Tuesday, February 14, 2012

Unit 1 Compilation







 Table of Contents
Chapter 1
Characteristics of Life
                How Humans fin into the Natural World
                Science is both a body of knowledge and a Process
                Sources of Scientific Information vary in Style and Quality
                Learning to be a Critical Thinker
                The Role of Science in Society
Chapter 2
                All Matter Consists of Elements
               Atoms Combine to form Molecules
               Life Depends on Water
                The importance of the Hydrogen Ions
                The Organic Molecules of Living Organisms
                Carbohydrates: Used for Energy and Structural Support
                Lipids: Insoluble in Water
                Proteins: Complex Structures Constructed of Amino Acids
                Enzymes
                Nucleic Acids Store Genetic Information
                APT Carries Energy
Chapter 3
                Cells are Classified According to their Internal Organization and Cell Structure Reflects Cell Function
                A plasma Membrane Surrounds the Cell
                Molecules Cross the Plasma Membrane in Several Ways
                Internal Structures Carry out Specific Functions
Cells have Structures for support and movement
Cells Use and Transform Matter and Energy
Chapter 4
                Tissues are Groups of cells with a Common Function
Epithelial Tissues cover body Surfaces and Cavities
Connective Tissue Supports and Connects Body Parts
Muscle Tissue Contract to Produce Movement
Nervous Tissue Transmits Impulses
Organs and Organ Systems Preform Complex Functions
The Skin as an Organ System
Multicellular Organisms Must Maintain Homeostasis


Chapter 1 Bio
Characteristics of Life
 Although all living and non-living things are made up of almost the same 100 different elements living things are very different.  Living things have a unique molecular composition that is considered the molecules of life.  All living things are made up of cells.  They are able to grow and reproduce.  Living things can respond to the environment around them making them unique to non-living things.  They can also maintain homeostasis which means the internal body regulates everything that happens within it.    All living things evolve enabling them to survive. Lastly, living things require energy, and besides plants, all living things need food and water. 

How Humans fin into the Natural World
I have discovered that how humans fit into the natural world is a lot more in depth than I had originally realized.  First it is best understood when starting at the beginning.  Living things are grouped by characteristics and placed into three domains and are then classified into kingdoms.  Domain Archaea is a single celled prokaryote (no membrane found nucleus) and is in Kingdom Archaea.  Domain Bacteria is also a single celled prokaryote (no membrane found nucleus) and is in Kingdom Bacteria. Domain Eukarya have a nucleus and are single or multi cellular.  Domain Eukarya has four kingdoms: Kingdom Animalia (have organs and must eat), Kingdom Plantae (plants who use the sun to photosynthesize), Kingdom Fungi (recycles waste into food) and Kingdom Protista (single complex cells).  Humans are classified in the Kingdom Animalia and are in the subgroup vertebrates.  Within vertebrates humans are mammals.  Down to primates and the scientific name is Homo Sapien meaning thinking man.  Species is the smallest unit of the classification system and the second smallest is genus. All humans belong to both the genus and species classification.
Humans have defining features that separate us from other animals.  Humans have a large brain in proportion to their bodies.  There are many theories as to why humans brains evolved but no one knows for sure.   Another feature that makes humans unique is opposable thumbs.  Even though other primates have thumbs, humans are the only animals who have the right muscles to precisely pick up tiny objects.  Humans are the only mammals who walk upright on two legs called bipedalism (excluding birds).  The last defining feature of humans is the capacity both written and spoken language.  All animals communicate but humans are the only ones who have two complex forms of communication. 
Science is both a body of knowledge and a Process
Science is the study of the natural word and can be divided into two groups.  The first group is knowledge about the world and the second is the process in which to acquire knowledge.  The second is also known as the scientific method and is used to test ideas.  There are five steps that might have to be repeated in the scientific method.  Step 1 Is to observe and generalize (inductive reasoning). Step 2 Is to come up with a hypothesis which is a tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation.
