Ch7 Mass transport

Question 1

Structure of xylem

Answer 1

1. long hollow tube
2. lignin wall
3. lignin- strong waterproof and adhesive
4. pits- lateral support

Question 2

Movement of water into xylem

Answer 2

1. water potential in xylem reduced by ions
2. water enters xylem by osmosis
3. down wpt gradient from xylem and surrounding cells
4. across partially permeable membranes
5. volume of water in xylem increase
6. pressure increases and forces water upwards

Question 3

Cohesion-tension theory

Answer 3

1. loss of water at the leaves by transpiration
2. transpiration pull - water moves via osmosis from top of xylem into leaf
3. applies tension to column of water
4. column of water moves up
5. water particles stick together due to cohesion
6. column doesn’t break because of adhesion with xylem walls

Question 4

Movement of water out through stomata

Answer 4

1. water vapour diffuse out through stomata
2. down water potential gradient
3. humidity atmosphere less than air spaces by stomata

Question 5

Transpiration

Answer 5

The loss of water vapour through stomata by evaporation

Question 6

Evidence for cohesion-tension

Answer 6

1. change in diameter of tree trunk
2. air bubble when xylem breaks

Question 7

Diameter of tree trunk

Answer 7

1. increased light during day
2. increased rate of transpiration
3. increased transpiration pull
4. tension in xylem creates inward pull
5. xylem vessels narrow
6. due to adhesion of water molecules

Question 8

Broken xylem

Answer 8

1. air is drawn in due to tension
2. air bubble breaks column of water
3. water molecules no longer adhesive

Question 9

Increased transpiration

Answer 9

1. light- more stomata open for large SA
2. temperature- higher kinetic energy
3. wind- maintains concentration gradient
4. less humidity- steeper concentration gradient

Question 10

Adaptations of xerophyte

Answer 10

1. thick waxy cuticle- waterproof
2. sunken stomata, curled leaves- traps moist air to reduce concentration gradient
3. densely packed spongy mesophyll- less air spaces

Question 11

Translocation

Answer 11

Organic molecules are transported in the phloem from the source to the sink

Question 12

Sucrose from source to sieve tube

Answer 12

1. sucrose produced from photosynthesising cells
2. facilitated diffusion down concentration gradient into companion cells
3. H+ actively transported from companion cells into cell wall
4. H+ diffuse down concentration gradient through co-transport proteins
5. co-transport with sucrose into sieve tube

Question 13

Mass flow of sucrose

Answer 13

1. sucrose lowers water potential in sieve tube
2. water moves via osmosis from xylem into sieve tube down water potential gradient
3. creates high hydrostatic pressure
4. sucrose diffuse into respiring tissue
5. water diffuses into respiring tissue down wpt gradient
6. mass flow down phloem down pressure gradient

Question 14

Companion cell advantage

Answer 14

1. produces ATP for active transport of H+
2. repairs and maintains phloem

Question 15

Sink

Answer 15

site where sugar is used (respiration) or stored for future use

Question 16

Source

Answer 16

site of production of sugars during photosynthesis

Question 17

Evidence for mass transport

Answer 17

1. concentration of sucrose is higher in leaves than roots
2. downward phloem flow occurs only in daylight
3. companion cells have lots of mitochondria
4. increase in lead sucrose are followed by increase in phloem
5. sap released due to pressure in sieve tube when cut
6. metabolic poison/ no O2 stops translocation

Question 18

Clashing evidence of mass flow

Answer 18

1. organic molecules move at same speed
2. sieve plate function unclear (reduce rate of translocation)
3. sucrose delivered at same rate to all regions(

Question 19

Ringing experiment observations

Answer 19

1. ring of bark removed alongside phloem
2. sugars of phloem accumulated above ring
3. swelling
4. death of tissue below region
5. phloem responsible not xylem

Question 20

Mass transport experiments

Answer 20

1. ringing
2. tracer
3. aphids
4. cutting