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Respiration Cellular respiration is the process in living organisms that extracts electron energy from the chemical bonds in food (organic molecules), and converts that energy into a more useful form of energy (called ATP) to run cell activities. This cell process uses oxygen and produces carbon dioxide. The complete equation is:

Organic Molecules (food)

+

Carbon Dioxide

+

Water

ATP Energy (runs cell processes)

+

Heat

Oxygen

Respiration occurs inside the mitochondria, which are cellular organelles in both plant and animal cells. Refer to your textbook for the structural and functional description of this organelle.

Mitochondrion

Cell

During this lab we will investigate some aspects of cellular respiration including the effects of environmental temperature on the rate of respiration in endotherms (internally heated animals) and ectotherms (externally heated animals).

Exercise Exercise Exercise Exercise Exercise

#1 #2 #3 #4 #5

“Heat Production During Respiration” ................................... 133 “Respiration in an Endotherm” ............................................... 134 “Comparison of Endotherm and Ectotherm” .......................... 138 “Food Demand for Humans” .................................................... 139 “Respiration in Plants” ............................................................. 140

EXERCISE #1 “Heat Production During Respiration” The Second Law of Thermodynamics states that heat is released whenever any form of energy is transformed into another form. Since respiration is described as the conversion of food energy into usable energy for the cell, we should be able to observe heat being given off during the process.

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Observe

Dead Seeds

Live Seeds

Two experimental containers were set up yesterday. One of the containers was filled with dead seeds killed by boiling, and the other container was filled with live seeds. These seeds demonstrate the basic respiration process that is going on in all living organisms. Record the temperature of each container. Temperature of live seeds = Temperature of dead seeds =

? QUESTION

1. What does the equation for respiration say about heat?

2. What does this experiment suggest is occurring in live seeds and not in dead seeds?

3. What would happen to the respiration process in the container of live seeds if we pumped the oxygen out?

What would happen to the temperature in that container?

EXERCISE #2 “Respiration in an Endotherm”

Right!

Mice are endotherms. That is, they get most of their heat from inside their own body (endo means inside). Cellular respiration generates the heat that keeps these animals warm. (Refer to the Equation for Respiration on the first page.) During this Exercise you will monitor the rate of respiration (also called metabolic rate) in a mouse. In addition, you will investigate the influence of environmental temperature on the mouse’s rate of respiration by comparing a mouse in a cold environment with a mouse in a warm environment. Later, in Exercise #3, you will compare the differences between an endotherm (mouse) and an ectotherm (frog).

How to Handle Mice Wrong!

Mice should be picked up by their tail and immediately rested on your hand, and then marched into the Metabolic Cage. Do not grab them. Grabbing scares the hell out of them, and they may bite you or pee on you because of that fear. Also, don’t play with the mice (on table tops, etc.) because there is a possibility of them getting loose on the floor. These are professional mice. They work several years for us, and we treat them very well. So, please be careful.

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Experimental Apparatus 1

2

3

4

5 ml

Moving “gushy” soap bubble CO2 absorber

Experimental Design The basic question is: What effect does environmental temperature have on the metabolic rate of an endotherm (mouse)? Do this experiment at two temperatures: Room Temperature and Packed in Ice.

Room Temperature Procedure

1

Weigh the wire cage part of the chamber:

2

Go get your mouse, and put it into the wire cage. Then weigh the cage with the mouse in it. Cage + Mouse g

grams.

Cage –

Weight of Mouse g

=

g

3

Put one tablespoon of CO2 absorber (soda lime) into the trough at the bottom of the Metabolic Rate Chamber.

4

Wet the inside of the glass tube with soapy water. This will help prevent the “gushy” bubble from “popping” during the experiment.

5

Put the caged mouse into the chamber and seal the cork tightly. Don’t worry! The mouse won’t suffocate. Leave the chamber alone for 10 minutes (sealed up—cork on—no soap bubble) to equalize the temperatures inside and outside of the chamber.

6

Use your finger to make a “gushy” soap bubble on the open end of the glass tube. Then, measure the time it takes (in seconds) for the bubble to move between the marks on the tube until 5 ml of O2 have been consumed by the mouse. Perform three trials. seconds Trial 1

seconds Trial 2

seconds Trial 3

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? QUESTION

1. Food + O2 CO2 + H2O. During respiration a mouse will consume O2, and CO2 will be produced in its place. If no CO2 absorber had been used in your experiment, would you have seen a change in air volume?

2. If you use a CO2 absorbing substance in the Metabolic Rate Chamber, then what happens to the CO2 that is produced during respiration?

3. Now, with the absorbing substance in the chamber, what happens to the air volume during your experiment as the O2 is consumed during respiration?

Packed In Ice Procedure

1

If ice is packed around a Metabolic Rate Chamber like the type we are using, the temperature inside will stabilize at 5°C. This cold air temperature will not harm the mouse as long as the mouse is removed before 45 minutes. Our experiment will take less than 20 minutes.

2

Now perform the “Packed in Ice” experiment. Let the chamber equalize the temperatures inside and out for 10 minutes before applying the “gushy” soap bubble.

