BIOLOGY 2402
GENERAL ZOOLOGY
LABORATORY TERMINOLOGY
AND
ACCESSORY MATERIAL
A GUIDE TO WHAT IS REQUIRED FROM LAB MANUAL EXERCISES
Revised August 2009
EXERCISE 1 – THE MICROSCOPE
Exercise 1A – Compound Light Microscope
base
in-base illuminator
iris diaphragm lever
stage
coarse adjustment knob
fine adjustment knob
transformer control knob
objectives:
scanning-power (4X)
low-power (10X)
high-power (40X)
oil immersion (100X)
parfocal lens
nosepiece
ocular (10X)
interocular distance scale
*Note: Never use the coarse adjustment knob while looking at an object with a high-powered lens.
**Omit: “How to Use the Oil-Immersion Objective” & “How to Measure Size of Microscopic Objects.”
Exercise 1B – Stereoscopic Dissecting Microscope
base
in-base illuminator
stage
zoom objective
substage mirror control
reflected vs. transmitted light
reflected light mirror
ocular
focus control knob
transformer
Exercise 1C – Electron Microscope
Be able to distinguish between micrographs taken through a transmission electron microscope and a scanning electron microscope. How does an electron microscope relate (in terms of magnification) to the other two types of microscopes you have used today?
EXERCISE 2 – CELL STRUCTURE AND DIVISION
Exercise 2A – The Cell—Unit of Protoplasmic Organization
Squamous Epithelial Cell Egg Cell of Sea Star
plasma membrane (or cell membrane) plasma membrane
cytoplasm cytoplasm
nucleus nuclear envelope
nucleus
nucleolus
Organelles
Electron Micrograph Cell Model cytoplasmic organelles (cont.)
endoplasmic reticulum nucleus endoplasmic reticulum (ER)
ribosomes nuclear membrane rough ER
mitochondria (look for the cristae) chromatin smooth ER
Golgi complex nucleolus ribosomes
nucleus cytoplasmic organelles centrioles
nucleolus mitochondria cytosol
Golgi complex cell membrane
Exercise 2B – Cell Division—Mitosis and Cytokinesis
Know the cell cycle:
interphase
mitosis (PMAT)
-prophase
aster
spindle fibers
centromere
chromosome
-metaphase
metaphase plate
-anaphase
daughter chromosome
-telophase
cytokinesis
cleavage furrow
EXERCISE 3 – EMBRYOLOGY
Exercise 3B – Cleavage Patterns—Spiral and Radial Cleavage [begins on page 37]
Spiral Cleavage: Early Embryology of the Ribbon Worm, Cerebratulus
Protostomia (protostomes are animals in which the embryonic blastopore forms the mouth)
Cerebratulus (a ribbon worm)
distinguish between unfertilized ovum vs. fertilized, undivided ovum (=zygote)
1
morula stage
blastula stage
-blastocoel
gastrula stage
-archenteron
-blastopore
1
In “Early embryology of Cerebratulus, a nemeterean worm,” (Fig. 3-8), omit figure J.
Radial Cleavage: Early Embryology of the Sea Star, Asterias
Deuterostomia (deuterostomes are animals in which a secondary embryonic opening forms the mouth.)
Asterias (the sea star) – on photos “Embryology of a sea star,” (Fig. 3-9), figures A-I only; omit J-L.
distinguish between unfertilized ovum vs. fertilized, undivided ovum (figures A and B)
1
morula stage
blastula stage
-blastocoel
gastrula stage
-archenteron
-blastopore
1
-blastocoel
Exercise 3C – Frog Development
1
fertilized egg (zygote)
vegetal pole/hemisphere
animal pole/hemisphere
morula stage
blastula stage
-blastocoel
gastrula stage
-blastopore
-yolk plug
-germ layers:
endoderm1
ectoderm2
mesoderm3
-archenteron4
-blastocoel
-neural plate
-notochord
1
“Early embryology of a frog to a tadpole stage”, (Fig. 3-10), figures A-H only; omit I-L.
1All yellow on models represents endoderm.
2All pink/orange to reddish color on models represents mesoderm.
3Ectoderm is the dark brown to black layer on the outer surface of the models.
4Space (or cavity) represented by the blue color on models is the archenteron.
EXERCISE 4 – TISSUE STRUCTURE AND FUNCTION
*Read the introductory paragraphs. Know the terms in bold print.
