Mass transport in plants

Question 1

What theory is there for transpiration?

Answer 1

Cohesion-tension theory

Question 2

In which tissue does the cohesion tension theory take place in?

Answer 2

Xylem

Question 3

In which tissue does transpiration take place in?

Answer 3

Xylem

Question 4

Which substances are transported in the xylem?

Answer 4

Water & inorganic ions

Question 5

Which substances are transported in transpiration?

Answer 5

Water & inorganic ions (minerals)

Question 6

In which direction do substances travel in the xylem for transpiration?

Answer 6

Upwards:
Roots to shoots &
leaves

Question 7

In transpiration, substances move from the ___ to the ___?

Answer 7

roots to the shoots/leaves

Question 8

What theory is there for translocation?

Answer 8

Mass-Flow Hypothesis

Question 9

In which tissue does the Mass-Flow Hypothesis take place in?

Answer 9

Phloem

Question 10

In which tissue does translocation take place in?

Answer 10

Phloem

Question 11

Which substances are transported in the phloem?

Answer 11

Organic solutes (sucrose and amino acids)

Question 12

In which direction do substances travel in the phloem for translocation?

Answer 12

Any direction.
Source to Sink(s) AKA leaves to the roots

Question 13

How does water enter the plant?

Answer 13

Water enters through the root hair cells within the epidermis by osmosis

Question 14

What are 2 adaptations of root hair cells?

Answer 14

hair like extensions
thinner cellulose cell walls

Question 15

Why do root hair cells have hair like extensions?

Answer 15

To increase their surface area to increase the uptake of water
Increase the area for channel and carrier proteins

Question 16

Why do root hair cells have thinner cellulose walls?

Answer 16

So they have a shorter diffusion distance

Question 17

How do root hair cells actively transport ions?

Answer 17

By using energy from the hydrolysis of ATP,
from soil across their membranes into their cytoplasm,
via carrier proteins.

Question 18

What does active transport of ions into the cell do to the water potential of the cytoplasm? What does this do to the water?

Answer 18

This lowers the water potential of the cytoplasm, compared to the water potential in the soil.
Water enters the root hair cells by osmosis DOWN a water potential gradient

Question 19

How does water enter into the xylem vessels from the root hair cell?

Answer 19

Water enters the root hair cells by osmosis
Water then passes across the cells of the cortex,
across the endodermis,
and into the xylem vessels

Question 20

Describe 4 features of the structure of xylem tissue

Answer 20

Dead cells that form hollow tubes with no cytoplasm
A continuous tube with no end walls
Cell walls, strengthened with lignin
Xylem pits

Question 21

How is a continuous tube formed in the xylem tissue, with no end walls?

Answer 21

End walls break down

Question 22

What are the cell walls strengthened by in xylem tissue?

Answer 22

Lignin

Question 23

What is the function of dead cells that form hollow tubes with no cytoplasm, in the xylem tissue?

Answer 23

Faster water flow

Question 24

What is the function of a continuous tube with no end walls in xylem tissue?

Answer 24

So that a continuous column of water can form (due to cohesion)

Question 25

Why can a continuous column of water form in the xylem?

Answer 25

Due to cohesion in the continuous tube with no end walls

Question 26

What is the function of the cell wall being strengthened by lignin, in the xylem?

Answer 26

This makes the xylem waterproof and rigid; **Enables adhesion of water**

Question 27

What is the function of xylem pits?

Answer 27

They allow for water to get around blocked vessels

Question 28

Key Points of Transpiration

Answer 28

1. Water is transpired from leaves; 2. Water lost from leaves, lowers water potential in leaf cells; 3. Water replaced from xylem; 4. Water potential gradient creates tension and pulls up water 5. Adhesion maintains continuous column of water;

Question 29

On a hot day, what will happen to the diameter of a tree trunk? Why?

Answer 29

The diameter of a tree trunk will reduce slightly, making the xylem vessels slightly narrower as the xylem experiences NEGATIVE PRESSURES

Question 30

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves. [6]

Answer 30

(In the root) 1. Active transport by endodermis; 2. (Of) ions into xylem; 3. Lower water potential in xylem so water enters xylem by osmosis down a water potential gradient; 5. Evaporation / transpiration (from leaves); 6. (Creates) cohesion ; 7. Adhesion so water molecules bind to xylem; 8. Creates continuous column of water

Question 31

Root pressure moves water through the xylem. Describe what causes root pressure. [4]

Answer 31

1. Active transport by endodermis; 2. ions move into xylem; 3. Lowers water potential in xylem; 4. Water enters by osmosis;

Question 32

Describe how a high pressure is produced in the leaves [3]

Answer 32

1. Water potential becomes lower as sugar enters phloem; 2. Water enters phloem by osmosis; 3. Increased volume of water causes increased pressure;

Question 33

What are four main factors that affect transpiration?

Answer 33

Light intensity Temperature Humidity Wind speed

Question 34

Light intensity as a factor that affects transpiration

Answer 34

High light intensity means that more stomata open

Question 35

Temperature as a factor that affects transpiration

Answer 35

Increased temperature = greater rate of transpiration This is due to increased kinetic energy increasing the rate of evaporation of water

Question 36

Increased humidity as a factor that affects transpiration

Answer 36

Increased rate of humidity means that the rate of transpiration decreases The greater the difference in humidity between the air spaces and the air outside the leaf, the greater the rate of diffusion of water vapour out of the leaf, so the greater the rate of transpiration.

Question 37

Wind speed as a factor that affects transpiration

Answer 37

Increased wind speed = Higher rate of transpiration Air movement over a leaf moves the water vapour away from the stomatal pores. This increases the water potential gradient between the inside and the outside of the leaf.

