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  Guess Bio 9th Class 2022  UNIT NO. 1. INTRODUCTION TO BIOLOGY SHORT QUESTIONS: 1. What is immunology ?  Immunology is  the study of the immune system  and is a very important branch of the medical and biological sciences. The immune system protects us from infection through various lines of defence. If the immune system is not functioning as it should, it can result in disease, such as autoimmunity, allergy and cancer. 2 . What are parasites ? A parasite is  an organism that lives on or in a host organism and gets its food from or at the expense of its host . There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites. 3. Write achievements of Bu Ali Sina in Biology . Ibn Sina  ( Persian :  ابن سینا ; 980 – June 1037 CE), commonly known in the West as  Avicenna  ( / ˌ æ v ɪ ˈ s ɛ n ə ,   ˌ ɑː v ɪ -/ ), was a  Persian [4]   polymath  who is regarded as one of the most significant  physicians ,  astronomers , philosophers, and wri