Animal Lab
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This lab is due Monday, 5/6, at midnight.  Every where the font is tiny, that is part of what you have to answer on the submission form (off BB).

    There are a lot animals in this world and we have begun to consider them with our recent diversity lab. But why are there so many different animals?  One reason is that there are a lot of different ways to solve the basic problems animals must face.  We all face similar problems, but different animals solve them differently.  One problem is eating.  We all have to eat, but different animals eat differently - these different styles can create the different body plans of animals.  Another animal problem is moving around in our world.  Different animals have different solutions as to how to move.  This lab examines some of the ways different animals solve the common problems of eating and moving.

Exercise #1, What is Digestion?

Introduction

    Understanding animal digestion is an important step to understanding the ways that animals eat.  In Principles of Biology I we have studied macromolecules, cells and the diversity of life among other things.  This lab will use information from all these areas to think about something we do every day - digestion. By thinking about animal digestion we will get a better understanding of these topics, and we may also come up with some new ideas.

    What makes an animal? How are animals different from Protists, Fungi, and Plants?  Please list three traits that all animals have in the space below (for review see your diversity lab). 

Animal Traits: (I've given you one of them to get you started)

1. multicellular     2.  _____   3. _____

    In many ways animals are like protists; both move around and both are heterotrophic.  Sometimes it is difficult to tell them apart, particularly when the animals are microscopic. One way that microscopic animals are distinguished from protists is that animals digest much of their food outside their cells, while protists digest all their food inside their cell/s.  What does this mean to you? - It plays a big role in determining how you're put together.

What is digestion?

Please write in a definition of digestion in your own words:  _____

Why do we digest?

Reason #1

    To do any good, the food we eat must get into our cells. One molecule commonly found in food is starch. To get into our cells, the starch must cross the plasma membrane.   Starch cannot easily cross a membrane (think back to the Diffusion Lab)... its transport requires ATP and uses vesicles.

What can cells do to starch to make it easier to bring it across the membrane?

When starch is broken down, what kind of molecule is released would be released?

Therefore, Reason #1 why we do digestion is to break foods down into small pieces for better absorption (transport) across a membrane.

Reason #2

    The food we eat contains proteins and other polymers that were originally assembled to meet the needs of the plant or animal they were part of.  When we eat them, we reassemble the polymers to meet our own needs. 

    For example, hair, skin and fingernails contain the protein keratin. Keratin is made from amino acids. One of its amino acids is leucine. We can not make leucine, we have to get it from our diet.  You would not be able to make new keratin, and your hair would not grow, if you did not eat protein that included leucine. To get the leucine out of the dietary protein, we have to digest the protein first.

    Example:  Imagine this word is a protein and each letter is one of the amino acids in the protein.

F L A T P A N T S S

  (digest)

                

       

 

 

 

(reassemble)

_______________

(to reassemble, it is just like a word scramble puzzle... make the letters meaningful)

Based on the above example, Reason #2 we do digestion is to recycle food parts into something more useful for ourselves.

Digestion wrap-up

Animals mainly digest their food outside of their cells and then absorb the monomers.  To do this, animals must do several things.  They must:

  1. Secrete enzymes that will digest the food.

  2. Absorb the monomers that are released from the food.

  3. Form a cavity where the food can be held until it is digested and the monomers absorbed. 

  4. Have a way to transport the monomers from the cavity to the rest of their body. 

  5. Have a way of emptying the cavity of non-digestible material.

Background on animal movement

    When you and I move around, we do so using specialized muscles.  Many animals have muscles.  In fact, when people consume meat (steak, chicken legs, etc.), what they are eating is muscle.  But not all animals have muscle... and all animals can move.  What's up with that?

    It turns out that whether or not an animal has true muscles depends on the way they develop embryonically.  Some animals develop as embryos from a ball of cells with 2 body layers, while others have 3 body layers.  For simplification here, you can think of these layers as concentric rings.

    All animals have at least 2 body layers-- that is important to make an organism's skin (the outer coating) and an organism's digestive tract (gut).  But it is not enough to also make true muscles.  Those organisms with a third body layer, in the middle of the other two, can now make true muscle.

    You can tell if an organism has true muscles by watching it move.  You have watched Hydra move and you will be watching Planaria move.

Exercise 2:  Animals Investigation

Animal #1:  Hydra (of Phylum Cnidaria)

    One of the simplest of animals is the Hydra.  The Hydra is related to jellyfish (all are in the Phylum Cnidaria).  They live in freshwater.  Any pond in Massachusetts is likely to have some Hydra in it.  A Hydra’s body consists of a central cavity surrounded by tentacles. As an animal, the Hydra digests its food outside of its cells.  To do this it needs to have a cavity to hold the food while it is digested.  The Hydra is about the simplest animal possible.  It has no brain or circulatory system. It really only consists of a digestive cavity and tentacles to put food in the cavity – that’s about it!  

    You were given Hydra to view at home.  To get one out of the tube, you that you have to look for them in the tube and specifically suck them up.  They are animals, and are big enough to see with the naked eye... if you just sucked out water from the tube, you probably did not see any Hydra.  Meanwhile, Hydra also tend to stick to the plastic walls of your container.  So, you will need to pry them off with the pipette as you suck them out.  Be gentle!

