Tuesday, October 23, 2007

Genetics/Cell Cycle

1. What is DNA? DeoxyriboNucleic Acid.
2. What are the 4 bases? A (Adenine), T (Thymine), C (Cytosine) & G (Guanine).
3. What 2 peices of information did the scientists need to solve the elusive structure of DNA? In order to solve the elusive structure of DNA, a couple of distinct pieces of information needed to be put together. One was that the phosphate backbone was on the outside with bases on the inside; another that the molecule was a double helix. It was also important to figure out that the two strands run in opposite directions and that the molecule had a specific base pairing.
4. What are the specific base pairs? G can only bind to C and A can only bind to T.
5. How does the pairing rule effect the shape and structure of DNA? According to the biochemist Erwin Chargoff even though different organisms have different amounts of DNA, the amount of adenine always equals the amount of thymine. The same goes for the pair guanine and cytosine. For example, human DNA contains about 30 percent each of adenine and thymine, and 20 percent each of guanine and cytosine. With this information at hand James Watson was able to figure out the pairing rules. On the 21st of February 1953 he had the key insight, when he saw that the adenine-thymine bond was exactly as long as the cytosine-guanine bond. If the bases were paired in this way, each rung of the twisted ladder in the helix would be of equal length, and the sugar-phosphate backbone would be smooth.
6. What does the DNA do during cell division? During cell division, the DNA molecule is able to "unzip" into two pieces. One new molecule is formed from each half-ladder, and due to the specific pairing this gives rise to two identical daughter copies from each parent molecule.
7. How many base pairs does E. Coli have? How long does it take to replicate? How is the DNA packaged in the cell? The DNA in E. coli bacteria is made up of 4 million base pairs and the whole genome is thus one millimeter long. The single-cell bacterium can copy its genome and divide into two cells once every 20 minutes. In order to fit, the DNA must be packaged in a very compact form. In E. coli the single circular DNA molecule is curled up in a condensed fashion.
8. How many base pairs does Human DNA have? How long does it take to replicate? How is the DNA packaged in the cell? The DNA of humans is composed of approximately 3 billion base pairs, making up a total of almost a meter-long stretch of DNA in every cell in our bodies. The human DNA is packaged in 23 distinct chromosome pairs. Here the genetic material is tightly rolled up on structures called histones.

1. What is RNA? How different is it from DNA? RiboNucleic Acid. DNA is made up of double strand while RNA is made up of a single strand. Also the base T (Thymine) in DNA is replaced by U (Uracil) in RNA.
2. How are the RNA messages formed? The alphabet in the RNA molecule contains 4 letters, i.e. A, U, C, G. To construct a word in the RNA language, three of these letters are grouped together. This three-letter word are often referred to as a triplet or a codon. An example of such a codon is ACG. The letters don't have to be of different kinds, so UUU is also a valid codon. These codons are placed after each other in the RNA molecule, to construct a message, a RNA sequence. This message will later be read by the protein producing machinery in the body.
3. How are the RNA messages interpreted? Every organism has an almost identical system that is able to read the RNA, interpret the different codons and construct a protein with various combinations of the amino acids. In fact every RNA word or codon, corresponds to one single amino acid. These codons and their correlation with the amino acids in a protein sequence is what defines the genetic code.

1. Describe cell cycle. The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication. These events can be divided in two broad periods: interphase—during which the cell grows, accumulating nutrients needed for mitosis and duplicating its DNA—and the mitotic (M) phase, during which the cell splits itself into two distinct cells, often called "daughter cells". The cell-division cycle is an essential process by which a single-celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed.
2. What is nuclear division. The division of the nucleus and its genetic information into more than one cell deriving from a parent cell, either via meiosis or mitosis.
3. What is interphase. A phase of the
cell cycle, defined only by the absence of cell division. During interphase, the cell obtains nutrients, and duplicates its chromatids. Most eukaryotic cells spend most of their time in interphase.
4. Cytokinesis. Cytokinesis is the process whereby the
cytoplasm of a single cell is divided to spawn two daughter cells. It usually initiates during the late stages of mitosis, and sometimes meiosis, splitting a binucleate cell in two to ensure that chromosome number is maintained from one generation to the next. In animal cells, one notable exception to the normal process of cytokinesis is oogenesis (the creation of an ovum in the ovarian follicle of the ovary), where the ovum takes almost all the cytoplasm and organelles, leaving very little for the resulting polar bodies, which then die. In plant cells, a dividing structure known as the cell plate forms across the centre of the cytoplasm and a new cell wall forms between the two daughter cells.

