- Cells are the basic structure or unit of all living organisms.
- It is thought that we have around 100,000, 000, 000, 000 cells, give or take a few!
- They are too small to be seen with the naked eye, but if they are magnified under the microscope it is possible to see differences between cells. There are many different types of cells each with a particular function. Cells of the same type group together to form the tissue and organs that make up the body.
- Each cell is a bit like a little world of its own, storing information (in our genes as DNA) which tells it what to do, so that it ‘knows’ when to grow and divide, when to stop and when to ‘self-destruct’ if damaged. The information also tells it what type of cell it is, for example, a muscle cell, blood cell, brain cell and so on, and where it should live in the body.
- How long they live for depends on what type of cell they are. Some live for a short time (days) others for longer (years).
- The outside surface of cells differs depending on the type of cell it is. It is thought that this tells the cell where it should be in the body. They can only stick to one with the same ‘outside’ surface, so if they are in the wrong place then they will die.
how do cells reproduce?
We are all formed when a sperm from our father meets an egg from our mother. As we grow in our mother’s womb, the cells multiply and specialise to do a particular job or function. Once a cell has specialised, it then produces ‘daughter’ cells that are an exact copy of itself. Enough cells are produced to form the particular tissue, organ, blood, cell or other part of the body that is needed. More cells are reproduced only when they are required.
Cells make an exact copy of themselves by copying the information they contain (the genes) and then splitting into two. This is called ‘cell division’ and it happens in an orderly, controlled and very precise way. One cell divides into two and those then divide again to become 4 and then they become 8 and so on.
When we are growing, cell division happens very quickly as we need not only to replace old cells which are worn out, but also to produce new ones so that we grow! When we are fully grown, this division of cells doesn’t need to happen so much and something in the cells tells them not to divide so often. This means we only replace old cells or those that have been damaged by injury or disease. Some cells lose the ability to reproduce themselves, like the brain cells.
