Lab Project: Milk, Juice, Carrot

Introduction: We are to take 1/2 cup of milk, pour it into a jar or glass and put it into a warm, dark place for two days. We are to observe any changes in the milk due to biological influences. Proteins are critical as well as the fermentation process and carbohydrates.

Hypothesis:  I believe the bacteria in the milk, once the temperature gets warmer, will start to grow. First the milk will turn sour or ferment and eventually it will get clumpy. If enough time passes, we would eventually see mold. But I do not believe that will happen this quickly.

1/2 cup of milk

milk in glass

milk in dark place

Procedure: I poured a 1/2 a cup of 2% milk into a small glass. I then placed it in a file cabinet and shut the drawer for a period of two days.

results

Results: There was film scum on the edges of the milk in the glass. It was sour to taste (I dabbed my finger into it). But no clumping yet and no mold.

Conclusion: A conversion of carbohydrates to alcohol and sugar to lactic acid occurs. Bacteria, called coliforms exist in milk. It metabolizes or ferments sugar to gain energy in order to grow and multiply. This process will continue until there is no sugar left. Coliforms include E-Coli. (As a side note: Pastuerization reduces the level of coliforms). Once all the lactose is consumed, the bacteria breaks down the protein to form amonia (the base pH of milk). The protein in milk denatures or loses their shape and clumps form together.



Lab Project: Milk, Juice, Carrot

1/2 cup of juice

Introduction: We are to witness the mixing action of molecules and describe the process. We take 2 cups of room temperature water, two cups of ice water and two cups of boiling water into separate cups or jars. Then we take a 1/2 cup of a dark juice and pour a third of this into each cup of water.The temperature of the water will have a definite impact on the way the molecules mix.

room temp juice/water

room temp water

 

ice water/juice

ice water/juice

broken glass

Hypothesis: I believe the temperature of the water will have a serious impact on how these molecules mix. Not sure what it will do, butI think hot water will mix fairly quickly, cold probably not so muchand room temperature may not have any effect.

boiling water

boiling water/juice

  Procedure: I first poured the juice into a measuring cup. Next, I poured room temperature water into a glass and proceeded to pour a third of the juice into this glass. Next, I poured cold ice water into a glass and them followed with another third of the juice. Then, I boiled 2 cups of water and poured that into a glass, at which point the glass cracked and the water leaked out. So I had to start all over, boil more water and then poured it instead into a measuring cup and then followed this with the remaining juice.

Results: In the room temperature water and juice combo, I did not notice much of anything. The mixture mixed fairly well, but was cloudy. When I mixed the ice water and juice, the juice sunk to the bottom and bubbles appeared on top. When I poured the boiling water into the glass, my glass cracked and all the liquid leaked out. So I redid, and poured it into a measuring cup and then added the remaining juice. Last, but not least, when I managed to combine the boiling water and juice, it mixed very quickly and was a fairly clear solution.
 
Conclusion:  The room temperature water had very little effect on the mixing action of these molecules compared to the ice and boiling water. When I mixed the ice water and juice, the moving action of the molecules was very slow. When the boiling water was poured into the glass, it broke because the inner surface of the glass gets the heat first and expands more quickly than the outside. The sudden pressure from the heated inside is so strong and sudden that the whole glass breaks. Once I managed to add boiling water and juice, the hot water caused the mixing action to speed up and molecules mixed quickly.

