be under water stress reducing rate of transpiration.

28
Q

Define translocation.

A

Movement of organic solutes in phloem from sources to sinks.

  • Active process (requires energy), substances transported up and down plants
29
Q

Define assimilates.

A

Products of photosynthesis that are transported around plant
- Glucose is made during photosynthesis but the main assimilate is sucrose
Cell sap sucrose level - 0.5%
Phloem sap sucrose level: 20-30%

30
Q

What are sources of assimilates?

A

Green leaves and green stem
Storage organs (in tubers and tap roots) - they unload stores at beginning of growth period
Food stores in seeds when they germinate

31
Q

What are sinks of a plant?

A

Roots that are growing and/or actively absorbing mineral ions
Actively dividing meristems
Any part of plants that are laying down food stores such as developing seeds, fruit stores in organs

32
Q

What are the 2 ways for phloem loading?

A

Passive route

Active route (uses apoplast route): Sucrose travels from source, through cell walls and inter-cell spaces to companion cells & sieve-tube-elements
- By diffusion down conc. gradient - gradient maintained by removal of sucrose from phloem vessels.

33
Q

What is a co-transporter?

A

Intrinsic protein that transports 2 substances simultaneously across a biological membrane

34
Q

Describe the process of active phloem loading.

A

H+ ions actively pumped (uses ATP, ATP + H2O > ADP + Pi + energy) out of companion cell into surrounding cell (creating conc. gradient)
Co-transporter transports H+ ions and sucrose molecules into the companion cells down the concentration gradient into the sieve-tube-elements.
(Sucrose moves through plasmodesmata into STE)
Since solute conc. increases, water potential decreases, so water moves into the STE by osmosis increasing turgor pressure
- Turgor pressure moves water carrying assimilates up and down plant.

35
Q

What are the features of companion cells?

A

Many infoldings in cell membrane to increase SA for active transport of sucrose
Contains many mitochondria to provide ATP for transport pump

36
Q

What is the effect of an increase in turgor pressure?

A

Creates pressure difference between phloem and sink, allowing rapid transportation of solutes and water up and down plant.

37
Q

Define mass flow

A

Assimilates flowing from source to sink down pressure gradient.

38
Q

Describe the process of phloem unloading.

A

Sucrose unloaded to sink via diffusion down conc. gradient

Sucrose moves to other cells to maintain the conc. gradient between cells and phloem
Increases water potential in STE, H2O then flows into sink, or into xylem and subsequently the transpiration stream.

39
Q

Give evidence for translocation.

A

Microscopy allows us to see adaptations of companion cells
If mitochondria in companion cells are poisoned, translocation is stopped
Flow of sugars in phloem is 10,000x faster than diffusion, suggesting it is an active process
Aphids feed off of plant tissue, they insert their stylet (mouth), if aphids are anaesthetised and removed, sap continues to move out of phloem.

40
Q

Define xerophyte and give examples.

A

Plants with adaptations that enable them to survive in dry habitats with short environmental water supply. Cacti, Marram Grass

41
Q

With regards to leaves, what adaptations do xerophytes have?

A

Reduced Leaves - Reduces SA:V ratio, minimises transpiration water loss. E.g. thin needles in conifers

Hairy Leaves - e.g. spine of cacti, creates microclimate of humid air, reducing water vapour potential gradient. -

Curled Leaves - Confines stomata to microclimate of still humid air. e.g. Marram grass

Leaf Loss - when water isn’t available, some plants shed leaves to prevent water loss

42
Q

With regards to stomata, what adaptations do xerophytes have?

A

Sunken Stomata - stomata located in pits, reduce air movement, produces microclimate of humid air

reduces water vapour potential gradient - e.g. in cacti, marram grass,
Reduced Stomata No - reduces water loss by transpiration, but also reduces gas exchange capabilities.

43
Q

What root adaptations do xerophytes have?

A

Long tap roots, grow deep into soil to access water
Widespread shallow roots
large surface area to absorb any water e.g. cacti roots grow 12-18m
Marram grass roots - grow vertically down, have a mat of horizontal rhizomes (modified stems) - roots develop from them

44
Q

What other adaptations do xerophytes have?

A

Thick Waxy Cuticle - 10% of water loss in plants attributed to cuticle by transpiration, thick cuticle prevents and minimises this

Succulents - store water in specialised parenchyma tissue in stems and roots

they are swollen (thick flesh), store water for times of drought (e.g. Aloe plants)
Some plants lose leaves and become dormant
Some die and let new seeds germinate
Some survive as storage organs (bulbs, tubers)

45
Q

Define hydrophyte and give an example.

A

Plants adapted to survive in wet habitats, submerged or on surface of water E.g. water lillies

46
Q

What issues do hydrophytes face even though they have an abundant supply of water?

A

Water-logging air spaces in plants, air spaces must have air

47
Q

Water-logging air spaces in plants, air spaces must have air

A

Reduced Plant Structure - water provides buoyancy for leaves and flowers

Wide Flat Leaves - e.g. water lilly, spread across surface to capture light small roots - water diffuses directly so no need for sole water uptake via a root

Thin/No Waxy Cuticle - don’t need to conserve water as water lost by transpiration is always replaced

Air Sacs - enables leaves to float

Large Stem/Roots - for underwater plants, maximises area for photosynthesis and oxygen diffusion

48
Q

What are the stomatal adaptations of a hydrophyte?

A

Always Open Stomata

on upper surfaces, maximised gas exchange, no risk of loss of turgor as water is always there
guard cells inactive
on water surface plants stomata must be on upper surface for gas exchange