3.4.2 mass transport in plants

Question 1

What environmental factors INCREASE the rate of transpiration?

Answer 1

Increasing temperature

Decreasing humidity

Increasing light intensity

Increasing wind speed

Question 2

What environmental factors DECREASE the rate of transpiration?

Answer 2

Decreasing temperature

Increasing humidity

Decreasing light intensity

Decreasing wind speed

Question 3

Why does the rate of transpiration increase with increasing light intensity?

Answer 3

Causes stomata to open

Question 4

Why does the diameter of the xylem decrease as the rate of transpiration increases?

Answer 4

Water lost from the leaf in transpiration

creates more tension

and pulling force on water molecules in xylem

Question 5

What does water lost from the leaf in transpiration creating more tension and pulling force on water molecules in xylem create?

Answer 5

The diameter of the xylem to decrease

Question 6

What device is used to measure the rate of transpiration?

Answer 6

Potometer

Question 7

What are the vital procedures to setting up a potometer?

Answer 7

Cut stem underwater

and at a slant - Ensure no air bubbles are present

Seal joints with vaseline to ensure airtight

Question 8

Why do potometers not truly measure the rate of transpiration?

Answer 8

Water used for support

Water used in photosynthesis

Water produced in aerobic respiration

Apparatus not fully sealed

Question 9

What is the benefit of xylem cells being dead, and therefore empty with no cytoplasm contents?

Answer 9

Allows water to flow easier

Question 10

What xylem specialization allows water to flow easier?

Answer 10

Cells are dead, and therefore empty with no cytoplasm contents

Question 11

What is the benefit of xylem cells being long, forming tubes, with no end walls, meaning it’s hollow?

Answer 11

Allows for continuous columns of water

Question 12

What xylem specialization allows continuous columns of water to flow?

Answer 12

Cells are long, forming tubes, with no end walls meaning they are hollow

Question 13

What is the benefit of xylem cells having a thickened cell wall with cellulose and lignin?

Answer 13

Support, and waterproofing

Question 14

What xylem specialization allows for support, and waterproofing?

Answer 14

Thickened cell walls with cellulose and lignin

Question 15

What is the benefit of xylem cells having pits in walls?

Answer 15

Allows lateral movement of water

Question 16

What xylem specialization allows for lateral movement of water?

Answer 16

Pits in walls

Question 17

Describe and explain the cohesion-tension theory.

Answer 17

1-Water lost from the leaves by evaporation, due to transpiration

2- Lowers the water potential of mesophyll cells

3- so water drawn out of xylem

4- Water **pulled up xylem creating tension

5- Due to cohesive forces between water molecules

6-caused by hydrogen bonding

7- Allows a continuous column of water to be pulled

8- Water molecules adhere to the xylem walls

Question 18

In the cohesion-tension theory how is water lost from the leaves?

Answer 18

By evaporation, due to transpiration

Question 19

In the cohesion-tension theory why is water drawn out of the xylem?

Answer 19

The water potential of mesophyll cells has been lowered

Question 20

In the cohesion-tension theory what creates tension?

Answer 20

Water being pulled up xylem

Question 21

In the cohesion-tension theory what causes cohesive forces between water molecules?

Answer 21

Hydrogen bonding

Question 22

In the cohesion-tension theory what allows a continuous column of water to be pulled?

Answer 22

Cohesive forces between water molecules, due to hydrogen bonding

Question 23

In the cohesion-tension theory what do water molecules adhere to?

Answer 23

Xylem walls

Question 24

In the phloem solution, what key molecules are transported?

Answer 24

Sucrose and amino-acids

Question 25

What key component are within the sieve tube element of the phloem?

Answer 25

Sieve plates

Question 26

What is the specialization of companion cells in the phloem?

Answer 26

Have lots of mitochondria, to actively transport sucrose into phloem from source

Question 27

What is the most general way of describing the route of the mass-flow hypothesis?

Answer 27

From source to sink

Question 28

Describe and explain the Mass-Flow Hypothesis.

Answer 28

1- Sucrose actively transported into sieve tube elements 2- from source, by companion cells 3- This lowers the water potential in the sieve tube element 4- so water moves in by osmosis from the xylem 5- Produces a HIGH hydrostatic pressure 6- Mass flow of sucrose from source to sink to** respiring cells ** 7- At sink, sucrose is unloaded** by AT** from phloem and used or converted to starch for storage

Question 29

In the Mass-Flow Hypothesis what actively transports sucrose into the sieve tube element from the source?

Answer 29

Companion cells

Question 30

In the Mass-Flow Hypothesis what does a low water potential in the sieve tube element allow?

Answer 30

Water to move in by osmosis from the xylem

Question 31

In the Mass-Flow Hypothesis what does the movement of water into the sieve tube element by osmosis from the xylem create?

Answer 31

High hydrostatic pressure

Question 32

In the Mass-Flow Hypothesis where is the mass flow?

Answer 32

From source to sink

Question 33

In the Mass-Flow Hypothesis what happens at the sink?

Answer 33

Sucrose is unloaded and used or converted to starch for storage

Question 34

Explain how the following provides evidence for the Mass-Flow Hypothesis: Translocation slows if respiration inhibitors used.

Answer 34

No active transport of sucrose from companion cells at source

Question 35

Explain how the following provides evidence for the Mass-Flow Hypothesis: If phloem punctured, contents flow out.

