13.4.3 Plant Transport: Absorption and Lateral Transport in Roots

Question 1

Plant Transport: Absorption and Lateral Transport in Roots

Answer 1

• Roots increase their surface area with root hairs and mycorrhizae in order to maximize the uptake of water.
• The three major compartments in plant cells are (1) the central vacuole, (2) the symplast, and (3) the apoplast.
• There are two general pathways for the lateral movement of water into the xylem of the root is the apoplastic pathway and the symplastic pathway.

Question 2

roots

Answer 2

• Water enters the xylem through roots via osmosis. Roots are specially adapted to maximize the uptake of water. Root hairs are extensions of epidermal cells of the root. They function to increase the surface area of the root, thereby allowing for increased water uptake. Mycorrhizae are symbiotic associations of the plant root and a fungus. The fibrous hyphae of the fungus provide an increased surface area for the absorption of water and minerals, which are eventually passed to the roots of the plant.

Question 3

note 1

Answer 3

• A plant has three general compartments:
  · central vacuole
  · symplast
  · apoplast
• Plasmodesmata are open channels in the cell walls of adjacent plant cells. The continuum of cytoplasm between plant cells is the symplast. The apoplast is the continuum of cell walls within plant tissues. The central vacuole is typically a large compartment bound by a membrane called the tonoplast.
• Water travels into the xylem of roots through either the
  symplastic pathway—through the cytoplasm, or through the apoplastic pathway—through the cell walls (depicted by arrows in the diagram to the left).

Question 4

note 2

Answer 4

• The two pathways for the movement of water and minerals into the xylem of the root include the apoplastic pathway (the upper pathway illustrated in the diagram) and the symplastic pathway (the lower pathway). In the apoplastic pathway, water and minerals move through a continuum of cell walls. In the symplastic pathway, water and minerals move through a continuum of cytoplasm.
• Water and minerals traveling through the symplastic pathway have already been filtered upon entering the plasma membrane of the root hairs. Thus, they pass freely through the endodermis into the xylem.
• In contrast, water and minerals traveling through the
  apoplastic pathway are diverted into the symplastic pathway when they reach the Casparian strip in the endodermis. The Casparian strip is a band of cell wall that contains suberin, a substance that restricts the movement of water across the endodermis. Upon entering the symplastic pathway, water and minerals are filtered by a cell membrane and can then enter the xylem.

Question 5

Considering the apoplastic pathway and the symplastic pathway, which one of the following is true?

Answer 5

• The apoplastic pathway is the movement of water through the cell walls.

Question 6

Which of the following is not an adaptation that enhances the uptake of water by roots?

Answer 6

• active transport of water into the roots

Question 7

What role does the symplastic pathway play in the movement of water and minerals through plants?

Answer 7

• It provides channels between cells allowing water to move through the cytoplasm of one cell to the next.

Question 8

The lateral transport of water can occur by 3 routes. Which of the following is not one of these?

Answer 8

• transnuclear

Question 9

Without root hairs which one of the following processes would be diminished?

Answer 9

• Movement of water into the epidermis of the root

Question 10

Which one of the following best describes the mycorrhizae?

Answer 10

• Combination of root hairs and fungal hyphae