Instructions:  This review is worth 75 points (12.5% of your course grade) and will be due in class Wednesday, 3/17/04.  No exceptions, and late reviews will result in at least a 5% deduction.  You may not consult any references or any other person while working on this review.  Your signature at the bottom of the last page signifies that the work is yours alone and is pledged under the Honor Code.  When you break the seal on the envelope you will have three hours to complete the review!  Please print legibly; I can only grade what I can read!  For each question or part to a question, limit your answers to the space below each question, unless otherwise specified.  Any part of your answer outside of the space provided will not be graded.

1.      Discuss convergent evolution of ichthyosaurs and sharks (from the Scientific American paper by R. Motani) (6 pts).

Variation in ichthyosaurs includes the three different types of ichthyosaurs discussed in the reading. The three are lizard-like, fish-like, and intermediate types. The full range of ichthyosaur diversity fell within this continuum.  Similarly, sharks have different body types, such as dogfish sharks and great whites.  The former were more similar to the lizard-like ichthyosaurs, and the latter more similar to the fish-like ones.  Body shape was more reptilian and vertebrae were longer and narrower in lizard-like ichthyosaurs and dogfish sharks.  In fish-like ichthyosaurs and open ocean sharks the body was bigger and more like a deep sea fish, and the vertebrae were shaped more like hockey pucks.  Ecological selective factors were primarily the different habitats in which the types lived and prey that they hunted. For instance, living near the coast in shallow water where prey was dense and plentiful, lizard-like ichthyosaurs retained some ancestral reptilian features. However, when ichthyosaurs evolved to live in the open ocean and hunt scattered prey that often lived deep and swam fast, the features discussed above led to their success, as it did with great white sharks.

2.      Discuss one of the following two questions (6 points):

a.      Describe metabolic and habitat diversity of prokaryotes, showing also how metabolism and habitat are related. 

Metabolic diversity must consist of a description of the multiple modes that different prokaryotes use to obtain chemical energy.  Prokaryotes, especially in Kingdom Eubacteria, show the full range of metabolic diversity – members of this kingdom exhibit chemoautotrophy, chemoheterotrophy, photoheterotrophy, and photoautotrophy.  This is the only kingdom to exhibit such a range.  Some of these metabolic modes can only occur in specific habitats.  For instance, chemoautotrophs usually occur in extreme habitats, such as hot springs or deep sea hydrothermal vents. Some modes are more likely to found in anaerobic habitats, and some can exist with or without oxygen. Ultimately, prokaryotes have a wider range of metabolic diversity and are found in many habitats in which eukaryotes don't or can't exist.

b.      Discuss the role of microbes in the nitrogen cycle – be specific.

There are three major steps in the nitrogen cycle in which microbes are essential.  Nitrogen fixers, nitrification, and denitrification are those steps and each must be described specifically to receive full credit.  Archaeans and bacteria are involved in the nitrogen cycle and without them, nitrogen cycling would grind to a halt.

3.      Address one of the following two questions (8 pts):

a.      Choose two of the following modes of metabolism in Archaeans and list how they obtain energy and carbon: anaerobic photoheterotrophs, methanogenic chemoautotrophs, sulfur-metabolizing chemoautotrophs, or photoautotrophs.

b.      Outline the endosymbiotic theory of the evolution of eukaryotes.  Include two pieces of evidence that support the endosymbiotic theory.

Endosymbiosis is a symbiotic relationship in which one individual (of a species) lives inside of another (of a different species). The endosymbiotic theory of the evolution of eukaryotes posits that endosymbiotic relationships between species of early eukaryotes and prokaryotes (or between two different prokaryotes) were so tight that ultimately the two species (or two individuals if considering just one cell) could not live without one another and they became one organism. These endosymbiotic events (we call them events, but they took many generations of living endosymbiotically to occur - they did not occur instantaneously) occurred 2-3 times, according to theory, leading to the evolution of mitochondria, chloroplasts, and peroxysomes. Evidence that supports this hypothesis includes genetic material of mitochondria and chloroplasts, prokaryote-like ribosomes in mitochondria and chloroplasts, phylogenetic relationships between mitochondria and chloroplasts and prokaryotes, the fact that antibiotic affects both types of organelle, and the endosymbiotic relationships between species existing today, such as corals and algae (zooxanthellae), and termites and their gut protozoan.