Lab Project: Milk, Juice, Carrot

Introduction: The objective of the carrot lab is to investigate the cellular functions and cellular structures using a carrot in both fresh water and salt water.

whole carrot

cut in half

Hypothesis: I believe that the carrot in the fresh water will swell  after soaking and the carrot in the salt water will either remain the same or shrink. The fresh water will probably diffuse into the carrots cells and just the opposite with salt water.

original measurement

Procedure: We were to pour two cups of water into two glasses or jars. In one cup was added a teaspoon of salt. Then I labeled them, "fresh" and "salt" respectively. I cut a carrot in half and measured both pieces in height and width. Then I tied a string around the cut end of each piece and put them into their water to soak for 24 hours.

glasses labeled

soaking overnight

Results: The initial width of the salt water carrot was 3/4" and the
height was 4 11/16". After soaking for 24 hours, the width and height were the same. So the salt water maintained the carrots size. The beginning width of the fresh water carrot was 3/4" and the height was 4 5/8". After soaking 24 hours, the width was 13/16" and the height was 4 11/16". So the carrot expanded by 1/16 of an inch both in width and height. 

measurement afterward

Conclusion: Osmosis is the diffusion of water through a membrane. A carrot is made up of tiny cells surrounded by cell membranes. The cell membrane keeps cell parts inside and protected. While this membrane stops most things, water can pass through it. Water moves through cell membranes towards a higher concentration of dissolved chemicals. When the carrot is soaking in salt water,  the water found in the carrot's cell will move into the salty water to equalize the amount of water inside and outside the cells' membranes. As more and more of the cells lose water, the carrot becomes soft and flexible. When the carrot is placed in the fresh water, the reverse happens. The fresh water around the  carrot moves into the carrot's cells. The string will tighten and the carrot will swell with water.

Human Biology

Table of Contents:

Human Biology, Science, and Society

The Characteristics of Life

How Humans Fit 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

The Chemistry of Living Things
All Matter Consists of Elements
Atoms Combine to From Molecules
Life Depends on Water
The Importance of 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
Nucleic Acids Store Genetic Information
ATP Carries Energy

Structure and Function of Cells
Cells are Classified According to their Internal Organization
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

From Cells to Organ Systems
Tissues are Groups of Cells with a Common Function
Epithelial Tissues Cover Body Surfaces and Cavities
Connective Tissue Supports and Connects Body Parts
Muscle Tissues Contract to Produce Movement
Nervous Tissue Transmits Impulses
Organs and Organ Systems Perform Complex Functions
The Skin as an Organ System
Multicellular Organisms Must Maintain Homeostasis

Human Biology, Science, and Society


The Characteristics of Life
www.youtube.com/watch?v=juxLuo-s

(accessed 1/20/2012)

I would like to encourage each one of my fellow students to take a few moments to watch this video. It is absolutely awesome!

Nonliving and living things are both composed of approximately 100 different chemicals. But only a few of these are found in abundance in living organisms. Living things can also combine elements, creating molecules in unique ways. It is these molecules (proteins, carbohydrates, lipids and nucleic acids) in varying forms, that create a diversity of life.

Living things require energy and raw materials. All living things take in raw materials and energy from the environment and metabolize that into the molecules and energy that are needed to survive. Plants get their energy from sunlight and chemicals from soil, water and air. Animals and all other forms of life use water, air, plants and other animals.

Living things are composed of cells. Cells being the smallest unit that has all the characteristics of life. There are unicellular and multi-cellular organisms.


We maintain homeostasis. Single cell organisms are encased in membranes that provide a selective barrier for fluids to exit or enter, thus maintaining a stable internal environment. In multi-cellular organisms, it is the tissues, organs and organ systems that provide that service.

http://www.phys.unsw.edu.au/biosnippets/biosnippets_container2.swf (accessed 1/20/2012)

Living things respond to their external environment. For example, humans sweat when too hot to cool down their system. Plants grow towards light and even bacteria move toward nutrients. Living things grow and reproduce. This ability is determined by DNA, a genetic material in cells. There are some nonliving things that can grow larger, such as a volcanic mountain, but it cannot recreate itself. Below you will find a link to an article on just what  DNA can tell us.

http://www.guardian.co.uk/science/2008/apr/27/genetics.cancer (accessed 1/20/2012)

