This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
Chemotaxis is 
Select and explain. 
A. Unidirectional increase in movement, B. Random movement increase, C. Margintion of leucocytes, D. Increase of leucocytes
A: Unidirectional increase in movement
Answer: A: Unidirectional increase in movement 
Explanation: .