1. What are the three domains of life and how are they different from each other? (3 marks) - The three domains of life are Bacteria, Archaea and Eukarya. They differ in their cell structure, genetic material, metabolism and evolutionary history. Bacteria and Archaea are prokaryotes, meaning they lack a nucleus and other membrane-bound organelles, while Eukarya are eukaryotes, meaning they have a nucleus and other membrane-bound organelles. Bacteria and Archaea have circular DNA, while Eukarya have linear DNA. Bacteria and Archaea have diverse metabolic pathways, while Eukarya mostly rely on glycolysis and oxidative phosphorylation. Bacteria and Archaea are more ancient than Eukarya and have distinct phylogenetic trees. 2. What are the main types of microorganisms that cause infectious diseases in humans and what are some examples of each type? (4 marks) - The main types of microorganisms that cause infectious diseases in humans are bacteria, viruses, fungi and parasites. Some examples of each type are: - Bacteria: Streptococcus pyogenes (strep throat), Escherichia coli (urinary tract infection), Mycobacterium tuberculosis (tuberculosis), Staphylococcus aureus (skin infection). - Viruses: Influenza virus (flu), Human immunodeficiency virus (HIV), Hepatitis B virus (hepatitis B), Herpes simplex virus (cold sore). - Fungi: Candida albicans (thrush), Aspergillus fumigatus (aspergillosis), Cryptococcus neoformans (cryptococcosis), Histoplasma capsulatum (histoplasmosis). - Parasites: Plasmodium falciparum (malaria), Giardia lamblia (giardiasis), Toxoplasma gondii (toxoplasmosis), Enterobius vermicularis (pinworm). 3. What are the main components of the innate immune system and how do they protect the body from infection? (4 marks) - The main components of the innate immune system are the physical barriers, the chemical barriers, the cellular defenses and the inflammatory response. They protect the body from infection by: - Physical barriers: Preventing the entry of microorganisms into the body by covering the skin and mucous membranes. - Chemical barriers: Killing or inhibiting the growth of microorganisms by producing substances such as lysozyme, acid, bile, mucus and antimicrobial peptides. - Cellular defenses: Recognizing and destroying foreign or abnormal cells by using phagocytes, natural killer cells, complement system and interferons. - Inflammatory response: Triggering a local reaction that involves vasodilation, increased permeability, recruitment of leukocytes, release of cytokines and activation of adaptive immunity.