5. Homologous chromosomes. (Science: genetics) a pair of chromosomes containing the same linear gene sequences, each derived from one parent. The chromosomes tend to pair or synapse during meiosis. They have the same genes, in the same location, but the genes have different versions (not like in sister chromatids that are exact replicas).
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6. Phases of mitosis (5 of them).
1. Prophase – In prophase, the
chromatin condenses into discrete chromosomes. The nuclear envelope breaks down and spindles form at opposite "poles" of the cell.
2. Metaphase – In metaphase, the chromosomes are aligned at the metaphase plate (a plane that is equally distant from the two
spindle poles).
3. Anaphase – In anaphase, the paired chromosomes (
sister chromatids) move to opposite ends of the cell.
4. Telophase – In this last stage, the chromosomes are cordoned off in distinct new nuclei in the emerging daughter cells.
Cytokinesis is also occurring at this time.
Interphase – G1 phase: The period prior to the synthesis of DNA. In this phase, the cell increases in mass in preparation for cell division. Note that the G in G1 represents gap and the 1 represents first, so the G1 phase is the first gap phase. S phase: The period during which DNA is synthesized.

7. Phases of meiosis and how it is different from mitosis.
Meiosis begins with Interphase I. During this phase there is a duplication genetic material,
DNA replication. Cells go from being 2N, 2C (N= chromosome content, C = DNA content) to 2N, 4C. Cells remain in this active phase 75% of the time. The chromatin remains in a nuclear envelope while a pair of centrioles lies inside a centrosome.
During Prophase I, the
chromatin condenses into chromosomes, the nuclear envelope disappears, and a spindle apparatus begins to form. Each chromosome consists of a pair of chromatids connected by a centromere. Cells are now 4N, 4C. The major occurrence in this phase is the coupling of these homologous chromosomes. Two double-stranded chromosomes form a four-stranded tetrad. In some cases, there is crossing-over of the two middle strands, at a site called the chiasma, such that there is genetic recombination. This process is extremely important for creating genetic diversity.
In Metaphase I, the tetrads line up on the "equator" of the cell. The centrosome has replicated and one has moved to each pole. Microtubules that extend out of each centrosome attach to kinetochores in the center of each side of the tetrads that have lined up on the equator.
Anaphase I occurs as the microtubules pull the pairs of homologous chromatids toward each pole, as the tetrad is divided. The cell begins to lengthen.
During Telophase I, the nuclear envelope begins to reform and nucleoli reappear. The cell begins to split, forming a cleavage furrow in the middle.
In Cytokinesis I, the cells finally split, with one copy of each chromosome in each one. Each of the two resulting cells is now 2N, 2C.
Interkinesis has not replication, unlike the previous Interphase I and the interphase of mitosis.Prophase II, Metaphase II, Anaphase II, and Telophase II repeats the same steps as Prophase I-Telophase I, with half as much genetic material.
Cytokinesis II is the final step of meiosis, where each cell splits into two daughter cells, for a total of four
gametes, each with half the number of chromosomes. Each of the four resulting cells is 1N, 1C. (30)
In Meiosis the first phase is Interphase but in Mitosis it is last. In addition, Meiosis process are seven stages while Mitosis process are five phases.
8. Describe the process and purpose of crossing over. Crossing over occurs when the sperm and egg chromosomes pair up and swap genetic information, reducing the number of chromosomes to a complete set. It is important because it makes the number of chromosomes the normal number and also allows the genetic information to remain present in the cell.


