Lymph differs from blood in having

The correct option is "no RBC".

To understand why lymph differs from blood in this aspect, let us look at the composition of both fluids and how lymph is formed:

1. Composition of Blood:
Blood is a specialized fluid connective tissue that circulates throughout the cardiovascular system. It is composed of plasma (the liquid matrix) and formed elements, which include:
- Red Blood Cells (RBCs or erythrocytes), which contain hemoglobin and transport oxygen.
- White Blood Cells (WBCs or leukocytes), which are involved in immune defense.
- Platelets (thrombocytes), which are responsible for blood clotting.

2. Formation and Composition of Lymph:
As blood flows through blood capillaries, water and small water-soluble substances filter out into the spaces between tissue cells. This fluid is known as interstitial fluid or tissue fluid.
Most of this tissue fluid is collected by a network of vessels called the lymphatic system. Once this fluid enters the lymphatic vessels, it is called lymph.
Because the capillary pores are relatively small, larger cellular elements like red blood cells (RBCs) and large plasma proteins cannot filter through. Therefore, lymph is structurally similar to blood plasma but lacks RBCs, platelets, and large plasma proteins.

3. Analysis of the Options:
- much more of water content: Both blood plasma and lymph consist mostly of water (over 90%), so this is not the main distinguishing factor.
- no WBC: Lymph is rich in white blood cells (especially lymphocytes), which help filter pathogens and maintain immunity.
- no RBC: Because RBCs are too large to escape the blood vessels during filtration, lymph contains no red blood cells. This is why lymph is colorless, unlike red blood.
- no protein: Lymph does contain proteins, although in a lower concentration than blood plasma.

Therefore, the primary difference is that lymph contains no RBCs.