What causes disease, how does the body defend itself, and how are new medicines developed?
Communicable and non-communicable diseases, types of pathogen and how they spread, the body's defences and the immune system, vaccination, antibiotics and the development and testing of new drugs.
A focused answer to the OCR Gateway GCSE Combined Science A topic B6 on health and disease, covering communicable and non-communicable disease, pathogens and their spread, the body's defences and immune system, vaccination, antibiotics, and the testing of new drugs.
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What this topic is asking
OCR wants you to distinguish communicable and non-communicable diseases, describe types of pathogen and how they spread, explain the body's defences and the immune system, explain vaccination and antibiotics, and describe how new drugs are developed and tested.
Types of disease and pathogens
There are four main types of pathogen: bacteria (which can release toxins that make us feel ill, for example causing food poisoning), viruses (which reproduce inside cells and damage them, for example causing measles or flu), fungi (such as the cause of athlete's foot), and protists (single-celled organisms, for example the malaria parasite, often spread by a vector such as a mosquito). Pathogens spread by direct contact, in contaminated water or food, in the air (droplets when we cough or sneeze), and by vectors such as insects. Knowing how a disease spreads tells you how to reduce its transmission, for example by hygiene, clean water, isolation, or controlling the vector.
The body's defences and immune system
The body has non-specific defences that try to stop pathogens entering: the skin is a physical barrier, the nose traps particles in hairs and mucus, the trachea and bronchi produce mucus that traps pathogens and cilia that waft it away, and the stomach produces hydrochloric acid that kills many pathogens in food. If a pathogen gets in, the immune system responds, mainly through white blood cells. Some white blood cells engulf and digest pathogens (phagocytosis). Others (lymphocytes) produce antibodies that lock onto the specific antigens on a pathogen, and antitoxins that neutralise toxins.
Antibiotics and developing new drugs
Antibiotics (such as penicillin) kill bacteria inside the body and have greatly reduced deaths from bacterial disease, but they do not kill viruses, because viruses live inside the body's own cells. Overusing or misusing antibiotics has led to antibiotic-resistant bacteria (such as MRSA) through natural selection, so doctors now prescribe them carefully. New drugs are developed and tested in stages: first preclinical testing in the laboratory on cells, tissues and sometimes animals to check for toxicity and whether the drug works; then clinical trials on healthy volunteers (to test safety and find side effects, starting with very low doses) and on patients (to find the optimum dose and check effectiveness). Trials often use a placebo and are double blind, so neither the patient nor the doctor knows who has the real drug, which keeps the results unbiased.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20186 marksExplain how vaccination protects a person from a disease, and how widespread vaccination can protect a whole population.Show worked answer →
A Biology Paper 2 six-mark extended response, marked on levels. Reward: a vaccine contains a dead or inactive (weakened) form of a pathogen, or its antigens. When injected, the antigens are recognised by white blood cells (lymphocytes), which respond by producing the correct antibodies; importantly, memory cells are also made. If the person later meets the live pathogen, the memory cells let the body produce the right antibodies quickly and in large numbers, destroying the pathogen before the person becomes ill (immunity). For a population, if a large enough proportion are vaccinated, the pathogen cannot spread easily because there are few susceptible people, so even unvaccinated individuals are protected; this is herd immunity. Top answers name antigens, antibodies and memory cells, and explain the faster secondary response and herd immunity.
OCR 20214 marksDescribe the stages a new drug must pass through before it can be prescribed, and explain why each main stage is needed.Show worked answer →
A B6 structured question on drug development. Reward: new drugs are first tested in the laboratory (preclinical testing) on cells, tissues and sometimes animals, to check the drug works and is not obviously toxic. Then they are tested in clinical trials on healthy volunteers (to test for safety and side effects) starting at very low doses, and on patients with the illness (to find the optimum dose and check it is effective). Trials often use a placebo and are double blind (neither the patient nor the doctor knows who has the real drug) so the results are not biased. Markers credit the order (lab then clinical), the reason for each stage (safety, then efficacy and dose), and the idea of placebo or double-blind testing.
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