Describe how a phagocyte destroys a pathogen.

It changes shape to surround and engulf the pathogen into a vacuole, then enzymes are released to digest it.

Give two ways a phagocyte is adapted to its function.

It has a flexible membrane that lets it change shape to engulf pathogens and squeeze out of capillaries, and it contains many digestive enzymes.

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

Its shape is complementary to one particular antigen only, so it cannot bind to the antigens of any other pathogen.

Small fragments of cells in the blood, with no nucleus, that clump together at a wound to help form a clot.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition, mutualism and parasitism

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination and characteristics controlled by many genes Variation within a population, and classification Natural selection and evolution Evidence for evolution from fossils and antibiotic resistance

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples White blood cells, antibodies and platelets Non-specific defences and the immune system Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc Hormones and the endocrine glands Hormones in reproduction and the menstrual cycle Methods of contraception Homeostasis and control systems in the body Insulin and the control of blood glucose Type 1 and type 2 diabetes

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Global Challenges

White blood cells, antibodies and platelets

3 things to know
Paper 2 (Biology)

Overview

How a phagocyte engulfs and digests a pathogen and is adapted to do so, antibodies made by lymphocytes and why each fits only one pathogen, antitoxins, what platelets are, how blood clotting keeps pathogens out, and why too few platelets raise the risk of infection.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is an antibody, and which cell produces it?

Key term

What are antitoxins and what do they do?

Key term

What are platelets?

Questions from this subtopic

Each one with the model answer underneath.

1
Describe how a phagocyte destroys a pathogen.
Model answer
It changes shape to surround and engulf the pathogen into a vacuole, then enzymes are released to digest it.
2
Give two ways a phagocyte is adapted to its function.
Model answer
It has a flexible membrane that lets it change shape to engulf pathogens and squeeze out of capillaries, and it contains many digestive enzymes.
3
What is an antibody, and which cell produces it?
Model answer
A protein that binds to a specific antigen on a pathogen; it is produced by a lymphocyte.
4
Explain why one type of antibody works against only one type of pathogen.
Model answer
Its shape is complementary to one particular antigen only, so it cannot bind to the antigens of any other pathogen.
5
What are antitoxins and what do they do?
Model answer
Proteins produced by lymphocytes that bind to the toxins released by bacteria and neutralise them so they cannot damage cells.
6
What are platelets?
Model answer
Small fragments of cells in the blood, with no nucleus, that clump together at a wound to help form a clot.

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Cell Level Systems

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Genes, Inheritance and Selection

Global Challenges

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Algae and .

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AA diet high in sugar and fat leads to obesity.

BBody cells then respond poorly to insulin.

CBlood glucose concentration cannot be controlled.

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Homozygous means carrying two identical alleles of a gene.

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