Final answer:
Lymph is similar to interstitial fluid due to its low protein content, in contrast to plasma which has higher protein concentration. Lymph carries white blood cells and returns proteins and fluid to the blood circulation.
Step-by-step explanation:
Lymph is more similar to interstitial fluid than to plasma because it has little plasma proteins. While plasma contains about 7% protein, lymph and interstitial fluid have much lower concentrations, with interstitial fluid around 1%. Lymph, being part of the extracellular fluid (ECF), shares a similar composition to interstitial fluid, including amino acids, sugars, fatty acids, salts, and vitamins, minus the higher concentrations of protein found in plasma. Lymph also differs from serum, which is plasma without coagulation factors, since serum still contains significant protein content. The main functions of the lymph include transporting white blood cells and returning proteins and excess interstitial fluid to the circulation.