Coursework on the heart rate of the daphnia
My aim is to investigate the heart rate of the daphnia whilst the temperature of the surrounding environment is the variable to be changed. This variable will increase or decrease the heart rate. I will need to do some research and preliminary work before I choose my temperature and the way I carry out the process efficiently and effectively.
Prediction
I predict during the investigation the heart rate of the daphnia will increase as the surrounding temperature increases and vice-versa. But at a certain point the daphnia will stop responding if the temperature decrease or increases too much.
I also predict that if the temperature doubles so should the heart rate of the daphnia. For example if at 10oC the heart rate is 50 then at 20oC the heart rate should be 100.
Scientific Knowledge
The daphnia adapts to its surroundings because it is a cold blooded animal and the daphnia doesn’t thermo regulate, meaning that there body temperature is the same as the water they are existing in. The daphnia’ internal body reactions increase as the temperature increases; this causes the heart to beat faster at higher temperatures. The heart rate increases because as the internal operations of a daphnia speed up the parts of the daphnia require oxygen. So, the heart beats quicker to provide oxygen to the cells as the metabolism increases. Also the heart beats slower when the temperature decreases because the chemical reactions have slowed down which decreases the amount of oxygen required. Heart rate, along with most metabolisms in a living organism, is controlled by the action of enzymes. The hearts pacemaker, (sino-atrial node (SAN), also controls the Daphnia's heart rate. The pacemaker sends out an electrical signal across the heart that makes it contract. Hormones and transmitters control the rate set by the pacemaker. The hormones communicate with the pacemaker in the membrane. The transmitter substance and hormone fit onto a protein molecule of the cell membrane, this causes the pacemaker to react. The theory is very similar to that of enzymes, more heat produces more kinetic energy and thus the hormones move more rapidly, this increases the chance that it will collide with the protein molecule on the cell membrane. Temperature, pH, enzyme concentration, substrate concentration and inhibitors affect enzymes. For a non-enzymic controlled reaction, the general rule is the higher the temperature, the faster the reaction. The same rule is true for a reaction catalysed by an enzyme, but only up to about 35˚C. the heart rate is at its fastest as this is when the enzymes are working at their fastest due to the large amount of kinetic energy the substrates have. Above 30˚C, the enzyme molecules begin to vibrate so violently that the delicate bonds that maintain tertiary and quaternary structure are broken, irreversibly changing the shape of the molecule. When this happens, the active site shape has changed and therefore an enzyme-substrate complex is no longer possible. This means that the enzymes and other protein structures controlling heart rate can no longer work. We then say it is denatured. Although not all of the enzymes are denatured right after 30˚C, enough will have been denatured to slow down to process sufficiently to stop almost all metabolisms.
