3.1.3 Transport in Plants

Question 1

Need for transport system in plants

Answer 1

• metabolic demands: CO2, O2, waste, hormones, mineral ions
• size: grow throughout life
• SA:V large in leaves but small overall. Can’t rely on diffusion alone to supply cells

Question 2

Dicotyledonous plants

Answer 2

Make seeds that contain two cotyledons – food stores for developing embryo and first leaves

Question 3

Herbaceous dicots

Answer 3

Soft tissues

Relatively short life cycle

Question 4

Woody (arborescent) dicots

Answer 4

Hard, lignified tissues

Long life cycle

Question 5

Stem

Answer 5

Xylem in middle

Phloem on outside

Question 6

Root

Answer 6

‘X’ shaped xylem in middle (penetrate soil,withstand tugging)
Phloem on outside

Question 7

Leaf

Answer 7

Xylem above

Phloem below

Question 8

Xylem

Answer 8

Non-living, transport water and mineral ions upwards, for support

Thick xylem parenchyma:food store,tannin deposits

Fibres w lignified secondary walls:strength

Lignin:rings, spirals,tubes. Bordered pits for H2O to leave – lateral transport. Kills living cells&adds strength

Question 9

Phloem

Answer 9

Living, non-lignified cellulose cell wall, transport organic solutes up and down

Sieve tube elements:cells joined end to end, linked by plasmodesmata (channels through cellulose) linking to adjacent cells

Rely on companion cells

Question 10

Osmosis

Answer 10

The net movement of water across a partially permeable membrane from an area of high concentration to an area of low concentration

Question 11

Water potential

Answer 11

The tendency of water molecules to diffuse to another area

Highest = 0kPa

Moves from high to low w.p gradient

Question 12

Symplast pathway

Answer 12

Through continuous cytoplasm

Question 13

Apoplast pathway

Answer 13

Cell walls and intercellular spaces (outer sides of cells)

Question 14

Transpiration

Answer 14

Loss of H2O vapour from plant

H2O evaporates from surface of mesophyll cells into air spaces of leaf then evaporate out via diffusion

Question 15

Transpiration happens thanks to ?

Answer 15

Capillary action
Root pressure
Cohesion-tension theory (mainly)

= uninterrupted flow of water

Question 16

Cohesion-tension theory

Answer 16

Movement of H2O down a concentration gradient

H2O forms H-bonds with itself = cohesion

Question 17

Evidence of cohesion tension theory

Answer 17

Diameter of tree changes throughout day

Thermo-electric method
Measuring flow rate of sap, changes during day

Question 18

Stomata; controlling rate of transpiration

Answer 18

Low turgor=closed
High turgor=open

On lower epidermis

Question 19

Factors affecting transpiration

Answer 19

Light intensity ^ rate ^

Humidity ^ rate decreases

Temp ^ rate ^

Air movement ^ rate ^

Water availability ^ rate ^

Question 20

Translocation

Answer 20

From source to sink

Sources of assimilates (products of photosynthesis); green leave, stems, storage organs, seeds

Sinks include: roots growing/absorbing mineral ions, meristems dividing, food stores

Question 21

Phloem loading

Answer 21

The active movement of sucrose into a companion cell across a cell membrane

Question 22

Plant adaptations to water availability; Xerophytes

Answer 22

Thick each cuticle
Sunken stomata
Hairy leaves 
Curled leaves (microclimate)
Reduced stomata/leaves
Succulents 
Leaf loss
Shallow/widespread roots

Question 23

Plant adaptations to water availability; Hydrophytes

Answer 23

Thin or no waxy cuticle

Many always open stomata on upper side

Reduced structure to plant - H2O provides support