Wednesday, October 17, 2007

Virtual Dissection - Crayfish

Internal anatomy of a crayfish: edible freshwater crustacean, with pincers on the two forelegs.
Encephalon: site of the mental functions of a crayfish.
Stomach: part of the digestive tract between the esophagus and the intestine.
Heart: blood-pumping organ of the crayfish.
Gonad: sex gland of a crayfish.
Extensor muscles: muscle that extends the tail of the crayfish.
Anus: outlet of the digestive tract.
Flexor muscle: muscle that bends the tail of the crayfish.
Digestive gland: glandular organ that produces digestive enzymes.
Ganglion of ventral nerve cord: budge related to a collection of nerves of the abdomen of a crayfish.
Ventral nerve cord: collection of nerves in the abdomen of a crayfish.
Maxilliped: pair of appendages of a crayfish used for holding prey.
Esophagus: part of the digestive tract between the mouth and the stomach.
Mandible: lower jaw.
Mouth: entrance to the digestive tract.
Green gland: antennary gland.
Eye: sight organ of a crayfish.

Taxonomy - Crayfish are members of the Decapod crustaceans.
External Anatomy

Female crayfish "In-berry".

Juvenile crayfish attached to the abdomen of a female.


Virtual Dissection - Squid

External Morphology
1 – This is the squids's dorsal surface. 2 – This is the squids's mantle.
3 – This is the fin portion of the mantle.
4 – This is the collar portion of the mantle.
5 – This is an eye.
6 – This is one of ten arms.
7 – This is one of a pair of tentacles.

1 – This is the squid's lateral surface.
2 – This is the squids's mantle. 3 – This is the fin portion of the mantle.
4 – This is the collar portion of the mantle.
5 – This is an eye.
6 – This is one of ten arms.
7 – This is one of a pair of tentacles.

1 – This is the squid's ventral surface. 2 – This is the squids's mantle.
3 – This is the fin portion of the mantle.
4 – This is the collar portion of the mantle.
5 – This is an eye.
6 – This is one of ten arms.
7 – This is one of a pair of tentacles.
8 – This is the squid's funnel; the equivalent of the clam's excurrent siphon.
9 – This is an incision that was made in preparation for injecting the circulatory system of the squid.

Funnel Area
1 - This is the collar area of the squid's mantle.
2 – This is the squid's funnel.
3 – This is the squid's eye.
4 – The arrows point to the two funnel retractor muscles.
5 – The arrow points to the squid's rectum. The two small flaps are called rectal papillae.
6 – The left arrow points to one of a pair of cartilaginous ridges in the mantle that fits into grooves on the funnel (right arrow).

Buccal Mass
1 – The arrow points to a sucker on one of the squid's arms.
2 – This is a part of the buccal membrane.
3 – This is the buccal mass, a muscular organ with chitinous teeth and a radula for masticating prey to prepare it for digestion.
4 – The arrow points to tissues associated with the squid's salivary glands.
5 – The arrow points to the esophagus. The tissue surrounding the esophagus is associated with the liver.

1 – This is the funnel area of the head. 2 – The arrow points to the right gill.
3 – The arrow points to the left funnel retractor muscle.
4 – The arrow points to the squid's rectum.
5 – The arrow points to one of the squid's branchial hearts. They receive deoxygenated blood from the precavae and the posterior vena cavae and pump it through the gills.
6 – The arrow points to one of the squid's precavae. These vessels containing the kidneys, receive deoxygenated blood from the head area via the anterior vena cava and direct it to the branchial hearts.
7 – The arrow points to one of the squid's posterior vena cavae. These vessels receive deoxygenated blood from the mantle area and direct it to the branchial hearts.
8 – The arrow points to the squid's caecum, a large chamber receiving masticated food from the stomach. Much of the digestion occurs here.
9 – The arrow points to the squid's single testis. Usually, it is partially covered by the caecum.

1 – This is the funnel area of the head. 2 – This is the squid's rectum. It is terminated by two ear-like flaps.
3 – This is the left funnel retractor muscle.
4 – The arrow points to one of the squid's gills.
5 – The arrow points to the ink sac. This melanin-containing sac is dorsal to the intestine an empties into it.
6 – The arrow points to the squid's pair of nidamental glands. They secrete material that becomes the egg casings.
7 – The arrow points to the squid's left branchial heart. They receive blood from the vena cavae and pump it through the gills.
8 – This is the squid's ovary. It occupies much of this part of the mantle cavity and covers the caecum.

