SPEAK OUR LANGUAGE

• CELL – Core Experience Learning Lab
• SDR – Scientist Data Record

ASK WHY

Great scientists question the world around them. We encourage our LabLearner students to do the same. In anticipation of this, we explain the importance of learning the concepts in the Ask Why section within the CELL. Our hope is that these explanations help students understand why science matters.

BRANCH OUT

Each Investigation introduces students to a different branch of science or STEM (Science, Technology, Engineering, Mathematics) career that utilizes the scientific concepts of the CELL. These real-world connections will help students see the relevance of what they are learning. STEM connections are also integrated into each Performance Assessment.

GET FOCUSED

The Focus Questions in each Investigation are designed to help teachers and students focus on the important concepts. By the end of the CELL, students should be able to answer the following questions:

Investigation 1:

• How does organization of cells within an organ relate to an organ’s function? The cells are organized into tissues. Each tissue provides a function that contributes to the function of the organ.

• How do cells in an organism replenish themselves after normal wear and tear to the tissue? Cells replenish themselves by a process of cell division.

Investigation 2:

• How do tissues replenish the cells contained within them? Tissues replenish cells through cell division. Cell division has four phases, G1, S, G2, and M phase.

• What controls the process of cell division? The cell cycle is regulated by different proteins.

Investigation 3:

• What is the relationship between the control of the cell cycle and cancer? Normally the cell cycle is regulated so that cell only progress through the cycle and divide when necessary. In cancer, the regulation of the cell cycle is lost and the cell divides constantly. The constant cell proliferation leads to a tumor and cancer.

Note: These are succinct responses to the Focus Questions and are placed here for easy reference. Fully developed responses to the Focus Questions can be found on each PostLab page.

Note: Some questions may be revisited as the CELL progresses. As students acquire additional knowledge, their responses should reflect this.

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced within the Backgrounds of the CELL. These terms should be used, as appropriate, by teachers and students during everyday classroom discourse.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.

Investigation 1:

• Tissue: a group of organized cells that share a common structure and function
• Organ: a group of tissues that work together to perform a specific set of functions for the organism

Investigation 2:

• Cell division: the production of two identical cells from a single parent cell
• Cell cycle: an ordered set of events that results in cell division
• Mitosis: M phase; the final phase of the cell cycle in which the sister chromatids produced in the S phase are separated and cell division (cytokinesis) occurs
• Chromosome: a structures in the nucleus of a cell containing two chromatids
• Chromatid: one double stranded DNA molecule complexed with protein

Investigation 3:

• Cancer: a group of diseases that involve the uncontrolled cell division of body cells
• Metastases: When a single cancerous cell breaks away from a tumor and it travels in the blood to other places throughout the body. At the new site, this single cancer cell can proliferate and form another tumor.
• Adenocarcinoma: a form of lung cancer

BE PREPARED

An overview of the materials for each lab is placed here for easy reference. Specific teacher preparation for the labs is placed at the beginning of each Lab page.

EXTEND YOUR THINKING

The following information is included so that teachers have additional background knowledge pertaining to the concepts introduced in the CELL. Teachers may choose to use this information to enrich students during instruction by integrating it into individual Concept presentations.

Multi-cellular organisms are made up of millions of tiny cells. In any one organism, there are many different types of cells. Cells that share a common structure and function can be found grouped and organized into tissues. There are four basic types of animal tissue: epithelial, muscle, nerve, and connective tissue. The cells of epithelial tissues pack tightly and form the lining of many parts of the body, for example in the intestine. Muscle tissue contains special cells that can contract, because they have long protein fibers that can slide past each other. Nerve tissue contains long cells that can generate electrical signals in the body. Connective tissue adds support and structure to the body, for example such as bones and tendons. There are other, less common tissue types including adipose or fat tissue. This type of tissue is made of large open cells that store lipids. These fats or lipids are used to produce energy and to keep us warm. Another less common tissue is glandular tissue. This type of tissue produces small signaling molecules (like hormones) that it releases into the surrounding tissues. These chemical signals are how cells communicate. Glandular tissue cells come in all sizes and shapes, so they can be difficult to identify.

