7. Transport In Plants

Question 1

What does the vascular system in plants consist of?

Answer 1

Xylem and phloem

Question 2

What is the name for the fluid transported in the tubes and where does it move?

Answer 2

Xylem sap moves in xylem vessels
Phloem sap moves in sieve tubes

Question 3

What do dicotyledons look like?

Answer 3

Leaves with wide blades
Narrow stalks (petioles)

Question 4

What is transpiration?

Answer 4

The loss of water vapor from a plant to its environment; it mostly takes place through the stomata in the leaves.

Question 5

What is the transport process of water in a plant?

Answer 5

energy from the sun causes evaporation of water from the leaves. This reduces the water potential in the leaves and creates a water potential gradient throughout the plant. Water moves down this gradient from the soil into the plant then moves across the root into the xylem tissue in the center of the root. Once in the xylem it moves upwards through the root to the stem and then into the leaves.

Question 6

State 4 adaptations of xerophytes and how it helps them.

Answer 6

1. Thick waterproof cuticle minimizes water loss by reducing evaporation
2. Hairs to trap a layer of moist air close to the leaf surface.
3. Leaves reduced to spines to lessen the surface are from which transpiration can take place.
4. Stems coated with wax to cut down water loss.

Question 7

What is the symplast pathway? And describe it.

Answer 7

When water moves from cell to cell via the plasmodesmata.
1. Water enters the cytoplasm by osmosis through the partially permeable cell surface membrane.
2. Water moves into the sap in the vacuole, through the tonoplast by osmosis.
3. Water may move from cell to cell through the plasmodesmata.
4. Water may move from cell to cell through adjacent cell surface membranes and cell walls.

Question 8

What is the apoplast pathway? And describe it.

Answer 8

When water moves through the cell walls

1. Water enters the cell wall
2. Water moves through the cell wall
3. Water may move from cell wall to cell wall through the intercellular spaces
4. Water may move directly from cell wall to cell wall.

Question 9

What are the structural features of xylem vessels?

Answer 9

-Xylem vessels are made from cells joined end to end to form tubes- allows mass flow of water
-The cells are dead
-The walls of the cells are thickened with lignin- adds strength to withstand the hydrostatic pressure so vessels don’t collapse.
-There are pits in the walls to allow water in and out of the tubes

Question 10

What aids the mass flow through the xylem?

Answer 10

Water molecules are attracted to each other by hydrogen bonding and this attraction is called cohesion.

Question 11

Describe the movement of water across the root to xylem.

Answer 11

Water is taken up by the root hairs which increase the surface area for absorption of water and mineral ions. After, water crosses the cortex of the root and enters the xylem in the centre of the root. It does this because the water potential inside the the xylem vessels is lower than the water potential in the root hairs. (Water moves down a water potential gradient across the root.)

Question 12

What is the Casparian strip? And what is its function?

Answer 12

The cells in the endodermis’s thick waterproof, waxy band of suberin in the cell walls.
It stops water moving through the apoplast.

Question 13

Name 5 common sinks

Answer 13

Buds, flowers, fruits, roots and storage organs

Question 14

Name 2 common sources

Answer 14

Leaves and storage organs such as tubers

Question 15

What are the most important cells used in phloem transport

Answer 15

Sieve tube element and companion cells

Question 16

How does transport occur in the phloem?

Answer 16

By loading a high concentration of sucrose into a sieve tube element it great decreases the water potential of the sap inside it. So water enters the sieve tube element moving down a water potential gradient by osmosis. This builds up pressure inside called hydrostatic pressure. This pressure difference between the source and sink causes a mass flow of water and dissolved solutes through the sieve tubes.

Question 17

Explain how sucrose is loaded into the phloem.

Answer 17

1. Sucrose is loaded into a companion cell by active transport and hydrogen ions are pumped out of the cell into its cell wall by a proton pump using ATP as an energy source.
2. The proton pump creates a large excess of hydrogen ions in the apoplast pathway outside the companion cell.
3. The sucrose molecules are carried through a co-transporter molecule into the companion cell against the concentration gradient.
4. Once inside the companion cell the sucrose molecules can move by diffusion into the sieve tube.

Question 18

Why do plants need transport systems?

Answer 18

Diffusion is too slow to meet their metabolic needs
Substances must be moves over long distances
They are multicellular with a low surface area to volume ratio

Question 19

What are the 4 cell types that make up a xylem tissue?

Answer 19

Tracheids
Vessel elements
Xylem parenchyma
Sclerenchyma cells

Question 20

What are the 4 types of phloem cells?

Answer 20

Sieve tube elements
Companion cell
Parenchyma
Fibers

Question 21

Describe and explain how the transfer of sucrose into a phloem sieve tube from a companion cell can lead to the transport of the sugar to a sink

Answer 21

The presence of sucrose in sieve tube lowers the water potential and water enters the sieve tube by osmosis down a water potential gradient. This increases volume in the sieve tube and increases the hydrostatic pressure in the sieve tube at the source.