 (http://www.thefreedictionary.com/hypothesis, 9 Febuary 2012, Page 1) Step 3 is to make a testable prediction that is both ethical and reproducible (deductive reasoning).  Step 4 Experiment and observe (inductive reasoning).  Step 5 if necessary modify and repeat the hypothesis as many times as needed.  A hypothesis can never be proved true, only supported or disproved.  Experiments are well planned and performed under controlled conditions.  Many controlled experiments are conducted to make sure a medicine or product is safe for consumers. Controlled experiments take into account all the variables except for the controlled variable. A group of people are specifically chosen to take part in the experiment.  That group is then split into two groups.  The people in the experiment don’t know which group is receiving the placebo and what group is receiving treatment.  Then observations and data is recorded on the two groups of test subjects.  At the end of the experiment the results are compared between the two groups of test subjects.  This is only the start to supporting the hypothesis. Many more experiments will be done to make sure all the information is complete enough to release a safe product.  
 (http://images.search.yahoo.com/images, 8 Feb 2012)
 Sources of Scientific Information vary in Style and Quality
There are many different information sources out there.  The source that is very popular right now is the internet.  On the internet you have to be careful that you are receiving correct information.  Due to the vastness of the internet it is hard to regulate and control if the information is accurate.  Other sources of scientific information are magazines and newspapers.  These sources are used to disperse new information quickly so many people can receive it.  Then there is books and science magazines that target a specific group of individuals who are educated enough to grasp what the author is saying.  Lastly, in peer-reviewed journals scientists often communicate with other scientists.  These journals are written very technical and the main goal is to be able to communicate with other scientists.
Learning to be a Critical Thinker
I believe learning to become a critical thinker will benefit many aspects of my life.  Being skeptical will allow me not to necessarily always believe what I am told but question the information given.  To find any evidence that can back up the information being offered.  By using statistics we are able to have confidence in what is being presented.   It is also very helpful to be able to read and understand graphs.  This is important because the information is sometimes shown in a way that is deceiving unless you can point it out.   Scientific evidence is defined as ….. Anecdotal evidence is different because it is short and unverified.  For example if a book was written guaranteeing you something but didn’t really know if they would deliver although some might get the intended results.  Another thing to consider when receiving information is to question who will profit from the information being given.  How are facts and conclusions different?  Facts are defined as something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability that is whether it can be shown to correspond to experience. Standard reference works are often used to check facts. (http://en.wikipedia.org/wiki/Fact, page 1, 9 January 2012) Where conclusions are the close or last part; the end or finish, the result or outcome of an act or process.  Or a judgment or decision reached after deliberation. (http://www.thefreedictionary.com/conclusion, 9 January 2012, Page 1) Next is to understand the difference between correlation and causation.  When someone gets bit by a shark this doesn’t mean that because people go to the beach that sharks will bite them (correlation).  Where in causation there is direct cause and effect.  For example someone who smokes cigarettes could get a health related problem directly caused by smoking. 
The Role of Science in Society
Science has done so much for us (humans) from helping us to better understand a more efficient way to grow food, harvest wind energy,  and the tsunami warning system in our oceans to name a few.  Science does have limits because it can’t determine what is morally right and wrong.  Most humans have some sort of faith or religion believed in but there isn’t any proof it exists.  We as humans use our minds and experiences to create our truth.  When making informed choices science defiantly helps us do this.  We use science all day long with decisions like what we are going to eat, smoking, using risky behavior ect.  What we decide is all because science has given us the knowledge to make informed choices.  (pic of tsunami warning systems and wind energy)
Chapter 2
All Matter Consists of Elements
Matter is anything that has mass and occupies space.  Chemistry is the study of matter and matter is made up of elements.  Elements cannot be broken down to simple form and all known elements are listed on the periodic table.  The smallest unit of an element is called an atom.  Atoms have a nucleus that is the core.  They have positive charged protons and have mass.  The shell surrounds the nucleus and is sometimes called a cloud or mist.  Electrons have a negative charge and lack mass (there is some mass that I haven’t learned about yet). 
Atoms have an atomic symbol containing one or two letters.  In neutral atoms the number of protons will be equal with the number of electrons.  Atomic mass is roughly equal to the number of protons plus neutrons.  Atoms that have either more or less neurons than the usual number are called isotopes.    These isotopes have the same atomic number but have a different atomic mass.  Unstable isotopes are called radioisotopes and they give off energy particles (radiation).  Some radioisotopes have been useful to scientists and people in the medical field.  They have been used in cancer treatment, used for dating fossils, in diagnostic imaging, and in cardiac pacemakers power supply. 