And last but not least, populations of living things evolve. Various forms of life may change over the course of many generations. This is known as evolution. Individual organisms don’t evolve and may not reproduce or respond to their environment, but  populations of similar organisms have the capability of doing so.
image source: http://office.microsoft.com/en-us/images/results.aspx

How Humans fit into the Natural World
Living things are grouped according to their characteristics. In the five-kingdom system, one kingdom, the prokaryotes, lack nuclei. The remaining four, eukaryotes,  have cell nuclei. Monera is the kingdom of bacteria. Then there is Animalia, Plantae, Fungi and Protista (consisting of algae, slime molds and protozoa).  http://users.rcn.com/mnar77/pdf/Five.Kingdom.Chart.pdf

Humans have very defining features. Opposable thumbs, large brains and bipedalism. We also have the capacity for complex language.

Science: A Body of Knowledge and a Process
Information about the natural world is scientific knowledge. The scientific method is the systematic way that knowledge is acquired.

Step 1: Observe and generalize
Step 2: Formulate a Hypothesis
Step 3: Make a testable prediction
Step 4: Experiment or observe
This must be a controlled experiment)
Step 5: Modify your hypothesis and repeat steps 3 and 4 as necessary

Of course, it does no one any good, if your findings are only known by you. The next step is to share them. Many scientists publish their findings in scientific journals.
image source: http://office.microsoft.com/en-us/images/results.aspx

Sources of Scientific Information vary in Style and Quality
As mentioned earlier, scientists generally communicate with one another via scientific journals like Science or Nature. But these are usually too technical for the layman. Science magazines and nonfiction books are helpful for those who would like to delve a little deeper but do not have a scientific background. Other sources include news magazines and your daily newspaper.

The two newest sources are television channels such as the Documentary channel and the World Wide Web. But it must be noted that not all information on the web is accurate. You must read it with a note of caution until you can verify the information.

Learning to be a Critical Thinker
Below are some tips on developing and/or improving   your critical thinking:

• Become a skeptic - question everything.
• Appreciate statistical value - use statistics to decide how much to believe or not believe the information.
• Learn how to read graphs - it can be worth a thousand words.
• Know the difference between scientific evidence and anecdotes - anecdotes are not based on empirical evidence.
• Separate fact from conclusions - a fact is verifiable, while a conclusion is a judgment based on facts.
• Understand the difference between correlation and causation - just because something has a close relationship to another thing does not mean that the one thing caused the other.

http://office.microsoft.com/en-us/images/results.aspx

The Role of Science in Society
Science improves our human physical condition and technology - examples would be better weather predictions, in some cases saving many lives; better health care; and saving our planet.

Science is limited to physical explanations for events we can observe in our world. It cannot prove or disprove anything outside of that natural world.  For instance, anything pertaining to faith or ethical decisions, to name a few.

We, as a society, must learn how to make informed choices. With the knowledge we now have available today, comes a great deal of responsibility. “When I was a child, I used to speak as a child, think as a child, reason as a child; when I became a man, I did away with childish things”. (1 Cor. 13:11, NAS)

The Chemistry of Living Things
Chemistry is the science of matter, covering chemical reactions, structure, composition and properties. It is sometimes called “the central science”, because it connects physics with other natural sciences such as biology and geology.

Chemistry can be traced back to alchemy, which has been practiced for millennia, especially in the Middle East. Let us now consider how the laws of chemistry promote life.

All Matter Consists of Elements
Matter is anything that has mass and occupies space and it is composed of elements. An element is the true form of matter that cannot be broken down to anything simpler.

Atoms are the smallest unit in an element. We know that atoms can be split apart ie… a nuclear reaction, but they are the smallest units of matter in a chemical reaction. The nucleus or center of the atom is made up of particle protons which are positively charged and neutrons, which are neutral.

Isotopes are atoms that have either more or less neutrons than the usual number for that element. The isotopes that are unstable are called radioisotopes, of which there are many. They give off energy (radiation) and particles until they become more stable. Measuring radioisotopes is the means used to determine when rocks and fossils were formed.


