The human body is a complex system made up of many different types of cells. Cells are the smallest units and the basic building blocks of the body's structures. A baby is born with all the cells needed to develop into a full-grown adult. Even though they are present in a child's body, some cells may not become fully mature until certain stages in the child's development (for example, puberty). The human body is made up of trillions of cells. Each cell has its own structure and specific function. Cells of the same type are grouped together to form tissues (such as the lining of the intestine or the surface of the skin). Several types of tissue together form an organ (such as the lungs, liver, bladder, heart and bones). A single organ can contain billions of cells. Even though these cells may not be identical, they work together to perform a specific function.
Examples of different types of cells are:
Human cells vary in size, but they are all very small and can only be seen with a microscope. All cells have the same basic structure. Cells have a membrane that holds the contents together and regulates what goes in and out of a cell. The inside of a cell contains many small parts called organelles (including the nucleus and mitochondria) and fluid that surrounds the organelles.
The nucleus is the organelle that controls the function of the cell. It contains 46 chromosomes (23 different pairs), which are rod-like structures made up of DNADNAThe molecules inside the cell that program genetic information. DNA determines the structure, function and behaviour of a cell. and protein. Each DNA molecule is made up of many genesgenesThe basic biological unit of heredity passed from parents to a child. Genes are pieces of DNA and determine a particular characteristic of an individual. (the basic unit of heredity), which instruct the cell to work, grow, divide and die.
The cytoplasm is the term for inner part of a cell. It contains the:
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Communication between organ systems allows the body to adjust the function of each organ to meet the needs of the whole body. Through this communication, the body keeps itself in balance. Communication occurs mainly through the nervous system or hormones, or directly between cells.