Receptors permit communication between neighbouring nerve cells, e.g. between the pacemaker neurons and the follower neurons, the receptors attach to a chemical called a neurotransmitter. The receptors can accidentally bind onto the other molecules. This can cause an unsuitable change.
Ethanol: Ethanol is an alcohol and is a depressant; therefore when it attaches to a nerve receptor, rate of heartbeat is most likely to slow down.
Adrenaline: Adrenaline is a hormone produced in the adrenal glands and is a stimulant and is sometimes referred to as the “fight or flight” hormone. Therefore when it attaches to nerve receptors, rate of heartbeat is most likely to slow down.
Variables
Independent variable: Type of chemical, this will be varied to see how different chemicals/concentrations of chemicals effects rate of heartbeat
Dependent variable: Rate of heartbeat, this will depend on the chemical/concentration of chemical used
Controlled variables:
Temperature: The entire experiment will be carried out at room temperature and must be maintained, Daphnia are poikilothermic so changes in temperature of the environment will effects its rate of heartbeat. If the temperature of the surrounding environment is increased, the metabolic rate will also increase, this requires energy, which is supplied through respiration, which requires increase in pumping of blood around the body to supply cells with oxygen for respiration, therefore rate of heartbeat is affected by temperature.
Amount of Chemical: The amount of chemical must be maintained, different volumes of chemical will affect the rate of heartbeat, more will increase it.
Daphnia: The same daphnia should be used as the rate of heartbeat may vary from daphnia to daphnia.
Procedure
See sheet
Hypotheses
The rate of heartbeat will slow down if ethanol is added (reason in background information) and the higher the concentration the more the rate of heartbeat will slow down, More ethanol molecules in the same volume so more chance of it attaching to nerve receptors.
Adrenaline will speed up the heart rate (reason in background information)
Analysis
Table of results
Looking at the graphs and the table of results, it is clear that ethanol decreases the rate of heartbeat as predicted, decreases when ethanol is added and the higher the concentration used, the more it slow down.
Adrenaline, also as predicted speeds up the rate of heart beat, doubling it from the normal rate.
Using just water (as the control) the average heart beats per minute was 42, when 1% ethanol was added it was proved that it did have an effect as the average rate of heart beat was slowed down to 19 beats per minute, when 10% ethanol was it added, the average rate of heartbeat was slowed down to 11 beats per minute proving increasing the concentration does decrease rate of heart beat. When adrenaline was added the rate of heartbeat was increased to 90 beats per minute, proving that adrenaline is a stimulant and increases rate of heartbeat.