White blood cell diagram

A white blood cell diagram shows the cells of the blood that defend the body against pathogens. Unlike red blood cells, white blood cells (leukocytes) have a nucleus, and its shape is the easiest way to tell the types apart. For GCSE you mainly need two: phagocytes, which engulf pathogens, and lymphocytes, which make antibodies and antitoxins.

White blood cells compared with a red blood cell

These cells are drawn to the same scale, using typical sizes from OpenStax Anatomy and Physiology. A red blood cell has no nucleus and is thin in the middle, which the dashed circle shows. Every white blood cell has a nucleus, and all are larger than a red blood cell.

The types of white blood cells

There are five types. Three have many granules in their cytoplasm (granulocytes) and two have few (agranulocytes):

Blood normally holds only about 5,000 to 10,000 white blood cells per microlitre, far fewer than red blood cells. White blood cells can squeeze out between the cells of a blood vessel wall to reach infected tissue.

Phagocytes and lymphocytes at GCSE

GCSE diagrams usually show just two kinds. A phagocyte is any white blood cell that engulfs pathogens: neutrophils and macrophages (from monocytes) are phagocytes, and the GCSE drawing usually has a lobed nucleus. A lymphocyte is drawn as a round cell almost filled by a large, round nucleus.

How white blood cells defend the body

AQA GCSE Biology says white blood cells help to defend against pathogens in three ways:

1. Phagocytosis. A phagocyte surrounds a pathogen, engulfs it into a vacuole, and digests it with enzymes. At A-level, these are enzymes from lysosomes.
2. Antibody production. Lymphocytes make antibodies, proteins that fit the antigens on one particular pathogen. Antibodies clump pathogens together and mark them for phagocytes. See the antibody structure guide.
3. Antitoxin production. Lymphocytes also make antitoxins, which neutralise the toxins that bacteria release.

After an infection, some lymphocytes stay in the blood as memory cells. That is how vaccination works: a dead or inactive form of a pathogen stimulates white blood cells to make antibodies, so if the real pathogen arrives later they respond quickly, preventing infection.

The parts of blood and their jobs

Blood is a tissue: a liquid, plasma, carrying red cells, white cells and platelets. GCSE asks for the job of each part:

Match each part of blood to its job in this question from the Human Physiology course.

Worked examples

Example 1: the real size of a cell

In a drawing made at × 3,000 magnification, a neutrophil is 33 mm across. What is its real diameter?

1. Convert the image size to micrometres: 33 mm = 33,000 μm.
2. Real size = image size ÷ magnification = 33,000 ÷ 3,000 = 11 μm.
3. That fits the 10 to 12 μm range for neutrophils. The magnification calculator handles the units for you.

Example 2: counting neutrophils

A blood sample has 7,000 white blood cells per microlitre, and 60% of them are neutrophils. How many neutrophils are there per microlitre?

• 7,000 × 0.60 = 4,200 neutrophils per microlitre, inside the normal 50 to 70% share.

How to draw white blood cells in the exam

1. Use a sharp pencil and clear, unbroken lines, with no shading.
2. Draw the nucleus the right shape: lobed for a neutrophil, large and round for a lymphocyte.
3. Keep sizes in proportion: white blood cells are larger than red blood cells.
4. Label with ruled lines that touch the part, and add the magnification or a scale bar if asked.

Common mistakes

• Saying white blood cells eat pathogens. Phagocytes engulf and digest them; use "engulf" and "digest".
• Saying all white blood cells make antibodies. Only lymphocytes do; phagocytes engulf.
• Mixing up antibodies and antitoxins. Antibodies target the pathogen's antigens; antitoxins neutralise its toxins.
• Drawing a nucleus in a red blood cell. Mature red blood cells have no nucleus.
• Calling platelets cells. They are fragments of a larger cell.

Practise with a short timed paper

Blood and the immune system are in AQA GCSE Biology and Combined Science. The daily GCSE Biology Higher and GCSE Combined Science Higher papers are short timed papers of 8 questions, with a new one every day.

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