Cells+to+Systems

= __Content Summary:__ =

//** Unit Overview: **//
Cells are the smallest living subdivision of the human body and are of great importance. Cells make up tissues, which in turn make up organs, which make up an organ system, which makes up an organism. Everything that occurs in the human body occurs in cells and if anything goes wrong on the cellular level, tissues, organs, organ systems, and the organism as a whole is greatly affected.



//__1. Cell Sturcure and Function:__//
====Cells are the basic unit of life and are composed of many different components - each of which has a specific purpose. Cells throughout the body are very different in what they are composed of and what their bodily function is. The cell is made up of the plasma membrane, the cytoplasm, and the nucleus.====

The **plasma membrane** is the protective, selectively permeable layer that separates the inside and outside of the cell. All cell membranes are composed of phospholipids, cholesterol, protiens, and carbohydrates. The //phospholipids// and //cholesterol// molecules promote the flexibility and sturdiness of the membrane. The //proteins// provide structure and act as carriers to transport certain moleucles in and out of the cell. And the //carbohydrates// act as ID tags to differentiate between types of cells. As well as the basic cell membrane components, some cells have //projections// that increase surface area (microvilli), move molecules (cilia), or move the cell itself (flagella). All of these components of the cell membrane are extremely important and vital to cell life.

The **cytoplasm** contains the cytosol (the semi-liquid gel-like part of the cell) and the organelles. The cytoplasm contains certain enzymes that regulate metabolism, stores fat, chemicals, and secretory vesicles, contains ribosomes that make proteins, and also contains many other organelles that are vital to cell life.

The //cytoskeleton// is a network of protein fibers throughout the cytosol that provides structural support and shape, helps move materials inside the cell, and assists in the movement of cellular projections (or the cell as a whole). //Lysosomes// are sac-like organelles that contain enzymes which break down large molecules. Another organelle, the //mitochondria//, is the "power source" of the cells and is very important. This organelle is very unique as it is surrounded by a double membrane and contains its own DNA. The fact that the mitochondria contains its own DNA enables it to make unique proteins that catalyze reactions to break down the food we eat, and because it can catalyze these reactions, its able to synthesizes ATP which is used as energy in the cell. Another important organelle is the //ribosome//. This organelle is important because it can make specific proteins based on the sequence of bases on an mRNA molecule. Ribosomes are found free floating or attached to a different type of organelle, called the //rough endoplasmic reticulum (rough ER).// The rough ER is responsible for making proteins for cell membranes, the interior of membrane-bound cells, or to be exported out of the cell. There is also an organelle that is called the //smooth endoplasmic reticulum (smooth ER)// that does not contain ribosomes. The smooth ER make lipids, stores calcium, and metabolizes toxins that are introduced into the body (alcohol, drugs, etc.). The //golgi complex// is a stack of cisternae (flattened sacs) that perfects products made in the ER and then sort and direct finished products to where they need to be. //Visicles// are small membrane-enclosed chambers that transport materials in the cell. The smooth and rough ERs, along with the golgi complex have the ability to pinch a part of themselves off and become visicles that can deliver products elsewhere in the cell - or rid the cell of waste products.

The last - but most imporant - part of the cell, is the **nucleus**. The nucleus is the cell's "control center" because it contains the "recipe" to make you - your DNA. The nucleus is responsible for making every part of your body and is obviously of great importance.



//__2. Cell Division:__//
 In order to replace dead cells, cell division is required to make new cells. Cell division is called **mitosis** and consists of pre-mitosis (interphase), prophase, metaphase, anaphase, and telophase.

In //interphase//, the nucleus is still visible in the cell under the electron microscope. The chromosomes are seen as chromatin which is unorganized DNA. In //prophase//, though, the chromosomes are paired up and are seen as chromatids joined by a centromere in the middle which holds them together. The two centrosomes begin to move to opposite poles and spindle fibers are extended from them. The nuclear membrane then starts to disappear in preparation for the next phase. //Metaphase// is the phase of cell division in which the chromosomes "meet in the middle" along the equator of the cell. The nuclear membrane has completely disappeared and the spindle fibers attach to each chromatid. In the next phase, //anaphase//, the centromeres holding the chromatids together splits and the spindle fibers pull each chromatid to its respectful pole. In the final stage, called //telophase//, a new nuclear membrane forms, the nucleolus reappears, and cytokinesis occurs. Cytokinesis is when the 'parent' cell pinches in half to make two different - but identicle - cells.

//__3. Tissues to Systems:__//
In the human body, there are four different types of tissues: epithelial tissue, connective tissue, muscle tissue, and nerve tissue. **Epithelial tissue** is tissue that lines the organs and blood vessels. Epithelial tissue forms a barrier for the specific body surface that they need to protect. The cells in this type of tissue are very close together and some of these cells may become differentiated and become epithelial glands which secrete material into (//endocrine//) or out of (//exocrine//) the epithelial layer. There are many different types of epithelial cells which are classified by the number of layers (//simple// = one cell thick; or //stratified// = many) and by the shape of the cells (//squamous// = flattened; //cuboidal// = cube-like; //columnar// = long and rectangular).



**Connective tissue** is tissue throughout the body that connects, provides structure and support, and aides in transporting molecules. Unlike epithelial tissue, the cells in connective tissue are very spread out with an extracellular matrix between the cells. These cells produce a matrix of protein fibers inside a gel-like ground substance which makes the tissue very elastic and strong. Loose connective tissue (fascia) has many cells in it, but not very many fibers while dense connective tissue (tendons, ligaments, etc.) only has a few cells but has many, dense fibers. There are also different types of specialized connective tissue that can be found within the body. Adipose (fat) tissue, cartilage, bone, and blood are some of these specialized tissues. //Adipose// tissue is made up of large cells that contain fat. //Cartilage// is a flexible, but sturdy kind of tissue found in the nose, ears, etc. //Bone// is hard connective tissue made of collagen and calcium phosphate crystals. And //blood// is a liquid matrix with cell fragments suspended in it.

