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Alevel Biology OCR > 3.1.3 - Transport in Plants > Flashcards

3.1.3 - Transport in Plants Flashcards

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1
Q

Why do plants need transport systems?

A
  • size
  • high metabolic rate
  • small surface area to volume rato (SA:V)
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2
Q

What are vascular plants?

A

plants that have specialised transport systems

-have vascular tissue

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3
Q

Why do some plants not need a specialised transport system?

A

small plants don’t

  • can absorb materials directly from environment
    eg. mosses
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4
Q

What is vascular tissue?

A
  • made up of xylem and phloem

- involved in transport and structure

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5
Q

What is the structure of the vascular bundle like in the roots of a plant?

A
  • drill like structure
  • X of xylem (in centre as it is the strongest)
  • sections of phloem around xylem cross
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6
Q

What is the structure of the vascular bundle like in the leaf of a dicotyledonous plant?

A
  • xylem located on top of phloem

- sections of vascular bundle throughout

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7
Q

What is the structure of the vascular bundle like in the stem of a plant?

A
  • several vascular bundles in circle
  • xylem vessels in inside of vascular bundles
  • phloem in middle of vascular bundles
  • cambium layers on outside of vascular bundles
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8
Q

What is the structure of the xylem vessel? (And why is this beneficial?)

A
  • non-living
  • lignified walls (lignin laid down in walls as rings, spirals or solid tubes which strengthens xylem and stops it from collapsing)
  • thick walls (prevents bursting/collapsing
  • no contents of cells (less resistance to flow)
  • pits in cell walls (allows water to leave xylem vessel to supply it to cells and tissues)
  • thick-walled xylem parenchyma cells pack around xylem vessels (contain tannin deposits -tannin is a bitter chemical that protects plants from being attacked by herbivores)
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9
Q

What does the xylem transport?

A

water and mineral ions up the plant (from roots to shoots and leaves)

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10
Q

What is the structure of the phloem vessel? (And why is this beneficial?)

A
  • living tissue
  • vessel made up of sieve tube elements (cells joined end-to-end -organelles broken down)
  • areas between cells called sieve plates
  • companion cells are linked to sieve tube by many plasmodesmata (companion cells have lots of mitochondria are active and provide energy for phloem)
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11
Q

What does the phloem transport?

A

food in form of organic solvents (eg. sucrose, amino acids, etc) up and down the plant

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12
Q

Why do plants need water?

A
  • it creates hydrostatic/turgor pressure (provides hydrostatic skeleton for support and drives cell expansion)
  • keeps plants cool (when it evaporates)
  • transports substances
  • needed in photosynthesis
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13
Q

How does water move from the soil to the xylem vessel?

A

-taken into roots via osmosis (down water potential gradient)
two options:
1) symplast pathway (moves through cytoplasm and plasmodesmata via osmosis)
2) apoplast pathway (moves through cell walls and intercellular places via diffusion -however at casparian strip in endodermis, it leaves apoplast pathway, passes through cell membrane and joins symplast pathway)

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14
Q

What is the symplast pathway ?

A

movement of water through cytoplasm and plasmodesmata

-each cell further from roots has lower water potential so water is drawn up plant

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15
Q

What is the apoplast pathway?

A

movement of water through cell walls and intracellular spaces
-fastest movement of water

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16
Q

What is the Casparian strip and what happens there?

A
  • waxy strip which is impermeable to water located in the endodermis
  • water in apoplast pathway is forced into symplast pathway
  • this prevents toxic solutes from the soil entering tissues and means plants use all the minerals
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17
Q

How does water move up the plant?

A
  • through the xylem
  • uses tension and cohesion -transpiration pull
  • as water evaporates of leaves, tension causes water to be pulled up because the water molecules cohere to each other (they are attracted to eachother due to hydrogen bonds) -capillary action
  • adhesion (water molecules are attracted to xylem walls
18
Q

What is the evidence for the cohesion-tension theory?

A
  • changes in tree diameter (at higher transpiration rates, diameter decreases due to tension)
  • cut flowers (draw water in rather than out -transpiration pull continues)
  • broken xylems (water stops being drawn up as air breaks transpiration stream)
19
Q

What is transpiration?

A

the loss of water vapour by evaporation from leaves (and stems) via stomata
-by diffusion out of leaf down water potential gradient

20
Q

What factors affect the transpiration rate?

A
  • light
  • relative humidity
  • temperature
  • air movement
  • soil water availability
21
Q

How does light affect the transpiration rate?

A

increased light intensity = increase no. stomata open => increased rate of transpiration

22
Q

How does relative humidity affect the transpiration rate?

A

high relative humidity = lower water vapour potential gradient => decreased rate of transpiration

23
Q

How does temperature affect the transpiration rate?

A

increased temp = increased kinetic energy of H2O molecules + decreased relative humidity => increased rate of transpiration

24
Q

How does air movement affect the transpiration rate?

