Option 1: Phloem transport occurs uni-directionally. This statement is incorrect. Phloem transport actually occurs bi-directionally, meaning that it can transport nutrients in both upward and downward directions in a plant.
Option 2: Gravity influences phloem transport. This statement is incorrect. Unlike the movement of water in xylem, which is influenced by gravity, phloem transport is not significantly affected by gravity. It is driven by osmotic pressure gradients and active transport processes.
Option 3: Ca+ is the most abundant cation in phloem sap. This statement is incorrect. The most abundant cation in phloem sap is actually potassium (K+), not calcium (Ca+).
Option 4: Sugar is transported in phloem as non-reducing sugar. This statement is correct. The primary sugar transported in phloem sap is sucrose, which is a non-reducing sugar. This means that it does not have a free aldehyde or ketone group and cannot undergo certain chemical reactions that reducing sugars can.
In summary, option 4 is the correct statement about phloem transport. It is important to note that the remaining options have been deemed incorrect based on the provided information.