Cellular structure of the human body
The human body, like animals and plants, is built of cells, but cells differ in shape and function: a nerve cell has long extensions, a muscle cell is elongated, and a red blood cell is a disc that is concave on both sides. A membrane surrounds the cell and lets substances pass selectively. Inside is dense cytoplasm, and in the centre is the nucleus, which controls the cell and keeps hereditary information. Organelles: ribosomes make proteins, the endoplasmic reticulum transports substances, the Golgi complex collects and distributes them, lysosomes break down nutrients, and mitochondria produce energy. Human body cells have 46 chromosomes (23 pairs) and sex cells have 23. The most abundant substance in a cell is water (water also makes up about 60–70% of whole body mass), along with salts, proteins, fats, carbohydrates and nucleic acids.
Model a cell from plasticine: give each organelle its own colour and a label. Safety: use materials neatly and keep small pieces away from the mouth.