1 – This is the head area, seen laterally.
2 – This is the dorsal groove in the collar. The cartilaginous ridge in the head fits into it. The groove is supported internally by the pen.
3 – This is the collar.
4 – This is the stellate ganglion, a mass of cell bodies with giant motor axions that innervate the muscles of the mantle for rapid swimming.
5 – This is the squid's left gill. It has been injected with red latex.
6 – This is the left funnel retractor muscle.

Latin.mollis = soft)
This phylum is one of the largest marine groups with over 80 000 species. All comprise of a soft, unsegmented body, consisting of an anterior head, a dorsal visceral mass and a ventral foot.The body is more or less surrounded by a fleshy mantle (an outgrowth of the body wall) and nearly all species in the group secrete a lime shell that covers and protects the body. All, except the class Bivalvia, have a ribbon-like rasping tongue (radula - unique to this phylum) with small chitinous teeth that processes the food. Most mollusks are free living, but slow moving creatures, showing a close association with the substrate. Some attach to rocks or shells, others burrow, others float, octopuses and squids swim freely.
1. Body usually short and partially or wholy enclosed by a fleshy outgrowth of the body wall called the mantle, which may be variously modified. Between the mantle and the visceral mass is a mantle cavity containing components of several systems (secondarily lost in a few groups).
2. A shell (if present) is secreted by the mantle and consists of one, two or eight parts. the head and the ventral muscular foot are closely allied (the foot being variously modified for burrowing, crawling, swimming, or food capture).
3. The digestive canals are complete and intricate with ciliary canals for the sorting of particles. The mouth with a rudula bearing traverse rows of minute chitinous teeth to rasp food , except in Bivalvia. The anus opening in the mantle cavity. A large digestive gland and often salivary glands are present.
4. The circulatory system is open, except in Cephalopoda and usually includes a dorsal heart with one or two atrias and one ventricle. This is situated in a pericardial cavity. An anterior aorta and other vessels and many blood spaces (hemocoels) exist in the tissues.
5. Respiration occurs via one to many uniquely structured ctenidia (gills) in the mantle cavity (secondarily lost in some), by the mantle cavity, or by the mantle.
6. Excretion by kidneys (nephridia), one or two or six pairs, or only a single one. They usually connect to the pericardial cavity and they exit in the mantle cavity. The coelom is reduced to the cavities of the nephridia, gonads and pericardium.
7. The nervous system is typically a circumesophageal nerve ring with multiple pairs of ganglia and two pairs of nerve cords (one pair innervating the foot and another the visceral mass). Many poses organs for smell, or touch, or taste. Eyespots or complex eyes present. A statocyst for equilibration present.
8. The sexes are usually seperate(some are monoecious, a few are protandric). Gonads add up to four, two or one, all with ducts. Fertilization occurs externally or internally. Most species are oviparous. Egg cleavage determinate, spiral, unequal and total (meroblastic in Cephalopoda). Trochophores and veliger larvae form, or a parasitic stage occurs(Unionidae), or the development is direct (Plumonata, Cephalopoda).
9. Unsegmented (except Monoplasophora). Symmetry bilateral or asymmetrical.


Prepared by the BioG 101-104 Course Staff.Comments to Jon C. Glase: jcg6@cornell.eduAll contents © 2000 Cornell University. All rights reserved.Revised: April 5, 2000URL: http://biog-101-104.bio.cornell.edu/