4.      Explain the adaptive value of segmentation and bilateral symmetry in animal body plans.  In addition, speculate on whether the evolution of these adaptations is linked evolutionarily, that is, was the evolution of one dependent upon the existence of the other (8 points).

Segmentation is advantageous because it allows compartmentalization of the body and regional specialization.  It also facilitates movement and support for animals with hydrostatic skeletons. It also allows finer control of the body, especially in things like earthworms, and redundancy in body parts.  Bilateral symmetry is adaptive for animals that are moving through their environment, actively foraging for food.  It is much more efficient for actively moving animals than asymmetry or radial symmetry.  Segmentation has arisen multiple times in bilaterally symmetrical animals, so it’s likely that bilateral symmetry arose first (although segmentation could’ve evolved and then been lost and regained – but that’s not very parsimonious).  Both traits led to success in groups that possessed them, and the two traits together are found in very successful groups, like arthropods, so they could be linked evolutionarily.  As animals got bigger over evolutionary time, more systems evolved, which required compartmentalization and protection (obtained from triploblasty), and at the same time, bilateral symmetry allowed those bigger animals to actively hunt prey. Segmentation evolved in fewer taxa (relatively), but is linked to other traits in that those other traits may have facilitated the evolution of segmentation - further compartmentalization was easier to obtain in triploblastic, bilaterally symmetrical animals.

5.      Is Kingdom Protista considered a monophyletic group?  Why or why not (4 pts)?

No, it is not.  Protista can be considered paraphyletic if one considers the ancestor of all eukaryotes, because various protist lineages led to other eukaryotic kingdoms, or they may be considered polyphyletic if one considers more recent ancestors.  There is no one ancestor that led to all protists and to no other group.

6.      How do animals regulate body temperatures with blood flow?  Answer this question using two specific examples, one of an ectotherm and one of an endotherm, each of which employs a different mechanism (8 pts).

Both ecto- and endotherms regulate temperature with blood flow. Ectotherms can divert blood to or from surface capillary beds to dissipate or retain heat.  They may also alter heart rate to increase or decrease blood flow.  Consider the example of marine iguanas.  For the latter, regulation of blood flow would probably include opening or closing arterioles leading to superficial capillary beds. Blood flow to the exterior parts of the body or to the extremeties is increased if the body is too hot, and this will allow for increased convection, evaporation, and conduction. Blood flow to the exterior is restricted if the environment is too cold and the individual is trying to retain heat - this way heat loss will be minimized. Slowing down heartrate in those situations will decrease the overall amount of blood flow to all parts of the body, including extremities, which is another mechanism for retaining heat.

7.      What are the advantages of the closed circulatory system of annelids (4 pts)?

The closed circulatory system of annelids allows for faster movement of nutrients, transport of respiratory gases, which are exchanged at their surface, a more efficient hydrostatic skeleton, and allows for filtration of blood into coelomic spaces for entry into the excretory system.

8.      Define an animal (3 pts).

Animals are multicellular, heterotrophic eukaryotes, which have gap junctions between cells, and muscle and nerve tissues (almost all have one or the other of the latter two).

9.      LIST two adaptations of the respiratory system that increase Q in Fick’s Law of Diffusion for both fish and mammals (6 pts).

Fish have large surface areas on their gills (lamellae), countercurrent exchange of water and blood, and short distance across lamellar surface.

Mammals have large surface area in lungs (alveoli), they breathe air, and have a short distance between alveoli and capillaries surrounding alveoli.

10.  Discuss one of the following as it relates to mammals (8 pts):

a.      How does regulation of the circulatory system affect homeostasis of the respiratory system? Provide two examples.

There are several examples you could use, and in general the two systems are tied closely together.  Chemosensors in the circulatory system monitor blood pH and oxygen concentrations.  When either, or both, begin to decrease, the circulatory system is adjusted appropriately, and breathing rate will change as well to supply more oxygen or get rid of more carbon dioxide.

b.      How does the endocrine system (hormones) help to maintain homeostasis in the circulatory system of mammals? Be specific.