Question 38

What does increased wind speed do in xerophytic plants?

Answer 38

As xerophytes have sunken stomata. This keeps a higher humidity outside the stomata, so reduces transpiration.

Question 39

For measuring transpiration, why is; A leafy shoot is diagonally cut under water.

Answer 39

This prevents damage to the xylem and ensures a continuous column of water.

Question 40

For measuring transpiration, why is; Care is taken to prevent getting water on the leaves.

Answer 40

Water could prevent the loss of water vapour through the stomata.

Question 41

For measuring transpiration, why is; The potometer filled completely with water making sure there are no air bubbles.

Answer 41

To prevent air entering the xylem and ensures a continuous column of water.

Question 42

For measuring transpiration, why is; Using a rubber tube, the leafy shoot is fitted to the potometer under water.

Answer 42

To prevent air entering the xylem and ensures a continuous column of water.

Question 43

For measuring transpiration, why is; The potometer is removed from under the water and all joints are sealed with waterproof jelly

Answer 43

To prevent water loss from potometer and prevent air from entering.

Question 44

For measuring transpiration, why is; An air bubble is introduced into the capillary tube.

Answer 44

As transpiration occurs, water moves through the capillary tube, and the bubble of air moves with it. To determine the volume of water entering the shoot. Using: 𝐿𝜋𝑟^2

Question 45

For measuring transpiration, why is; The distance moved over a period of time recorded and the mean is calculated of a number of repeats.

Answer 45

To determine a reliable mean.

Question 46

How can the volume of water uptake over a period of time can be calculated?

Answer 46

Rate of uptake = 𝐿𝜋𝑟^2 / time

Question 47

What are limitations of the potometer experiment?

Answer 47

Volume of water taken up does NOT always equal volume of water lost through transpiration. Although over 90% is lost though transpiration.

Question 48

What else do plants use water for, that isn't transpiration?

Answer 48

Photosynthesis Storage Support Hydrolysis reactions

Question 49

Give four precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot.

Answer 49

Cut shoot under water; Cut shoot at a slant; Dry off leaves; Ensure no air bubbles are present;

Question 50

Features of xerophytic plants

Answer 50

1. Reduced number of stomata 2. Stomata in pits 3. Hairs to trap water 4. Leaves reduced to spines 5. Thick waxy cuticles

Question 51

What does the phloem transport, and where to?

Answer 51

Transports **sucrose** and organic substances from **leaves** where they are formed (by PHOTOSYNTHESIS) to where they are needed for example **shoots**, flowers and fruits and in the **roots**.

Question 52

What are solutes?

Answer 52

Dissolved substances

Question 53

How is phloem tissue formed?

Answer 53

From cells arranged in long tubes

Question 54

What are sieve tube elements?

Answer 54

Living cells that form the tube for transporting solutes

Question 55

Do sieve tube elements have a nucleus?

Answer 55

No

Question 56

What does each sieve tube element have?

Answer 56

It's own companion cell

Question 57

What does the companion cell do for the sieve tube element?

Answer 57

It carries out living functions for sieve cells.

Question 58

What do companion cells have loads of?

Answer 58

Mitochondria

Question 59

Why do companion cells have loads of mitochondria?

Answer 59

To synthesise ATP through aerobic respiration for the active transport of solutes.

Question 60

How are sieve tubes connected to each other?

Answer 60

Through sieve plates.

Question 61

How do enzymes maintain a concentration gradient from the leaves to the roots/sink?

Answer 61

By converting the solutes at the sink to other storage substances (e.g., Starch)

Question 62

By converting solutes to other storage substances, what does this ensure?

Answer 62

There is always a lower concentration at the sink than the source.

Question 63

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

Answer 63

1. In the leaf sucrose is actively transported into the phloem; 2. By companion cells; 3. This lowers the water potential of sieve tube and water enters by osmosis; 4. Increase in pressure causes mass movement towards the root; 5. Sucrose are converted into starch in the root for respiration;

Question 64

How happens to the pressure in the phloem when water enters it by osmosis?

Answer 64

There is an increase in pressure which causes mass movement towards the root

Question 65

What is the method for the ringing experiment?

Answer 65

If a ring of bark is removed, a bulge forms above the ring

Question 66

What is the name of the three experiments for the mass flow hypothesis?

Answer 66

Ringing experiment Aphid Autoradiography

Question 67

Evidence for the ringing experiment (1 point)

Answer 67

1. The fluid from the bulge has a higher concentration of sugars than the fluid from below the ring. This is because the sugars can’t move past the area where the bark has been removed – 2. This is evidence that there can be a downward flow of sugars

Question 68

Evidence against the ringing experiment (3)

Answer 68

1. Not all solutes move at the same rate 2. Sucrose travels to many different sinks, not just to the one with this highest water potential as the model suggests 3. The sieve plates would create a barrier to mass flow.

Question 69

What is the method for the aphid experiment?

Answer 69

The aphids will pierce the phloem, then their bodies are removed leaving mouth parts behind, which allows sap to flow out

Question 70

Evidence for the aphid experiment (1 point)

Answer 70

The sap flows out quicker nearer the leaves than further down the stem – this is evidence that there is a pressure gradient

Question 71

What is the method for the autoradiography experiment?

Answer 71

Leaves are supplied with radioactive 14C (CO2) which is converted to glucose, then sucrose * This allows the radioactive 14C to be tracked through the plant as is is transported throughout the plant.

Question 72

Evidence for the autoradiography (1)

Answer 72

1. Lack of oxygen inhibit translocation in phloem. This is evidence that active transport is involved