Atoms Combine to form Molecules
A molecule forms when two or more atoms are in a firm link.  Energy is what fuels life’s activities and is the capacity to do work.   There are two types of energy.  Kinetic energy is the body in motion and potential energy which is stored energy.  Potential energy is energy that can be turned into kinetic energy.  Electrons have potential energy and each shell matches to a specific level of potential energy.  Shells that are farther away from the nucleus contain electrons with more potential energy.  Atoms that have a full shell are most stable and atoms will interact with each other in hopes of filling their shells.  Chemical bonds link atoms to form molecules.  Chemical bonds are the attractive forces that hold atoms together.    There are three types of chemical bonds 1. Covalent bonds 2. Ionic bonds 3. Hydrogen bonds.  Covalent bonds form when atoms share an electron.  An example is water H2O.  A nonpolar covalent bond has electrons that aren’t shared.  Ionic bonds are electrically charges atoms or molecules.  Ionic bonds have attractive forces between oppositely charged ions.  A negatively charged ion forms when an atom or molecule gains electrons.  Positively charged ions form when an atom or molecule loose electrons.  Hydrogen bonds form between polar molecules where electrons are not equally shared.  Polar molecules have polar covalent bonds with unequal electrons.  They have an uneven charge distribution but overall are electrically neutral.  
Life Depends on Water
We couldn’t survive without water and not only that but 60% of our body weight is made up of water.  Water molecules are polar. Water is liquid at our body temperature; it can also absorb and hold heat energy.  Water helps to regulate body temperature and is a biological solvent.  A solvent is liquid in which other substances dissolve.  Solute is any dissolved substance.  Hydrophilic are polar molecules that are attracted and interact with water.  Hydrophobic is nonpolar neutral molecules that don’t like water and try to stay away from it.  Water pushes away molecules that aren’t polar. 
The importance of the Hydrogen Ions
The hydrogen ion is one the most important ions in the body.  The covalent bonds between hydrogen and oxygen in water are strong and rarely break.  An acid can donate hydrogen ions (protons) and increase hydrogen ion concentrations in solutions.  A common acidic drink is orange juice and soda.  Bases can accept hydrogen ions and lower hydrogen ion concentrations in solutions (alkaline).  The pH scale measures the hydrogen ion concentration. The pH range is between 0-14 with the neutral at 7.  Acidic solutions are higher than 7 and alkaline solutions are below 7.  Carbonic acid and bicarbonate act as one of the bodies most important pair of buffers.  Their job is to minimize the pH change within the body and help to maintain a stable pH level within body fluids. 
The Organic Molecules of Living Organisms
Although organic molecules were once believed to only originate from living organisms scientists now know this isn’t true.  Carbon is the building blocks of all living things.  Carbon is abundant in the human body but is much rarer in the natural world.  Carbon is diverse because it can form single or double bonds.  There is no size limit of organic molecules derived from carbon.   Macromolecules consist of thousands + smaller molecules of carbon and are made and broken down within cells.  Macromolecules are built within the cell by a process called dehydration synthesis.  In this process by removing a water molecule this in turn links molecular units.  Dehydration synthesis builds macromolecules from smaller subunits but it does require energy to do so.  Sometimes macromolecules need to be broken down in a process called hydrolysis.  This process actually releases energy and uses water to break the macromolecules apart.  (Dehydration is the opposite of hydrolysis)
Carbohydrates: Used for Energy and Structural Support
General formula: Cn(H2O)n
Carbohydrates have the same number of carbons as oxygens as hydrogen molecules.  Lots of living things use carbohydrates as energy.  The simplest form of sugars is called monosaccharide.    Monosaccharide includes glucose, fructose, galactose, ribose and deoxyribose.  Dehydration synthesis can link monosaccharaides together called disaccharides.  Polysaccharides are composed of thousands of monosaccharide by chains and branches.  This makes it so cells can stock pile energy to be used later.  Plants make and store starch to be used by plants later.  Animals store and make glycogen for animals to use at a later time.  Cellulous is made by plants to be used for structural support but can be used by animals for energy. 
Lipids: Insoluble in Water
There are three important classes of lipids.  Triglycerides are energy storing molecules.  Triglycerides are known as fats or oils.  Saturated is fats and unsaturated is in oils. Triglycerides are stored in adipose tissue and are energy storing molecules.  Phospholipids make up the main components of the cell membrane structure.  One end of the phospholipid is hydrophobic and the other end is hydrophilic.   Steroids are carbon based and made of four rings.  One type of steroid is cholesterol which hormones, estrogen, testosterone, and pigments are made from.   
