Science revision

Cloning occurs naturally in some plants and in human identical twins, and it is now possible to clone animals artificially. The subject of cloning raises a number of ethical issues that need to be considered.

The body’s first line of defence against harmful pathogens is the skin and stomach acid, the second is white blood cells. Vaccination involves exposing the body’s immune system to a weakened or harmless version of the pathogen in order to stimulate white blood cells to produce antibodies.

In the correct conditions (with warmth, moisture, nutrients) bacteria can multiply rapidly. The human body can provide these conditions for bacteria to multiply, for example in a cut. Each bacterium splits into two up to every 20 minutes.

Vaccination involves exposing the body’s immune system to a weakened or harmless version of the pathogen in order to stimulate white blood cells to produce antibodies. Antibiotics are used to treat bacterial infections. Bacteria can mutate and become resistant to antibiotics. This is one reason why new drugs are constantly being developed.

The atmosphere surrounding the Earth is a mixture of gases. In some places, human activities have added other gases to the atmosphere, which are called pollutants.

When there is a chemical reaction, air pollutants are produced. You can understand how these pollutants…