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Problem : What vascular tissue is responsible for transporting organic materials, such as sugars, throughout the plant body?

Phloem.

Problem : How do sources and sinks compare to one another in relation to osmotic concentration and water pressure (turgor pressure)?

Due to the influx of sugars through active transport and water (diffusion), the source is characterized by high osmotic concentration and high water pressure, or turgor pressure. The sink, on the other hand, from which sugars and water are removed through active transport, has low osmotic concentration and low water pressure.

Problem : Where are the sugars that the plant relies upon for nutrition produced?

Sugars are produced in plant leaves during photosynthesis.

Problem : Sites of nutrient storage, such as the roots, can be either sources or sinks. Why might this be?

Under ordinary conditions, the roots act as a sink, collecting sugars for storage. When the plant needs to use its food stores, however (such as in periods of heavy growth), the roots can act as a source.

Problem : How is turgor pressure created in the sieve elements?

Turgor pressure is created at the source by the osmotic influx of water that follows the active transport of sugars into the sieve elements. The force that this water exerts on the cell walls gives rise to turgor pressure.
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