The Pressure Flow Hypothesis refers to the transport of phloem sap through sieve tube from the source cell to the sink cell. This hypothesis explains how sugars are moved in plants from "source" tissues (like leaves) to "sink" tissues (like roots, fruits, and flowers). Here's a step-by-step explanation:

1. In the source tissues (like leaves), sugars are produced by photosynthesis. These sugars are loaded into the phloem sieve tubes, which causes water to flow in from the xylem due to osmosis, creating a high pressure.

2. This high pressure pushes the phloem sap, which contains the sugars, down the sieve tubes.

3. The sap reaches the sink tissues (like roots, fruits, and flowers), where the sugars are unloaded and used for growth, storage, or energy.

4. As the sugars are unloaded, the water potential in the sieve tubes increases, causing water to flow out of the phloem and back into the xylem. This reduces the pressure in the sieve tubes.

5. The cycle then repeats, with more sugars being loaded into the phloem at the source tissues, and water flowing in from the xylem to create high pressure. This pressure pushes the sap down to the sink tissues, where the sugars are unloaded and the water flows back into the xylem.

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The Pressure Flow Hypothesis refers to the transport of phloem sap through sieve tube from the source cell to the sink cell. This hypothesis explains how sugars are moved in plants from "source" tissues (like leaves) to "sink" tissues (like roots, fruits, and flowers). Here's a step-by-step explanation:

1. In the source tissues (like leaves), sugars are produced by photosynthesis. These sugars are loaded into the phloem sieve tubes, which causes water to flow in from the xylem due to osmosis, creating a high pressure.

2. This high pressure pushes the phloem sap, which contains the sugars, down the sieve tubes.

3. The sap reaches the sink tissues (like roots, fruits, and flowers), where the sugars are unloaded and used for growth, storage, or energy.

4. As the sugars are unloaded, the water potential in the sieve tubes increases, causing water to flow out of the phloem and back into the xylem. This reduces the pressure in the sieve tubes.

5. The cycle then repeats, with more sugars being loaded into the phloem at the source tissues, and water flowing in from the xylem to create high pressure. This pressure pushes the sap down to the sink tissues, where the sugars are unloaded and the water flows back into the xylem.

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The Pressure Flow Hypothesis refers to the transport of phloem sap through sieve tube from the source cell to the sink cell. This hypothesis explains how sugars are moved in plants from "source" tissues (like leaves) to "sink" tissues (like roots, fruits, and flowers). Here's a step-by-step explanation:

1. In the source tissues (like leaves), sugars are produced by photosynthesis. These sugars are loaded into the phloem sieve tubes, which causes water to flow in from the xylem due to osmosis, creating a high pressure.

2. This high pressure pushes the phloem sap, which contains the sugars, down the sieve tubes.

3. The sap reaches the sink tissues (like roots, fruits, and flowers), where the sugars are unloaded and used for growth, storage, or energy.

4. As the sugars are unloaded, the water potential in the sieve tubes increases, causing water to flow out of the phloem and back into the xylem. This reduces the pressure in the sieve tubes.

5. The cycle then repeats, with more sugars being loaded into the phloem at the source tissues, and water flowing in from the xylem to create high pressure. This pressure pushes the sap down to the sink tissues, where the sugars are unloaded and the water flows back into the xylem.

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