Final answer:
The primary food in phloem sap is sucrose, a sugar that is transported with other nutrients through the plant's phloem tissue. This allows for the distribution of photosynthesis products from sources to sinks within the plant.
Step-by-step explanation:
The main type of food found in the phloem sap is sucrose, which is a type of sugar. Phloem, a vital component of the plant's vascular system, mainly translocates sucrose along with other substances like amino acids, minerals, and plant growth regulators throughout the plant. This transportation process is pivotal for distributing the products of photosynthesis from the 'source,' such as leaves, to various 'sinks' in the plant, which include growing tissues and storage organs.
Phloem sap's aquatic solution contains up to a 30 percent concentration of sucrose, contributing to a decrease in overall water potential. This gradient promotes the movement of water from the adjacent xylem into the phloem tubes by osmosis, leading to an increase in pressure and enabling the bulk flow of the sap from the source to the sink. The sucrose in the sap is transferred into sink cells either by diffusion or active transport and is utilized for growth or transformed into other forms like starch or cellulose for storage and structural purposes, respectively.