3

After 10 minutes, apply a “gushy” soap bubble and perform the three separate measurements of the rate of respiration. seconds Trial 1

4

seconds Trial 2

seconds Trial 3

Disassemble the chamber, carefully returning your mouse to its home, and dump all CO2 absorber and feces into the special waste jar. Don’t wash the apparatus unless you are told to do so. The chamber must be dry for the next lab class. Wash your hands!

Respiration Calculations You must convert the mouse’s O2 consumption to an hourly metabolic rate. This is accomplished by dividing the bubble time (in seconds) into 3,600 (the number of seconds in one hour). That number is to be multiplied by 5 (5 ml of O2 used in each trial).

Calculation 1

Calculate the average time of the three trials at room temperature. 5 ml O2 consumed in

seconds (average time)

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Calculation 2

Based on Calculation 1, how much O2 would your mouse consume in one hour? 3,600 x 5 = Calculation 1

Calculation 3

ml O2 consumed in one hour

In order to have a metabolic rate that can be compared with an animal of different weight, we must correct the calculations considering the mouse’s weight. Calculation 2 = Weight of Mouse 1

You have finished the calculations for room temperature. Record your answer below. Repeat the three calculations for “Packed in Ice,” and record your answer below. Metabolic rate of your mouse = at room temperature (20°C)

ml O2 per hour per gram of weight

Metabolic rate of your mouse = packed in ice (5°C)

ml O2 per hour per gram of weight

Put a dot on the graph for each of the metabolic rate values in your experiment.

3

Draw a line between those two dots, and write the word endotherm on the line.

Metabolic Rate

2

(ml of O2 per hour per gram weight)

Procedure

ml O2 per hour per gram of weight

15

10

5

5°C

20°C

Environmental Temperature 4

Check with other lab groups to see how your calculations compare with theirs.

138

EXERCISE #3 “Comparison of Endotherm and Ectotherm” An ectotherm gets its heat from the environment (ecto means outside). The body temperature of an ectotherm is warm when the environment is warm, and the body is cooler when the environment is cold.

Information

The following results are taken from some experiments that measured the metabolic rate in a frog (ectotherm) of about the same size as your mouse. Metabolic Rate Packed in Ice (5° C) Frog #1

0.05

0.30

Frog #2

0.03

0.28

Frog #3

0.04

0.25

2

Put a dot on the graph for each of the average values.

3

Draw a line between those two dots, and write the word ectotherm on the line.

(ml of O2 per hour per gram weight)

Calculate the average metabolic rate for the three frogs at each of the two temperatures.

0.30

0.20

0.10

5°C ? QUESTION

ml O2 per hour per gram of weight

1

Metabolic Rate

Procedure

Metabolic Rate at Room Temperature (20° C)

Environmental Temperature

20°C

1. Which organism has the slowest rate of respiration? (circle your choice) Endotherm

or

Ectotherm

2. Which organism needs less food to survive? (circle your choice) Endotherm Explain why.

or

Ectotherm

139 3. How much food does the ectotherm need compared to the endotherm? % 4. Which organism would do better if the amount of food is very limited, but the environment is fairly warm? (circle your choice) Endotherm

or

Ectotherm

5. In what areas of the world would you expect to find ectotherms?

6. Which organism would do better in cooler environments where the food is plentiful? (circle your choice) Endotherm

or

Ectotherm

7. Will the organism in question #6 do fine in warmer environments if the food is plentiful?

Why or why not?

EXERCISE #4 “Food Demand for Humans” How much food does a human need to survive one hour of biology lab class? We can borrow data from experimental research to help us estimate the amount of food that is required to support a human. Our calculations will be based on grams of sugar as the nutrient. Also, notice that the word Calorie is capitalized. When capitalized, this term represents 1000 times the value of a single calorie. The Caloric demand for food varies greatly for a human depending on activity and environmental conditions. The energy demand might be as slow as 50 Cal per hour during sleep to as fast as 2,000 Cal per hour during extreme exercise. (Although that high rate of metabolism could be maintained for only about 2 minutes without total exhaustion.) An average student in biology lab class uses about 100 Calories per hour as long as they aren’t walking around all of the time.

140

Information

1. Assume a food demand of 100 Cal/hour for students. 2. A human gets about 3.85 Cal of energy from 1 gram of sugar.

? QUESTION

How many grams of sugar are required to “fuel” an average student during one hour of biology lab class? grams of sugar used in one hour

Procedure

Weigh out that much sugar and show it to your lab instructor.

EXERCISE #5 “Respiration in Plants” The Respiration Equation states that CO2 is produced as O2 is used. If that is true, then we should be able to use CO2 production as an indicator that respiration is occurring.

Phenol Red Test for CO2

There is a very simple way to show changes in CO2 level. Phenol red is a substance that turns yellow when CO2 is added, and then turns back to red when CO2 is removed. Add CO2 Turns Yellow Phenol Red

Remove CO2

Phenol Red

Experimental Setup

? QUESTION

Turns Back to Red

Yesterday we put a small piece of Elodea plant into a test tube filled with dilute phenol red solution. The tube was red because the water had very little CO2 in it. We put this experimental setup into a closed cabinet until today. Ask your instructor where the plant is, and make your observations. What do you conclude about plants in the dark?