A

windier conditions = increased water potential gradient => increased the rate of transpiration

25
Q

How does soil water availability affect the transpiration rate?

A

damp soil => increased the rate of transpiration

dry soil => decreased the rate of transpiration

26
Q

What is a potometer?

A

apparatus used to measure the water uptake of a plant (estimates transpiration rates)

27
Q

How do you set up a potometer?

A
  • cut healthy shoot under water (to stop air entering xylem)
  • cut shoot at slant (increases SA)
  • check apparatus is full of water (no air bubbles)
  • insert shoot into apparatus under water
  • remove potometer from water and ensure airtight/watertight joints around shoot
  • keep leaves dry (to keep conditions constant and not affect water potential gradient)
  • allow time for shoot to acclimatise
  • shut screw clip
  • keep ruler fixed + record position of air bubble on scale
  • start timing + measure/calculate distance moved per unit time
28
Q

What are mesophytes?

A

plants that can take up sufficient water to replace transpiration

29
Q

What are hydrophytes?

A

plants that live partially or completely submerged in water

eg. water lilies

30
Q

What are xerophytes?

A

plants that live in areas where water loss via transpiration is greater than water taken in by plants
eg. cacti and marram grass

31
Q

How are xerophytes adapted to their environment?

A
  • thick waxy cuticle (prevents water loss by transpiration)
  • sunken stomata (reduces air movement -creates a microclimate of still, humid air => reduces water potential gradient + transpiration)
  • less stomata (reduces gas exchange + transpiration)
  • reduced no. leaves (lower SA:V => reduces water loss)
  • hairy leaves (creates a microclimate of still, humid air => reduces water potential gradient + transpiration)
  • curled leaves (confines stomata to a microclimate of still, humid air => reduces water potential gradient + transpiration)
  • succulents (swelled/fleshy -water stored in parenchyma tissue which can be used in drought)
  • leaf loss (loose leaves when water isn’t available)
  • root adaptions (surface roots -collect rain water after short rain shower +long roots -go deep into ground to deep water sources
32
Q

How are hydrophytes adapted to their environment?

A
  • very thin/no waxy cuticle (water doesn’t need to be conserved)
  • many always-open stomata on upper surfaces (maximises gas exchange)
  • reduced structure to plant (water supports leaves/flowers -no strong supporting structures needed)
  • small roots (water can diffuse directly into stems/leaves so roots aren’t needed)
  • air sacs (enable leaves/flowers to float)
  • arenchyma (large air spaces -makes plant more buoyant)
  • wide, flat leaves (spread across the surface of water -capture as much sunlight as possible for photosynthesis)
  • large SA of stems/leaves under water (maximises area for photosynthesis)
33
Q

What is translocation?

A

the movement of assimilates (dissolved substances, eg. sucrose and amino acids) from parts of the plant where the substances are made to other parts of the plant where they’re needed

  • active process
  • occurs in phloem in both directions
34
Q

What are sources?

A

places in plant where assimilates (eg. sucrose) are loaded into phloem

  • high hydrostatic pressure
    eg. leaves, storage organs
35
Q

What are sinks?

A

places in plant where assimilates are unloaded from phloem (ie. where they are used for growth or respiration)

  • low hydrostatic pressure
    eg. meristem, growing roots, flowers, fruit, seeds
36
Q

What is mass flow?

A

how solutes are transported from source cells into sinks through the phloem

37
Q

What happens in mass flow?

A
  • assimilates enter the phloem (decreases water potential near source end)
  • water enters by osmosis (down water potential gradient)
  • this causes an increase in hydrostatic pressure (because source/sink can’t expand)
  • assimilates move down the pressure gradient towards the sink end of the phloem.
  • assimilates move into sink cells (are converted into other molecules eg. starch)
  • removal of assimilates increases the water potential at the sink end -causes water to move out of the phloem by osmosis (this maintains the hydrostatic pressure gradient between the source and the sink)
38
Q

How are assimilates loaded into sources?

A
  • companion cell actively transports hydrogen ions into the surrounding cells
  • creates a hydrogen ion gradient between the surrounding cells and the companion cell
  • hydrogen ions diffuse back into the companion cell with a sucrose molecule through a co-transporter protein
39
Q

How are assimilates unloaded into sinks?

A
  • sucrose is unloaded from phloem at any point it is needed
  • occurs via diffusion
  • sometimes it is converted into substances (eg. glucose, starch) to maintain sucrose concentration gradient
40
Q

What is the evidence for translocation?

A
  • microscopes allow us to see adaptions for active transport
  • if mitochondria (in companion cells) are poisoned, translocation stops
  • flow of sugars is faster than by diffusion alone
  • aphids can be used to demonstrate the translocation of organic solutes in phloem

Alevel Biology OCR (26 decks)

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