Two or more tissues work together to form organs. An organ is a group of tissues that work together to perform a specific set of functions for the organism. There are many different organs throughout the human body. The lung, heart, liver, breast, and skin are just a few of the organs that maintain our bodies. In this Core Experience Learning Lab students will learn about how the organization of cells within a tissue can determine the function of that tissue. They will have the opportunity to examine three tissue sections, skin, lung, and breast.

The skin is an organ that contains several types of tissues including connective, epithelial, nerve, and muscle tissue. It is the largest organ in the human body! The function of this organ is to protect the body from external harm like the sun, heat, cold, and germs. The skin is composed of the epidermis, dermis, and subcutaneous layers. The epidermis is the outermost layer and it contains several cell types including epidermal and connective tissue cells. It also contains the pigment producing cells called melanocytes. The pigment produced by these cells is called melanin. Melanin production increases when you are exposed to the UV light from the sun (this is why you get sun tan!) The dermis contains primarily connective tissue and muscle tissue. The muscle cells contract to make your hair stand up when you are frightened or cold! Finally, the subcutaneous layer contains adipose cells or fat cells. These cells are important because they are like a layer of insulation to keep us warm. This layer of the skin also contains the sweat glands and hair papilla. The hair papilla are the “root” or place where your hair grows from. Each layer of skin, epidermis, dermis, and subcutaneous, helps contribute to the overall function of the skin, to protect us from harmful UV light, heat and cold.

The lung mostly contains epithelial and connective tissues. The function of the lung is to allow exchange of oxygen from the air we breathe to blood so that it can be delivered to other tissues in the body where it is needed for normal cell function. It also allows carbon dioxide waste in the blood that came from the tissues throughout the body to leave the body through exhalation.

Air enters the body when we breathe through the nose and mouth. The air travels down the trachea (wind pipe) and into the bronchioles. There are bronchioles for the left and right lung lobe. The bronchioles lead to the terminal bronchioles and than the respiratory bronchioles that terminate in the alveolar ducts. The alveolar ducts are passageways that lead directly to the pulmonary alveoli which are small air sacs where the oxygen in the air is absorbed. These alveoli are composed of balloon like structures with the walls of the balloon being made of a single layer of epithelial cells.

These epithelial cells are surrounded by tiny blood vessels called capillaries. The single cell layer and tiny blood vessels allow for a very short distance for the oxygen in the air to travel into the blood and for the carbon dioxide in the blood to travel out into the air.

The breast is made of a combination of fatty, glandular, and connective tissue. These tissues function to supply milk for growing infants. Glandular tissue produces and releases substances for use in the body. In the breast glandular tissue contains lobes that store the milk and ducts that transport the milk from the lobes to the nipple. During the majority of a woman’s life, the breast is inactive and does not produce milk. Milk production only occurs when the tissues become active 3-5 days after a woman gives birth to a child. When the tissues become active, the lobules fill with milk and grow larger, the ducts expand and fat or adipose cells become smaller. This transition from inactive to active tissue requires large increases in the number of cells lining the lobules and ducts within the breast tissue. When you look at active breast tissue, you will see large open areas (the lobes and ducts) where the milk is stored. Inactive tissue does not have as many large open areas because it is not storing milk, the lobes and ducts become smaller.

All of these tissues require increases in cell number through out the life of the human body. The skin has constant cell loss due to exposure to UV light from the sun and various other external insults. The lung alveoli cells are repeatedly exposed to damaging chemicals inhaled with the air in our environment including pollution and cigarette smoke. This damage causes cell death of the cells lining the alveoli and therefore requires replenishment of these cells. The breast must transform from the inactive tissue to the active tissue within days after a woman gives birth. This transition requires production of many new cells lining the breast ducts and lobes.

