AP BIOLOGY

Detailed explanation-1: -Xylem conducts minerals and water only in the upward direction i.e. from the roots towards the stem. The phloem transports food material from leaves to other parts of the plant body.

Detailed explanation-2: -As transpiration occurs, it deepens the meniscus of water in the leaf, creating negative pressure (also called tension or suction). The tension created by transpiration “pulls” water in the plant xylem, drawing the water upward in much the same way that you draw water upward when you suck on a straw.

Detailed explanation-3: -Once water is in the xylem, it travels upwards-against the force of gravity-towards the rest of the plant. Water is able to move against gravity due to two forces: tension and cohesion. Tension is a ‘sucking force’ which is created when water evaporates from leaves (transpiration), pulling more water into the leaf.

Detailed explanation-4: -The movement of water in the xylem is unidirectional and is always upward. The upward movement of water is due to pressure created by transpiration, i.e. transpiration pull.

Detailed explanation-5: -There are two main reasons due to which the xylem is unidirectional, namely positive root pressure and transpiration pull. Positive root pressure means it is against the gravitational pull, and the transpiration pull acts as a suction pump for the xylem tube. Thus, the water rises upwards.