Virtual Dissection - Starfish

The echinoderms include only marine animals -- starfishes, sea urchins, sea cucumbers, and sand dollars. The starfish will be studied as the representative for this group. Their unique feature is the water vascular system, which is used as a means of locomotion. They also have a carbonaceous endoskeleton, whose projecting spines give the phylum its name - "spiny skin" in Greek. The echinoderms seem the most unpromising of all as potential ancestors of the vertebrates. They are radially symmetrical, in contrast to vertebrates; they have no internal skeleton, no trace of any of the three major chordate characters of notochord, nerve cord, or gill slits, and they have many peculiar and complicated organs of their own. But the embryology sheds an unexpected gleam of light. The early embryo of the echinoderm is a tiny creature, which floats freely in the sea water. Unlike the adult, the larva is bilaterally symmetrical, suggesting that the radial symmetry of the starfish is a secondary affair, assumed when the ancestors of these forms look up a sedentary existence. Then, too, the type of development of certain of the body cavities is identical with that found in the embryos of some primitive vertebrates. It is believed that the bilateral larva developed types which retained the original symmetry, and gradually evolved into the chordates and, finally, the true vertebrates.
Circulatory - Coelomic fluid, circulated by ciliary action, performs many of the normal functions of a circulatory system.
Digestive - Starfishs feed on mollusks. When a starfish attacks a clam, it arches its body over the shell, and by the concerted action of the tube feet, forces the clam to open. Then it everts a portion of its stomach to digest the contents of the clam. The mouth of a starfish opens into a narrow esophagus, which in turn leads to an expanded stomach. The stomach has two portions: the saclike cardiac, which can be everted as described, and the narrower pyloric, which is connected to a short intestine. The anus opens on the aboral or upper side of the animal.
Exocrine - Each of the five arms contains a well-developed coelom, a pair of large digestive glands that secrete powerful enzymes into the pyloric portion of the stomach, and gonads.
Excretory - Starfish has no excretory organs.
Immune - Sea urchins are long lived, normally healthy animals that display remarkable abilities to heal wounds and combat major infections. From an external point of view, their immune systems obviously work very well. Thus, their cellular defense systems are extremely sensitive, and they respond rapidly to minor perturbations, all without any specific adaptive capabilities. These systems probably function through the transduction of signals conveying information on injury and infection, just as do the equivalent systems that underlie and back up the human immune systems, and that provide the initial series of defenses against pathogenic invasions.
Musculo-skeletal - The water vascular system is purely for locomotion. Water enters this system through a structure on the aboral side called the sieve plate, or madreporite. From there, it passes through a short canal called the stone canal, to a ring canal, which surrounds the mouth. From the ring canal, five radial canals extend into the arms. From the radial canals, many lateral canals extend into the tube feet. One lateral canal goes to each tube foot, where it ends in the ampulla. When the ampulla contracts, the water is forced into the tube foot, expanding it and giving it suction. By alternating the expansion and the contraction of the tube feet, the starfish moves along slowly. Typically, echinoderms have an endoskeleton (internal skeleton) consisting of hard calcite ossicles embedded in the body wall and often bearing protruding spines or tubercles.
Nervous and Sensory - The nervous system consists of a central nerve ring that supplies radial nerves to each arm. A light-sensitive eyespot is at the tip of each arm.
Reproductive - The starfish usually becomes sexually mature at about 12-14 months. Mating mainly takes place between May and June (water temp. about 8 °C) when the whole population are at the same depth and like an epidemic. The lifecycle of most starfishes starts by shedding their eggs and sperm freely into the water, so fertilization is externally. The very small chance of fertilization is compensated by the enormous amounts of eggs and sperm cells. A female starfish sheds in two hours several millions of eggs into the water, with a mean diameter of 0.16-0.19 mm . After fertilization, a hollow ball develops, called the blastula. The cells of the blastula possess cilia on the outside for swimming. After one day a deep groove develops, leading to the gastrula. The gastrula's of all types of echinoderms are very similar. But then differentiation starts. The common starfish develops a so-called bipinnaria larva, with ciliated bands running about the periphery. After several weeks the bipinnaria larva takes on a more elaborate form, with longer projecting arms and after some more weeks, a brachiolaria larva is formed. The larvae have their own gut, with inside cilia to inhale and transport food particles. They feed themselves with diatoms and other organisms in the plankton. The stomach is large and round and situated at the backside. After this phase a large part of the larva degenerates and at the rear side a rudimentary formed juvenile starfish develops. The organs of the young starfish are formed anew.
Respiratory - There are skin gills, which project from the coelomic cavity, serve the function of respiratory exchange.

Virtual Dissection - Clam

Overview images of clam, left mantle removed

1 – This is the clam's foot, a muscular organ used for digging. Two retractor muscles withdraw the foot into the shell.
2 – This is the anterior adductor muscle, a major muscle for closing the valves.
3 – This is the posterior adductor muscle, a major muscle for closing the valves.
4 – This is the visceral mass, a thickened region extending from the foot dorsally to the pericardial cavity and bordered by the mouth and siphons. The visceral mass contains the organs of digestion and reproduction.
5 – These are the siphons. The upper arrow points to the excurrent siphon, the lower arrow, the incurrent siphon.
6 – These are the gills. Two pairs of gills are found on each side of the clam.
7– These are the labial palpi. The palpi form the boundry of the mouth on their anterior end. They are covered with heavily ciliated cells and direct food toward the mouth.
8 – The arrow shows the ventral margin of the right mantle. Note that the right mantle joins the reminants of the left mantle to form the incurrent and excurrent siphons.
9 – The arrow points to the pericardial cavity, covered with a thin, dark membrane.

