Which theory explains the unidirectional movement of water against gravity in plants/trees?

Guttation may be defined as a process in which plants can

Stomata open during day time because the guard cells

Which of the following exhibits a direct proportionality to transpiration?

Identify the purposes of transpiration.
$I -$ Transpiration creates a transpiration pull for absorption and transport in plants.
$II -$ It supplies water for photosynthesis.
$III -$ It transports minerals from the soil to all parts of the plant.
$IV -$ It cools leaf surfaces by $10-15^{\circ} C$ through evaporation.
$V -$ It maintains the shape and structure of plants by keeping cells turgid.

$A$ metal ion involved in stomatal regulation is