The increased numbers of cells are supplied through increased cell replication (or cell division). Cell division must be closely regulated so that cells only divide when needed or the organization of these tissues would be destroyed making it impossible for them to function properly.

Cell division is also important in early childhood. During this time of growth the human body grows at a very fast rate. This is due to a constant increase in the total number of cells making up the body. Cell division is the process by which two identical cells are produced from a single parent cell. This process requires that the original (parent) cell copies all of its contents, including DNA and organelles, and splits these materials evenly into two new (daughter) cells. In this way the cell has made an exact copy of itself and the number of total cells is increased.

Once an adult human is fully grown, most cells either stop or slow down this process of dividing. However, in certain tissues, like the skin, lung, or active breast tissue, cell division is still needed. Whether cell division is occurring rapidly as in a growing child, or at a slower rate as in certain adult tissues, this process must be carefully controlled. Too much or too little cell division interferes with normal tissue function. The process that controls cell division is called the cell cycle.

The cell cycle is an ordered set of events that results in cell division – the production of two identical cells from a single parent cell. The cell cycle can be broken down into 4 distinct phases:

1. G1 or GAP phase

2. S or DNA synthesis phase

3. G2 or GAP2 phase

4. M or Mitosis phase

During the G1 phase, the cell produces proteins and grows in size. During this phase the cell is functioning normal, constantly making proteins. This constant increase in proteins is what causes the cell to get larger. The G1 phase ends when the cell has reached a certain size. Then, the S phase, or DNA synthesis phase, begins.

During the S phase the cell will make an exact copy of the DNA contained in the cell nucleus through DNA replication. At the end of the S phase, each chromosome inside the nucleus of the cell consists of 2 identical sister chromatids. Each chromatid is made up of a double stranded DNA molecule.

Next, the G2 or GAP 2 phase occurs. During this phase the cell has very little activity. The cell is no longer changing in size and is doing minimal metabolic activity.

Finally, the M phase, or Mitosis phase, occurs. During this phase, the sister chromatids produced in the S phase are separated and cell division (cytokinesis) occurs.

The diagram below shows the phases of the cell cycle.

The M phase or Mitosis phase of the cell cycle is made up of four distinct stages. These stages are:

When a cell is not in one of these stages it is said to be in interphase.

Mitosis begins with prophase. In prophase the chromosomes, which each contain sister chromatids produced in the S phase of the cell cycle, condense in the nucleus of the cell. At this stage the nuclear membrane dissolves.

The cell then enters metaphase. During metaphase, the duplicated chromosomes line up on the spindle fibers in the center of the cell.

The cell then enters anaphase, in which the sister chromatids separate and move down the spindle fibers to the opposite ends of the cell.

Finally, during telophase, the chromatids have moved to the ends of the spindle fibers. The spindle fibers disappear and new nuclear membranes form around each set of chromosomes. At this point the cytoplasm splits in half and cell division (cytokinesis) occurs.

The length of time for a cell to complete one full cell cycle (from one phase of mitosis to the next) varies depending on cell type. For example, a cell in an embryo may go through one round of the cell cycle in 1 hour while a cell in an adult breast tissue may take 1 year. The length of time of the full cycle varies primarily in the G1 (GAP1) phase. Cells can stay in the G1 phase for up to 1 year. How does a cell “know” when to move between the phases of the cell cycle?

Control of the cell cycle occurs through specific proteins that are translated from specific genes in the cells DNA. When the cell makes these proteins they allow the cell to transition into the next phase of the cell cycle. These proteins induce or turn on the cell cycle. There are also genes that code for proteins that block the cell from moving into the next phase of the cell cycle. These proteins inhibit or stop the cell cycle. It is the balance of these cell cycle inducing and inhibiting proteins that controls the cell cycle.

