An investigation into how alcohol and caffeine affect the heart.

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In this investigation I am going to investigate how alcohol and caffeine affect the heart.  Because it is not easy to conduct experiments into the effect of these substances on humans, I will conduct experiments using a daphnia to find out what effect the substances have on the heart.  Although humans and daphnia are very different organisms, the effect that alcohol and caffeine have on the heart should be similar.

Hypothesis and Background information

Hypothesis

The hypothesis that I am going to test during this investigation is:

Increasing the concentration of caffeine (a stimulant) solution in which a daphnia is immersed will cause its heart rate to increase, whilst increasing the concentration of alcohol (a depressant) solution in which it is immersed will cause its heart rate to decrease.

Background information

In this investigation I am going to investigate how alcohol and caffeine affect the heart.  Because it is not easy to conduct experiments into the effect of these substances on humans, I will conduct experiments using a  to find out what effect the substances have on the heart.  Although humans and daphnia are very different organisms, the effect that alcohol and caffeine have on the heart should be similar.
A stimulant, like caffeine, is a drug that excites the central nervous system, increases alertness and reduces drowsiness.  A depressant is 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 0.25 cm (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, using the bristles on its legs as strainers.  Because algae are the daphnia’s main food source, it is clearly and advantage for the daphnia to stay where the algae are most densely populated.  This is done by sight, but not by spotting the algae at a distance and heading for it.  If the daphnia stumbles across a group of algae, the light seen by the daphnia will be slightly red, as most of the blue light in sunlight is removed as it passes through the cloud of algae.  The slight redness of the light will cause the daphnia to remain in the location of the algae.  The daphnia is in turn eaten by other, larger organisms, making it an important link in the aquatic food chain.
The fact that the daphnia has a transparent body means that it is very easy to study the internal organs under the microscope.  This, and the fact that the daphnia reproduces very quickly, means that it is often used to study the effects of drugs on the heart.

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Key Variables, Predictions and Abstract,

Key Variables

In order to test out my hypothesis, I am going to look at how different concentrations of caffeine and alcohol affect the heart rate of a single daphnia.  In this experiment, the variable that changes is the concentration of the alcohol or caffeine.  All of the other variables- for example temperature- remain the same.  Also, I will try to use the same daphnia for all of the experiments, because different daphnia will have different natural heart rates, in the same way that humans do.  However, it may not be possible to use ...

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