Overview image of clam, left valve removed

1 – This is the clam's left mantle. The mantle secretes the shell and is attached to it along the pallial line seen on the inner surface of an empty valve. Note: the left mantle was detached from the left valve when it was removed. The black arrows show the border of the left mantle.
2 – This is the anterior adductor muscle, a major muscle for closing the valves.
3 – This is the posterior adductor muscle, a major muscle for closing the valves.
4 – This is the pericardial cavity, a region covered with a thin, dark membrane that contains the heart, kidney, etc.
5 – This is the margin of the right mantle. The right and left mantles join together to form the incurrent and excurrent siphons.
6 – This is location of the incurrent and excurrent siphons.

Image of inner surface of valve

1 – This is the inner surface of the clam's left valve. In the dissection you performed, this valve was removed for you.
2 – This is the posterior adductor muscle, a major muscle for closing the valves. The sea food we call scallops are the adductor muscles of the bivalve known as the pecten.
3 – This is the anterior adductor muscle, a major muscle for closing the valves. To open a clam, a thin knife is slid between the valves and the two adductor muscles are cut.
4 – This is the hinge area of the shell. A hinge ligament holds the valves together. Interlocking teeth in this area prevent the valves from side slipping when closed.
5 – Small teeth border the margin of each valve. These teeth prevent the valves from sliding laterally when the shell is closed.
6 – The arrow points to the posterior shell region where the incurrent and excurrent siphons are positioned.
7 – This structure indicated is the umbo of the shell. This is the oldest part of the shell.
8 – This narrow line (called the pallial line) on the inner surface of the shell connecting the two adductor muscles is the region where the mantle was attached to the shell. An indentation in this line marks the location of the two siphons.

Image of intact clam

1 – This is the clam's left valve. In the dissection you performed, this valve was removed for you.
2 – This indicates the anterior or head end of the clam.
3 – This indicates the posterior or tail end of the clam.
4 – This indicates the dorsal or upper surface of the clam.
5 – This indicates the ventral or lower surface of the clam.
6 – This structure indicated is the umbo of the shell. This is the oldest part of the shell.
7 – This faint line indicated on the surface of the shell is a growth ring. Notice how all growth rings emanate from the umbo.

(Venus mercenaria)
Kingdom: Animalia
Phylum: Mollusca
Class: Pelecypoda
Order: Eulamellibranchia
Family: Veneridae
Genus: Venus
Species: mercenaria

