Water Transport in Plants As

Question 1

what are xylem

Answer 1

hollow tubes that transport water. dead hollow cells that form continuous column

Question 2

define transpiration

Answer 2

water evaporates out of stomata on leaves of plant

transpiration helps to transport materials in plants

Question 3

what does cohesion tension theory explain

Answer 3

the tension caused by water loss from the top (stomata) and water moving in at the bottom (root pressure)

Question 4

what is transpiration increased by

Answer 4

light intensity
temperature
air molecules
air humidity

Question 5

process of transpiration

Answer 5

lower water potential in mesophyll
water pulled up xylem
water molecules cohere/stick together by hydrogen bonds
forming a continuous water column
adhesion of water to walls of xylem

Question 6

what equipment is used to measure water uptake

Answer 6

potometer

Question 7

how to step up a potometer

Answer 7

must be airtight
cut shoot at slant and place underwater
insert apparatus
no air bubbles at start
note where bubble is to start 
measure distance moved by bubble

Question 8

how to calculate the rate of transpiration with photometer

Answer 8

Πr^2 x distance air bubble moved

Question 9

why does light intensity affect rate of transpiration

Answer 9

the stomata open to allow CO2 in for photosynthesis

Question 10

how does temperature affect rate of transpiration

Answer 10

the kinetic energy of water molecules increases. molecules move faster

Question 11

how does air movement affect rate of transpiration

Answer 11

removing the moist air surrounding the leaf lowering the water potential

Question 12

how does air humidity affect rate of transpiration

Answer 12

affects the water potential gradient

Question 13

how to find rate loss per mm2 of surface area of leaves

Answer 13

draw around leaves on graph paper and count square/repeat on both sides of leaf/ divide rate by total surface area

Question 14

why is potometer rate not really transpiration rate

Answer 14

water lost in respiration
used in photosynthesis
leaks in apparatus

Question 15

define xerophyte

Answer 15

plant which needs very little water

Question 16

how do xerophytes reduce water loss

Answer 16

thick cuticle
rolled up leaves (traps air becomes moist and reduces water potential gradient)
hairy leaves (for same reason)
smaller surface area/volume ratio of leaves (slower diffusion)
water potential gradient is reduced by keeping water vapour close to the outside of the stomata

Question 17

define phloem

Answer 17

tissue that transports biological molecules in either direction

Question 18

what are phloem made of

Answer 18

made of sieve elements arranged end to end. walls perforated by sieve plates. companion cells associated with sieve tube elements

Question 19

what is evidence for cohesion-tension theory

Answer 19

tree trunks have a wider diameter at night when transpiration is at lowest point (less tension)

Question 20

what happens if xylem is broken

Answer 20

water doesn’t leak out and air enters so water can no longer enter plant

Question 21

define sources

Answer 21

where sugars are made during photosynthesis

Question 22

define sinks

Answer 22

where sugars are used or stored

Question 23

what is the mass flow hypothesis

Answer 23

sugars in source actively transported into phloem by companion cells
lower water potential of sieve cell/tube
water enters by osmosis
increase in pressure causes mass movement (towards sink/root)
sugars used/converted in root for respiration for storage

Question 24

what is evidence of translocation in the phloem

Answer 24

ringer and tracer experiments
phloem sap feeders are used to show phloem transports sugars. they feed without jaw muscles because there is a high hydrostatic pressure in phloem