How Does Temperature Affect Daphnia Heart Rate? Student Study Guide

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1 TM How Does Temperature Affect Daphnia Heart Rate? Student Study Guide The body temperature of the Arctic squirrel drops from 98.6 F to 26.4 F, which is below the freezing point of water and is the lowest known body temperature of any living mammal. The average body temperature of the following warmblooded animals are: Humans: 98.6 F Rabbit: F Polar bear: 99.1 F Blue whale: 95.9 F Owl: F Ostrich: F BACKGROUND Every animal has an ideal temperature range in which they are best able to survive. For some this may be in the intense desert heat while others may prefer frigid polar climates. But in each case, the body temperature must remain within the acceptable limits that are inherent to that species. For example, although humans have adapted to survival in a wide range of environmental temperatures, the temperature of the body must remain relatively close to the ideal 37ºC in order to avoid any impairment of physiological functions. The ideal body temperature may change with each species, but the general principle remains the same: the normal physiological processes of an organism can only be carried out within a relatively narrow range of temperatures. Fortunately, humans, like most mammals and birds, are endothermic, which means that most of the body s heat is derived from its own metabolism. In order to maintain a fairly constant body temperature, a combination of behavioral and physiological adaptations is utilized. For example, when endotherms get too cold, they may increase heat production by moving around, shivering, and releasing hormones that increase their metabolic rate. When they get too hot, they may pant or sweat. In addition, endotherms may alter their blood flow, utilize their insulation (fat, feathers, or fur), or simply relocate to a warmer or cooler area. This type of thermal physiology is especially advantageous for a few reasons. First, it enables marine and terrestrial endotherms to maintain a relatively constant body temperature when faced with severe environmental temperature fluctuations (homeostasis). Second, it allows these animals to endure vigorous activity for fairly long periods of time due to their high levels of aerobic metabolism (cellular respiration). This is especially important to terrestrial animals because moving on land requires a much greater effort than moving in water. An alternative type of thermal physiology is referred to as ectothermy. Ectotherms rely almost entirely on environmental sources of heat to warm their bodies. Most invertebrates, fishes, reptiles, and amphibians are included in this classification. The term coldblooded is often used to describe ectotherms, but this is sometimes misleading. Often times these so-called cold-blooded animals actually have active body temperatures that are higher than those of mammals. An example of this is seen in the desert iguana 1

2 Daphnia produce most of their young without mating. This is known as parthenogenic reproduction. (Dipsosaurus dorsalis), which has one of the highest preferred body temperatures known for any vertebrate - 100º to 108º Fahrenheit! The advantage of being an ectotherm is that very little energy is used to maintain body temperature, since this is taken care of by the environment. For example, when a lizard s body temperature is cool, it will sit in the sun to raise its temperature back up again. When it gets too warm, the lizard will seek shade to cool off again. In addition, ectotherms are able to produce a small amount of heat metabolically at low rates, and use some physiological means of thermoregulation. However, ectotherms have a bit of a disadvantage in that they are somewhat limited as to the environments that they can inhabit. Alaska is certainly not an ideal home for a lizard! We can easily study an ectotherm s rate of metabolism by examining the water flea, Daphnia magna. Daphnia are of great importance in the aquatic food chain and are a principle food staple for young and adult fish. The body of a Daphnia is translucent which makes the beating, football-shaped heart readily visible under a microscope. Because the heart rate is variable with water temperature, it is easy to alter the Daphnia s heart rate and observe the changes. 2

3 OBJECTIVES Illustrate and label the main anatomical structures of a Daphnia Alter the temperature of a Daphnia s environment and quantify the changes in its heart rate Differentiate between endothermic and ectothermic animals Understand the advantages and disadvantages of each type of thermoregulation MATERIALS MATERIALS NEEDED PER GROUP 1 Microscope slide 1 Pipet 1 Petri dish 1 Stereomicroscope 1 Thermometer Scissors Ice SHARED MATERIALS An adult blue whale, with a heart the size of a small car, has one of the slowest heart rates...5 to 6 beats per minute. Petroleum jelly Daphnia culture PROCEDURE 1. Obtain each of the following: 50 ml room temperature water 50 ml ice water 250 ml beaker Thermometer Petri dish Microscope slide GLOVES Heat protective gloves are recommended when working with hot plates 2. Place 150 ml of tap water in the beaker and allow it to boil on a hot plate. While you wait, proceed to Step Set the lid of the Petri dish aside and fill the bottom of the dish with 25 ml of room temperature water (approximately 25 C). 4. Place a dab of petroleum jelly in the center of a microscope slide. 3