Atoms Combine to Form Molecules
Energy is life’s fuel, if you will, allowing the capacity to cause change. Both breaking up molecules and joining them require energy.  There is potential energy, which lays dormant and kinetic energy, which is in motion.

Chemical bonds link atoms to form molecules. The three main types are ionic, hydrogen and covalent.

An ionic bond takes place between opposite charged ions. Hydrogen bonds are weak and form between polar molecules. And last, but not least, covalent bonds share electrons. Covalent bonds are the strongest chemical bonds in nature.

Living organisms contain only certain elements. Even though there are close to 100 elements in nature, living organisms are only made of a few. For instance, our human bodies are mainly constructed of 6 elements: oxygen, hydrogen, carbon, nitrogen, calcium and phosphorus.


Life Depends on Water
Water is the most important molecule in existence. Some of the most critical properties being that it has polar molecules, is a liquid at body temperature and can absorb and hold heat. Water is the biological solvent, meaning it is a liquid that can dissolve other substances. Because water is a liquid at body temperature, it is ideal for transporting solutes from one area to another. And because of its ability to hold heat, it helps to maintain body temperature when there are changes in the environment or metabolism.

The Importance of Hydrogen Ions
Hydrogen is a single proton without an electron. Acids give up hydrogen ions, while bases accept them. When combined, they neutralize each other. We use the pH scale to measure hydrogen ion strength in a solution. Ranging from 0-14, with 7.0 being neutral. A buffer is critical in maintaining homeostasis of pH in our bodies. In our blood and urine, buffers are paired and have opposite effects.

The Organic Molecules of Living Organisms
Organic molecules contain carbon and other elements and are held together by covalent bonds. Carbon is fairly rare in our natural world (only .03% of earths crust). But living organisms actually accumulate it. It is the foundation for all organic molecules.

Macromolecules are  synthesized and broken down within cells. Organic molecules are created by dehydration synthesis, which requires energy. This enables new cell membranes, muscle fibers and other tissues to form. Hydrolysis is the process that breaks down macromolecules. Being the opposite of dehydration synthesis, the process releases energy.

Carbohydrates Are Used for Energy and Structural Support
Monosaccharide (or one sugar), is the simplest carbohydrate. It is a source of quick energy.  Ribose, glucose, fructose and deoxyribose are the most important monosaccharides in humans. 

Oligosaccharides consist of short strings of monosaccharides and are linked together by dehydration synthesis.

Polysaccharides are complex carbohydrates made up of thousands of monosaccharides. Polysaccharides are the way in which cells store energy. In plants it is done through starch and in humans it is through glycogen.

Lipids are Insoluble in Water
The most important subclasses of lipids in our bodies are triglycerides, phospholipids and steroids. Triglycerides are stored in adipose  tissue and are a source of stored energy. Phospholipids are the main component of cell membranes and are a modified form of lipid. Just like triglycerides, their backbone, if you will, is made of glycerol. But they only have two fatty acid chains instead of three. There is also either a negatively charged or positively charged phosphate present. Steroids do not look the same as a lipid, but are classified as one because they are fairly insoluble in water. One of these is cholesterol, which we are all familiar with. Cholesterol is a structural component of animal cells and is the source of estrogen and testosterone.    

Proteins are Complex and Constructed of Amino Acids
The proteins structure, which is three-dimensional,  depends on the amino acid sequence. They are created by dehydration synthesis just like carbohydrates and fats. The human body has thousands of proteins, all constructed of only 20 amino acids, with thousands of functions.

An enzyme is a protein that acts as a catalyst. It speeds up the rate of a chemical reaction without being consumed. Some break molecules apart and others join them together. Without enzymes,  our bodies chemical reactions would be too slow and would not sustain life.

Nucleic Acids Store Genetic Information
Another important organic molecule is the nucleic acid, both DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA is the genetic material directing everything that a cell does. It is the key to life itself, controlling our growth, development and reproduction.