General Description of Basic Tissue Types
Epithelial Tissue (simple):
simple squamous epithelium
simple cuboidal epithelium
simple columnar epithelium
pseudostratified epithelium
Epithelial Tissue (stratified):
stratified squamous epithelium, keratinized
stratified squamous epithelium, nonkeratinized
Connective Tissue:
areolar connective tissue
adipose connective tissue
hyaline cartilage (contains lacunae)
bone
-osteocyte
-osteon
-osteon canal
-lamellae
-lacuna
-canaliculi
blood -- (erythrocytes, leukocytes, platelets)
Muscle Tissue:
smooth muscle
skeletal muscle
-striations
cardiac muscle
-striations
-intercalated disk
Nervous Tissue:
neuron
*Note: There are only four basic types of tissue—epithelial, connective, muscle, and nervous. All types within each of the four categories will be referred to as specific tissue types.
Exercise 4A – Tissues Combined into Organs
Cross-section through the Trachea (pg. 63)
hyaline cartilage
pseudostratified epithelium
loose connective tissue
smooth muscle
SOME IMPORTANT CONCEPTS IN ZOOLOGY
The purpose of this exercise is to demonstrate the concepts of homology and primitive vs. derived characters and the use of these concepts in the classification of organisms. These ideas provide an important framework for the study of relationships among organisms in that they demonstrate first, the similarity of structure among closely related organisms and second, the modifications of basic structural plans that distinguish specific organisms. Such studies of relationships among organisms are known as the subdiscipline in biology called systematics. In addition, you will examine the similarities and differences among serially homologous structures; that is, structures that are repeated within an individual organism.
Today's exercise uses mammalian structures to illustrate these principles.
Homology and Convergence
Homology is defined as equivalence of structure that results from inheritance from a common ancestor. That is, structures in different organisms are homologous if each has been derived (in evolutionary time) from the same structure in the common ancestor of those organisms.
Consider structure S in organism A. Suppose that two subpopulations of A become geographically isolated from one another for a long period of evolutionary time and are subjected to different selection pressures, mutation rates and/or genetic drift in isolation. Individuals of the descendent populations A' and A" may now possess the modified structures S' and S", respectively. These structures (S' and S") are homologous, no matter how similar or different they appear because they were both derived from the ancestral structure, S.
S'A'
SA =Homologous Structures
S"A"
Similarity due to convergence occurs when the organisms B' and C' having similar structures S' and S", respectively, did not share a common ancestor with structure S that gave rise to both S' and S". Rather, structures of different origin, say Q (in B) and R (in C), became modified, presumably under similar selection pressures, to resemble one another in their respective descendents, B' and C'.
QB S'B'
=Convergent Structures
RC S"C'
The problem arises: How do we distinguish homologous from convergent structures? We certainly have very little chance of discovering the common ancestor of divergent organisms, and even if we did, the processes that led to modification of structure took place over long periods of time and would be impossible to follow through all descendent populations. We therefore must look for some other types of evidence to distinguish homologous similarity from convergent similarity. One approach is to examine the structures in question in detail. Because homologous structures were (by definition) from the same ancestral structure and because the processes of replication of structure from generation to generation via DNA replication are basically conservative, then homologous structures should resemble one another in many details, such as shape, composition, relationships to other structures, and developmental processes. Convergent structures, on the other hand, may resemble one another in ways that only reflect functional similarity.
The problem of distinguishing homologous from convergent structures can be quite complex, however. On the one hand, convergence can lead to remarkable similarities among distantly related organisms. Perhaps the most striking examples of convergence in the mammals are those between some of the marsupials and the placentals that exploit similar ecological habitats on different continents. Note the overall resemblance in the following placental/marsupial pairs:
Placentals Marsupials
Large
Predators
Gliders
Large
Rodent
Habits
Small
Rodent
Habits
Despite the superficial resemblances, the differences in internal structure and reproductive biology between marsupials and placentals suggest very early divergence between these two subgroups and consequently, very distant relationships between members of these pairs.
Conversely, homologous structures may appear quite dissimilar at first glance due to major modifications of the ancestral structure in one or all lines of descendent. As a further complication, modifications may even be associated with functional changes. For example, the wing of a bat and the human hand are homologous structures because both were derived from the manus (hand or forefoot) of a primitive mammalian ancestor. The ancestral structure probably resembled the following diagram:
Dorsal View: Right Manus
Careful inspection of the bat wing and the human hand will reveal the same arrangement of bones, although the relative sizes of bones are different. Examine skeletons of the bat wing, human hand, and forefoot of a cat. Identify the homologous bones among these structures (you do need to know the names of these bones). Note the modifications that have evolved in these different organisms. How are these modifications related to changes in function? (A diagram of the vertebrate forelimb is at the end of this section)
Now consider another type of wing: that of a bird. Note the arrangement of bones that contribute to the wing skeleton. Is it the same as that supporting the bat wing? In birds the number forelimb digits have been reduced and the carpals and metacarpals are fused as the carpometacarpus.
