Building Blocks of the Body

The building blocks of the body are cells. Cells are found in both plant and animal body. The body contains trillions of cells. Each cell has a job to perform, and all cells must work together to keep the organism alive and well. Most cells are too small to be seen with unaided eye. The largest human body cell is an ovum, female sex cell, with a diameter of about 0.008 inches (0.02 cm). The smallest cells in the body are found in the brain, with a diameter of about 0.0002 inches (0.0005 cm).
Our eyes are aided with an instrument known as the microscope to see the cells. The diagram below shows a microscope
The microscope shows three major parts of the cell, as follows, even though there are many more
A cell membrane keeps all parts of the cell together and controls the movement of materials in and out of the cell.
A cytoplasm is a jelly-like fluid in which all the cell contents are suspended. Most of the chemical work of the cell takes place in here.
A nucleus is a governing body of the cell.
The following is the model which demonstrates a cell. It is made of 100 ml resealable plastic bag which represents the cell membrane as it is transparent and not rigid, uncooked egg-white which stands for the cytoplasm as it is jelly-like, and a small grape suspended in the egg-white to stand for the nucleus.
Most of the cells in your body change the shape when pressure is applied to them, but bone cells are more rigid and keep their shape. The model shown above can also take the shape of the container as shown below

Cells in our bodies live for different amounts of time. Bone cells can last for many years, while cells lining the intestine live for only few days.
Cells die in our bodies every second but new cells are constantly being made to replace them. New cells are made when a cell divides into two identical new cells. The steps showing how cells reproduce to make new cells are in the following pictures;
One cell
The cell starts to divide

The cell membrane starts to divide

Two identical cells

The above process also explains why our bodies grow in size