| (a) | All parasites are pathogens as they cause harm to the host. | 
| (b) | Pathogens have to adapt to live within the environment of the host, | 
| (c) | Pathogen of amoebic dysentery lives in the gut of host organism. | 
| (d) | Pathogens can enter human body by various means causing functional damage but do not interfere with normal vital activities. | 
| 1. | Vaccine prepared by traditional method | 
| 2. | Antigens present in the body of humans | 
| 3. | Memory of the immune system | 
| 4. | Site of interaction between antigen and antibody | 
| 1. | lgG is the smallest and most abundant antibody. | 
| 2. | Antigen-binding sites are present at C-terminal of an antibody. | 
| 3. | Natural killer cells are type of lymphocytes associated with innate immunity. | 
| 4. | Cell-mediated immune response is responsible for graft rejection. | 
| 1. | Tissue matching is essential before undertaking any graft | 
| 2. | T-lymphocytes play an important role in graft rejection | 
| 3. | Patient takes immunosuppressants for few weeks only | 
| 4. | Blood group matching is important before transplantation |