The human body is made up of millions of tiny cells that can only be seen under a microscope. They vary in size and shape and have different functions, but every cell in the body has three features in common:
* The cell membrane, which is the outer covering of the cell
* The nucleus, which controls the cell’s activities.
* Cytoplasm, a fluid-like material.
One of the substances in the nucleus is DNA. This is the material that provides all t6he information about your genetic make-up that you have inherited from your parents and grandparents. This will determine things like the colour of your eyes and hair and will influence how tall you will be.
As an embryo grows inside the uterus, its new cells will develop differently depending on what part of the body they will become and what functions they will perform. For example, some will become muscle cells and others will become nerve cells. This means that they will look and act differently. It doesn’t matter what function each cell has, they all need oxygen and food in the form of glucose so that they can release the energy they need.
Cells group together to form tissues. A tissue is a group of cells of the same structure that perform the same function. An example of this is skin tissue, which is made up of lots of skin cells. They all work together to provide a waterproof protective covering for all the internal organs of the body. Another example is a heart muscle, which is strong enough to beat for a whole lifetime.
Organs are made up of different tissues that work together to carry out a particular function. An example is the heart, which is made up of different types of tissue. The heart muscle pumps blood around the body, but it has its own system of blood vessels too: arteries to deliver oxygen and nutrients to the muscle, and veins to remove carbon dioxide from it. There may be several different organs in one whole body system.
A system is made up of...