Different cell types have different amounts of these proteins and therefore different lengths of time that they will stay in each phase of the cell cycle. The majority of cells spend most of the time in the G1 phase before quickly moving through the other phases. In some rapidly dividing cells, the G2 phase is only lasts a few minutes. For example, an embryonic cell is rapidly dividing to provide all the cells for the various developing organs. These cells have a very short G2 phase and rapidly move throughout the other phases of the cell cycle. In contrast, an inactive breast cell it may take 1 year for the cell to move from the G1 into the S phase and another month to go from G2 to the M phase.

Regulation of the cell cycle is very important. If cells divided at random, the organization of the tissue would be lost and the function of the organ would be affected. The proteins that control the cell cycle are produced when stimulated by external factors. For example, some cells, like the lung alveolar cells, must only grow in a single layer. When these cells come into contact with one another, interactions between the cell membranes stop the production of the proteins that move the cell into the cell division phase. This is called contact inhibition. In this way, the alveolar cells will only divide when they are not in contact with other cells, when there is a hole in the alveolar wall.

If the gene that codes for the controlling protein is damaged or mutated, then a properly functioning protein cannot be produced. If there is no production of the controlling proteins, the cells will go through the cell cycle and divide unregulated. Each new (daughter) cell will inherit the mutated gene for this controlling protein because the cell receives an exact copy of the DNA in the original (parent) cell. This means that every daughter cell produced from the originally damaged cell will also divide continuously.

Cancer is defined as a group of diseases that involve the uncontrolled cell division of body cells. Cancer begins when one normal body cell breaks free from normal controls of the cell cycle and begins to follow its own rate of cell division. This happens after damage to the cell’s DNA has occurred, which affects the production of a cell cycle controlling protein. All cells produced by this cell, and all cells from those daughter cells, will also follow a uncontrolled rate of cell division.

If this process continues a tumor, a mass of cells, will develop. A tumor can invade normal tissue and therefore alter its overall organization and structure. This disorganization leads to an inability of the tissue to function, which in turn means that the organ cannot function properly.

If a single cancerous cell breaks away from the tumor it can travel in the blood to other places throughout the body. At a new site, this single cancer cell will proliferate and form another tumor. This is called metastases and is how cancer spreads.

Lung cancer, called adenocarcinoma, is one of the leading causes of death in adults. One of the primary causes of lung cancer is cigarette smoke. The chemicals in cigarette smoke are inhaled and absorbed by cells in the lung. Often when looking under the microscope at a lung tissue section from a smoker, deposits of tar (toxins) can be seen in the cells as small black specks. These toxins damage DNA. If the damage occurs on a gene that normally codes for a cell cycle controlling protein, cancer can develop.

However, since the damage to the DNA is random, some people can smoke for many years and not develop cancer, while others may only smoke a few times and even quit and still get cancer. Even second-hand cigarette smoke (smoke inhaled from other people smoking) can cause damage to cells DNA. Lung cancer is not only caused by smoking, but this is thought to be one of the leading, preventable causes of lung cancer.

Breast cancer develops when a normal duct or lobule cell transforms into a cancerous cell that divides in an uncontrolled manner. This transformation occurs after a mutation occurs in the gene that controls the production of a cell cycle controlling protein. Unlike lung cells, breast cells are not exposed directly to external factors. This means that this transformation occurs when there is a random mutation in one of these genes. This most likely occurs during normal DNA replication. Some mutations in DNA can be inherited. These inherited mutations often do not directly cause cancer to develop, but put a person at a higher risk to develop mutations that do cause cancer. In the general population, 1 in 500 to 1,000 people have a mutation in the BRCA1 gene, which increases their risk of developing breast cancer. Individuals inherit an increased risk of cancer, not the disease itself. Not all people who inherit mutations in these genes will develop cancer. Today, if breast cancer is diagnosed early, many patients can be successfully treated with chemotherapy. Chemotherapy is when a cancer patient is given a medication that will stop cancer cells from dividing.