In: Biology
Summary of daphnia must be 5 paragraphs explaining how it gets affective what happens to the organism? How does the heart rate gets affective?
Ans.
Daphnia belong to the genus of small planktonic crustaceans and are members of order cladocera. They are about 0.2 -5 mm in length. They are one of among the smallest aquatic crustaceans called water fleas because their saltatory swimming style resembles the movement of fleas. They are found living in various aquatic environments like ponds, fresh water lakes and acidic swamps. The two most commonly found species of Daphnia include D.magna and D.pulex.
Daphina is about 1-5mm in length and has a segmented body which is usually not visible. The head appears fused and bent towards the body and there is a visible notch seperating them. In most of the species their body is covered by carapace which is translucent making the very suitable for microscopic study of their heart beat. The other most evident features of Daphnia are second antenna, compound eyes and a pair of abdominal setae.
There are various features of Daphnia that can be studied even under a low power microscope. For example we can observe their feeding mechanisms, blood cells being pumped around the circulatory system by the simple heart rate, their eye movement caused by ciliatory muscles etc. Their heart is located at the top of the back, behind the head. Under normal circumstances they have an average heart rate of 180bpm. Like many other animals Daphnia are also prone to alcohol intoxication making them excellent subjects for studying the affects depressants on nervous system. Being intermediate in size , Daphina utilises both diffusion and circulatory mechanisms for producing hemoglobin in low oxygen environment.
Daphina has a visibly altered heart rate when it was subjected to alcohol intoxication therefore for studying the heart rate scientists have conducted various experiments where they have subjected Daphina to caffeine, adrenaline and nicotine.
Daphnia being poikilothermic in nature their body temperature and metabolic rate are affected directly by the temperature of the environment. The heart rate is affected by the change in metabolic rate. The effect of temperature on metabolic rate is expressed in terms of temperature coeffiecient(Q10). It is expressed as below.
Q10 = rate at (T+10) 0C/ rate at T o C
The metabolic rate of Daphnia doubles for every 10 degrees rise in temperature.
Heart rate of Daphnia when exposed to Adrenaline:
The heart rate of Daphnia increases when exposed to adrenaline. Adrenaline otherwise called epinephrine functions along with nor adrenaline as a fight or flight hormone. Adrenaline is released when we experience fear or performing some exercise. The release of adrenaline increases the blood flow from heart as a result there is more blood flow to the skeletal muscle and hence skeletal muscles are supplied with more amounts of oxygen. In this experiment adrenaline is used to demonstrate the heart rate in Daphnia. Drugs that are known to increase heart rate are called positive chronotropes.
Adreanline is known to increase the heart rate via the action of secondary messenger called cAMP ( cyclic adenosine monophosphate). The neurotransmitter adrenaline activates the beta 1 adrenoreceptor in the sinoatral node which leads to increase in cAMP present at that node, The increase in cAMP increases the heart rate.
Heart rate of Daphnia when exposed to caffeine:
Heart rate of Daphnia increases when exposed to caffeine because caffeine mimics the activity of adrenaline and nor adrenaline. Caffeine also increases the cAMP at sinoatrial node but by a different mechanism that does not involve beta 1 adrenoreceptor. Increased cAMP increases the electrical activity of sinoatrial node causing its depolarisation leading to faster heart beat.
Heart rate of Daphnia when exposed to nicotine:
Exposure to nicotine reduced the heart rate of Daphnia. The lower the nicotine solution the slower was the rate at which heart rate decreased.