Laboratory 4: Photosynthesis, Respiration and Metabolism

Laboratory
4: Photosynthesis, Respiration and Metabolism

Autotroph
or Heterotroph?

.jpg”>One of the
most fundamental divisions among all living things is based upon where an
organism derives its energy. As we know,
energy is critical for life. It fuels all actions in a living thing, from
movement to sensory processing, to cell repair and growth. And while all organisms must undergo some
processes that require energy—not all move and process stimuli, but all living
things grow and repair—the source of that energy is a great dividing line
amongst living things, dividing the heterotrophs
(who get their food from outside
of themselves) from the autotrophs(who
make their own food). The distinction is a relatively clear one
most of the time. The question boils
down to whether an organism can make its own energy (usually using the sun—see the
plant below) or it needs to take in the energy from the world at large (by
consuming some food source—see tiger to the left). While it may at first appear to be a simple matter
of plant versus animal, it is actually a little more complex than that. There is a plethora of microorganisms (like bacteria,
fungi, and protozoans) that are either autotrophic
(usually photosynthetic—using the sun to make sugars for food) or heterotrophic (taking in an energy
source from their environment).
.jpg”>
Some
living things are extremely specific about the type of food source they require
in order to fuel the reactions for life.
This requirement is not unlike the engines in our cars…we cannot “feed”
our cars water, soda, or lemonade if we want them to run properly. Other organisms, on the other hand, will take
in whatever is available (think of a vulture or a rat!) in order to obtain the
energy needed to fuel their body’s functions.

Respiration
or Fermentation?

.jpg”>Once and
organism has the energy it needs, the sugar must to be converted into a form
that is useable by that organism—typically into a molecule called ATP
(adenosine triphosphate). ATP is the
molecule responsible for all activity within the cell. In most organisms the conversion from raw
energy (sugar) into usable energy (ATP) is called respiration. Don’t confuse the respiration that involves
us breathing with the respiration that produces ATP. Keep in mind, though, that in vertebrates,
respiration is related to breathing
because breathing provides the needed oxygen and helps remove the byproduct
carbon dioxide. External respiration is
breathing while aerobic cellular respiration is the
conversion of sugar into a usable form in the presence of oxygen.

.jpg”>Some organisms,
however, do not require oxygen at all to break down sugar into ATP; these
undergo a process known as fermentation. Fermentation requires an anaerobic
environment (no oxygen) and produces byproducts that are different from those
produced during cellular respiration. One of these byproducts is alcohol, a
major ingredient in beer. Beer is produced by yeast that is undergoing
fermentation. Many organisms can do
either process, depending on the availability of oxygen or other
nutrients. If the required materials are
not present, this affects an organism’s ability to grow and sometimes to
survive. Factors that can affect an organism’s
metabolic pathway include temperature, sugar availability, and the presence or
absence of oxygen. All of the processes
in an organism, from creating molecules to breaking them down, are collectively
known as that organism’s metabolism.

Overview
You
will be demonstrating the differences in the metabolic rate of yeast at a
variety of temperatures and with a variety of energy sources.

Materials
2
3-packs of yeast (rapid-rise— 6 total!)3
Styrofoam or plastic cupsWaterThermometer
(from your Kit)3-17
to 20 oz soda or water bottles (empty and clean!)1
T Salt1
T Sugar1
T “Equal” or “Splenda” or any other
sugar substitute (use 3 or 4 packets—pick these up at the store or
“borrow” from your local coffee house or restaurant)3
small balloons (just large enough to fit over the mouth of the soda
bottles)

Procedure

Part 1—Yeast
and Temperature
Label
your cups:Room
tempHot
ColdFill
your “Room temp” cup with about 100 ml of tap water. It should measure
about 35º C.Fill
your “Hot” cup with about 100 ml of warm water. Heat water in the microwave at 15 second
intervals until it measures about 95 ºC.Fill
your “Cold” cup with about 100 ml of cool water. Add a few ice cubes until it measures
about 15 ºC.Once
your cups are full and the water is at about the correct temperatures, add
a packet of yeast (Use rapid rise, available in the baking section of the
grocery store) to each.Make
an initial observation and record on the Answer Sheet what you see again
every 5 minutes for 30 minutes.You
may start Part 2 while Part 1 is reacting, just don’t forget your
observations!

Part 2—Yeast and
Energy Source
Label
your three bottles:SaltSugarSugar
substituteFill
each of the bottles with 100 ml water at 35º C.Add
a packet of yeast to each of the three bottles.Add
a tablespoon of salt to the “Salt bottle”, a tablespoon of sugar to your
“Sugar” bottle, and a tablespoon of sugar substitute to the “Sugar
Substitute” bottle. Swirl
the bottles to be sure the yeast has access to the energy source.Attach
the balloons to the tops of the bottles.Make
an initial observation and record on the Answer Sheet what you see again
every 5 minutes for 30 minutes.

Name:

Section
Number

Name
of Lab: Lab
4-Respiration and Fermentation

Date
Completed:

Directions:
·
Fill in the following fields as completely
and accurately as possible. Please be
sure to practice appropriate grammar, punctuation, and spelling.
·
When finished, save your document with a file
name that includes your name, section number, and the assignment (i.e.
RoyMason_Lab4_Sect3536.doc). Please only send .doc or .rtf files. Work submitted in any other format will not
be graded.
·
Attach your Lab 4, in the assignment section
of BB, before midnight on the day it is due.
Late work will not be accepted.
·

Be sure you are using your own words!
Plagiarism in any form will not be tolerated!
If you are unsure what constitutes
plagiarism, consult the most recent college catalog or ask the Instructor or
Teaching Assistants. Labs that are judged to be plagiarized will receive no
credit.

We
would like you to time yourself on these labs to see how long it takes you to
work through them. Please take notice of
the time you start your lab and note it down. When you’re completed write the
time lapsed at the top of your answer sheet. ­In the box provided.

Time:

Part 1—Yeast and
Temperature

Observations:
Your observation should be short, 5 or 10 word descriptions of what you see.

Time

Cold

Room Temp

Hot

Initial

5 min

10 min

15 min

20 min

25 min

30 min

Part 2—Yeast and
Energy Source
Observations:
Your observation should be short, 5 or 10 word descriptions of what you see.

Time

Salt

Sugar

Sugar Substitute

Initial

5 min

10 min

15 min

20 min

25 min

30 min

Questions:

1. What is the
difference between a typical
autotroph and a typical
heterotroph? Why is the answer not as simple as “one is a plant and one is an
animal”?

2. Define
metabolism. What would cause an
organism that normally produces ATP by respiration to switch to producing it
by fermentation?

3. In which of your
temperature experiments (Part 1) did the yeast show the most activity? Why,
from a biological perspective, do you think this is?

4. In which of your
energy source experiments (Part 2) did the yeast show the most activity? Why,
from a biological perspective, do you think this is?

5. Based on what you
know about respiration and fermentation, which was happening (respiration or
fermentation) in the bottles? What filled (or should have filled) the
balloons in your experiment?