7b. MASS TRANSPORT IN PLANTS

Question 1

Name the two transport vessels in a plant

Answer 1

Xylem and Phloem

Question 2

What is transported through the xylem, and in which direction?

Answer 2

Water and ions are transported up the plant

Question 3

Describe the four structural features of a xylem vessel

Answer 3

Long tubes with no end walls
No organelles
Lignin
Bordered pits

Question 4

Why are xylem long tubes with no end walls?

Answer 4

To allow a continuous stream of water to flow

Question 5

Why do Xylem have no organelles?

Answer 5

So as not to obstruct the flow of water

Question 6

Why are Xylem are surrounded by lignin?

Answer 6

To waterproof them

Question 7

Why do Xylem have bordered pits?

Answer 7

To allow lateral movement of water

Question 8

Name the theory by which water move up the xylem of a plant

Answer 8

Cohesion-tension theory

Question 9

What is transpiration is driven by?

Answer 9

Evaporation from the stomata, which is driven by energy from the sun

Question 10

As water evaporates from the stomata, describe the effect on the water potential of the mesophyll tissue

Answer 10

It reduces it

Question 11

Which force causes water to be drawn up the xylem in one continuous column?

Answer 11

Cohesion

Question 12

Which force draws the walls of the xylem inwards?

Answer 12

Tension

Question 13

The tension in the xylem is caused by evaporation from the stomata, and which two forces acting together?

Answer 13

Cohesion and adhesion

Question 14

Describe the pressure inside the xylem

Answer 14

It is more negative than the atmospheric pressure

Question 15

Describe the relationship between the rate of evaporation from the leaf, and the amount of tension inside the xylem

Answer 15

As rate of evaporation increases, tension increases

Question 16

Describe the relationship between the rate of evaporation and the pressure inside the xylem

Answer 16

As rate of evaporation increases, pressure becomes more negative

Question 17

Name the five factors that affect the rate of transpiration

Answer 17

Temperature, humidity, light intensity, wind speed, number of stomata per area

Question 18

Why does increasing temperature increase the rate of transpiration?

Answer 18

It would increase the KE of the particles

Question 19

Why does increasing light intensity increase the rate of transpiration?

Answer 19

It would cause more stomata to open

Question 20

Why does increasing humidity decrease the rate of transpiration?

Answer 20

It would decrease the water potential gradient between the inside and outside of the leaf

Question 21

Why does increasing wind speed increase the rate of transpiration?

Answer 21

It would increase the water potential gradient between the inside and outside of the leaf

Question 22

Describe the structure of the phloem

Answer 22

Sieve tube elements with sieve plates at either end. Attached to companion cells.

Question 23

Describe the two adaptations of the phloem

Answer 23

No organelles, and thick walls.

Question 24

Explain why the phloem has no organelles

Answer 24

To allow easier flow of dissolved sugars.

Question 25

Explain why the phloem has thick walls

Answer 25

To withstand pressure.

Question 26

How are the companion cells adapted to carry out their function?

Answer 26

They contain mitochodria to release energy for the active process of phloem loading.

Question 27

What is translocation?

Answer 27

The movement of dissolved sugars from sources to sinks.

Question 28

Why is sucrose translocated instead of glucose?

Answer 28

To prevent glucose being used in metabolic processes during translocation.

Question 29

Define what a source is

Answer 29

Where glucose is produced or stored.

Question 30

Give examples of a source

Answer 30

Leaves, tubers, tap roots

Question 31

Define what a sink is

Answer 31

Where glucose is used or stored.

Question 32

Give examples of a sink

Answer 32

Meristems, seeds, tubers, tap roots.

Question 33

Explain how something can be a source and also a sink

Answer 33

When dissolved sugars are translocated to the organ for storage it is acting as a sink. But when glucose is removed for use, it is acting as a source.

Question 34

How do sugars travel from the sources to the companion cells?

Answer 34

Diffusion

Question 35

How do sugars move from the companion cells to the phloem?

Answer 35

Active transport

Question 36

How does the introduction of sugars into the phloem affect the water potential inside the phloem?

Answer 36

It reduces it / makes it more negative

Question 37

What is the effect of the reduction of the water potential inside the phloem?

