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OCR BIOLOGY (MODULE 3) > TRANSPORT IN PLANTS > Flashcards

TRANSPORT IN PLANTS Flashcards

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1
Q

Why do plants need transport systems?

A
  • plants are multicellular so not all cells will be in direct contact with he environment
  • constantly growing
  • the large size of plants can mean they have a relatively low SA:V. Their branching structure and adaptations of leaves help increase the ratio
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2
Q

What are assimilates?

A

Products of photosynthesis

-amino acids, fatty acids, glycerol, etc

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3
Q

What does the xylem transport?

A

Transport water and soluble mineral ions up the plant

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4
Q

What does the phloem transport?

A

Transport assimilates such as sucrose up and down the plant

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5
Q

Describe the structure of the xylem

A
  1. Column of living cells lined with lignin in the cell wall
  2. Cell contents die and need walls break down
  3. No endplates= long vessel elements are formed
  4. Long vessels are arranged in spirals
  5. Gaps in the lignin where there is cellulose, gaps are called pits
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6
Q

What are adaptions of xylem vessels to functions?

A
  1. Continuous column
  2. No cell contents or end walls to impede flow
  3. Lignin prevents walls collapsing
  4. Lignin allows for adhesion of water molecules
  5. Arrangement of lignin allows for plants to grow, bend and branch
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7
Q

What does the phloem consist of?

A
  1. Sieve tube elements- columns of cells that transport assimilates
  2. Companion cells- linked to sieve tubes
  3. Parenchyma- packing tissue fro support
  4. Fibres- thick walls
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8
Q

Describe sieve tube elements

A
  1. thin layer of cytoplasm
  2. contains mitochondria
  3. no nucleus or ribosome
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9
Q

Describe a companion cell

A
  1. linked to sieve tubes by plasmodesmata

2. increased surface area for more carrier proteins for. more active transport

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10
Q

Describe water potential

A

A measure of the concentration of free water molecules
The more solute in a solution the lower the water potential
Water moves from higher water potential to a lower water potential

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11
Q

Describe the apoplast pathway

A

THROUGH CELL WALL

  • cellulose wall is fully permeable
  • water moves through spaces in cellulose cell wall
  • doesn’t pass through cell membrane (not osmosis)
  • stops at epidermis which stops it reaching xylem/phloem so enters symplast
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12
Q

Describe the symplast pathway

A

THROUGH PLASMODESMATA

  • water travels through cytoplasm of cells via osmosis
  • cytoplasm of cell in root connected by plasmodesmata through holes in cell wall
  • needs water to get into living plants of cells
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13
Q

Describe the vacuolar pathway

A

THROUGH VACUOLE

-via osmosis

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14
Q

What is the casparian strip?

A
  • cells in endodermis contain band of waterproof material (caspaprian strip)
  • made from waxy Suberin
  • blocks apoplast
  • water needs to pass through cell surface membrane which is selectively permeable via osmosis
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15
Q

How does root pressure move water up a stem?

A
  • movement of mineral ions by active transport into xylem at roots can force water up through the stem
  • root pressure affected by metabolic poisons, temp and oxygen concentration
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16
Q

How does the transpiration pull move water up the stem?

A

-created tension (negative pressure causes water to move up the plant)
-water molecules attracted via cohesive forces
-forms a long column of water in the xylem
-as water lost at the top via transpiration the column is pulled through the xylem
-pull of water= tension in column, lignin prevents xylem collapsing
COHESION TENSION THEORY

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17
Q

How does capillary action move water up a plant?

A
  • thin tube, water travels up (adhesion)- aided by lignin
  • adhesive forces between water molecules and narrow walls of the xylem help to pull water up the xylem
  • water can rise up tube against the force of gravity
  • a narrower container= greater proportion of water in contact with the walls= greater adhesive forces
18
Q

Define transpiration

A

The loss of water vapour from the upper parts of the plant, especially the leaves

19
Q

What are the stages of transpiration?

A
  1. water enters leaves travelling in the xylem, then passes into mesophyll cells by osmosis. Water moves from symplast to apoplast pathway
  2. water evaporates from the surface of the mesophyll cells to form water vapour, which collects in the air spaces between mesophyll cells (raising the water vapour potential)
  3. once water vapour potential is higher inside the leaf than outside water molecules will diffuse out of the leaf through stomata, water vapour carried away from leaf by air movement
20
Q

How can you estimate the rate of transpiration?

