Práctica de laboratorio sobre el efecto de sustancias tóxicas en la pulga de agua

1. LABORATORY PRACTICE: OBSERVATION OF WATER FLEA
INTRODUCTION:
Water fleas belong to the Animal Kingdom, Phylum Arthropoda, Subphylum Crustacea,
Branchiopoda Class, Cladocera Order.
Cladocera animals have 4 thoracic appendixes (thoracopods). By moving these
appendixes, Cladocera create water flows to feed, move and breathe through their gills.
They feed by filtering suspended particles. Among their appendixes they have an
alimentary canal, where food particles go in towards their mouth.
The best known Cladocera are Daphnia magna and Daphnia pulex. They are
approximately 3 mm long. Daphnia are particularly interesting animals to study because
they are easy to keep and their exoskeletons are transparent. So, it's easy to observe and
identify their internal organs through a magnifying glass or a microscope.
Their heart beats very fast, pumping blood throughout their body. Their tubular intestine
goes from mouth to their anus. They feed on microscopic organisms such as bacteria,
seaweeds and protozoa. Daphnia drive food towards their mouth by using the water
flows thay they generate with their leg movements. Female Daphnia have a large brood
chamber just below their heart. It holds the female’s eggs.
Daphnia can survive in almost any fresh water environment like lakes, ponds, streams,
swamps, and marshes.
You will watch some features and behaviors of an organism called Daphnia. You will
also observe the organism through a microscope and prepare a scientific drawing of a
Daphnia and some of its structures. And finally, you will measure a Daphnia's
heartbeat before and after the organism has been treated with two different chemicals.
OBJECTIVES
To observe and draw a Daphnia by using a microscope or magnifying glass, and
identify its major structure.
To describe the structure and behavior of a Daphnia.
To determine the heartbeat of a Daphnia under different conditions or circumstances.
MATERIALS
Optical microscopes
Microscope slides
Daphnia

2. Fig. 1. Microscope image
ACTIVITIES
1. Observing Daphnia
Prepare a slide with a Daphnia in a drop or two of spring water.
Use your microscope to focus on the Daphnia at the highest zoom at which you can see
the entire organism. Look for the intestine, which runs from the mouth to the anus.
Notice its color.
Find the Daphnia's heart. Notice how fast it
beats.
Find the "brood chamber", a sac located
just below the heart of the female Daphnia.
Focus on your Daphnia's eye. Switch the
microscope to a higher zoom to observe the
eye in greater detail.
Focus on one or the antennae at high zoom.
Focus on one of the legs at high zoom.
Notice the bristles.
2. Preparing a scientific drawing of a Daphnia
Switch the microscope to 40x.
Draw the Daphnia in as much detail as you can.
DRAWING 4x10= INCREASED 40 TIMES

3. 3. Exploring the effect of alcohol and cola solutions on the heartbeat of a Daphnia
Prepare a slide with a Daphnia in spring water, a weak alcohol solution or a weak cola
solution (your teacher will provide you with the appropriate product).
Measure the Daphnia's heartbeat during 10 seconds. You can do this by writing a dot on
a paper every time the Daphnia's heart beats. Count the number of marks to determine
the number of times your Daphnia's heart has beaten in 10 seconds. Calculate the
heartbeat per minute.
Repeat this procedure three times and calculate the average heartbeat.
Compare the different heartbeats of Daphnia’ heartbeats in spring water, alcohol and
cola with your partners. What effect does cola have on the heartbeat of a Daphnia?
Why? What effect does alcohol have on the heartbeat of a Daphnia? Why?

4. 4. Answer the following questions in your science notebook and share your
responses with the class.
1. Observe different water flea parts through a microscope and color the bodies
following this color key:
 Heart: Red
 Esophagus and intestine: Green
 Eggs: Yellow
 Eye : Black
 Antennae: Brown
 Thoracic appendixes: Pink
2. Look at the Daphnia’s eyes. How many eyes does a Daphnia have?
3. Does the brood chamber hold the female’s eggs? How many eggs does it have?
4. Look at the photograph. Are water fleas oviparous, viviparous or ovoviviparous?
Why?
5. Has Daphnia's carapace transparency helped you in your observations?
6. Is the heart in dorsal or in ventral position? How many times does the heart beat
in a minute?
7. Write down the functions of the thoracic appendixes (thoracopods).