Various hormones are used to maintain circulatory system homeostasis.  Renin and vasopressin are released from the kidney and hypothalamus, respectively, when blood pressure falls.  Renin activates angiotensin, and angiotensin and vasopressin constrict arterioles in peripheral systems.  Adrenaline is another hormone that affects the circulatory system.

11.  Explain the concept of countercurrent exchange, using a specific example related to the respiratory system (8 pts):

Countercurrent exchange is a mechanism used to transfer some component of a fluid from one flowing current to another across a permeable barrier between them.  Heat or molecules may be the components transferred.  Because the substance to be exchanged transfers across the barrier from high to low concentration, the countercurrent exchange is more efficient than concurrent exchange – there is a concentration difference across the entire length of the two flows.  Fish gills exchanging oxygen, and blood vessels exchanging heat are good examples.

12.  Briefly outline the general mating habits of either earthworms or scorpions (6 pts).

Earthworms are hermaphroditic, but generally mate with a partner (they either can’t or don’t fertilize their own eggs).  Mating tends to take place on or just below the soil surface, at night.  Two worms line up facing in opposite directions. Sperm packets are released from the seminal vesicles through the sperm duct and then travel up a groove on the outside of that worm.  Sperm packets are then transferred to the other worm and stored in the spermatheca until cocoon formation.  Cocoons are formed by the clitellum and slide anteriorly over the worm, like a sleeve.  As it passes over the segments with the oviduct, eggs are released, and then sperm are released from the spermatheca.  Fertilization thus takes place externally.  The cocoon continues to slide over the head, and then is deposited and hardens to protect the eggs. 

In scorpions, courtship is usually initiated by male.  During courtship other ritual activities may be observed, among these are clubbing, where one partner strikes the other with the metasoma (the tail) without stinging, sexual stinging, where the male inserts sting into female through a membrane, cheliceral kiss, where the male grabs the females chelicera with his chelicera, promenade, a courtship dance which involves the pair gripping each other with their pedipalps, walking backward and forward in tandem until a suitable place is found for the male to deposit spermatophore, postmating escape, where the male disengages suddenly and violently and rapidly makes a get-away after the spermatophore has been taken up, and mate cannibalism.

Scorpions transfer the sperm externally. The male scorpion usually actively seeks out females for mating. When encountering the female the male starts juddering. The juddering must somehow signal to the female that the male is advancing for reasons of a sexual nature. The juddering is a behavior in which the scorpion jerks its whole body back and forth quite rapidly. During this time pedipalps are extended in front with the body held well off the ground. The female will respond with a similar juddering, approach the male and attack aggressively.  The males of some species have a long tail compared to the female. Females can be quite aggressive and will not hesitate to kill the male.  Males hold females at bay and sting them. This sexual sting makes female easy to control, and is necessary for successful sperm transfer.  The male grips the female's pedipalps with his and starts to drag her about with the female offering resistance to his movement. The male gives the female the cheliceral kiss where he locks his mouthparts onto hers. This behavior keeps their bodies in perfect alignment, which is of utmost importance.  The male continues to drag the female around until he locates a suitable surface on which he can deposit spermatophore. The spermatophore houses the sperm and is placed onto a rock from the male's genital opening.  The sticky foot of the spermatophore adheres to the rock and remains upright. The male must pull the female in a direct straight line so her body and genital opening are directly over the spermatophore. The female's genital operculum or plate is at 90 degrees to her body allowing the genital opening to be exposed at a maximum. With the spermatophore at the correct position the female lowers her body allowing the portion of the spermatophore containing sperm to enter her body. The sperm are released, the female raises her body from the spermatophore and without hesitation the pair quickly break apart.

Litter size is variable and observed data give a range of between 1 and 105 young per birth, with an average of about 26. Young scorpions ride on their mothers back until some time after they first molt into second instars, which may be from a few days to four weeks.  Young scorpions do not feed whilst on the mothers back, although observations have been made of young feeding on food items left by the mother.  Many first instar scorpions do not have chelicerae specialised enough for their own feeding so relying on internal nutrients is essential.

Return to CP's BIOLOGY 112 Page

Return to CP's Home Page

Go to Biology Home Page