In this investigation I am going to see how alcohol affects the heart. Due to the ethical and safety issues involved in using in an investigation such as this I am going to use Daphnia (water flea) to conduct this experiment. Although humans and Daphnia are very different organisms, the affect that alcohol has upon the heart should be similar.
The hypothesis I am going to test during the investigation is:
‘Increasing the percentage of concentration of alcohol (a depressant) solution, into which a Daphnia is immersed, will significantly cause its heart rate to decrease.’
One of the most common crustaceans to be found in lakes, ponds and quiet streams is the 'water flea', Daphnia. These tiny animals are usually less than 3mm in size, so you could put dozens of them on a single fingernail. They're not really fleas – in fact they're not insects at all, but rather crustaceans, more closely related to crabs and shrimp. Water fleas are extremely important in the food chains of ponds and lakes - they harvest the tiny algae cells that convert sun energy into food, and then they pass this energy along to other animals such as fish or other predators.
Below is a diagram that shows the anatomy of the daphnia and where everything is in its body:
 - Second antenna, used for swimming and sensing the environment.  - Eye controlled by muscles with nerve connections to the brain.  - Legs used for collecting food and stabilizing the animal as it slowly sinks.  - An intestine where ground up food particles are digested.  - A brood pouch for incubating young that hatch from large yolk filled eggs.  - A protective outer shell.
 - A heart that pushes clear circulatory fluid around the body.  - Undigested material is eliminated out the anus.
Alcohol is a depressant, which is classed as a drug or chemical, that decreases the activity of any bodily function. The term is most often used to refer to drugs that reduce the activity of the central nervous system. These agents cause sedation or a sleep like state at low doses and reduce general anxiety. Although this information is of particular relevance to humans, it is also true of daphnia. The daphnia, or water flea, is less than 3mm (0.1 in) in length. It is globular in shape and reddish in colour, and is encased in a transparent, bivalve shell, or carapace. The head bears feathery, branched antennae that are used for swimming. They are used, in a dried form, as fish food, and are often seen as a cloud of specks in pond or aquarium. They are very distant relatives of aquatic animals like crabs and shrimps. The transparent carapace makes it possible to watch the internal organs at work, particularly the heart, which is usually red as it is full of oxygen rich blood. There are about twenty-five British species in the family Daphniidae, with the largest being Daphnia Magna. A daphnia spends much of its time bobbing up and down in the water, with its head uppermost. It tends to sink down a short way before propelling itself back towards the surface of the water with a stroke of its powerful antennae. Like many other creatures living in the upper waters of seas and lakes, the daphnia also migrates up and down every day to different depths. At dusk, the daphnia moves upwards, but during the night the whole population may gradually sink, only to rise again at dawn. As the day persists, the daphnia may gradually sink again. The daphnia feeds on bacteria and single-celled algae that float on the surface of the water. It must also filter large amounts of water to strain these particles, and it does this by rhythmically beating its legs, pumping water through the space under its carapace, and using the bristles on its legs as strainers. Because algae are the daphnia’s main food source, it is clearly and advantage...