An antigen is a molecule on the surface of a pathogen that the immune system recognises as foreign.

Explain what happens when a lymphocyte meets a pathogen carrying an antigen it recognises.

The lymphocyte is activated and divides many times to make cells that produce antibodies against that antigen.

Explain why one type of antibody works against only one pathogen.

The antibody has a shape complementary to one particular antigen, so it cannot bind to any other.

Describe how antibodies help to destroy pathogens.

They bind to the antigens and stick the pathogens together, so white blood cells can engulf and digest them.

What are memory lymphocytes?

Memory lymphocytes are long-lived cells made during an infection that stay in the blood ready to recognise the same antigen again.

Edexcel GCSE Biology 1BI0

Key Concepts in Biology

Topic overview Eukaryotic and prokaryotic cells Specialised cells and their adaptations Microscopes and magnification calculations Size, scale and units in cell biology Enzyme action and denaturation Factors affecting enzyme activity Enzymes in synthesis and digestion, and rate calculations Food tests and the energy in food Diffusion, osmosis and active transport Osmosis in potatoes and percentage change in mass

Cells and Control

Topic overview Mitosis and the cell cycle Why mitosis matters: growth, repair and cancer Growth, differentiation and percentile charts Stem cells and their use in medicine The structure and function of the brain Neurones, receptors and the reflex arc The structure and function of the eye Eye defects and how they are corrected

Genetics

Topic overview Asexual and sexual reproduction Meiosis and the formation of gametes DNA structure, genes and the genome Extracting DNA from fruit Mendel's work and the inheritance of blood groups Alleles, genotype and phenotype Monohybrid crosses and sex determination Probability and ratios from genetic crosses Causes of variation: genes and environment The Human Genome Project Genetic variation and the effects of mutation

Natural Selection and Genetic Modification

Topic overview Darwin, Wallace and the theory of evolution Natural selection and antibiotic resistance Fossil evidence for human evolution Stone tool evidence for human evolution The pentadactyl limb and the three domains Selective breeding Tissue culture Genetic engineering and modern agriculture Benefits and risks of GM organisms

Health, Disease and the Development of Medicines

Topic overview Health, disease and susceptibility Pathogens and common infections How pathogens spread, and the virus life cycle Sexually transmitted infections How plants defend themselves Physical barriers and chemical defences The immune system, immunisation and herd immunity Antibiotics and developing new medicines Aseptic technique in culturing microorganisms Testing antiseptics and antibiotics on bacterial cultures Lifestyle factors and non-communicable disease Treatments for cardiovascular disease

Plant Structures and Their Functions

Topic overview Photosynthesis as an endothermic reaction Limiting factors in photosynthesis Light intensity and the rate of photosynthesis Root hair cells, xylem and phloem Transpiration and translocation Leaf structure for photosynthesis and gas exchange Factors affecting the rate of transpiration Plant adaptations to extreme environments Plant hormones, phototropism and gravitropism

Animal Coordination, Control and Homeostasis

Topic overview Hormones, endocrine glands and homeostasis The menstrual cycle and its hormones Hormonal and barrier contraception Homeostasis and thermoregulation Controlling blood glucose, and type 1 diabetes Type 2 diabetes and body mass The urinary system and the production of urea The nephron, filtration and selective reabsorption Treating kidney failure: dialysis and transplants

Exchange and Transport in Animals

Topic overview Why multicellular organisms need exchange surfaces Alveoli and gas exchange Rate of diffusion and Fick's law The blood and its components Arteries, veins and capillaries The heart and the circulatory system Cellular respiration as an exothermic reaction Aerobic and anaerobic respiration compared Investigating the rate of respiration Cardiac output, stroke volume and heart rate

Ecosystems and Material Cycles

Topic overview Levels of organisation and interdependence Abiotic and biotic factors in a community Parasitism and mutualism Sampling with quadrats and transects Estimating population size from field data Energy transfer between trophic levels Human impact on ecosystems and biodiversity Food security The carbon cycle The water and nitrogen cycles Factors affecting the rate of decomposition Calculating the rate of decay

Health, Disease and the Development of Medicines

The immune system, immunisation and herd immunity

3 things to know
Paper 1

Overview

Antigens, lymphocytes and why each antibody works against only one pathogen, memory lymphocytes and the primary and secondary responses, vaccines, boosters and yearly influenza vaccines, herd immunity, and the advantages, disadvantages and savings of immunisation programmes.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain how vaccination protects against a later infection, why boosters are given, and why the protection is specific.

Key term

What is an antigen?

Key term

Which cells produce antibodies?

Questions from this subtopic

Each one with the model answer underneath.

1
What is an antigen?
Model answer
An antigen is a molecule on the surface of a pathogen that the immune system recognises as foreign.
2
Which cells produce antibodies?
Model answer
Lymphocytes, which are a type of white blood cell.
3
Explain what happens when a lymphocyte meets a pathogen carrying an antigen it recognises.
Model answer
The lymphocyte is activated and divides many times to make cells that produce antibodies against that antigen.
4
Explain why one type of antibody works against only one pathogen.
Model answer
The antibody has a shape complementary to one particular antigen, so it cannot bind to any other.
5
Describe how antibodies help to destroy pathogens.
Model answer
They bind to the antigens and stick the pathogens together, so white blood cells can engulf and digest them.
6
What are memory lymphocytes?
Model answer
Memory lymphocytes are long-lived cells made during an infection that stay in the blood ready to recognise the same antigen again.

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Key Concepts in Biology

Cells and Control

Genetics

Natural Selection and Genetic Modification

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ANitrates cause an algal bloom that blocks the light.

BWater plants die and decay.

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