WJEC GCSE Biology 2.8 Disease, Defence and Treatment Exam Questions

About WJEC GCSE Biology 2.8 Disease, Defence and Treatment

Disease, defence and treatment is the final topic in Unit 2. You need to know that most micro-organisms are harmless and some are pathogens, describe the types of pathogen and the structure of bacteria and viruses, and explain how communicable diseases spread. HIV and AIDS, Chlamydia and malaria are the named examples. The topic covers the body's defences, how vaccination gives immunity, why antibiotics do not work on viruses, and the problem of MRSA. You must also describe how new drugs are tested and how monoclonal antibodies are made and used. Examiners commonly ask for explanations of immunity involving memory cells and specific antibodies.

What you need to know

• Pathogens Pathogens are micro-organisms that cause disease: bacteria, viruses, protists and fungi. Bacteria have a cell wall, cytoplasm and DNA not in a nucleus; viruses are a protein coat around genetic material and reproduce only inside cells.
• Named diseases HIV is a virus spread by sexual contact and blood; it attacks the immune system and leads to AIDS. Chlamydia is a bacterial sexually transmitted infection that can cause infertility. Malaria is caused by a protist spread by mosquitoes. Know how each is prevented.
• Defences The skin is a barrier, and blood clotting seals wounds. Phagocytes engulf and digest microbes. Lymphocytes recognise antigens and make specific antibodies; some also make antitoxins that neutralise toxins.
• Vaccination A vaccine contains antigens from a weakened or dead pathogen. Lymphocytes make antibodies and memory cells, so a later infection triggers a faster, larger response. Parents weigh up factors such as perceived risks when deciding on vaccination.
• Antibiotics and MRSA Antibiotics such as penicillin (first from a fungus) kill bacteria but not viruses. Overuse has led to resistant bacteria such as MRSA; control by finishing courses, not prescribing for viral infections, and hospital hygiene.
• Drug testing and monoclonal antibodies New drugs go through preclinical testing on cells, then animals, then trials on healthy volunteers and then patients, checking safety, side effects and effectiveness. Monoclonal antibodies are identical antibodies made from one type of activated lymphocyte; they are used in diagnosis (e.g. Chlamydia and HIV tests), tissue typing, monitoring malaria and supporting chemotherapy.

Common mistakes in 2.8 Disease, Defence and Treatment

• Saying antibiotics can treat viral infections such as colds. Antibiotics only work on bacteria; viruses live inside cells where antibiotics cannot affect them.
• Writing that a vaccine contains antibodies. A vaccine contains antigens, which stimulate lymphocytes to make antibodies and memory cells.
• Stating that phagocytes make antibodies. Phagocytes engulf microbes; lymphocytes produce antibodies and antitoxins.
• Saying the body becomes immune to antibiotics. It is the bacteria that become resistant, through mutation and natural selection.

Try three 2.8 Disease, Defence and Treatment exam-style questions