Modeling Metabolic Rate in Homeotherms and Poikilotherms A

What are homeotherms and poikilotherms? • Homeotherms are organisms that maintain a constant internal temperature regardless of the environmental temperature • Example: Humans 50 • Poikilotherms are organisms whose internal temperature is directly determined by the environmental temperature • Example: Houseflies 40 30 20 10 0 0 © 2017 Marcheschi, Montgomery College 10 20 30 40 50

What is Metabolic Rate? • Metabolic rate is the amount of energy an organism uses in a certain amount of time • Measured in kcal/(day·kg) • Living organisms must have a metabolic rate that is greater than zero • An organism uses energy to do or support the following: • • Growth Maintenance of cells Activity or Movement Keep internal temperature constant (if needed) © 2017 Marcheschi, Montgomery College

Humans and Flies can be modeled using simple shapes that are filled with water A 2 cm 2 3 cm 22 cm 18 cm 200 cm 160 cm B 1 2 cm 3 cm These are Flies (2 weeks old) These are Humans (20 years old) 22 cm • Calculate surface area, volume, and mass (in kg) of: Human A, Human B, Fly 1, and Fly 2 • Density of water is 1 g/cm 3 © 2017 Marcheschi, Montgomery College

Handout 1: We can predict metabolic rate in Humans and Flies at different temperatures • Draw a line on the charts below representing your hypothesis regarding metabolic rate at different temperatures Fly 1 Arbitrary Units Human A 0 10 20 30 40 50 0 © 2017 Marcheschi, Montgomery College 10 20 30 40 50

Metabolic Rate can be modeled by using Equations Humans Flies © 2017 Marcheschi, Montgomery

Handout 2: Using the metabolic rate equations, we can graph the metabolic rate vs. temperature for Human A and Fly 1 Human A Metabolic Rate (kcal/(day · kg) Fly 1 0 10 20 30 40 50 0 Temperature (°C) © 2017 Marcheschi, Montgomery College 10 20 30 Temperature (°C) 40 50

Activity: Think/Write/Pair/Share 1. Do the graphs of metabolic rate vs. temperature look like your predictions? • Compare Handout 1 to Handout 2 2. What might be an explanation for why the graphs do or don’t look like your predictions? 3. In the graph of Fly 1, what might be an explanation for the metabolic rates shown at 15 C and below? © 2017 Marcheschi, Montgomery College

Handout 2: Using the metabolic rate equations, we can graph the metabolic rate vs. temperature for Human B and Fly 2 Human B Metabolic Rate (kcal/(day · kg) Fly 2 0 10 20 30 40 50 0 Temperature (°C) © 2017 Marcheschi, Montgomery College 10 20 30 Temperature (°C) 40 50

Class Q&A: Comparison of Humans A & B and Flies 1 & 2 • Which human (A or B) had a higher metabolic rate at the following temperatures? • • 15 °C 25 °C 35 °C 45 °C • Which fly (1 or 2) had a higher metabolic rate at the following temperatures? • • 15 °C 25 °C 35 °C 45 °C © 2017 Marcheschi, Montgomery College

Activity: Think/Write/Pair/Share 1. Other than weight and size, what is a difference between Human A and Human B? 2. Other than weight and size, what is a difference between Fly 1 and Fly 2? 3. How might these differences account for the differences observed in metabolic rate when comparing Human A to Human B and Fly 1 to Fly 2? © 2017 Marcheschi, Montgomery College

Class Q&A: Comparison of Human A to Fly 1 • Which organism (human or

Activity: Think/Write/Pair/Share 1. What might be an explanation for why you observed humans having

What Generalizations can be determined from this exercise? 1. Homeotherms have higher metabolic rates than poikilotherms • Homeotherms need to expend a lot of energy to maintain their internal temperature • Humans spend about 70% of their daily energy just to stay warm 2. Bigger organisms have lower metabolic rates than smaller organisms of the same species. • More heat is lost in smaller organisms due to their higher surface area-to-volume ratio • Other reasons for this are unknown. © 2017 Marcheschi, Montgomery College