The structure of which of the following consist of a layer of single cell thickness

The structure of which of the following consists of a layer of single cell thickness 1. artery 2. venule 3. capillary 4. arteriole

Which of the following side of wall of guard cells is thick?

Which of the following made of several layers of cells?

Which of the following is arranged in a single layer?

Which one of the following consists of a thin layer of endothelium only?

Which of the following is a single membranous structure?

Which of the following structures has single membrane ?

Which of the following structures has single membrane ?

Which of the following structures has single membrane ?