3.3.4.2 Mass Transport in Plants

Question 1

Q: What is the main function of xylem tissue in plants?

Answer 1

A: The xylem tissue transports water and dissolved minerals from the roots to the stems and leaves.

Question 2

Q: What theory explains water movement in the xylem?

Answer 2

A: The cohesion-tension theory.

Question 3

Q: What is the cohesion-tension theory?

Answer 3

A: The cohesion-tension theory suggests that water molecules stick together (cohesion) and are pulled up through the plant as water evaporates from the leaves (tension).

Question 4

Q: What is the main function of phloem tissue in plants?

Answer 4

A: The phloem tissue transports organic substances, like sugars, from sources (e.g., leaves) to sinks (e.g., roots, fruits).

Question 5

Q: What hypothesis explains the movement of substances in the phloem?

Answer 5

A: The mass flow hypothesis.

Question 6

Q: What is the mass flow hypothesis?

Answer 6

A: The mass flow hypothesis suggests that organic substances move through the phloem due to pressure differences between the source (high pressure) and the sink (low pressure).

Question 7

Q: What is a ringing experiment and what does it demonstrate?

Answer 7

A: A ringing experiment involves removing a ring of bark (including the phloem) from a stem. It demonstrates that sugars are transported through the phloem because the region above the ring swells with accumulated sugars.

Question 8

Q: What evidence supports the mass flow hypothesis?

Answer 8

A: Evidence includes the accumulation of sugars above the ring in ringing experiments and the movement of radioactive tracers through the phloem.

Question 9

Q: What is a potometer used for?

Answer 9

A: A potometer is used to measure the rate of transpiration in plants.

Question 10

Q: How can a potometer be used to investigate the effect of an environmental variable on transpiration?

Answer 10

A: By changing one environmental variable (e.g., light, temperature) and measuring the rate of water uptake by the plant using the potometer.

Question 11

Q: What is transpiration?

Answer 11

A: Transpiration is the process by which water evaporates from the leaves of a plant, creating a negative pressure that pulls water up through the xylem.

Question 12

Q: What is the role of cohesion in water transport through the xylem?

Answer 12

A: Cohesion refers to the attraction between water molecules, which helps to form a continuous column of water in the xylem.

Question 13

Q: What is the role of tension in water transport through the xylem?

Answer 13

A: Tension is created by the evaporation of water from the leaves, pulling the column of water upward through the xylem.

Question 14

Q: What factors can affect the rate of transpiration?

Answer 14

A: Environmental factors such as light, temperature, humidity, and wind.

Question 15

cohesion tension theory step 1

Answer 15

1. Water is lost from the leaf by transpiration as water evaporates from the mesophyll cels and
   diffuses out of the Stomata down a water potential gradient.

Question 16

cohesion tension theory step 2

Answer 16

this lowers water potential in mesophyll cells

Question 17

cohesion tension theory step 3

Answer 17

water moves between mesophyll cells by osmosis and water is draw out the xylem

Question 18

cohesion tension theory step 4

Answer 18

waters pulled up the xylem as a continuous column due to cohesion between water molecules due to hydrogen bonds between water molecules-transpiration pull

Question 19

mass flow hypothesis step 1

Answer 19

Sucrose is atively transported by the
companion cells using ATP into the phloem sieve tube at the source

Question 20

mass flow hypothesis step 2

Answer 20

decreases water potential in sieve tube

Question 21

mass flow hypothesis step 3

Answer 21

water moves into phloem by osmosis from the xylem

Question 22

mass flow hypothesis step 4

Answer 22

increase in volumes causes increase in hydrostatic pressure in sieve tube

Question 23

mass flow hypothesis step 5

Answer 23

sucrose is actively transported out the phloem at the sink to respiring cells or storage

Question 24

mass flow hypothesis step 6

Answer 24

increases water potential in phloem

Question 25

mass flow hypothesis step 7

Answer 25

water moves out the sieve tube via osmosis and decreases hydrostatic pressure

Question 26

mass flow hypothesis step 8

Answer 26

water and dissolved sucrose move down the pressure gradient due to mass flow