RNA is responsible for carrying out the instructions of DNA and at times, regulates DNA’s activity. It contains the instructions for producing proteins. RNA is a single strand, representing a portion of one strand of DNA.

ATP Carries Energy
ATP (adenosine triphosphate) is a nucleotide and is a universal source of energy for cells. Their energy is stored in the bonds between phosphate groups. The breakdown of ATP produces ADP (adenosine diphosphate). This energy source is responsible for a wide variety of processes in both plants and animals.

The Structure and Function of Cells
In 1674, scientists discovered living cells under a microscope. Out of this came the cell doctrine, consisting of three basic principles:

1. All living things are composed of cells and cell products

2.  A single cell is the smallest unit that exhibits all the characteristics of life.

3. All cells are formed from only preexisting cells.

Cells are Classified According to their Internal Organization
Every cell has a plasma membrane as the outer layer. It encloses the material inside, consisting of water, ions, enzymes and other structures that maintain life. Living cells are either eukaryotes or prokaryotes, which is determined by the way they are organized internally.

A eukaryote, meaning “true nucleus”,  has three basic parts: a plasma membrane, a nucleus and cytoplasm. The cytoplasm contains everything in the cell except the nucleus. It is composed of cytosol, a gel-like fluid. Within this fluid are organelles (little organs” that carry out specialized functions.

Prokaryotes. Meaning “before nucleus”, do not have a nucleus or organelles. These are bacteria in the Kingdom Monera.

Cell Structure Reflects Cell Function
Cells remain small to stay efficient, but they vary in size and shape according to their function. For example, muscle cells contain numerous mitochondria. Nerve cells are long and thin - some over 3 feet long! The cells along the kidneys are cube shaped and bound tightly together. The really amazing thing is that cells that have the same functions often look vary similar in other species.

The larger a cell gets, the more inefficient it becomes. As they become larger their volume increases more than their surface area. They have to be able to obtain raw material and excrete waste.This is done only by crossing the plasma membrane.

A Plasma Membrane Surrounds the Cell
http://is3whathappenedtoday.files.wordpress.com/2011/09/membrane.jpg
The plasma membrane is made of two layers of phospholipids, plus some cholesterol and proteins.  This phospholipid bilayer is only approximately 3.5 nanometers thick, way to small to see in detail, even with microscopes.

Cholesterol increases the strength of the membrane. It keeps it from becoming too rigid or too flexible. Cholesterol also anchors the proteins. Various proteins provide transport for molecules across the plasma membrane. Below is a link to an animation of the plasma membrane.

http://www.youtube.com/watch?v=ULR79TiUj80

Molecules Cross the Plasma Membrane in Several Ways
Molecules and ions cross the plasma barrier in several ways: passive transport, active transport, and endocytosis or exocytosis.

Passive transport does not require any energy to be expended. It relies on diffusion. Diffusion is a random motion as molecules float around in a gas or liquid, colliding and changing direction. The plasma membrane is very selective in what substances it lets cross. The diffusion of water across a the membrane is called osmosis. Passive transport moves with the concentration gradient which is always downhill. It can diffuse through the lipid bilayer, through channels or what they call facilitated transport. With this facilitated diffusion, the molecule attaches to a protein and crosses the barrier. It in essence, hitches a ride. You can click on the link below to watch a video on passive and active transport. (You may have to copy and paste it into your browser window)

http://www.youtube.com/watch?v=j5Qway4LAkk&feature=related

Active transport can go against the concentration gradient in the opposite direction as passive transport through the plasma membrane. These are active proteins again, but rather than passive transport, they require a source of energy to transport certain molecules. ATP is one of these sources. One of the most important protein pumps is that of the sodium-potassium pump, which get its energy from breaking down ATP. Both the sodium-potassium pump and isotonic extracellular fluid help maintain cell volume.

