Illustration of a cross-section of a human cell.
It shows a thin slice of tissue or a cell, revealing its internal structures such as the nucleus, cytoplasm and organelles.
The nucleus occupies the centre and contains DNA on 46 chromosomes in human cells. The cytoplasm surrounding it contains organelles such as mitochondria for energy production and ribosomes for protein synthesis. The plasma membrane envelops the whole and regulates exchanges with the environment.