Sem 2 Week 3 Starfish Description

Starfish is classified under the phylum Echinodermata.

Symmetry
A starfish typically possess a 5-rayed symmetry.  Most starfish have a radical symmetry, but some has bilateral symmetry.

Germ cell layers
The body wall of echinoderms consists of three layers.  The outer layer is called the epidermis, which is a single layer of cells which covers the entire animal including its various spines.  The middle layer is much thicker compare to the epidermis, which is called the dermis.  The dermis is composed of connective tissue and contains the exoskeleton.  This exoskeleton takes three different forms: a set of closely joined plates with little individual movement that exist as a test or shell, a set of separarely ariculating small plates called ossicles, and a collection of widely separated microscopic ossicles lying in the dermis.  The ossicles are always made from calcite.  The exoskeleton of echinoderms grows continuously throughout the animals life.  The exoskeleton supports the spines, warts, and tubercles that are often found on the echinoderm surface.  These various protuberances are also generally made from calcite.  The third layer is also a single layer of cells.  The main difference is that these cells are ciliated.  This layer enclosed the animal's coelom separating the animal's guts from its skin (called coelomic lining).     

Coelom
Starfish has a true coelom body cavity.

Circulatory system
Echinodermata has a poorly defined open circulatory system and posses a water vascular system, which hydraulically operates the tube feet or feeding tentacles.  Echinoderm contact with the external world through its water vascular system.  The water vascular system of the echinoderms is unique in the living world and easily distinguishes them from all other phyla. The system takes slightly different forms in the different classes. In the Crinoidea, which are believed to be the most ancient of the echinoderms, the tube feet are branched and secrete mucous. In the Ophiuroidea the tube feet are simple and slender. In Asteroidea, Echinoidea and Holothuroidea they are thicker and end in suckers. The water vascular system starts with an opening to the external environment called a madreporite. From this a short straight canal called the 'stone canal' leads to the 'ring canal'. The ring canal is a ring as might be expected and it has five longitudinal canals branching off from it into each of the arms, or their morphological equivalents in Echinoidea and Holothuroidea.

Reproduction
Starfish reproduce sexually and gonochoristically.  Fertilization is always external.  The larvae are planktonic and biradial.  Develop into pentaradial symmetry as adults.

Feeding
Most Echinodermata possesses a through gut with an anus.  The gut is U-shaped in the Crinoidea with the mouth and anus being on the same surface.  Other groups have straight-through gut with mouth and anus on opposite sides.  They are filter feeders.  Echinodermata feeds on fine particles in the water, detritus, or other animals living in marine environment. 

Excretion
Without excretion organ.  Use the water vascular system to excrete waste.  Many uses their tube feet as organs for gaseous exchange.

Nervous system
The nervous system includes a circum-oesophageal ring.  Echinoderms have sub-epidermal nerve net running all over their body.  They also have a circum-oral nerve ring with 5 radial nerve cords, connecting sub-epidermal nerve net.

 Crinoidea (Sea lilies, feather stars, and comatulids) 

http://www.ucmp.berkeley.edu/echinodermata/comatulid.gif

Ophiocistioidea (a class of extinct echinoderms, similar to sea urchin) 

http://www.geomuseum.uni-goettingen.de/people/mreich/pdf/images/neuweb_seegurken11.gif

Astroidea (starfish)

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmx6YMSalSQSdg5CV0sDOvRGKSfQJjKZWdXQ0blakoFUdpDJxezl-8lwjKJDpWW0D5hbDo2peBv_QVf4N-dTVNxdII3aOZ7BbTsw5m9zfe37ANY7iWUhYq0vXp4O2o3rSpwDAtpKcSCwkW/s1600/5284ba28ba80d72f.jpg

Echinoidea (sea urchin, sand dollars are closely related)

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Riccio_Melone_a_Capo_Caccia_adventurediving.it.jpg/250px-Riccio_Melone_a_Capo_Caccia_adventurediving.it.jpg

Holothuroidea (sea cucumbers)

http://madmikesamerica.com/wp-content/uploads/2011/05/Bohadschia-argus1.jpg

Sem 2 Week 3 Genome Chapter 3 Summary: History

In chapter 3 of Genome by Matt Ridley, Ridley introduces Dr. Archibald Garrod who published a hypothesis in 1902 called "the inborn errors of metabolism" through his research with the disease alkaptonuria.  During the experiments, he assumed that each gene produced one chemical catalyst.  The invorn errors of metabolism were caused by genetic mutations, which he described as "loss or malfunction of an enzyme" and that proteins manage virtually every function in the body.  Dr. Garrod's thesis was well received, but all the readers missed the point.   Both Mendel and Darwin was confused about genetics and mutations.  Later discoveries about mutations revealed that genes codes for proteins and mutations were altered proteins made by altered genes.  The structure of DNA was discovered by Watson and Crick in 1953.  Crick coined the term genome.  In 1995, scientists return to alkaptenuria and found it is caused by a single base substitution.

