Transport in Plants

Question 1

What are the two types of vascular tissues in plant organs?

Answer 1

xylem and phloem.

Question 2

What is xylem?

Answer 2

It transports water and dissolved minerals from the roots to tissue cells. it is made of vertical columns of tracheids and vessel elements that conduct water from roots to leaves.

Question 3

What are tracheids?

Answer 3

They are specialised, water conducting cells. They have a modified cell wall known as the pit membrane which permits the flow of water but prevents damaging air bubbles.

Question 4

What are vessel elements?

Answer 4

they are specialised, water conducting cells. They have pores that allow unrestricted flow of water between cells.

Question 5

Describe the process of transport of water in plants.

Answer 5

1. Absorption of water from soil
2. diffusion of water into xylem vessels through intracellular or extracellular pathways
3. conduction of water through xylem
4. evaporation of water from aerial parts of the plant

Question 6

What are intracellular pathways?

Answer 6

Involve the movement of water through the cytoplasms of root cells.

Question 7

What are extracellular pathways?

Answer 7

Involves the movement of water through cell walls.

Question 8

What is xylem sap?

Answer 8

a continuous column of water and dissolved nutrients in the xylem vessels, driven upwards by several forces.

Question 9

What are three forces that drive xylem sap upwards?

Answer 9

root pressure - diffusion of water into root xylem vessels creates pressure that forces xylem sap up
capillary action - xylem sap is forced upwards by a combination of cohesive forces between water molecules and adhesive forces between water molecules and the cell walls of xylem cells.
transpirational pull - evaporation of water into the atmosphere creates a negative pressure, pulling xylem sap up

Question 10

What is the transpiration stream?

Answer 10

the flow of water s a result of the transpiration pulling xylem sap upwards. it transports minerals and water to leaf cells for photosynthesis and metabolism.

Question 11

What is phloem?

Answer 11

A type of vascular tissue which transports sugars and other organic compounds for photosynthesis. it is composed of sieve tube elements and companion cells.

Question 12

What is phloem sap?

Answer 12

The resulting material from sugars and other compounds produced in photosynthesis. It is transported from the leaves to tissue cells in phloem.

Question 13

What are sieve tube elements?

Answer 13

specialised conducting cells that transport phloem sap. They have modified cell walls called sieve plates that permit unimpeded flow of phloem sap between cells.

Question 14

what are companion cells?

Answer 14

specialised conducting cells that carry out lilfe processes, that support sieve tube elements.

Question 15

What is translocation?

Answer 15

The transport of photosynthesis products in phloem sap between nutrient rich cells called source cells and nutrient deficient cells called sink cells.

Question 16

where are source cells in the plant?

Answer 16

Typically located in leaves, but tissue cells in stems and roots also function as source cells when leaves become nutrient deficient.

Question 17

Explain the pressure-flow hypothesis.

Answer 17

1. materials produced by source cells (including sugars) are actively transported into phloem vessels.
2. water flows into phloem vessels by osmosis - it does this as there is an increase in solute concentration after step 1.
3. increased water pressure forces phloem sap through the phloem vessels towards sink cells.
4. materials are transported into sink cells from phloem vessels. water diffuses back into xylem vessels and is transported back to source cells.