**Muscle tissue** are cells designed for contraction, movement, and heat production. There are three types of muscle tissue: skeletal muscle, smooth muscle, and cardia muscle. //Skeletal muscle// is striated, voluntary tissues with the fibers running parellel to each other which increases the strenght of the tissue. //Smooth muscle// is involuntary muscle with no striations and is seen primarily in the digestive system and the blood vessels. And //cardiac muscle// is involuntary muscle with striations found only in the heart.

**Nerve tissue** makes up the body's communication network. Neurons are the functional cells in nerve tissues that are designed to send and receive information and neuroglia are the cells that make sure neurons get nutrients, lay down more blood vessels near the neurons, and clean up dead cells. There are three parts to a neuron: the cell body, the dendrites, and the axon. The //cell body// contains the nucleus and organelles, the //dendrites// receive information from other neurons, and the //axon// delivers messages to other tissues.

When these different tissues come together as one, they form an organ which then forms an organ system. Most organs have all four types of tissue combined to make them, but some are only composed of two or three different types of tissues. Regardless of how many different types of tissue make up each organ, though, it is obvious that tissues are very important throughout the human body.

= __Application:__ = = = The understanding of the different types of tissues is extremely important - especially in today's world when there is such extensive research taking place. One example of such research is what scientists are doing with stem cells. **Stem cells** are cells that have the potential to become many different types of cells; they have not been differentiated yet. These cells have the potential to be very useful in curing diseases such as Alzheimer's disease, diabetes, heart disease, leukemia, etc. They could also be used for skin grafting in burn patients or injected into the a specific organ in hopes that it would help regenerate healthy tissue so that individual wouldn't need a transplant.

Stem cells are either embryonic or adult stem cells. **Embryonic stem cells** are taken from a human embryo in the blastocyte phase. The blastocyte phase occurs about five days after the sperm has fertilized the egg, but before the embryo has implanted in the uterus and become a fetus. Usually the researchers use extra embryos left over from in vitro fertilization procedures (eggs are fertilized in the lab, several become embryos, but only one is implanted into the woman's uterus). **Adult stem cells** are cells that are taken out of tissues within an adult's body. It is possible to find these cells in the brain, bone marrow, blood, muscles, skin, and the liver. Adult stem cells remain un-differentiated and are in a dormant state until there is an injury to tissue in the body. When the body is injured, though, these cells can go regenerate and keep the body tissues functioning properly.

Stem cells are categorized by their potential (**potency**) to become several other tissue types. //Totipotent// cells can differentiate into all different cell types; //pluripotent// cells can become most - but not quite all - different types of cells; //multipotent// cells can become several different types of cells - but they are all inter-related (family of cells); //oligipotent// cells can differentiate into only a few cells; and //unipotent// cells can only become one certain type of cell. The only type of totipotent cell is the fertilized egg and the first few cell divisions from it. Embryonic stem cells are only pluripotent because they can't become the placenta or other membranes normally around a fetus. Adult stem cells are either unipotent, oligipotent, or multipotent. No adult stem cells have been found to be pluripotent yet.

<span style="font-family: Georgia,serif; font-size: 110%;">Stem cells are capable of multiplying indefinitely which makes them extremely important to human life. If our bodies didn't have stem cells, we wouldn't be able to heal wounds to our skin, fuse broken bones back together, recovery from surgery, etc. The possibilities that stem cell research could eventually offer are exponential!

media type="youtube" key="mUcE1Y_bOQE" height="315" width="560" Stem Cell Video (From:http://www.youtube.com/watch?v=mUcE1Y_bOQE)

= __Essential Questions:__ =

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif;">**//1. Cells are considered the basic structure and function of the human body. What is meant by that statement?//**
<span style="font-family: Georgia,serif; font-size: 110%;">Cells are considered that basic structure and function of the body for many reasons. Cells are the basic structure of the human body because everything in the body is made up of cells. Without cells, we wouldn't have tissues, organs, or organ systems, and we would no longer be able to live.

<span style="font-family: Georgia,serif; font-size: 110%;">Cell are the basic function of the human body as well though. In the cells is where everything begins in our bodies. Cells contain our DNA which makes proteins, which differentiates us from everyone (and everything) else in the world, catalyze basic chemical reactions, allow cell transport, etc. Cells break down our food and provide us with energy every day. Without cells - or without properly functioning cells - we would not be able to exist.

===<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif;">**//2. Create a graphic organizer (chart) to summarize the stages of cellular respiration in your cells. Include the stage, molecules produced (output), and the purpose of each stage.//** ===



<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif;">**//3. What is the role of ATP in your cells? Be specific!//**
<span style="font-family: Georgia,serif; font-size: 110%;">ATP (adenosine triphosphate) is the energy source for every reaction that takes place in the body and is adenosine diphosphate (ADP) attached to another phosphate molecule(Pi). Cells take in usable (free) energy from the breakdown of food (in the form of glucose), send it to the mitochondria, and then the mitochondria (using 2 energy molecules [ATP]) makes more ATP for the cell to use. The mitochondria is the 'power generator' of the cell and is of vital importance.

<span style="font-family: Georgia,serif; font-size: 110%;">In cellular respiration, only a few ATP molecules are needed to make another 30-32 ATP molecules (if aerobic respiration occurs).