STRUCTURE AND FUNCTION
IN Hydra

In Biology we can ask these questions: What is the basic common nature of all living organisms? What does being alive actually mean?  How does a living organism differ from a dead one? In what general ways do individual organisms perform the functions of living?
Every organism is a variation on structural and functional themes created many millions of years ago.  Although the living world today is a varied collection of unicellular and multicellular organisms, most organisms perform the same basic activities. Thus, the study of one animal teaches us something about many animals.
We shall concern ourselves, for the present, with the animal way of life, By closely examining the ways in which a single animal performs its life functions we call come to it better understanding of how the great variety of animals meet their problems of living.  We do not need a walking, stalking beast for this purpose.  Sea anemones, jellyfish and corals all belong to the phylum Cnidaria.  The cnidarians are mainly marine animals.  They exist in one of two body forms: a vase-shaped polyp or an umbrella-shaped medusa.  Hydra is a typical cnidarian polyp.  This organism, depending on the species, may be colorless, green or brown.  Hydra is the only common freshwater cnidarian.  It lives in slow-moving streams and ponds attached to sticks, rocks and the undersides of leaves.  Although hydras spend much of their lives attached to a surface, they are not really sessile organisms.  Hydras can detach themselves from a surface and somersault to a new location.  
The multicellular organism Hydra carries out all metabolic and reproductive functions within the confines of one small cell.  For this and other reasons, Hydra is a convenient organism for our study of the way of life of animals in general.
In our studies, you will study Hydra in great detail, not simply observing it.  You will see it move, ingest and digest food, get rid of waste materials, respond to its environment, and reproduce its kind.  There are other life functions, which you may read about them from other sources.

* The purpose of this exercise is to examine a typical animal (Hydra) and to begin to correlate the functions of living with the structures observed.

MATERIALS

Culture of Hydra
Compound microscope
Methyl cellulose solution
Iodine or methylene blue stain
Medicine-dropper pipettes for transfer of organisms and solutions
Slide and cover glass



PROCEDURE

1. With a medicine dropper, obtain a hydra from the culture jar.  You may have to gently scrape the hydra loose from the glass.
2. Place the hydra and some of the water from the jar in the depression of a concave microscope slide.  Cover the depression with a coverslip.
3. With a dissecting microscope or a hand lens, observe the hydra for a few minutes.
4. Using the prepared slides, and the compound microscope, make observations regarding the structures of the hydra.