Wings of birds and bats are convergent structures. Each type of wing was derived independently; that is, birds and bats never shared a winged ancestor. If we examine these structures at another level however, we find that they are homologous. Wings of birds and bats, although not homologous as wings, are homologous as forelimbs. Birds and bats did share a common ancestor (one that we would probably classify as a reptile) that had an arrangement of bones in the forelimb that was probably very similar to that illustrated above for our primitive mammalian ancestor.
Classification
The goal of evolutionary classification is to construct groupings of organisms which reflect the phylogenetic relationships among them. For example, in the Linnaean hierarchy of classification (kingdom, phylum, class, order, family, genus, species), if two species are placed in the same genus, those two species are presumed to be more closely related to one another than either is to a third species placed in another genus. That is, those two congeneric species shared a more common ancestor with one another than either did with the third species. The following diagram illustrates the relationships among six taxa, A-F. (A taxon is any grouping of organisms in the hierarchical classification.) In this diagram we see that taxa B and C are more closely related to one another than either is to A or D, as indicated by their sharing a common ancestor (which shall remain nameless) at node I. Now consider taxon A. Taxon A is more closely related to the lineage containing taxa B and C than it is to taxon D, by virtue of the common ancestor which A and (B+C) share at node II. Taxon A is said to be the sister group of (B+C). (And, for that matter, at another level, B is the sister group of C.) Now consider taxon D. What is D's sister group? That is, with which taxon or taxa did it share the most recent common ancestor?
A B C D E F
I
II
III
In theory, evolutionary classification is very straightforward, but in practice, the determination of phylogenetic relationships is not always easy. The characteristics one should use to construct an evolutionary classification are those which reflect the common ancestry of the organisms in question. Certainly this means that the characters for study should be homologous (by now you should have an appreciation for the potential difficulties in determining those homologies). Additionally, the characteristics chosen should reflect modifications of ancestral structure that are unique to lineages of organisms. The criterion for evolutionary classification, then, is the use of shared, derived (specialized) characteristics rather than primitive characteristics.
Consider the genealogy illustrated on the next page. Although it is contrived, it demonstrates some important concepts in evolutionary classification.
In this example, characteristics are listed for each of the taxa, A-F. 1, 2, 3, and 4 are the ancestral or primitive states of the characters in question. 1', 1", 2', 3', 3", and 4' represent derived character states.
A B C D E F
(1', 2, 3', 4) (1', 2', 3', 4) (1', 2', 3', 4') (1, 2, 3', 4) (1, 2, 3", 4) (1", 2, 3", 4)
Which characteristics distinguish the following groups from one another?
B from C ______
A from (B+C) ______
(A+B+C) from D ______
E from F ______
(E+F) from (A+B+C) ______
Note that characteristic 4 is shared by most taxa in this diagram. Also notice that it carries almost no information as to the relationships among organisms except to distinguish B from C. Remember, 4 is a primitive characteristic; one that has not been modified in most lineages but has been inherited, unaltered, from the common ancestor shared by all the taxa in this example. Also note that each taxon has a unique mixture of primitive features retained from its ancestors and new, evolved or derived traits.
In the example above you were given information on the relationships of the taxa in question. In most instances, however, the true genealogy of a group of organisms is not known, and we infer relationships based on shared, derived characteristics. It becomes important to distinguish primitive from derived characteristics. This task is complicated by the fact that the ancestor of a lineage is very unlikely to be available for examination. What other characteristics might be used to decide if a characteristic is likely to be primitive? (By the way, this question has occupied many evolutionary biologists for a long time, and continues to do so.)
Now, try your hand at discovering characteristics that serve to define groups. On one of the tables, you will find a variety of mammal skulls. Your task is to examine these skulls and decide which characteristics serve to define groups (such as rabbits, rodents, carnivores, etc.) and distinguish them from other groups. Compare notes with the other students in the class. We will compile a list of distinguishing characteristics on the board.
Serial Homology
The homology between structures in different organisms that we have just been discussing is phylogenetic homology: similarity due to common ancestry. In addition, there can be similarity among repetitive structures within the same organism due to common embryonic origin. Such similarity is called serial homology. For example, individual vertebrae along the human vertebral column are serially homologous.
Use the figure below to find the basic regions of a lumbar vertebra. Then examine the vertebrae along the length of the vertebral column and determine the serial homology (noting both similarities and differences) of the following parts: