CP1 write up - Investigate the effect of caffeine on heart rate in Daphnia
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Course
Core Practicals
Institution
PEARSON (PEARSON)
Edexcel A Biology A level core practical Write ups. All include an introduction, hypothesis, variables, method, results, evaluations...
CP1 - Investigate the effect of caffeine on heart rate in Daphnia
Core practical 1 - investigating effect caffeine on heart rate in Daphnia
Aim: to investigate how varying the concentration of caffeine can affect the heart rate of
daphnia
Introduction:
The genus ‘daphnia’ are planktonic crustaceans which are commonly known as ‘water fleas’
and commonly found in freshwater. Its heart beats at around 200 times per minute at 20°C
and as it is a poikilothermic being, its temperature is dependent on its environmental
temperature. Therefore its heartbeat will get slower in cold water and increase in hot water.
(Tomar, n.d.).
Caffeine is a central nervous system stimulant found in the seeds, fruits, nuts, or leaves of a
number of plants native to Africa, East Asia and South America and is the most widely
consumed psychoactive drug. Caffeine works by leading to the blockading of adenosine
receptors and increasing autonomic nervous system (ANS) activity through the release of
plasma catecholamines, inducing tachycardia and increased blood pressure.
When adenosine binds to its receptors, neural activity slows down, and you feel sleepy.
However caffeine acts as an adenosine-receptor antagonist meaning that it binds to these
same receptors, but without reducing neural activity (Lazarus et al., 2011). This means that
adenosine cannot bind, preventing you from feeling sleepy. Therefore causing you to stay
alert and agitated.
Catecholamines are a group of hormones produced in the adrenal glands that are released
in response to emotional or physical stress as part of the fight or flight response. The main
types of catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline) and
dopamine. (www.medicalnewstoday.com, 2020). Catecholamines increase heart rate, blood
pressure, breathing rate, muscle strength, and mental alertness. They also reduce the
amount of blood going to the skin and increase blood flow to the major organs, such as the
brain, heart, and kidneys. Both of these responses cause the body to be more agitated and
speeds up heart rate.
Hypothesis : The heart rate of daphnia will increase as the concentration of the caffeine
increases as caffeine is a stimulant that triggers release of adrenaline and speeds up heart
rate.
Variables :
Independent variable : the concentration of caffeine given to the daphnia ranging from 0%
to 0.5%
Dependent variable : the heart rate of the daphnia in bpm
Control variables
- Use daphnia of similar size from the same stock and of the same age to ensure that
each daphnia used have a similar resting heart rate. Smaller and younger will have
faster heart rates than bigger and older ones.
, Core Practical 1
- Use the same equipment and the same method so that any variation in heart rates is
due to the caffeine solution and not any other factor such as differences in equipment
or method to record results.
- volume of solutions - use the same number of drops on daphnia each time so that
they are exposed to the same conditions and amount of caffeine and prevent any
unwanted variations in results.
- stress of daphnia - try minimise stress of daphnia (explained in ethical considerations
section)
- Time to acclimatise : leave daphnia in caffeine solution for the same amount of time
to acclimatise (eg 5 minutes) as the longer the daphnia is exposed, the longer the
caffeine has to diffuse into their system. They need to be exposed for the same
amount of time so they have roughly the same amount of caffeine in their system and
variations in results are caused by changes in the concentration alone.
- PH doesnt need to be controlled because it doesn't affect the daphnia
- Daphnia is poikilothermic meaning its metabolic rate is affected directly by the
temperature of the environment. Therefore the temperature of the environment
should be recorded and considered to give the heart rate at any given temperature.
Ethical Considerations
We use daphnia because
- Very common so no threat to species existence or dependent species (does not affect food web)
- No threat to their reproduction because they reproduce asexually → no lost genetic
variation
- Transparent so heart is visible
- Daphnia have a simple nervous system so dont not suffer physical or mental stress. However, there
are still debates over animal rights and due to lack of consent, we try to minimise the amount of
suffering.
To reduce suffering :
- Daphnia may be killed by chlorine in tap water. Any tap water used should be left to stand for 24 hours
first to let the chlorine dissipate
- May need too long to recover after the caffeine to use the same one for different concentrations in the
same practical
- After usage, place them in a ‘used’ daphne container and Dispose of Daphnia ethically, preferably by
returning them to a freshwater pond or stream (natural habitat)
- Store in conditions that replicate their natural habitat
- Working at good pace to minimise time daphnia are under stress
- Daphnia are poikilothermic (cold blooded). Turn off the microscope lamp when not viewing
the fleas → ethical
- Not using an excessive concentration of caffeine
- Use a lot of water and do not use a coverslip in order to maintain sufficient oxygen to the daphnia
Risk Assessment
- wear goggles to protect your eyes from any solutions or pond water getting in your eyes.
- Do not touch microscope or cables with wet hands as it uses electricity
- wash hands after handling daphnia and pond water to prevent any cuts from getting
infected by pond water or solutions
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