Week 2 Day 2 Double Fertilization

Unlike humans, plants have to undergo double fertilization.  Double fertilization is essential for fertility and seed production.  Double fertilization involve two "twin" sperm cells and one egg cell.  One sperm cell (haploid) join with the egg cell to produce the embryo (diploid) and the other join with a second cell in the ovary to produce the endosperm (triploid)  inside the seed.

The ovule contains a reproductive cell called the megaspore cell (diploid), which undergoes meiosis to produce four haploid megaspores, but only one typically survive out of the four.  The surviving megaspore undergoes three rounds of mitosis to produce eight haploid nuclei.  The eight nuclei is in the embryo sac.  Within the embryo sac, cell walls form between most of the nuclei.  Three cells form opposite the micropyle opening of the ovule.  Three also form near the micropyle (one of them is the egg).  Two polar nuclei remain together in one large central cell.
 
After that step, the pollen (sperms) come into action.  A pollen grain reach the stigma and begin to germinate.  Then it sends a long pollen tube through the style and ovary.  One of the two sperm cells fertilizes the egg cell.  The second sperm cell fuses with both of the polar nuclei, fertilizing them to produce an unusual triploid cell.  The endosperm serves as the embryo's food supply.

When the pollen grain reaches the stigma, the gene, FBL17 triggers the destruction of another protein that inhibits cell division.  The gene acts as a switch to trigger precursor cells to divide into twin sperm cells. 

Week 2 Day 2 Genome Chapter 2 Summary: Species

In this chapter for Genome, Ridley began with the introduction of how people used to mistaken that a human genome has 24 chromosomes.  However, more well developed studies show that human has only have 23 chromosomes because Chromosome 2 is slightly modified by fusing two ape chromosomes.  There are some religious figures believe that the human soul is somewhere near the centromere of Chromosome 2.  Many people believe that human are an ecological success because we are able to occupy 300 million tons of biomass.  However, the human and chimps genetics are 98% the same.  There must be some point in time that the split occur when a chimpanzee population "isolated" and developed a genetic mutation that prevented the two population from breeding and forming a new species.  Monogamy shaped our "division of labor".  Ridley concluded by saying that the differences between species are in the genes but genes do not totally control behavior.

Week 2 Day 5 Genome Chapter 1 Summary: Life

In the first chapter of the book Genome by Matt Ridley, Ridley introduced the word that builds up the world.  Later, he reveals the word to be RNA, not DNA.  This first chapter is the introduction to the beginning, with RNA.  RNA is more chemically active than DNA, but it is more unstable.  Perhaps many prehistoric organisms came up with DNA through the trial and error process.  Ridley briefly explained the correlation between RNA and DNA within the human genome, and some scientists' discovery in relations with RNA and DNA.  Ridley also brings up LUCA, the Last Universal Common Ancestor, which is believed to be a protozoan, rather than bacteria.  Ridley concludes this chapter with the explanation that the human genome is made up of the genetic code of DNA.

Extra Credit Blog

From first semester, I think the topic that confuse me the most is the functional groups and the topic I feel very clear on is probably the ecology chapters and the simple macromolecules.  I think my favorite lab/activity is HPLC lab because it is interesting and you can see the color change.  I think the lab/activity that is my least favorite lab is the plant pigment chromotography because I do not think my lab actually worked.  

Week 1 Day 3 BOW 1: Genome Chapter 4 Summary: Fate

In chapter 4 of the book Genome by Matt Ridley, the author specifically wrote about the genetic diseases on chromosome 4.  Ridley start off with talking about how people tend to have the wrong perception of a gene related disease.  When stating how the Wolf-Hirschhorn gene affect the disease, Ridley states it is because the person lack the gene, thus the Wolf-Hirschhorn disease occur.  Ridley then goes on into the Huntington's disease.  Huntington's disease is a mutated genetic dominant disease that occur as the sequence CAG continuously repeat itself.  If CAG is repeated more than thirty-nine times, then an individual has Huntington's disease.  Huntington's disease will cause the patient to lose balance, deteriorate the brain, jerking limbs, and occasional hallucination and delusions.  The disease cannot be cured.  The rest of the chapter describes that people with a family history of Huntington's disease has a 50% chance of getting it.  This means either you get the disease or you do not.  The chapter also explore several villages with Huntington's disease and how scientists go out into the villages to trace the ancestry as well as diagnose people with the disease.