“Iago”
- Daphnia and Hydra Lab
Prelab
questions:
Use
classroom researches to answer these questions on a separate sheet of
paper. Prelab questions must be complete before you can begin the
lab!
What
is a Daphnia? What phylum does it belong to? What do they eat?
Sketch
a Daphnia below, labeling anterior and posterior ends.
What
phylum do Hydra belong to? What do hydras eat?
What
are nematocysts and how do hydras use them?
Sketch
a hydra below, and label the oral and aboral ends. Show where the
mouth of the hydra is.
What
do you predict will happen when a hydra and a daphnia are introduced
into the same dish? Explain your reasoning.
Feeding
the Hydra!
Answer
all questions and make all drawings on your own paper - you will be
using these notes and sketches for you typed lab report.
In
this lab, you’ll observe the feeding behavior of the brown
hydra. The brown hydra is a predator; it uses it tentacles, lined
with stinging cells called nematocysts,
to capture prey. In this case, we’ll be feeding them tiny
aquatic crustaceans called daphnia.
Procedure
Use
a pipette to carefully take a hydra from the shipping container and
place it on a microscope slide. (You may need to use the pipette to
shoot a gentle stream of water at the hydra and then suck it into
the pipette while it’s floating loose.)
Let
the hydra settle down and observe it for a few minutes under the
microscope. (Do not
use the highest power!) Use your notebook to
record careful, detailed notes describing
the behavior of the hydra. (What parts of it are moving? How are
they moving? How fast or slow?
Draw
a picture of the hydra.
The hydra sits on a strong muscle called the basal disk. At the
other end, the tentacles surround the hydra’s mouth. Label the
basal disk, tentacles. Also label the oral and aboral ends.
Get
a separate dish and use a pipette to carefully take a daphnia from
the shipping container and place it on a microscope slide. Try to
get the smallest daphnia you can.
Observe
the daphnia for a few minutes and
make notes about its
appearance and behavior.
Draw
a picture of the daphnia.
Use
the pipette to re-capture the hydra and add it to the dish
containing the hydra. Watch carefully what happens when the hydra
and daphnia touch. Take
good notes - you will be writing up your observations. (Watch
the daphnia’s heartbeat - you can see the heart of the hydra
through its skin.) In your notebook, describe what happens every 30
seconds from first contact for at least 10 minutes or until the
daphnia is completely eaten. Draw a few sketches to show what the
daphnia and hydra look like.
Post-Lab
Hydras
have only a single opening to their gut - the mouth. Does a hydra
have a stomach? Explain your answer.
What
will happen to the parts of the daphnia that the hydra cannot digest?
How does this differ from the human digestive system?
Would
the hydra have been able to capture the daphnia without nematocysts?
Explain your answer.
Lab
Report
Your
completed typed lab report on this part of the lab should have all
your drawings and observations, as well as answers to all questions.
The lab report must be typed
and in complete sentences with correct grammar and spelling. It
should describe the actions you observed in
detail.
Be
careful not to use the word “it” if there’s any
doubt about what “it” means. Use correct terminology.
Your
report should also include the labeled drawing of the hydra and your
sketches of what happened as it attempted to capture the hydra.
BAD:
It’s grabbing it
with the things.
GOOD:
The hydra is using its tentacles to grab the daphnia.
BETTER:
The hydra is stretching out three of its tentacles to grab the
daphnia. The daphnia is struggling and kicking, but it’s
kicking more and more slowly and weakly.
Posts
No comments:
Post a Comment