Red blood cells (RBCs)
- ICSE Class 10, Unit 3 Human Anatomy and Physiology
Red blood cells are the blood cells that carry oxygen from the lungs to every part of the body, using a red pigment called haemoglobin.
Red blood cells are also called RBCs or erythrocytes. They are the most common cells in blood. Each one is a small disc, thin in the middle and thicker at the rim. This shape gives it a large surface for taking in oxygen.
A human red blood cell has no nucleus and no mitochondria. That sounds like a weakness, but it helps the cell do its job.
- No nucleus: there is more room for haemoglobin, so each cell can carry more oxygen.
- No mitochondria: the cell does not use up the oxygen it carries. All of it reaches the tissues.
A small example
When you climb stairs, your leg muscles need more oxygen. Your red blood cells pick it up in the lungs and drop it off in the muscles. None is spent on the cells' own needs on the way.
Where marks go
Question 8(iv) of the 2024 ICSE Biology paper asked why RBCs work well without a nucleus and mitochondria, for 2 marks. The marking scheme in CISCE's 2024 Biology report gives one reason for each missing part. So an answer about the nucleus alone leaves out half of what the marking scheme sets out. The report lists this question among the topics candidates found difficult.
The 2027 specimen paper also asks for a labelled drawing of a blood smear. Practise showing red cells without a nucleus, next to the white blood cells, which have one.
Sources
Facts last checked against these sources on 30 September 2026.
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