Lab 2: What is Life?
Objectives
Track Daphnia response to alcohol and caffeine
Observe a protist cell, plant cell, and human cell
Compare living specimens in three eukaryotic kingdoms
Introduction
In a world that focuses on differences, it is sometimes difficult to comprehend the true
interconnectedness of life on our planet. In actuality, there are many characteristics that all
organisms have in common. An understanding of our mutual attributes can pave the way to
appreciation, respect, and a feeling of kinship for all life.
Throughout history, humans have been curious about the world around them. In fact, the
word science means “to know.” Humans have been influenced by superstition, religion, and
logic to find answers to the world around them. When the answer can be supported by empirical
evidence, we can label this as science. Generally, scientists use logical steps to arrive at an
answer. These steps make up what is known as the scientific method. The scientific method
consists of observing, predicting, testing, and interpreting. It is a powerful tool that has allowed
scientists to unravel life’s mysteries and characteristics.
The characteristics that all living things share can include: (1) organization, (2) energy
use and metabolism to maintain homeostasis, (3) reproduction, (4) growth and development, (5)
adaptation, (6) movement, and (7) response to stimuli. In addition, whether the organism is a
single celled protozoan like Amoeba or Paramecium or a multicellular organism composed of
several trillion cells, like a human being, the cell remains the fundamental building block of all
living things.
An organism acquires and uses energy to build new structures, repair, or break down old
ones. The term metabolism refers to the collection of chemical reactions within cells that direct
this acquisition and use of energy. Metabolic reactions both build up (anabolism) and break
down (catabolism) organic compounds. Producers are organisms that extract energy from the
nonliving environment, such as light energy from the sun. Plants, algae, and cyanobacteria are
producers that extract this energy through photosynthesis. Consumers, in contrast, obtain energy
by eating nutrients that make up other organisms. Decomposers obtain nutrients from dead
organisms. Bacteria are important decomposers in any ecosystem. This close association
between organisms illustrates the interdependence of life on Earth.
Organisms produce individuals capable of reproducing new individuals. Reproduction
can be as simple as a bacterium dividing asexually into two identical copies or as complex as the
sexual reproduction of a mammal where the offspring contains characteristics of both parents. In
either case, reproduction transmits genetic instructions (DNA) for developing the defining
characteristics of the organism from one generation to the next.
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Lab 2: What is Life?
2.1 Observing Daphnia magna
1. Capture a living Daphnia with the appropriate plastic pipette and place it (plus some
water from the jar/aquarium) onto a clean glass slide. Examine the Daphnia under the
scanning power objective. Do NOT place a cover slip on the Daphnia.
2. Develop a hypothesis about the effects of alcohol and caffeine on the Daphnia heartbeats.
Write your hypothesis on the data sheet now before proceeding forward.
3. Calculate the number of heartbeats per minute for your Daphnia. The simplest way to do
this is to calculate the number of heartbeats in 15 seconds. Then multiply the number of
heartbeats by 4 to get the number of heartbeats in one minute. Record your data in Table
1. This will be your control.
4. Remove the water from the slide with the edge of a tissue. Place one drop of 1 % alcohol
on the Daphnia. Wait 1 minute and then again count the heartbeats. Record your value
in Table 1.
5. Remove the 1 % alcohol with the edge of a tissue. Place one drop of 2 % alcohol on the
Daphnia. Wait 1 minute and then again count the heartbeats. Record your value in
Table 1.
6. Using the same procedure as above, monitor the effects of 3 % and 4 % alcohol solutions.
Record your results.
7. At the end of the alcohol series, switch to the caffeine series, first 1 %, then 2 %, then 3
%. Record your results.
8. When finished with the Daphnia, return it to the appropriate jar/aquarium.
9. Also record the class average in Table 1.
2.2 Observing Paramecium
1. On the center of a clean glass slide, place 2-3 drops of Detain. This chemical will slow
the fast moving Paramecium.
2. Place one drop of water containing Paramecium on top of the Detain drops.
3. Gently place a cover slip over the drop of water with the Detain.
4. Observe your sample under the scanning power objective first. Once you have focused
the sample, go to low power, fine focus, and then go to high power and fine focus.
5. Draw one Paramecium as seen under the high power objective.
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Lab 2: What is Life?
2.3 Observing a living plant leaf
1. On a clean slide, place one drop of distilled water.
2. Put a young leaf from the tip of the Elodea plant in the water drop. Orient the leaf so that
its upper surface faces you. Cover the leaf with a coverslip.
3. Observe the leaf first under the scanning power objective, then the low power objective,
and then the high power objective. Draw a couple representative cells as seen under the
high power objective.
4. Label the chloroplasts and the cell membrane/cell wall area.
2.4 Observing human cheek cell
1. On a clean slide, place one drop of distilled water.
2. Gently scrape the inside of your cheek with a clean toothpick.
3. Swirl the toothpick in the drop of water.
4. Add a VERY SMALL drop of methylene blue. Cover with a coverslip.
5. Observe first under scanning power objective, then lower power objective (fine focus
only), and then high power objective (fine focus only).
6. Draw a few representative cells as seen under the high power objective.
7. Label the cell membrane and the nucleus.
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Lab 2: What is Life?
Daphnia Experiment
Hypothesis:
Procedure: (already written for you; no need to rewrite)
Results:
Table 1. The values are in heartbeats per minute.
Your Group’s Results Class Average
water
1% alcohol
2% alcohol
3% alcohol
4% alcohol
1% caffeine
2% caffeine
3% caffeine
Conclusion:
1. Explain and discuss if the class average numbers support your hypothesis or not. If there
are discrepancies somewhere, explain those discrepancies.
2. Provide two possible ways that your Daphnia experiment could have been improved or
you can discuss possible errors that you may have made.
3. Every controlled experiment needs a control group. Describe the control group in this
Daphnia experiment.
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Lab 2: What is Life?
Drawings
Paramecium a few Elodea cells a few cheek Cells
Total mag = 400X Total mag = 400X Total mag = 400X
(Label the chloroplasts and (Label the nucleus
cell wall/cell membrane area) and cell membrane)
Complete the following table of comparisons. All these living things would be categorized into
Domain Eukarya.
Animal Animal (Homo Plant (Elodea) (Protist)
(Daphnia sapiens) (Paramecium)
magna)
Unicellular or
multicellular?
Consists of
prokaryotic or
eukaryotic cell?
Genus?
Remember to write
genus name
properly
Which
characteristics of
life did you
observe for this
organism?
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