Proteins: Complex Structures Constructed of Amino Acids
Proteins are made up of long chains of amino acids made by the dehydration synthesis.  There are twenty different types of amino acids that are connected by peptide bonds.  Every protein has a specific function that depends critically on its construction.  The simple primary structure of a protein is represented by the amino acid sequence.    Secondary structure is in an alpha helix (twisted) form.
Alpha Helix
 It can also be in a beta pleated form (like a fan) stabilized by hydrogen bonds.  Tertiary structures are 3D and stabilized by other bonds such as disulfide and hydrogen bonds.  The grooves and pockets created by the three dimensional figure create polar and non-polar areas within the molecule.  Quaternary structure is two or more tertiary structures together.
Enzymes
Enzymes are proteins and function as biological catalysts.  They speed up chemical reactions but can’t change reactions.  Without enzymes many biological reactions couldn’t take place quick enough to sustain life.  The functional shape of an enzyme depends on temperature, pH, ion concentration, and the presence of inhibitors.
Nucleic Acids Store Genetic Information
Two types: DNA deoxyribonucleic acid and RNA ribonucleic acid
Nucleic acids function is to store genetic information.  DNA provides instructions for making RNA.  RNA provides instructions for making proteins. Proteins direct most of life’s processes.   Nucleotides are the building blocks of nucleic acids.  The nucleotides are made of a sugar base and one or more phosphate group.  The structure of DNA is double stranded and in the nucleotides is deoxyribose (sugar).  The nitrogenous bases of adenine + thymine and guanine +cytosine are paired together.  Sugar and phosphates are the backbone of the structures and hydrogen bonds in the middle make the structure strong.
RNA ribonucleic acid is single stranded.  The nucleotides contain ribose and nitrogen bases.  The nitrogen bases are adenine, guanine, cytosine, and uracil.
APT Carries Energy
ATP is a universal energy source.  Bonds between phosphate groups contain potential energy.  When bonds break energy is released (a+p=ADP + P + energy).
Chapter 3 Bio
Cells are Classified According to their Internal Organization and Cell Structure Reflects Cell Function
The cell doctrine is the theory that cells form the fundamental structural and functional units of all living organisms (http://dictionary.reference.com/browse/cell+doctrine, 10 February 2012, page 1).  The cell doctrine is made up of 3 principles: 1. all living things are made up of cells 2. A single cell is the smallest unit that displays all the characteristics of life 3. All cells come from preexisting cells. 
There are two different cell types that are classified by their internal organization.  A Prokaryotic cell has a plasma membrane, do not have a nucleus, and has jelly like cytoplasm without any true organelles.  Eukaryotic cells have a plasma membrane and have an information center called the nucleus. They too have a cytoplasm but do have organelles that perform functions like digesting nutrients or shipping waste.  Eukaryotic cells are very important to us because all human cells are eukaryotic.  Eukaryotic cells come in many shapes and sizes.  Muscle cells are made up of many organelles because muscles require extra energy.  Nerve cells are long and thin enabling them to carry impulses for long distances.  Needless to say, human cells vary in many different shapes but stay small to be efficient.  This is efficient because with a higher surface area the volume ratio can get rid of cell waste and acquire nutrients easier.  Cells are so small that they can’t be seen without a microscope.  There are three types of microscopes 1. Light microscope that has been used for a few hundred years. 2. A transmission electron microscope that has greater clarity at any magnification.  3. Scanning electron microscope gives amazing images of the cells and the outer surface of the cell. 
A plasma Membrane Surrounds the Cell
Cells are surrounded by a plasma membrane which is the cells house.  It is a barrier that protects the inside of the cell regulating temperature.  The cell membrane also controls what comes inside the cell and what doesn’t.  When looking at what makes up the plasma membrane we find it is a lipid bilayer.  The lipid bilayer is made up of phospholipids that have non polar tails that aren’t attracted to water and a polar head that is attracted to water.  There is also cholesterol that helps make the plasma membrane firm.  Proteins provide transport through the plasma membrane and regulate what is allowed in or out. 