4 5. Obtain a graduated pipet and cut the pipet at the line marked.5. Use this pipet to place one large Daphnia on the dab of petroleum jelly. Make sure that the Daphnia cannot swim away and then pour off all of the extra water from the slide into the upside-down lid of the Petri dish. 6. Dispense 25 ml of room temperature water into the Petri dish (not the lid). Place the slide with the Daphnia in the dish, and allow it to sit for at least one minute to equilibrate. 7. Place the entire dish on the stage of a stereomicroscope. 8. Look through the microscope and locate the beating heart of the Daphnia, which sits behind the dark line of the digestive tract. Draw what you see in the space below. Be sure to label the heart as well as any other anatomical structures you may recognize. A hummingbird s heart beats about 1,000 times per minute. 9. Practice counting the number of heart beats in a 15 second period: Have one partner keep track of the time while the other observes. Once the observer indicates that they are ready, the timing should begin. Switch positions and repeat this practice. Do not move on to the next step until both partners feel comfortable measuring the heartbeat. HINT It may be helpful for the observer to count in increments of ten and keep track of every tenth beat by counting off with their fingers (i.e., three fingers would equal thirty beats). 10. Take the temperature of the room temperature water in the Petri dish and record this number in Table 1. Count the number of times the heart beats over a period of 15 seconds and record this data in Table 1. Repeat the count three more times and record your results in Table 1. 4

5 11. Remove the slide and empty the Petri dish of the water. Fill the dish with approximately 30 ml of ice water and place the slide in the dish. Let the preparation acclimate for one minute on the stage of the stereomicroscope. 12. Again locate and focus in on the heart of the Daphnia. Record the temperature of the water and measure the Daphnia s heart rate as before. Record the data in Table Gradually add the boiling water to the Petri dish while gently stirring and keeping track of the temperature. At 5ºC intervals, take a heart rate measurement and record the temperature and the number of heart beats in Table 1. If the Petri dish gets too full, simply remove some of the water to make room for more. The average human heart beats 72 times per minute. Within one day, the heart beats over 100,000 times. 14. Stop taking heart rate measurements when the Daphnia s heart rate stops changing, or when you can no longer measure the heart rate of the specimen. 15. Study Figure 1 below and compare it to your Daphnia drawing. Identify and label any structures on your drawing that you were previously unable to identify. Figure 1 5

6 WARD S How Does Temperature Affect Daphnia Heart Rate? Lab Activity Name: Group: Date: ANALYSIS Table 1 Temperature (ºC) 25 (Room Temperature) # of Heartbeats per 15 seconds Avg. # of Heartbeats per Minute Trial 1 Trial 2 Trial 3 Trial

7 WARD S How Does Temperature Affect Daphnia Heart Rate? Lab Activity Name: Group: Date: ASSESSMENT 1. What were the dependent and independent variables in this experiment? 2. Create a graph below to summarize Table 1 from the Analysis section. 3. In a few sentences, summarize what you have learned about the relationship between temperature and Daphnia heart rate. 4. Design an experiment that demonstrates the effects of another environmental factor on a particular ectotherm and summarize it below (or on another sheet of paper). 7

8 5. List at least three ways in which each of the following types of animals can regulate their body temperature: Ectotherms - Endotherms - 6. Create a Venn diagram in the space provided below that shows the similarities and differences between endothermy and ectothermy. 7. Name at least three other factors that can influence the heart rate of organisms. 8. Which of the following would be considered FALSE when discussing ectotherms? a. Use physiological means of thermoregulation b. Tend to have low thermal conductivity because of good insulation c. Primarily use behavioral thermoregulation d. Produce heat metabolically at low rates 8

9 9. Research an endotherm and an ectotherm and use the following thermometers to indicate the temperature ranges in which their thermoregulatory capabilities will: function normally become slightly impaired become severely impaired completely cease causing death Be sure to indicate the organism you have chosen below the appropriate thermometer. Ectotherm Endotherm C F C F 9