Unit 6 learning aim A: Undertake a literature search and review to produce an investigative project proposal
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Course
Unit 6 - Investigative Project
Institution
PEARSON (PEARSON)
A.D1 Evaluate the different methods of investigation considered for the investigative project proposal, justifying the hypothesis chosen.
A.M1 Analyse a literature search and discuss its relevance to inform the investigative project proposal.
A.M2 Produce a project proposal for a scientific i...
Unit 6A: Scientific investigation
Effects 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 (Medline Plus (2017). 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, respiratory rate,
and heart rate (Petre, A. (2020). 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. Humans aren’t used in this
experiment as to see the effects the human should be conscious, and his heart should be
visible (although it could be done by listening to the heart rate using a stethoscope, but no
volunteers can be found and to do experiments on humans the time needed to be covered
both legally and safety is long. 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 (Ebert, D. (2005). 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 living 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 table, I will record the heartbeat of the daphnia.
Background research
Daphnia have an open blood circulation. The heart is located anterior and dorsally
from the brood chamber. Daphnia’s heart rate isn’t only affected by caffeine it is also
affected by alcohol. Both are stimulants but they have an opposite effect on
daphnias’ heart rate. While caffeine speeds up the heart rate alcohol slows down the
heart rate. Another effect that alcohol has is that it also slows down the movement
speed of the daphnia, but caffeine doesn’t affect their movement (Bianca Kurien Uni.
Oklahoma 2018). Daphnia magmas are very simple organisms compared to mammals so it’s
easier to distinguish their body/system parts. Daphnia generally obtains oxygen for
respiration through diffusion because it does not have a complex respiratory system.
Oxygen and water are carried in and out through the outer carapace of the daphnia.
Daphnia do not have lungs or red blood cells, but they do contain haemoglobin. Under
stressful conditions, haemoglobin production in daphnia can increase. As mentioned before
caffeine increases the heart rate because it is a stimulant that changes the levels of a
neurotransmitter called epinephrine (adrenaline). (Süudhof, T. C. 2008).
Method
- Remove 1 Daphnia with a pipette and place it in a cavity slide under a
microscope. Dab around the Daphnia with a tissue to remove the pond
water and replace it with drops of caffeine solution (e.g., 0.1M).
- Leave the Daphnia for 5 minutes to acclimatise and then observe & count
(using a counter) the heart rate under the microscope for 30 seconds (multiply
the number by 2 to calculate beats per minute).
- Repeat this for measurements across 5 different caffeine concentrations (e.g.,
0.2M, 0.3M, 0.4M and 0.5M). Repeats can then be carried out with two other
Daphnia.
- While on the microscope, turn off the microscope light between observations
to prevent the daphnia from overheating.
Control variables
- Volume of solutions: the same amount of caffeine should be used
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