Molecules Cross the Plasma Membrane in Several Ways
Molecules cross the plasma membrane in a few different ways.  They can pass by passive transport through means of diffusion and osmosis where the cell doesn’t use any energy.  There is passive transport that moves with the concentration gradient.  Concentration gradient is defined as the graduated difference in concentration of a solute per unit distance through a solution http://www.thefreedictionary.com/concentration+gradient, 10 February 2012).  This can happen through protein channels, diffusion through the lipid bilayer and by facilitated transport where no energy is used. Another means of transport is active transport where the cell must use energy. In active transport substances are moved from an area of lower concentration to an area of higher concentration.  This requires a plasma membrane protein to transport and either ATP or a different energy source.  Lastly, bulk transport is used when molecules are too large or used to move molecules in bulk.  Endocytosis is bulk transport moving molecules into the cell.  Exocytosis is bulk transport moving molecules out of the cell.   Receptor proteins span over the plasma membrane gathering and giving information.  Receptor sites on the receptor proteins interact specifically with signal molecules.  When a signal molecule fixes itself to a receptor site changes within the cell are triggered.  Different types of cells have different types of receptor sites.  When determining what comes and goes, a sodium potassium pump helps to maintain cell volume.  It also gets rid of unwanted ions and maintains the ions that are needed.  For instance when a cell gets rid of 3 sodium ions, 2 potassium ions are brought into the cell.  The sodium potassium pump can increase cell volume by decreasing pumping and allowing more sodium inside.  The pump can decrease cell volume by increasing pumping and getting rid of more sodium.
Internal Structures Carry out Specific Functions
The nucleus is the information center of the cell.  The outer layer of the nucleus is the double layered nucleus membrane.  Inside the nucleus is the nucleolus where components of ribosomes are created.  Ribosomes are responsible for making certain proteins by connecting amino acids in certain sequences.   Ribosomes that are attached to the endoplasmic reticulum release their proteins into the folds of the endoplasmic reticulum.  They are industrial plants making materials that are not in their final form.  The materials are polished and packaged by the Golgi apparatus.  Then the products are put in the vesicles to go to their final destination.  There are many different types of vesicles. Two powerful vesicles that have potent enzymes are peroxisomes and lysosomes. Peroxisomes destroy waste within the cell including alcohol.  Lysosomes have great digestive enzymes that digest bacteria and large particles, cellular waste and debris.  The power plant of the cell is the mitochondria.  The more energy a cell needs the more mitochondria will be present.  Mitochondria can generally make ATP when needed but some cells also store raw energy.   One way cells store energy is in fat (lipids).  When you work out and get thinner you are not reducing the amount of fat but rather making your fat cells skinny.
Cells have Structures for support and movement
The plasma membrane is soft and flexible.  Structural elements support the plasma membrane and enable cells to move.  The cytoskeleton is made up of protein and fibers called microtubules and microfilaments.  These fibers create the supports and anchors within a cell.  Some cells have hair like cilia or flagella on one surface of the cell.  Cilia are common on cells that line airways and certain ducts within the body.   The flagella are only found on sperm cells enabling them to move relatively quickly.  The last cell structural support is centrioles.  These centrioles are very important in cell division because they align and divide all the genetic material.   
Cells Use and Transform Matter and Energy
All the chemical reactions that happen within living cells is called metabolism.  Within a single cell thousands of different chemical reactions happen which are called the metabolic pathways.  There are two types of metabolic pathways; the first is anabolism in which molecules are made into larger molecules using energy. The second is catabolism where larger molecules are broken down and energy is made.  Cells need energy (ATP) and can use a variety of fuels.  Glucose is the most available source of fuel but cells can use fats or proteins as well.   We eat and glucose is usually always available throughout our bodies.  When glucose isn’t available our energy reserves are mostly fat and some protein.  This is when fat is broken down in our bodies.    
Chapter 4
Tissues are Groups of cells with a Common Function
Tissue(s) is made up of cells that arrange themselves in a way to function as a whole.
Epithelial Tissues cover body Surfaces and Cavities
One of the four tissue types is epithelial tissue.  It is formally called Glandular Epithelia.  It lines body cavities and also our skin.  Other epithelial tissues line the bladder, blood vessels, lungs, digestive tract and tubules of kidneys.  There are many layers to epithelial tissue.  There are three shape classifications for epithelial cells.  The first is squamous cells that are flat, line the body’s surface, line the lungs and vessels.  Second are cuboidal cells that are cube shaped and form the lining of tubules and gland tissue.   Lastly are columnar cells that are column shaped, line the respitory tract, digestive tract and reproductive glands.   There are single layers (simple) of epithelial tissue that are adapted to diffusion and line the glands, respitory, digestive and reproductive systems.  There is also multiple layers (stratified) that provide protection to the skins surface.   Underneath the epithelial tissue is the basement membrane.  This membrane provides support and attaches the epithelial tissue to the tissues under it.   Types of junctions hold epithelial cells together.  Gap junctions are in the form of protein channels for the direct transfer of water and ions between cells.   Adhesion junctions anchor two cells together allowing some movement between cells.  Tight junctions don’t let anything pass between cells.  Depending on where the epithelial cells are determines the type of junctions between the cells. 