A
  1. fill apparatus with water, ensure there are no air bubbles
  2. take fresh healthy shoot and cut under water at a slant
  3. insert shoot into apparatus under water
  4. remove apparatus from water and seal with vaseline
  5. dry leaves off and allow time to acclimatise
  6. adjust water in capillary tube to the start of scale with screw clip
  7. keep conditions constant and measure how far the water moves in a set period of time
21
Q

What are precautions to consider when measuring the rate of transpiration?

A

Ensure no air bubbles- breaks cohesion of water molecules
Ensure shoot is fresh and healthy- will have open stomata pores
Cut stem at angle- increases SA in contact with water
Allow shoot to climates- goes time for stomata pores to open and close

22
Q

How does number of leaves affect the rate of transpiration?

A

More leaves= more stomata= more transpiration= more gaseous exchange

23
Q

How does the presence of a cuticle affe t the rate of transpiration?

A

Cuticle is waxy (waterproof) which prevents excess water loss from upper surface
Decreasing rate of transpiration

24
Q

How does light intensity affect the rate of transpiration?

A

Required for photosynthesis and to open stomata pores for gas exchange
Increased light intensity= increased amount of open stomata pores- leads to more water vapour diffusing out and evaporating

25
Q

How does air movement affect the rate of transpiration?

A

Leaf surrounded by air

Increases diffusion gradient= increase in transpiration

26
Q

What is a xerophyte?

A

Plant which is adapted to dry conditions

27
Q

What are examples of xerophytes?

A

Cacti and marram grass

28
Q

What features do xerophytes have to conserve water?

A

Hairs- create microclimate off humid air which decreases water potential gradient= decreasing water loss from surface of leaf
Rolled leaves- confines all stomata in microenvironment of humid air reducing diffusion of water vapour from stomata
Leaves reduced to spines- decreases SA= decreased transpiration

29
Q

What is a hydrophyte?

A

Plants which are adapted to living in water

30
Q

What features do hydrophytes have to survive in water?

A

Wide flat leaves- spread across water to absorb as much light as possible
Air spaces- buoyant
Stomata on upper surface- more gas exchange with the more stomata

31
Q

Define translocation

A

The movement of assimilates up and down the plant in the phloem

32
Q

Why is glucose converted to sucrose for transport?

A

Sucrose is soluble

33
Q

What is a source?

A

Where assimilates are loaded into the phloem
When?
-photosynthesising green leaves and stem
-seeds when they germinate

34
Q

What is a sink?

A

Assimilates are removed from phloem
When?
-in growing roots
-buds/any active dividing meristem

35
Q

During mass flow, what happens at the source?

A
  • sucrose landed into save tube elements (active process)
  • decrease water potential in sap
  • therefore water flows sucrose into sieve tube elements mango down a water potential gradient via osmosis
  • increased hydrostatic pressure (turgor)
36
Q

During mass flow, what happens at the sink?

A
  • sucrose diffuses out of five tube elements (low concentration in surrounding cells as they are using it up)
  • increased water potential of sap
  • therefore water flows the sucrose out of sieve tube elements down water potential gradient by osmosis
  • decreased hydrolytic pressure in phloem at the sink
37
Q

What is mass flow?

A

Water moving in at source and out at sink creating hydrostatic pressure difference in sieve tube elements
Forcing sap to move from source to sink by mass flow

38
Q

How is the symplast route used when loading sucrose into the phloem (source)?

A

In plants with plasmodesmata between photosynthesising cells and companion cells, sucrose moves freely into the companion cell

39
Q

How is the apoplast pathway used to load sucrose into the phloem (source)?

A
  1. hydrogen ions are pumped out of the companion cell using ATP
  2. leading to a higher concentration of H+ ions outside the cell than inside
  3. H+ ions can move back into companion cell down concentration gradient through a special co transporter protein (facilitated diffusion- as polar so can’t diffuse over phospholipid bilayer)
  4. H+ ions carry sucrose with them moving against a concentration gradient
40
Q

At the sink, how is sucrose unloaded from the phloem?

A
  1. sucrose moves in via facilitated diffusion
  2. once in tissue sucrose is converted into something else by enzymes- maintains a concentration gradient from phloem to tissue
    Enzyme invertase converts sucrose to glucose and fructose, breaking the GLYCOSIDIC bond

OCR BIOLOGY (MODULE 3) (3 decks)

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