CIE A Level Biology (9700) 2019-2021

Revision Notes

8.1.4 Cells of the Blood

Cells of the Blood

  • Blood is a tissue composed of a number of important specialised cells
  • Red blood cells, monocytes, neutrophils and lymphocytes all have distinguishable structures which enable them to be recognised on microscope slides, in photomicrographs and in electron micrographs

Red blood cells

  • There are approximately 5 million red blood cells per mm3 of blood
  • Red blood cells contain haemoglobin, a protein with a quaternary structure that contains haem iron groups which can bind reversibly to oxygen
  • Distinctive features of erythrocytes when viewed under a microscope, are their distinctive biconcave disc shape (caused by their lack of nucleus)

Monocytes

  • Monocytes are identifiable by their size – they are the largest of the leukocytes and have a nucleus shaped like a kidney or a bean
  • The nucleus of monocytes tends to appear lighter after staining than other leukocytes
    The nucleus should appear a light blue colour, while the chromatin inside is distinct and fine

Neutrophils

  • Neutrophils are distinguished by their multi-lobed nuclei
  • Up to 70% of all leukocytes are neutrophils – this makes them easy to spot on a micrograph
  • The granules of neutrophils typically stain pink or purple-blue

Lymphocytes

  • Lymphocytes are small leukocytes that are identifiable by their very large nuclei, which typically stains a dark colour
  • Lymphocytes constitute around 20-25% of all leukocytes
  • Lymphocytes are around the size of red blood cells

Exam Tip

When looking at micrographs, ensure you distinguish between the kidney-shaped nucleus of a monocyte and the multi-lobed nucleus of a neutrophil, as these can appear similar at first. As with all things, practice is key here!

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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