Question

Which of the following statements regarding transport in phloem is true?

a. it always moves in the direction of leaves to roots
b. it proceeds from source tissue to sink tissue
c. it requires no energy inputs from the plant
d. it is the same as the transport process in xylem
e. none of the above

Answer 1

b. it proceeds from source tissue to sink tissue

Step-by-step explanation:

Transport in the phloem involves the movement of sugars and other organic nutrients from source tissues (where they are produced or stored, such as leaves) to sink tissues (where they are used or stored, such as roots or developing fruits). This movement is typically from areas of higher concentration (source) to areas of lower concentration (sink).

Answer 2

The true statement regarding phloem transport is that it proceeds from source tissue to sink tissue and requires energy, contrasting with xylem transport which is unidirectional and predominantly upward. The correct option is b.

Step-by-step explanation:

The correct statement regarding transport in phloem is b. it proceeds from source tissue to sink tissue. This process involves the movement of sugars, such as sucrose, from the source, where they are produced through photosynthesis or released from storage, to the sink, where they are consumed for growth or stored.

During this process, sucrose is actively transported into the phloem sieve-tube elements (STEs), which reduces the water potential and causes water to enter the phloem from the xylem, generating pressure that drives the bulk flow of phloem from source to sink.

Phloem loading at the source requires energy in the form of ATP, contradicting the idea that transport in phloem requires no energy.

Moreover, transport in phloem can occur in multiple directions, such as upwards to the growing shoots or downwards to the roots, depending on where the sink tissues are located at that particular stage of the plant's growth and development.

This is different from transport in xylem, which primarily facilitates the unidirectional upward movement of water and minerals from the soil to the rest of the plant. Option b. is the correct one.