This activity contains 5 questions.
Root pressure is positive pressure that helps to push water up out of the roots and into the aboveground plant. How is it formed?
Root cells bring water directly into the root using active transport.
Root cells bring mineral nutrients into the root using active transport. This sets up a concentration gradient that draws water into the root by osmosis.
Root pressure develops as a consequence of adhesion and cohesion. Active transport is not involved.
Root pressure is generated by transpiration.
Water vapor moves out of leaves through open stomata. This process is known as _____.
Xylem tissues create a system of very thin pipes that connect plant roots and leaves. Which option best describes the nature and function of xylem tissue?
Xylem tissue is composed of living cells. They use active transport mechanisms to move xylem sap.
Xylem is dead tissue. The pipes convey xylem sap from the leaves to the roots and other nonphotosynthetic parts of the plant.
Xylem includes some dead tissue, but living cells line the pipes. They use active transport mechanisms to move xylem sap.
Xylem is dead tissue. The pipes convey xylem sap from the roots to the leaves. Active transport is not important in moving xylem sap.
Imagine that you spray a large, actively growing tree with a sealant that instantly seals off all of the stomata. What would happen in the xylem system?
The flow of xylem sap would stop, except for some minimal upward movement that might be generated by root pressure.
The flow of xylem sap would continue, leading to a buildup of pressure within the xylem tubes. Eventually the xylem tubes would rupture.
The flow of xylem sap would reverse. Root pressure would draw all of the xylem sap into the roots.
The xylem system is independent of the stomata and would not be affected.
What happens to the xylem system during drought, when water is scarce?
The transpiration rate increases, creating extreme negative pressure at the roots. The xylem tubes may collapse as a result.
Falling moisture levels in the leaf cause the guard cells to change shape, closing the stomata. This reduces water loss from the plant.
Falling moisture levels in the leaf cause the guard cells to change shape, opening the stomata even wider. This increases the transpiration rate.
The transpiration rate decreases because the air outside the leaf is less humid. This helps reduce water loss from the plant.
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