4.3 Infection & response

Unit Summary

This unit is aligned with the AQA GCSE Biology specification and is designed for flexible delivery within a coherent, knowledge-rich curriculum. It builds progressively on prior learning about cells, transport processes and organisation, while continuing to develop students’ scientific enquiry skills established in earlier units and key stages.

The unit integrates both substantive knowledge (core biological concepts) and disciplinary knowledge (working scientifically), enabling students to understand not only how infectious diseases affect organisms, but how scientific knowledge about infection has been developed, tested and applied in real-world contexts.

At the heart of this unit is the understanding that pathogens are microorganisms, including bacteria, viruses and fungi, that cause infectious disease in animals and plants. Students examine how pathogens invade hosts, access nutrients, reproduce rapidly and, in many cases, produce toxins that damage tissues and disrupt normal physiological processes.

Vaccination is studied as a deliberate enhancement of the body’s natural immune system. Students analyse how vaccines stimulate an immune response without causing disease and evaluate their role in preventing epidemics and protecting vulnerable populations.

The unit also examines the development and use of antibiotics since the 1940s, focusing on their effectiveness against bacterial infections and the growing global threat of antibiotic resistance. Students explore how resistant strains arise through variation and selection, and why the development of new antibiotics is both scientifically challenging and medically urgent.

Students extend their understanding of immunity by studying monoclonal antibodies. They learn how these laboratory-produced antibodies are generated from a single clone of cells and are designed to bind to one specific antigen. Applications in diagnostics, pregnancy testing and targeted medical treatments are explored, allowing students to connect immune system knowledge to biotechnology and modern medicine.

Practical microbiology is embedded within the unit through the study of culturing microorganisms. Students learn aseptic techniques, safe handling procedures and how to prepare uncontaminated cultures using nutrient media. They analyse patterns of microbial growth and investigate factors that influence growth, strengthening their practical skills and understanding of laboratory safety.

The unit also broadens to include plant diseases and plant defence responses. Students examine how plants can be infected by viruses, bacteria and fungi, how diseases spread in crops, and the economic and ecological consequences of plant infection. Plant defence mechanisms such as structural barriers, chemical defences and responses to pathogen attack are explored, alongside methods of disease control including resistant crop varieties and the use of chemicals or biological control agents.

Working scientifically is embedded throughout the unit. Students interpret data on infection rates, analyse graphs showing the spread of disease, evaluate the reliability of vaccine trials, design investigations into antimicrobial substances, and consider evidence for the effectiveness of hygiene measures. Opportunities for structured discussion and critical evaluation support deeper reasoning about public health decisions and medical treatments.

Beyond the specification, this unit highlights the societal and global importance of infection biology. Students gain insight into careers in medicine, microbiology, epidemiology, biotechnology, agriculture and pharmaceutical research, and understand how scientific research underpins public health policy and food security.

By connecting biological mechanisms to real-world challenges such as pandemics, antibiotic resistance and crop disease, this unit develops students not only as knowledgeable GCSE biologists, but as scientifically literate individuals able to engage thoughtfully with modern health and environmental issues.