Adductor muscle(s)
Removal of the mantle shows the underlying soft body parts, a prominent feature of which are the adductor muscles in dimyarian species (clams and mussels) or the single muscle in monomyarian species (oysters and scallops). In clams and mussels the two adductor muscles are located near the anterior and posterior margins of the shell valves. The large, single muscle is centrally located in oysters and scallops. The muscle(s) close the valves and act in opposition to the ligament and resilium, which spring the valves open when the muscles relax. In monomyarian species the divisions of the adductor muscle are clearly seen. The large, anterior (striped) portion of the muscle is termed the "quick muscle" and contracts to close the valves shut; the smaller, smooth part, known as the "catch muscle," holds the valves in position when they have been closed or partially closed. Some species that live buried in the substrate (e.g. clams) require external pressure to help keep the valves closed since the muscles weaken and the valves open if clams are kept out of a substrate in a tank.
The prominent gills or ctenidia are a major characteristic of lamellibranchs. They are large leaf-like organs that are used partly for respiration and partly for filtering food from the water. Two pairs of gills are located on each side of the body. At the anterior end, two pairs of flaps, termed labial palps, surround the mouth and direct food into the mouth.
At the base of the visceral mass is the foot. In species such as clams it is a well developed organ that is used to burrow into the substrate and anchor the animal in position. In scallops and mussels it is much reduced and may have little function in adults but in the larval and juvenile stages it is important and is used for locomotion. In oysters it is vestigial. Mid-way along the foot is the opening from the byssal gland through which the animal secretes a thread-like, elastic substance called "byssus" by which it can attach itself to a substrate. This is important in species such as mussels and some scallops enabling the animal to anchor itself in position.
Digestive system
The large gills filter food from the water and direct it to the labial palps, which surround the mouth. Food is sorted and passed into the mouth. Bivalves have the ability to select food filtered from the water. Boluses of food, bound with mucous, that are passed to the mouth are sometimes rejected by the palps and discarded from the animal as what is termed "pseudofaeces". A short oesophagus leads from the mouth to the stomach, which is a hollow, chambered sac with several openings. The stomach is completely surrounded by the digestive diverticulum (gland), a dark mass of tissue that is frequently called the "liver". An opening from the stomach leads to the much-curled intestine that extends into the foot in clams and into the gonad in scallops, ending in the rectum and eventually the anus. Another opening from the stomach leads to a closed, sac-like tube containing the crystalline style. The style is a clear, gelatinous rod that can be up to 8 cm in length in some species. It is round at one end and pointed at the other. The round end impinges on the gastric shield in the stomach. It is believed it assists in mixing food in the stomach and releases enzymes that assist in digestion. The style is composed of layers of mucoproteins, which release digestive enzymes to convert starch into digestible sugars. If bivalves are held out of water for a few hours the crystalline style becomes much reduced and may disappear but it is reconstituted quickly when the animal is replaced in water.
Circulatory system
Bivalves have a simple circulatory system, which is rather difficult to trace. The heart lies in a transparent sac, the pericardium, close to the adductor muscle in monomyarian species. It consists of two irregular shaped auricles and a ventricle. Anterior and posterior aorta lead from the ventricle and carry blood to all parts of the body. The venous system is a vague series of thin-walled sinuses through which blood returns to the heart.
Nervous system
The nervous system is difficult to observe without special preparation. Essentially it consists of three pairs of ganglia with connectives (cerebral, pedal and visceral ganglia).
Urogenital system
Sexes of bivalves can be separate (dioecious) or hermaphroditic (monoecious). The gonad may be a conspicuous, well defined organ as in scallops or occupy a major portion of the visceral mass as in clams. The gonad is generally only evident during the breeding season in oysters when it may form up to 50% of the body volume. In some species such as scallops, the sexes can be readily distinguished by eye when the gonad is full since the male gonad is white in colour and the female is red, even in hermaphroditic species. Colour of the full gonad may distinguish the sexes in some species such as mussels. In other species, microscopic examination of the gonad is required to determine the sex of the animal. A small degree of hermaphrodism may occur in dioecious species.
Protandry and sex reversal may occur in bivalves. In some species there is a preponderance of males in smaller animals indicating that either males develop sexually before females or that some animals develop as males first and then change to females as they become larger. In some species, e.g. the European flat oyster, Ostrea edulis, the animal may spawn originally as a male in a season, refill the gonad with eggs and spawn a second time during the season as a female.
The renal system is difficult to observe in some bivalves but is evident in such species as scallops where the two kidneys are two small, brown, sac-like bodies that lie flattened against the anterior part of the adductor muscle. The kidneys empty through large slits into the mantle chamber. In scallops, eggs and sperm from the gonads are extruded through ducts into the lumen of the kidney and then into the mantle chamber.


Prepared by the BioG 101-104 Course Staff.Comments to Jon C. Glase: jcg6@cornell.eduAll contents © 2000 Cornell University. All rights reserved.Revised: April 5, 2000URL: http://biog-101-104.bio.cornell.edu/

Monday, October 15, 2007



Frustule (glassy shell) – consists of two tightly fitting halves often resembling a flat, round, or elongated box. Also has intricate perforations and ornaments such as spines or ribs. The Frustule allows light to pass through so that the conspicuous golden-brown chloroplasts can capture light energy for photosynthesis.


Chloroplast – are the most noticeable internal component of almost all diatoms, giving the diatom its color and photosynthetic capabilities. Diatom chloroplasts are usually yellowish-brown in color, ranging between yellowish-green and dark brown. This coloration is due to the presence of photosynthetic pigments such as chlorophyll, beta carotene, and fucoxanthin. The pigment chlorophyll is also a key component of terrestrial plants. Without this pigment, neither plants nor diatoms grow very well.