Answer 35

Occurring at high pressure

Question 36

Explain how the following provides evidence for the Mass-Flow Hypothesis: Plants can be supplied with radioactive CO2 and traced.

Answer 36

Sucrose moves from source, up and down stem, to sinks

Question 37

Explain how the following provides evidence for the Mass-Flow Hypothesis: Ring of bark removed, so that xylem remains, but phloem removed.

Answer 37

Bulging above ring due to build-up of fluid in phloem; Tissues die below, as no sucrose for respiration

Question 38

The mass flow hypothesis is used to explain the movement of substances through phloem. Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube.

Answer 38

1. Sucrose actively transported into phloem; 2. Lowering/reducing water potential; 3. Water moves in by osmosis

Question 39

Describe the mass flow hypothesis for the mechanism of translocation in plants.

Answer 39

1. In source sugars actively transported into phloem; 2. 2. By companion cells; 3. 3. Lowers water potential of sieve tube and water enters by osmosis; 4. 4. Increase in pressure causes mass movement towards sink

Question 40

The scientists concluded that this heat treatment damaged the phloem. Explain how the results in Figure 9 support this conclusion.

Answer 40

1. The radioactively labelled carbon is converted into sugar/organic substances during photosynthesis; 2. Mass flow/translocation in the phloem throughout the plant only in plants that were untreated/B/control OR Movement of sugar/organic substances in the phloem throughout the plant only in plants that were untreated/B/control; OR 3. Movement in phloem requires living cells/respiration/active transport/ATP; 4. Heat treatment damages living cells so transport in the phloem throughout the plant only in plants that were untreated/B/control OR Heat treatment stops respiration/active transport/ATP production so transport in the phloem throughout the plant only in plants that were untreated/B/control;

Question 41

The scientists also concluded that this heat treatment did not affect the xylem. Explain how the results in Table 4 support this conclusion.

Answer 41

1. (The water content of the leaves was) not different because (means ± 2) standard deviations overlap; 2. Water is (therefore) still being transported in the xylem (to the leaf) OR Movement in xylem is passive so unaffected by heat treatment;

Question 42

Unlike plants, Ulva lactuca does not have xylem tissue. Suggest how Ulva lactuca is able to survive without xylem tissu

Answer 42

Short diffusion pathway (to cells) OR It has a surface permeable (to water/ions into cells);

Question 43

Ulva prolifera also produces haploid, mobile single cells that can fuse to form a zygote. Suggest and explain one reason why successful reproduction between Ulva prolifera and Ulva lactuca does not happen.

Answer 43

1. They are different species; 2. (So) if fused together they would not produce fertile offspring OR (So) they have named characteristics that means they are reproductively isolated;

Question 44

use the Information form graphs and your knowledge of cohesion zsnion therapy of water to explain why diameter of trunk smaller at mddday light intensity increase temp increases

Answer 44

1. Diameter of trunk minimal at warmest 2. Stomata open in light → more water loss 3. Water evaporates more when warm / more heat energy for water evaporation; 4. Hydrogen-bonding between water molecules / cohesion ( / described) between water molecules; 5. Adhesion (described) between water molecules and walls of xylem vessels; 6. (Xylem) pulled inwards by faster flow of water / pulled in by tension;

Question 45

(b) Describe and explain three ways in which the leaves of xerophytic plants may be adapted to reduce water loss.

Answer 45

1- thick waxy layer - waterproof/ impereable 2- sunken stomata - saturated later of still air outside 3- leaves small - reduces SA for water loss

Question 46

Phloem pressure is reduced during the hottest part of the day. Use information in the graph above along with your understanding of transpiration and mass flow to explain why. (3)

Answer 46

  High (rate of) transpiration/evaporation; 2.      Water lost through stomata OR (High) tension in xylem; 3.      (Causes) less water movement from xylem to phloem

Question 47

The student measured the time taken for water movement. Give two other measurements he made to calculate the rate of water movement.

Answer 47

1- change in mass 2-number of xylem vessels

Question 48

)  Give the reason for adding a layer of oil to the water in the beaker.

Answer 48

stops evaporation

Question 49

 The student used a sharp scalpel to cut the celery. Describe how she should ensure she handled the scalpel safely during this procedure.

Answer 49

1- cut away from body 2- against a hard surface

Question 50

The mass flow hypothesis is used to explain the movement of substances through phloem. Evaluate whether the information from this investigation supports this hypothesis. Do not consider statistical analysis in the answer.

Answer 50

yes: 1.      phloem is involved; 2.       respiration / active transport is involved 3.      The agar block is the source; 4.      Roots are the sink; NO: 6.      No bulge above ringing 7.      No osmosis or hydrostatic pressure / water movement; 8.      Movement could be due to gravity; 9.      Roots still grow without phloem; 10.    No leaves / sugars / photosynthesis to act as a source;

Question 51

 The student wanted to determine the rate of water loss per mm2 of surface area of the leaves of the shoot in Figure 1. Outline a method she could have used to find this rate. You should assume that all water loss from the shoot is from the leaves.

Answer 51

 Method for measuring area; e.g. draw round (each) leaf on graph paper and count squares; 2.      Of both sides of (each) leaf; 3.      Divide rate (of water loss / uptake from potometer) by (total) surface area (of leaves);

Question 52

 The rate of water movement through a shoot in a potometer may not be the same as the rate of water movement through the shoot of a whole plant. Suggest one reason why.

Answer 52

plant has roots OR xylem cells very narrow;