    View them by mounting them on the well-slide you got with your kit (not a regular flat slide).  First just view them on the slide without the coverslip and without your microscope.  When you have seen all you can, go ahead and coverslip the Hydra and view using your microscope (lowest power).  When viewing them, you may have noticed that their inside looked brownish/orangish and their outside looked clearish.  They only have two body layers, and they are color-coded!  Pretty cool.

    The "digestive cavity" in the drawing above is actually a gastrovascular cavity (or GVC).  The "gastro-" part is for the digestive function of it and the "-vascular" part is due to the fact that this organism uses this cavity like a vascular system (heart and blood vessels), and does not have a separate vascular system.  The drawing does not depict another cool thing-- that the gastrovascular cavity also extends into each tentacle.

Questions for Discussion

1.  Digestion produces monomers.  With no circulatory system, how do you think the monomers get distributed to a Hydra’s cells?

2.  We use a circulatory system but Hydra don’t need one. Why might we need a circulatory system to distribute the products of digestion?

3.  How did Hydra move?

4.  Based on the number of body layers in Hydra and on the speed with which they moved, does this organism have true muscles?

Animal #2:  Planaria (of Phylum Platyhelminthes)

    Planaria are quite a bit more complicated than Hydra.  Planaria have three body layers and the beginnings of a nervous system. They need a basic nervous system because they go out and search for food.  Hydra just wait for their food to swim by, but Planaria go out and hunt their food down.  If you’re going to go hunting, you’ll need senses and at least the beginnings of a brain.

    Place a Planaria on your well-slide with a drop of water and watch it move for a little bit before coverslipping it or using your microscope.  Do you see it moving?  How does it move?

    If you are feeling adventurous, put a (tiny!) bit of food in the drop, too-- then coverslip it.   For food, use a tiny, tiny bit of raw liver (smaller than the Planaria itself).  Wait a moment for the organism to get used to its environment-- and then it might eat!  Planaria's mouth is in the middle of its body... it can extend its pharynx (throat) so that it can reach its mouth out.  You might get to see that.  Planaria brings its food into a gastrovascular cavity.

    Whether or not you feed Planaria, be sure to coverslip your slide and view this organism under the microscope.

    Here is an image of Planaria taken from a web site devoted to this creature.  I added labels to it.  You should be able to see that the GVC in this organism is highly branched... not just a big sack as it was in Hydra.  In this image, Planaria looks rather transparent-- but that is only a staining and microscopy trick... your Planaria won't be see-through.

Questions for Discussion

1.  Planaria have no circulatory system.  How is their digestive system designed to make sure that the products of digestion are distributed to their cells?

2.  How do Planaria move?

3.  Do Planaria have true muscles?

Animal #3:  Earthworms (of Phylum Annelida)

    Earthworms are pretty sophisticated animals.  They have a brain, circulatory system and complicated digestive system. 

    The earthworm digestive system is complicated because they have something that Hydras and Planaria do not have. Hydra bring their food in through their mouth, digest it, and then eject the waste products back out through their mouth. Planaria do the same. Earthworms have two openings; a mouth to bring the food in and an anus to release waste.  This makes worms more efficient.  The development of a second opening was a great accomplishment in the history of life. With an anus, worms can process their food in an assembly line manner and get a lot more out of it.

Lab Activities

View a live earthworm

    Watch how an earthworm moves around.  Can you tell which end is the head?  Can you see the method it uses for movement?  Does it move quickly or slowly?

    Use these observations to answer the questions that follow.

1.  Does the earthworm have true muscles?

2.  The clitellum (used for secretions) is closer to the:

Earthworm dissection

    Your earthworm should have been frozen overnight prior to beginning your dissection.  It is best to freeze your earthworm in a very tiny bit of water (just enough to make it moist and a bit icy, but not enough to end up with a big ice cube).

    Be sure before you continue that you have watched the video showing how to do the dissection.

  1. Thaw your earthworm briefly.  It works well to thaw it by soaking it in some cold water.  You should be able to feel the gizzard through the outside of the earthworm at this point.

  2. You will only need the anterior (head) half of the earthworm.  So cut it in half and discard the posterior (rear) half.

  3. Pin down the tip of the head at one end of your dissecting tray.  As you pin down the cut end, stretch out the earthworm.  Be sure that you pin it so that the ventral surface (the side that normally faces the earth) is on the bottom.

  4. Cut the earthworm open with one long cut down the dorsal midline of the earthworm (the side that normally is kept up).

  5. Pin your earthworm open, rinse it in the sink, and view the regions.

We are interested in finding two of the sophisticated organs that set earthworms apart from lower worms. These are:

1.      A digestive system with two openings. Note, this allows the worm to have a lot of subregions (pharynx, crop, gizzard, etc…) that allow efficient processing of food.

2.      A circulatory system with heart and blood vessels.  The circulatory system carries the products of digestion to all tissues. This allows the worm to be much bigger than the Planarian or Hydra.

Locate the following worm organs/areas on your dissection:

pharynx dorsal blood vessel septa
esophagus hearts ventral nerve cord
crop gizzard intestines

Questions for Discussion

1.  How is the earthworm digestive system different from the Planaria digestive system?

2.  Earthworms have a gizzard that aids digestion by physically breaking food. Why is the gizzard important in digestion for an earthworm?

3.  Earthworms have a circulatory system with a heart and blood vessels.   Why do an earthworms need a circulatory system to distribute the products of digestion when Planaria do not need one?

 

 

© 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.

Last changed: January 21, 2007