Oil Droplet

Reproduction – Under the right conditions, diatoms can reproduce very rapidly and a population of a small species can double each day. Diatoms normally reproduce by binary fission, where one ‘mother cell’ splits into two daughter cells. The two halves of the mother frustule become the ‘lids’ for the daughter frustules- the ‘box’ parts are made inside, as the daughters separate. One daughter cell will therefore be the same size as the parent, and the other will be slightly smaller. Over time, a lineage of diatoms will get smaller and smaller, although a few species avoid this problem by having stretchable frustules. When cells get too small, they discard their old frustules and build new, much larger ones. This process can be connected to sex. In many centrics, some individuals will break up into many small sperm-like cells. These ‘fertilise’ other diatoms, which then produce new, large frustules. In pennates, ‘sex’ involves two adult cells lining up alongside each other, dividing and then swapping one daughter cell each. The new pairs of daughter cells fuse, giving two cells that are each half of each ‘parent’. They then produces new, large frustules and glide away.

Scientific Classification
Domain: Eukaryota
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Bacillariophyceae
Centrales and Pennales

Almost all living diatoms require sunlight to survive and photosynthesize, limiting them to the uppermost 200 meters of the water column. This sunlit region of the water column is referred to as the photic zone. Since the entire surface of the ocean is exposed to sunlight at least part of the year, diatoms live practically everywhere at the sea surface. Diatoms are classified into two categories according to their lifestyle: planktonic or benthic. Since all diatoms are photosynthetic, both planktonic and benthic diatoms are restricted to living within the photic zone. Centric diatoms are mostly planktonic, floating near the sea surface, while pennate diatoms are mostly benthic, living on the seafloor, or attached to floating objects.





Like many micro-organisms, diatoms can bloom when conditions of nutrients, light and temperature are ideal. While diatom blooms are a major source of energy for the ocean, which ultimately supports the large predators such as fish and marine mammals and birds, severe blooms can be harmful. One diatom can kill farmed fish because its barbed spines can wound gills. Chemicals present in diatoms can build up in the bodies of animals that eat them and if concentrated enough, can affect people that eat the animals. In Australia, diatom blooms have been responsible for making shellfish unpleasant to taste and unsaleable for long periods of time. One diatom is responsible for Amnesic Shellfish Poisoning, a potentially fatal illness whose symptoms include memory loss. Worldwide outbreaks to date have been very rare, however there is concern that human activities are increasing the frequency of many sorts of micro-organism blooms (see silicoflagellates).

Wednesday, October 10, 2007

September 18, 2007 Presentations by Dr. Houk & Mr. Villagomez


During the presentation of the "Walk It, Don't Drive It" campaign by Dr. Houk and Mr. Villagomez, I learned the significance of keeping automobiles away from the sand of our beaches. The important reasons why automobiles should never be driven on our sandy beaches are summarized below:

D = Drips - oil that drips end up in our ocean and is deadly to our marine organisms.

R = Ruts - turtles lay their eggs on the sand and we should do everything humanly possible to protect them.

I = Illegal - It is illegal to drive on the beach of the CNMI! Everyone must follow the Law!

VE = Vegetation - vegetation on beaches are essential because they keep the sand from running off.

We viewed first hand that police officers were not following the Law while patrolling on the beaches. According to Dr. Houk and Mr. Villagomez, they have done a presentation with the DPS so hopefully their message came across.

I for one will admit that I have driven on the beaches of our island but after this presentation I definitely have a better understanding of why I should not be driving on our beaches. Good Job! Dr. Houk & Mr. Angelo. Rest assured your message will be passed on to many more that are not educated of the importance of keeping automobiles away from our beaches.

Watershed Ecology

CITE: Picture obtained from US EPA http://www.epa.gov/watertrain/ecology/index.html

Chapter 19 - Level 2 Quiz

Chapter 6 - Level 2 Quiz

Chapter 5 - Level 2 Quiz

Chapter 4 - Level 2 Quiz

Chapter 3 - Level 2 Quiz

Chapter 1 - Level 2 Quiz