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biology Unit 6 learning aim A
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Unit 6A: Scientific investigationEffects of caffeine on the heart rate of daphnia
Introduction
This project proposal will investigate the effects of caffeine on the
heart rate of daphnia. Caffeine is a compound that occurs naturally
and is soluble in both oil and water. It is generally extracted from
leaves beans and fruits of plants (mostly coffee beans, cocoa beans,
and tea leaves). Scientifically caffeine is classified as a recreational
drug even though its effects are milder than other recreational drugs
like cocaine amphetamines and heroin. So, it is used all around the
world to make different kinds of foods and drinks like tea, coffee,
and energy drinks. When daphnia is exposed to caffeine their heart
rate increases as with the concentration this is because caffeine can
block receptors on the surface of the heart muscle cells. Caffeine
which is known as 1,3,7-trimethyl xanthine in chemistry binds to the
receptors on the surface of the heart muscles and increases the level
of cAMP inside the cells, causing an increase in the heart rate. This
result in an overall increase in the rate of glycolysis and the amount
of ATP available for muscle relaxation and contraction. Caffeine also
inhibits a class of enzymes called cyclic nucleotide
phosphodiesterase. (Robertson, D., Frölich, 1978) Part of these
enzymes’ responsibility is to degrade a stimulatory signal produced
when excitatory neurotransmitters activate neurons in the CNS. So, if
caffeine inhibits them, the stimulatory signal remains active for a
longer time, resulting in a greater sense of alertness and higher
blood pressure, higher respiratory rate, and higher heart rate.
Caffeine also causes an increase in stimulatory neurotransmitters to
be released. Neurotransmitters are the key mediators of
communication between nerve cells. In my research, daphnia is used
to investigate how its heart responds to caffeine and its chemicals.
daphnia is a tiny crustacean that has a clear outside skeleton, they
, are very small with lengths between 0.2- 5 mm. They are one of the
several small aquatic organisms called water fleas because of their
jumpy swimming style.
They have hearts that are comparable to human hearts. Daphnia has
a myogenic heart meaning their heart rhythm is controlled or
generated by a specialized muscle in the heart rate. Daphnia also has
a transparent body which can easily allow us to see its heart with a
microscope while it is alive. There is no threat to daphnias’ existence
or reproduction as they reproduce asexually as clones. Their central
nervous systems are not as developed as humans/vertebrates
therefore they are not self-aware. The type of daphnia used is
daphnia magma. The rationale behind this research was that caffeine
is known to affect/alter the nervous system functions and if the level
of consumption is high enough caffeine is known to cause
restlessness, anxiety and insomnia which causes raised blood
pressure and stress. And to research this a live and unhurt subject is
needed. Therefore, daphnia is used in this research as we can see the
effects without making any other change to the surroundings or the
daphnia itself.
Aim
To investigate the effect of caffeine on the heart rate of daphnia
Hypothesis
The concentration of caffeine will affect the heart rate of daphnia
accordingly which means if the caffeine concentration increases the
heart rate of daphnia will increase same goes for the opposite.
Objective & technique
The objective is to test how caffeine and its chemicals affect the
heart rate of daphnia (magma). this is done by observing and
calculating the heart rate of daphnia under a microscope. Using a
beeper, I will record the heartbeat of the daphnia.
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