Medhavi Mathur 12J
PAG 11: Investigation into the measurement of plant or animal
responses
PAG 11.2 requires access to Daphnia and investigates how their heart rate
changes with temperature.
INTRODUCTION
Daphnia magna can be found in freshwater
lakes, ponds, and rivers all over the world and
are very sensitive to changes in their
environment. The outer carapace of a Daphnia is
transparent so all the internal organs, even the
beating heart, can be seen, therefore it can easily
be viewed under a light microscope.
HYPOTHESIS:
As Daphnia is an ectothermic organism, its core body temperature is heavily
dependent on the temperature of its surroundings. This means that ectotherms
cannot internally regulate their body temperature using their metabolism. They have
an optimum temperature at which they perform most efficiently. Most physiological
processes take place more rapidly at higher temperatures, as an increased
temperature allows enzymes (involved in enzymatic reactions throughout the body)
to gain more kinetic energy. Therefore, we can hypothesise that the temperature of
the surrounding medium affects heart rate in Daphnia. As the temperature of
surroundings increase, the Daphnia’s heart rate will increase.
EQUIPMENT LIST
• Daphnia magna
• Microscope, stage micrometre and eyepiece graticule
• Cavity slide
• Plastic dropping pipettes
• Petri Dish
• Crushed ice
• Beakers
• Stopwatch/ Timer
• Calculator
• Scissors
• Modelling clay
VARIABLES
As we need to consider a range of temperatures, in °C, the independent variable is
the temperature of the water in the petri dish. Temperature should be measured in
5°C intervals, starting from 10°C going to 30°C.
PAG 11: Investigation into the measurement of plant or animal
responses
PAG 11.2 requires access to Daphnia and investigates how their heart rate
changes with temperature.
INTRODUCTION
Daphnia magna can be found in freshwater
lakes, ponds, and rivers all over the world and
are very sensitive to changes in their
environment. The outer carapace of a Daphnia is
transparent so all the internal organs, even the
beating heart, can be seen, therefore it can easily
be viewed under a light microscope.
HYPOTHESIS:
As Daphnia is an ectothermic organism, its core body temperature is heavily
dependent on the temperature of its surroundings. This means that ectotherms
cannot internally regulate their body temperature using their metabolism. They have
an optimum temperature at which they perform most efficiently. Most physiological
processes take place more rapidly at higher temperatures, as an increased
temperature allows enzymes (involved in enzymatic reactions throughout the body)
to gain more kinetic energy. Therefore, we can hypothesise that the temperature of
the surrounding medium affects heart rate in Daphnia. As the temperature of
surroundings increase, the Daphnia’s heart rate will increase.
EQUIPMENT LIST
• Daphnia magna
• Microscope, stage micrometre and eyepiece graticule
• Cavity slide
• Plastic dropping pipettes
• Petri Dish
• Crushed ice
• Beakers
• Stopwatch/ Timer
• Calculator
• Scissors
• Modelling clay
VARIABLES
As we need to consider a range of temperatures, in °C, the independent variable is
the temperature of the water in the petri dish. Temperature should be measured in
5°C intervals, starting from 10°C going to 30°C.
