Chapter 6- Transport in plants

Question 1

Name the parts of a non-woody herbaceous dicotyledonous stem.

Answer 1

Cortex, pith, vascular bundle (phloem, cambium and xylem) and the epidermis.

Question 2

Name the parts of a non-woody herbaceous dicotyledonous root.

Answer 2

Endodermis, casparian strip, vascular cylinder (phloem, cambium and xylem), root hair, piliferous layer and the cortex.

Question 3

What are the functions of a xylem vessel?

Answer 3

1. To conduct dissolved mineral salts / ions and water from the root of the plant to the other parts of the plant.
2. To provide mechanical support for the plant.

Question 4

How is the xylem adapted to perform it’s function?

Answer 4

1. It has long, hollow tubes stretching from the root to the leaves.
2. It is made up of dead cells and has no protoplasm or nucleus.
3. Long and empty lumen with no cross walls (cell walls).
4. Lignin (which is a hard and rigid substance) is deposited on the walls of the xylem.

Question 5

How is lignin deposited on the xylem?

Answer 5

1. Annular - in rings
2. Spiral - in spiral bands
3. Pitted - lignin is deposited all over, except for pits (pores) on the walls which allow transport of water from one xylem to another.

Question 6

Describe the components of a phloem tube.

Answer 6

1. Companion cell at the side of the phloem.

2. Sieve plates with pores (to allow faster / rapid flow of manufactured food substances).

Question 7

Describe the functions of the companion cell and phloem tubes.

Answer 7

1. Companion cells - to provide energy and nutrients for the phloem to transport sugars to the rest of the plant.
2. Phloem tube - to conduct manufactured foods (sucrose and amino acids) from the leaves to the other parts of the plants. (Translocation)

Question 8

How is the phloem tube adapted to perform its function?

Answer 8

1. Columns of long and elongated thin walled living cells.
2. Degenerate protoplasm.
3. No nucleus, vacuole and most organelles.
4. Thin cytoplasm connected with cells above and below through the sieve plates.

Question 9

How is the companion cell adapted to perform its function?

Answer 9

1. Has a very dense cytoplasm.

2. Has a lot of mitochondria. (To provide enough food and nutrients and energy for itself and the phloem.)

Question 10

What is the appearance and function of the cambium?

Answer 10

Appearance:
1. Cambium cells are relatively smaller
2. They are stuck between the xylem and the phloem.
Function:
1. The cambium cells divide and differentiate to form new xylem and phloem cells, which helps to thicken the stem.

Question 11

What are the two methods that are used to take up mineral salts from the soil?

Answer 11

1. Diffusion - mineral salts diffuse through the cell membrane and enters the cell because it is of higher concentration than the cell sap. This goes on from the first root hair cell.
2. Active transport - pumping of dilute mineral salts up, where energy is used to move molecules against a concentration gradient.

Question 12

How is water taken up from the soil?

Answer 12

1. Through osmosis as the water around the root hair is more concentrated with ions than the cell sap.
2. Three methods in which water flows - apoplastic pathway (through the fully permeable cell wall), symplast pathway (through the cytoplasm) and vacuolar pathway (osmosis through vacuole).

Question 13

What is the function of the casparian strip?

Answer 13

1. To control the amount of water entering the cell.
2. To block out any unwanted materials carried through the apoplastic pathway.
3. To force the water to go down the symplast pathway.

Question 14

How is the casparian strip / endodermis adapted to perform its function?

Answer 14

1. It is made up of hydrophobic lipids that do not allow water to pass through. Hence, it is waxy and non-permeable.
2. The casparian strip is lined along the cell wall, blocking the flow of water along the apoplastic pathway.
3. The endodermis filters out substances through chemical reactions.

Question 15

How does the water flow upwards from the root to the stem?

Answer 15

1. Root pressure
2. Capillary action
3. Transpiration pull

Question 16

Describe how root pressure forces water to move up the stem.

Answer 16

• There is upward push of the xylem sap
• because of active transport of ions into the vascular cylinder
• hence, the water is pushed up to accommodate the new flow of ions into the vascular cylinder.

Question 17

Describe how the capillary action forces water to move up the stem.

Answer 17

• There is an upward movement of water due to
• the adhesive (Hydrogen bonds between water and cell wall of the stem) and cohesive (Hydrogen bonds between molecules of water) nature of water.

Question 18

Describe how transpiration pull forces water to move up the stem.

Answer 18

• There is a negative pressure / suction force
• introduced by the loss of water vapor from aerial parts of the plant
• as well as through the stomata
• hence, water is pulled up to replace the empty space.

Question 19

Define transpiration.

Answer 19

Transpiration is defined as the loss of water vapor from the aerial parts of a plant as well as through the stomata of the leaves.

Question 20

What are the processes in wilting?

Answer 20

1. When the rate of transpiration > rate of absorption of water.
2. The cells lose their turgidity and decreases in size.
3. The cell membrane and cytoplasm shrink away from the cell wall.
4. The cell becomes plasmolysed / flaccid.
5. Stem becomes soft and limp and leaves start to fold up.

Question 21

What are the factors affecting the rate of transpiration?

Answer 21

1. Presence of light
2. Air movement / wind
3. Temperature
4. Humidity

Question 22

What is the importance of transpirational pull?

Answer 22

1. It forces water to go up the xylem from the roots to the stem / leaves.
2. It reduces latent heat in the plant- helps cool the plant down.
3. It pumps water up for photosynthesis.
4. It replenishes water lost by the plant.
5. It makes cells turgid so that leaves are spread out to maximize photosynthesis rates.

Question 23

How does the marram leaf adapt?

Answer 23

1. Leaves unroll when there is sufficient water in the environment.
2. Leaves fold up again when transpiration is excessive.
3. Sunken stomata prevents too much transpiration.
4. Stiff root hairs trap water vapor escaping.
5. Thick cuticle prevents evaporation.

Question 24

How does water move out of a leaf cell?

Answer 24

1. Film of moisture formed when water moves out of mesophyll cells.
2. Evaporation / accumulation of water at stomata/ intercellular spaces.
3. Diffusion of water vapor out of stomata.
4. Cell sap potential of mesophyll cells decrease. Water is drawn.
5. Huge suction force pulls up whole column of water in xylem.

Question 25

What are the reasons for water loss / transpiration?

Answer 25

1. Excess water that is absorbed from the soil and are not used up by the plant.
2. Water produced by the plant cells during respiration.

Question 26

What is the translocation process?

Answer 26

1. Loading of sucrose into the phloem, which causes the tube to take in water from the xylem via osmosis (WP decreases).
2. Uptake of water generates a positive pressure that forces sap down.
3. Pressure is relieved by the unloading so of sucrose and subsequent water loss.
4. Water is recycled from sink to source via xylem.

Question 27

What are the three experiments that show that the phloem is a translocation tissue?

Answer 27

1. Ringing experiment- swelling because of food accumulation.
2. Using aphids- aphids are able to take in sucrose.
3. Isotopes / autoradiography- phloem will show radioactivity as glucose formed contains 14C.