According to the pressure-flow hypothesis, which of the following statements is not true
• Water moves from the xylem to the phloem of a plant.
• Water is necessary for sugars to move through phloem.
• Phloem is able to move sugars in either direction to meet the nutritional needs of the plant.
• The movement of water into a nutrient-rich region of the phloem decreases the pressure in that region.
To determine which of the following statements is not true according to the pressure-flow hypothesis, let's examine each statement and its corresponding hypothesis:
1. Water moves from the xylem to the phloem of a plant.
According to the pressure-flow hypothesis, this statement is not accurate. It suggests that water moves from the xylem to the phloem, but in reality, the movement is from the phloem to the xylem. In the phloem, water moves by osmosis from a region of higher pressure (source) to a region of lower pressure (sink).
2. Water is necessary for sugars to move through phloem.
This statement aligns with the pressure-flow hypothesis. According to this theory, sugars are actively transported from a source (place of sugar production, e.g., leaves) to a sink (place of sugar storage or utilization, e.g., roots) in the phloem. The movement of sugars in the phloem is aided by water, which creates a pressure gradient.
3. Phloem is able to move sugars in either direction to meet the nutritional needs of the plant.
This statement is accurate and supported by the pressure-flow hypothesis. The phloem is capable of transporting sugars in any direction required by the plant. For example, sugars can move from leaves to roots, leaves to fruits, or leaves to growing shoots.
4. The movement of water into a nutrient-rich region of the phloem decreases the pressure in that region.
According to the pressure-flow hypothesis, this statement is not true. The movement of water into a nutrient-rich region of the phloem increases the pressure in that region. This pressure gradient drives the flow of sugars from the source to the sink.
Therefore, the statement that is not true according to the pressure-flow hypothesis is:
"The movement of water into a nutrient-rich region of the phloem decreases the pressure in that region."