Endocytosis and exocytosis move molecules in bulk. This method is used when the molecule is too large or several types of molecules need to move in bulk. Endocytosis moves material into the cell and exocytosis moves it out.

Information can be transferred across the plasma membrane via receptor proteins. The information received and transmitted across the membrane causes as series of biochemical reactions even though no molecule crossed over.

Internal Structures Carry Out Specific Functions
https://upload.wikimedia.org/wikipedia/commons/5/5a/Animal_cell_structure_pt.svg

• The most prevalent organelle in a living eukaryote is the nucleus. The nucleus is the center of information for that cell, containing the DNA.
• Ribosomes are composed of RNA and proteins. They assemble amino acids into proteins. Some ribosomes are attached to the endoplasmic reticulum and release their proteins into the folds of the reticulum.
• The endoplasmic reticulum is the manufacturing center and synthesizes most chemical compounds along with the attached ribosomes.
• The Golgi apparatus is the cell’s shipping center, where it refines and packages the molecules.
• Vesicles are membrane-bound and enclose something within the cell. There are several types, each with a different purpose. There are secretory, endocytotic, peroxisomes and lysosomes.
• Mitochondria are the organelles that provide most of the usable energy. They are responsible for creating ATP.
• Some cells store energy in raw form, such as fat and glycogen. They are not stored in  an enclosed membrane, but are awaiting delivery to the mitochondria for conversion into ATP.

Cells have Structures for Support and Movement
The structural supports for the plasma membrane include the cytoskeleton, cilia and flagella, and centrioles. The cytoskeleton is a loose structure of microtubules and microfilaments that support the cell.

Cilia and flagella are hair-like and similar in structure. Flagella are found only in sperm cells and move the sperm cell from one location to another. Cilia are found on the surface of some cells and move material along with a brushing motion. They are found in airways and certain ducts.

Centrioles are short and rod-like. They help with cell division, aligning and dividing genetic material of the cell.

Cells Use and Transform Matter and Energy
Living cells can release stored energy to build, store or break down other molecules to maintain life. ATP is the most readily available form of energy. The most available “fuel” for ATP is glucose.

The process of ATP from glucose has four steps: glycolysis, where six-carbon glucose is split into three-carbon pyruvate; pyruvate is converted to acetyl CoA; citric acid cycle or Krebs in which acetyl CoA combines with the four-carbon fragments left over from the previous cycle to form citric acid; and then the electron transport system produces ATP.

Another source of energy are fats and proteins. In our bodies, approximately 78% is stored fat, 21% stored protein, and only 1% stored glycogen.

ATP requires oxygen, for the most part. Only a very small amount can be produced without oxygen by anaerobic metabolism.

http://www.sciencedaily.com/releases/2012/01/120130130419.htm

In the above article, there have been new strides regarding the hypoxic response related to cancer metastasis and other diseases. The hypoxic response is how our bodies respond to reduced levels of oxygen.  Every cell in our bodies has the ability to respond and change to  available levels of oxygen. When that response is not working properly, this is how cancer spreads. Click on the link above to find out more.

From Cells to Organ Systems
While single-celled organisms are at the mercy of their external environment; when cells join together to form tissues, organs, and organ systems, you now have a way to maintain stability.

Tissues: Groups of Cells with Common Function
Tissues are cell groups with a common function. In fact, all multicellular organisms have specialized functions, although that in itself, is not enough. They also need to be organized and work together. Tissues have four types: epithelial, connective, muscle, and nervous.

Epithelial Tissues Cover Body Surfaces and CavitiesLayers of sheet cells, known as epithelial tissue, cover various surfaces. Two of the most well known are your skin and mouth. The inner surfaces lined with epithelial tissues are your digestive tract, bladder, the tubules of your kidneys, lungs and blood vessels.

A few of these tissues are glandular epithelia. Glands synthesize and secrete some type of product. Examples being the exocrine glands that secrete saliva ,sweat, and digestive acid and endocrine glands that secrete hormones.