 Connective Tissue Supports and Connects Body Parts
Connective tissue is a very diverse tissue and is made up of cells, ground substrate, and protein fibers.  Connective tissue supports softer organs, connects and cushions parts of the body, stores fat and produces blood cells.  There are two types of connective tissue.  The first is Fibrous which also has four types 1. Loose- surrounding organs 2. Dense- making tendons and ligaments 3. Elastic- surrounds the stomach and bladder 4. Reticular- makes up the frame work to the liver and lymph system.  The other type of connective tissue is called special.  There are specialized connective tissues that have special functions including blood, bone, cartilage, and adipose tissue.  Blood is made of red and white blood cells, platelets and a fluid matrix of plasmas.  Bone is an inorganic matrix with calcium salts for hardness.  Cartilage doesn’t have any blood vessels and contains a high amount of collagen.   Some cartilage turns to bone and other cartilage remains flexible.  Adipose tissue store energy, help protect, and store energy in the form of fat.  The amount of adipose tissue someone has is due to genetics. 
Muscle Tissue Contract to Produce Movement
Muscles are made up of cells that are tightly fit together called fibers.  These fibers line up parallel and are tight together.   There are three different types of muscle tissues in the human body.  First is skeletal muscle which connects to tendons then connecting to bones.  They are controlled muscles , multinucleated, with many nuclei.  Second is the cardiac muscle that contains a single nucleus.  These muscles are only found in the heart and are an involuntary muscle.  Last are smooth muscles that contain a single nucleus and is an involuntary muscle.  These muscles surround hollow organs and tubes and are found in the bladder, uterus, blood vessels, and digestive tract. 
Nervous Tissue Transmits Impulses
Nervous tissue forms fast communication throughout the body.  Nervous tissue is located in the brain, spinal cord, and within the nerves that transmit information from one place to another.  The electrical impulses are called neurons.  Neurons can be very long so the body can receive impulses from other parts of the body.  They have three main structural components; the cell body, dendrites (that receive impulses) and the axon (that transmit impulses).  The glial surrounds and protects neurons giving them the nurturance they need.
Organs and Organ Systems Preform Complex Functions
Organs have two or more tissue types joining together to preform specific functions.  An organ system is a group of organs that preform a common purpose.   A few types of organ systems are mouth, throat, esophagus, stomach, and intestines.  All the organs have to work together to accomplish their overall functions. 
There are four tissue membranes.  First is serous membrane that reduces the friction between the organs.  The second is mucous membrane that lubricates surfaces and catches debris.  Third is synovial membrane that lines the spaces in all movable joints.  Last is the cutaneous membrane which is our skin.  Serous tissue membrane lines our body cavities.  Humans have a thoracic cavity (lungs and heart), abdominal cavity, cranial cavity (brain), spinal cavity, and pelvic cavity. 
There is a unique language used to accurately describe a certain part of the body. It is best shown in the picture below. 
The Skin as an Organ System
Many would not think of the skin as being an organ system but it is.  The proper name is the integumentary system that includes not only the skin but also hair, nails and glands.  The skins functions are to prevent the body from any injury, prevent dehydration, regulates the body temperature, makes vitamin D, helps defend against microorganisms, and to provide sensation.  The outermost layer of the skin is called the epidermis.  The layer of skin under the epidermis is called the dermis. The dermis provides protection and supports tissues under it.  There are some accessories to the dermis like sweat glands that help to regulate body temperature.  Blood vessels supply necessary nutrients and remove waste.  There are also sensory nerve endings that can detect hot and cold, pressure, and touch.  The skin in an amazing organ that is overlooked at times.
Multicellular Organisms Must Maintain Homeostasis
Homeostasis is defined as the ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes. (http://www.answers.com/topic/homeostasis, 11 Feb 2012)  So whenever conditions become abnormal in the body the negative feedback control system flies into action.  The parts of a negative feedback control system are a sensor, controlled variable, control center, and an effector.  The negative feedback control center keeps all changes within the body at suitable limits.   

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