13.4.2 The Role of Xylem Tissue and Stomata Flashcards Preview

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Flashcards in 13.4.2 The Role of Xylem Tissue and Stomata Deck (12)
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1
Q

The Role of Xylem Tissue and Stomata

A

• Xylem is the water-conducting tissue of a plant.
• Two types of cells that make up xylem tissue include tracheids and vessel elements.
• Plants regulate transpiration by opening and closing their stomata.
• Stomata will open and close in response to light, CO2
, and circadian rhythms.

2
Q

note

A
  • Review: Transpiration is the process by which the
    evaporation of water from plant leaves pulls water through the plant from the roots.
  • Xylem is the vascular tissue in plants that conducts water and minerals. Xylem consists of tracheids, vessel elements, and other specialized cells.
3
Q

tracheids

A
  • Dead at functional maturity, tracheids are long cells with tapered ends that function as water-conducting cells of xylem. Tracheids have tough secondary cell walls and have pits on their ends and sides to allow for the conduction of water both vertically and laterally to neighboring tracheids.
4
Q

vessel elements

A
  • Also dead at functional maturity, vessel elements are short and less tapered than tracheids. They are aligned end to end to form continuous vessels for water conduction. The end walls of vessel elements can be almost completely perforated in some plants. Water travels through perforated end walls and laterally through pits.
5
Q

stomata

A
  • Stomata are small pores in the lower epidermis of a leaf that allow for the exchange of water and gases between the plant and the atmosphere. The opening and closing of stomata are controlled by guard cells. Typically, a plant opens its stomata only when there is enough light to maintain an adequate amount of photosynthesis.
  • Light is one factor that is involved in the opening of stomata. Light hits a photoreceptor in a guard cell and triggers an ATP-powered proton pump which causes K+
    (potassium ions) represented by small dots in the diagram, to enter the guard cell. The K+ in the guard cell then set up an osmotic gradient that causes water to rush in. The guard cell swells, allowing the stomata to open.
  • Carbon dioxide is another factor involved in the opening and closing of stomata. Even in the dark, a plant deprived of CO2 will open its stomata. When placed in the dark, stomata will continue to open and close in daily patterns, which suggests that circadian rhythms are involved in stomatal opening and closing.
6
Q

Which one of the following structural aspects of a cell would not be advantageous to the function of xylem cells?

A
  • The cell is full of cytoplasm.
7
Q

Which one of the following weather conditions would cause the greatest rate of transpiration?

A
  • High temperatures, low humidity, breezy
8
Q

Pits are regions in the xylem in which

A
  • water can be conducted laterally.
9
Q

Which one of the following best describes the difference between tracheids and vessel elements?

A
  • Tracheids are longer and have smaller openings at their ends than vessel elements
10
Q

Stomata are located on the underside of the leaf and are flanked by guard cells. These guard cells close the stomata by

A
  • losing water by osmosis due to a loss of K+. This results in a loss of turgor in the guard cells that seals off the stomata.
11
Q

Which of the following is not true of xylem?

A
  • It is functional only while the cells are alive and is replaced frequently.
12
Q

Which of the following does not affect the opening and closing of stomata?

A
  • Na+ concentration

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