Epithelial tissues are classified into three main types according to their shape: squamous epithelium has one or more layers of flattened cells. Cuboidal epithelium has cube-shaped cells. And columnar epithelium is tall and rectangular.

Epithelial tissues are also classified by the number of cell layers in the tissue. Simple is a single layer and stratified has multiple layers.

The basement membrane is a support structure beneath the epithelial tissue. It is a noncellular layer and most often is composed of connective tissue.

Connective Tissue Supports and Connects Body Parts
Connective tissue, for the most part, have very few living cells. Their strength lies in their matrix.  Fibrous connective tissues give strength, elasticity, and support. They connect various body parts and have several types of fiber and cells. There are collagen fibers, made of protein and slightly flexible. Most of these also have elastic fibers coiled within. And some have reticular fibers, thinner than collagen. Last, but not least, are the fibroblasts. These are the cells that produce and secrete the proteins that make up the collagen, elastic and reticular fibers.

Bone, cartilage, blood and adipose tissue are specialized connective tissues. Bone and cartilage have very few living cells. Blood cells are connective tissue because they derive from stem cells within the bone. Adipose tissue has mainly what is called adipocytes or fat cells that store fat.

Muscle Tissues Contract to Produce Movement
Muscle tissue is made of cells tightly packed, called muscle fibers. They are specialized to contract, resulting in movement of some kind. There are three kinds of muscle tissue: skeletal, cardiac, and smooth.

• Skeletal muscle connects tendons and cause body parts to move.
• The cardiac muscle is only in the heart and only has one nucleus. It is considered involuntary because it can move on its own, without any conscience thought.
• Like the cardiac muscle, smooth muscle only has one nucleus. They surround hollow organs and tubes. And like the cardiac, is involuntary.

Nervous Tissue Transmits Impulses
Nervous tissue are cells that specialize in generating and transmitting electrical impulses through our bodies. They are located in the brain, spinal cord and the nerves. The neuron is the functional part that generates and transmits these electrical impulses. Glial cells surround the neurons to protect them and supply them with nutrients.


Organs and Organ Systems Perform Complex Functions
Organs are composed of two or more tissue types. Organ systems are groups of organs that come together for a broad function, for example, respiration. There are 11 organ systems in the human body.

Tissue membranes are made of an epithelial layer and a layer of connective tissue. They line body cavities. The four types being serous, mucous, synovial and cutaneous membranes.

When we speak of body parts, we are divided into three planes: midsagittal, frontal, and transverse. The planes are divided further into left and right, front and back, and top and bottom.

The Skin as an Organ System
The integumentary system is made of skin, hair, nails, and glands. It protects from dehydration and injury, is a defense against bacteria and viruses, regulates body temperature, synthesizes vitamin D, and provides sensation. The skin has two layers, the epidermis  - the outer layer of epithelial tissue, and dermis - the inner layer of connective tissue. Also included in the dermis is hair, smooth muscle, sebaceous glands, sweat glands, blood vessels, and sensory nerve endings.

Multicellular Organisms Must Maintain Homeostasis
Homeostasis is the relative constancy of conditions within the internal environment. It is maintained by a negative feedback system. This meaning that it has a controlled variable, a sensor (receptor), a control center, and an effector (corrects any imbalance). It is called negative feedback because any change in the controlled variable sets off a series of events that opposes the initial change and returns it to “normal”.

One of the best examples of negative feedback at work is the bodies ability to maintain a core body temperature. The variable is your core temperature, the sensors are in your skin and internal organs, the control center is your hypothalamus and the effector used is either nerve impulses that constrict blood vessels to reduce heat loss or stimulate skeletal muscles to contract, which causes shivering, which generates heat.

Positive feedback systems are fairly uncommon in living organisms. Childbirth being one process that uses positive feedback. However, positive feedback does not maintain homeostasis.