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Biology Lab Essay

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Scientific Method to Study Daphnia
Effects of Temperature, Acetylcholine, and Adrenaline on the Heart Rate of the Daphnia Introduction
Heart rate is affected by several internal and external factors. The external factors that can affect the rate of the heart are exercise, smoking, drugs, and temperature. If the temperature is decreased 1 degree, it can affect the rate of the heart by ten beats per minute. The lower the temperature is, the lower the heart rate of an organism. The internal factors that can affect the heart beat of an organism are hormones and nerve signals. For example, the chemicals acetylcholine and adrenaline are neurotransmitters that affect heart rate. Adrenaline has a strong effect on the heart rate In contrast, heart rate is increased by the sympathetic nervous system and the hormone adrenaline circulating in the blood via activation of cell surface receptors . This occurs during exercise or fear. The effect is to increase the rate of ejection of blood by the heart. This means that there will be more blood flow to skeletal muscle (in ...

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