# Oxygen transport

Haemoglobin in red blood cells binds oxygen in the lungs, where oxygen is plentiful, and releases it in tissues, where oxygen is low. Each haemoglobin carries up to four oxygen molecules. More acidic, warmer tissues make it release oxygen more readily.

Biology (university) · Part 09: Animal physiology · Card 6 of 9 · Last updated 2026-10-19

## Analogy

A delivery lorry that loads up at the warehouse and unloads where the demand is.

## In practice

Working muscle makes carbon dioxide and heat, so it receives extra oxygen from haemoglobin.

## Practice

### Flashcards

- **Why does haemoglobin release oxygen in muscle?** Low oxygen, more carbon dioxide, more acidity and more heat make it let go.

## Questions people ask

### What is carbon monoxide poisoning?

Carbon monoxide binds to haemoglobin about 200 times more strongly than oxygen does. Less oxygen is carried, and the oxygen that is bound is released less easily. The result is oxygen starvation in tissues, causing headache, confusion and death. It is dangerous because the gas has no smell or colour.

### Why is foetal haemoglobin different?

A foetus gets oxygen from its mother's blood across the placenta. Foetal haemoglobin binds oxygen more tightly than adult haemoglobin, so it can take oxygen from the mother's blood and pass it on to the baby's tissues. After birth, the body switches to making the adult type.

## Related concepts

- [Double circulation](https://studyvisually.com/learn/science/biology-university/biology-university-part-9/biology-university-part-9-concept-5)

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