Download BIOL212DigestionLabAPR2012

BIOL 212 Lab
Name:
Animal Digestion and Digestive Structures
OBJECTIVES:
· Compare the
basic layout and functions of the different forms of animal digestion
· Learn proper dissecting techniques
· Use histological examinations to help identify functions of various digestive organs
INTRODUCTION
In this Lab exercise, we will explore the digestive structures of animals. The two main objectives of
this lab are to 1) compare the various digestive structures of the animal kingdom and 2) use the histology
of the digestive structures to help identify the function of digestive structures as a whole.
The evolution of digestive structures and systems play a big part in the differences we see in
various animal bodies. Briefly, we began our look at the animal kingdom by examining animals with body
cavities that took on numerous roles for the organism. For instance, the gastrovascular cavity of
Cnidarians and Platyhelmintheans served the animals as digestive, circulatory, and excretory structures.
The spongocoel of a Poriferan serves as the excretory and circulatory structures, and is the only animal
we will be viewing that has intracellular digestion – takes food inside its cells via phagocytosis and digests
rather than dumping enzymes into an opening within the body. In the “simpler” animals, one cavity must
serve many roles. These cavities we considered as “incomplete”. Later, in the more “complex” animals we
examined “complete” digestive tracts that functioned almost entirely for digestive function (along with
removal of solid waste). These complete digestive tracts were one-way, two-opening tracts, which were
often “regionalized” and included specific segments that handled various digestive and absorptive functions.
For instance in the earthworm (Phylum Annelida), the digestive tract is organized into a mouth, a pharynx,
an esophagus, a crop, a gizzard, an intestine and an anus that all have specific functions for the overall
process of the digestive system. Not all animals contain these regions, but the overall processes are
basically the same. In Part I of this lab, we will focus our attention on some of the various digestive
structures. As you are examining these slides and organisms, try to decipher how the system works based
on the layout and the structures you observe.
STUDENT PREPARATION AND GENERAL LAB PROCEDURES FOR THIS LAB.
Prepare for this laboratory by reading Chapter 41 in Campbell text (particularly Concepts 41.2 to
41.3, pp. 880 to 891). Familiarizing yourself in advance with information and procedures covered in this
laboratory will give you a better understanding of the material and improve your efficiency. As you work
your way through the lab, you will examine slides and some models. For each slide you view under the
scope, draw and label the specimen. When you label the drawings, be sure to include all the structures that
you can identify on the specimen and the total magnification you used.
I. A Tour through the Animal Kingdom, Gazing at the Digestive Systems and Structures
Background: As mentioned above, there is a wide array of digestive systems and structures we have
already looked at as we examined the ―evolutionary trendsǁ‖ of the Animal Kingdom. This is an opportunity
to bring all of these different digestive structures into view at one time for comparison. As you examine the
slides, consider the following questions…
· What are the digestive structures you can see and identify?
· Is this a complete or an incomplete digestive system (you may have to look and consider beyond the
cross-sectional slides)?
· How are digestion and absorption processes handled by these structures?
· How are the products of digestion (basically organic and inorganic nutrients) distributed from these
structures to the other cells of the body?
Lab: Animal Digestion
1
Materials Needed
Preserved Specimens for dissection, each set of lab partners: one Rat, one earthworm
For viewing: Demonstration pigeon
Live specimens: Clams (if available)
Various slides (listed below)
Plastic Earthworm model, Hydra model, Clam model, Human digestion model
Structures and cells to look for and identify (some of these slides you may have seen in diversity lab):
• Microscope Slides:
* Hydra (c.s. and w.m)—Identify gastrodermis, epidermis, gastrovascular cavity, cnidocytes
* Planaria digestive(w.m.)—Identify the gastrovascular cavity, pharynx
* Mammalian columnar epithelial cells (small intestine) – Identify microvilli, apical surface, basal lamina
• Earthworm model: Use this to help identify the regions of the digestive tract. Using your textbook and
other resources, label the mouth, pharynx, esophagus, crop, gizzard, and intestine.
• Clam model. Identify the palps, intestine, stomach.
II. Hydra Model. Identify gastrodermis, epidermis, gastrovascular cavity, cnidocytes, tentacles.
III. Animal Dissections
Use the pdf files from the website for instructions on proper dissection techniques. There is more information
on the pdf files than you are responsible for knowing. However, you will be asked to identify the list of digestive
structures and their functions included below for each of the dissected organisms:
Earthworm – information specific to dissection technique and digestion are highlighted in yellow in the pdf file!
External Anatomy: mouth, anus
Internal Anatomy: pharynx, esophagus, crop, gizzard, intestine
Rat
External Anatomy: mouth incisors, anus
Internal Anatomy: epiglottis, liver (medial lobe, left & right lateral lobes, caudate lobe), esophagus, pharynx,
stomach, pyloric sphincter, (spleen- not digestive!), pancreas, small intestine (specific area of duodenum as well
as entire intestine), cecum, large intestine, rectum, salivary glands, coelom
Demo Pigeon: External anatomy: beak, vent
Internal Anatomy: esophagus, crop, stomach, gizzard, small intestine, large intestine, cecum, rectum
Prelab:
1. How is the shape of the flatworms well suited to their feeding style?
2. How does the cnidaria (hydra) feed? The sponge? The rat?
3. Which of the organisms you will be viewing in lab today have complete digestive systems (digestive tracts)? What
is meant by this term complete digestive system?
Postlab: Compare and contrast the digestive systems of the bird and the rat, two vertebrate animals. Describe
common structures and features, and how these features are modified for the particular organism’s diet and lifestyle.
Notebook Check:
1. Labeled drawings of the slides – include specimen name, total magnification, and any notes that will help you with
identification for study and for the practicum!
2. Labeled sketches and notes on dissected animals.
3. Any other notes, etc. that my help you in learning the material. I will not be grading your additional notes, but you
may find them helpful during practicum!
NOTE: Get checked off for each dissection before leaving lab! For Lab Quiz: Be able to identify and describe the
function of the different organs and structures you viewed in lab. Be able to discuss how feeding styles, body plans,
specific digestive organs, etc. are modified to suit each animal’s environment and lifestyle
Lab: Animal Digestion
2