AS Level Biology Chapter 7 Transport in Plants

Which statement correctly identifies the movement of sucrose and amino acids in plant vascular tissue?

• They are carried from source to sink by mass flow in upward and downward directions

• They are carried from sink to source by cohesion-tension in upward and downward directions.

• They are carried from sink to source by mass flow in one direction.

• They are carried from source to sink by cohesion-tension in one direction.

Xylem vessel elements are specialised cells that are adapted for the transport of water. Which statement correctly matches an adaptation of a xylem vessel element to its function?

• Cytoplasm is only found in a thin layer next to the cell walls and does not contain any organelles. This reduces resistance to the flow of water in the xylem vessels.

• The end walls between xylem vessel elements have partially broken down, forming end plates. This reduces resistance to the flow of water in the xylem vessel.

• The walls of the xylem vessel elements contain cellulose that is hydrophilic and can form hydrogen bonds to water, allowing adhesion of water molecules to the vessel walls.

• Xylem vessel elements have plasmodesmata that connect them with companion cells. The companion cells provide ATP, which is needed for the transport of water.

A student makes an accurate labelled plan diagram of a section of a leaf containing a vascular bundle.

Which statement correctly describes part of their plan diagram?

• The vascular bundle has labels for the xylem vessel elements, phloem sieve tube elements and companion cells.

• The vascular bundle is divided into two sections, with the section closer to the upper epidermis labelled as xylem and the other section labelled as phloem.

• In the section of the vascular bundle positioned closer to the lower epidermis, each sieve tube element has an associated companion cell.

• The phloem sieve tube elements are drawn with thick cell walls to represent the lignin in the walls.

Which sequence of events could lead to mass flow in a phloem sieve tube?

1 Sucrose moves into a sieve tube element.

2 Protons (H+ ) and sucrose molecules move into a companion cell through a co-transporter protein.

3 A very high hydrostatic pressure is produced.

4 The water potential of the sieve tube element decreases.

5 Protons (H+ ) are actively pumped out of a companion cell.

6 Water moves down a water potential gradient by osmosis.

• 1 --> 2 --> 5 --> 6 --> 4

  --> 3

• 3 --> 1 --> 2 --> 5 --> 6

  --> 4

• 3 --> 5 --> 1 --> 2 --> 4

  --> 6

• 5 --> 2 --> 1 --> 4 --> 6 --> 3

The table shows the observations made by a student about three different cell types, P, Q and R, seen in a transverse section of a plant stem, using a light microscope.

• A

• B

• C

• D

Water molecules are attracted to each other. T

his property is important in the upward movement of water in xylem.

Which term is used to describe the attraction of water molecules to each other?

• adhesion

• cohesion

• hydrophilic

• polar

The diagram shows a model to demonstrate mass flow.

• A

• B

• C

• D

The diagram shows the relationship between phloem sieve tube elements, xylem vessel elements and companion cells.

• A

• B

• C

• D

Why does an air bubble in a xylem vessel element stop the flow of water?

1 loss of adhesion

2 loss of cohesion

3 collapse of xylem vessel element

• 1, 2 and 3

• 1 and 3 only

• 1 only

• 2 only

Which changes to the water potential and the volume of solution in a phloem sieve tube occur when amino acids are moved into a sink from the phloem sieve tube?

• A

• B

• C

• D