Answer 37

It causes water to move by osmosis from the xylem to the phloem down a water potential gradient

Question 38

How is the hydrostatic pressure inside the phloem increased?

Answer 38

More water is introduced into the phloem

Question 39

What is the effect of the increasing hydrostatic pressure inside the phloem?

Answer 39

It causes the dissolved sugars to move through the phloem by mass flow

Question 40

Which three gradients do dissolved sugars travel down in the phloem?

Answer 40

A hydrostatic pressure gradient, a concentration gradient, a pressure gradient

Question 41

What two things can the sugars be used for at sinks?

Answer 41

Respiration and storage

Question 42

Name the entire process by which dissolved sugars move from sources to sinks

Answer 42

Mass flow

Question 43

How can a potometer be used to measure the rate of water uptake?

Answer 43

As water is taken up into the plant, the bubble in the capillary tube moves. We can measure the distance travelled by the bubble in a time.

Question 44

Potometers can be used to measure the effect of variables on the rate of water uptake. Name these factors.

Answer 44

Light intensity, temperature, humidity.

Question 45

If the IV was light intensity, name the CVs.

Answer 45

Temperature, humidity, same plant.

Question 46

If the IV was temperature, name the CVs.

Answer 46

Light intensity, humidity, same plant.

Question 47

If the IV was humidity, name the CVs.

Answer 47

Temperature, light intensity, same plant.

Question 48

Why does using the same plant help make the results reliable?

Answer 48

Because the leaves will have the same surface area.

Question 49

Why might the rate of water uptake into a plant not be the same as the rate of transpiration?

Answer 49

Because water can be used for turgidity, in photosynthesis, and produced in respiration

Question 50

Which is faster - the speed of water movement through the capillary tube, or the speed of water movement through the plant roots?

Answer 50

Through the plant roots is faster

Question 51

Why is the speed of the water movement through plant roots faster in the roots of the plant compared to the potometer?

Answer 51

Because the roots have a smaller diamater

Question 52

Name five precautionary measures taken when setting up the potometer

Answer 52

Cut the shoots and insert the plant into the potometer underwater, dry the leaf, seal the joints with vaseline, and shut the tap

Question 53

Why should you cut the shoots and insert the plant into the potometer underwater?

Answer 53

To prevent bubbles entering the xylem

Question 54

Why should you dry the leaves?

Answer 54

Excess water on the leaves would lower the rate of transpiration

Question 55

Why should you seal the joints with vaseline?

Answer 55

To prevent bubbles entering the capillary tube

Question 56

Why should you shut the tap?

Answer 56

To ensure water isn't introduced into the capillary tube from the reservoir

Question 57

How would you return the bubble to zero to carry out repeats?

Answer 57

By opening the tap to introduce water from the reservoir

Question 58

How would you calculate the distance the bubble travelled during the allocated time?

Answer 58

Final length - Initial length

Question 59

How would you calculate the volume of water taken up?

Answer 59

πr2h

Question 60

How would you calculate rate of water uptake?

Answer 60

volume of water uptake ÷ time

Question 61

How would you calculate the surface area of a leaf?

Answer 61

Draw around the leaf onto graph paper. Count the whole and half squares. X2 for both sides.

Question 62

How would you calculate rate of water uptake per surface area?

Answer 62

Rate of water uptake ÷ surface area

Question 63

What is a xerophyte?

Answer 63

A species of plant that has adaptations to survive in an environment with little liquid water, e.g. cactus.

Question 64

Describe five adaptations of xerophytes

Answer 64

Sunken stomata Hairy leaves / hairy stomata Thick waxy cuticle Curled leaves Spines instead of leaves

Question 65

Explain how sunken stomata reduces water loss

Answer 65

Water vapour is trapped around the stomata, reducing the water potential gradient

Question 66

Explain how hairy leaves / hairy stomata reduce water loss

Answer 66

The hairs trap water vapour around the leaves / stomata, reducing the water potential gradient

Question 67

Explain how a thick waxy cuticle reduces water loss

Answer 67

It reduces evaporation

Question 68

Explain how curled leaves reduces water loss

Answer 68

It traps water vapour around the leaf, which reduces the water potential gradient

Question 69

Explain how having spines instead of leaves reduces the water loss

Answer 69

They reduce the surface area to volume ratio