WEB QUEST of cell organelles

1. A WebQuest about cell organelles and structures
   
   
   q Introduction
   Every Organism is composed of one or more cells, and these cells are the basic unit of organization in all living things. All the processes of metabolism and heredity occur within these same cells.
   
   In this web quest you will learn about the different structures that conform the eukaryotic cell structures and their functions within the cell.
   
   q The Task
   In this WebQuest you will fin a list of questions that you need to answer correctly. For each question you will find an specific Internet address that you will have to visit to find out the proper information.
   
   q Process
   Instructions: Answer the following questions by going to the specific Internet address that is given in each one:

1. How does the structure of the phospholipid bilayer permits the cell to be selective?
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/phosphb.htm

2. How is chromatin different than chromosomes?
http://www.biology-online.org/biology-forum/about2407.html&highlight=

3. Compare the function of the nucleus of the cell with the one of the nucleolus and ribosomes.
http://www.cellsalive.com/cells/nucleus.htm

4. What is the difference between the vacuoles of the plant cell to those present in the animal cell?
http://sun.menloschool.org/~cweaver/cells/c/vacuole/

5. Compare and contrast the Rough Endoplasmic Reticulum to the Smooth Endoplasmic Reticulum in structure and in function.
http://sun.menloschool.org/~cweaver/cells/e/smooth_er/

6. Describe the organelles in charged of the transformation of energy in the eukaryotic cell.
http://www.beyondbooks.com/lif71/4g.asp

7. What is the function of the cytoskeleton?
http://www.biology.arizona.edu/Cell_BIO/tutorials/cytoskeleton/main.html

8. What is the cell wall of the plant cell made of? (carbohydrates, protein, or lipids)?
http://www.biologie.uni-hamburg.de/b-online/e26/26.htm

9. Describe all functions of the following structures:
* Cilia
* Flagella
http://sun.menloschool.org/~cweaver/cells/e/cilia_flagella/


q Evaluation
You will be graded as follows: (rubric description):
Ø Followed instructions precisely…………………………….20 points
Ø Quality of writing…………………………………………….....20 points
Ø The question is answered correctly and in a concise
and clear matter.…………………………………………...........20 points
Ø Usage of Internet addresses and info……………………20 points
Ø Completeness………………………………………………........20 points
TOTAL of….........................................................100 points

q Conclusion
By now you should be able to understand the basic function of each of the cell’s organelles. Each one of this structures has a specific function, but also all of them work together to ensure that the cell can maintain suitable conditions for its survival, or in other words… complete its function and maintain homeostasis! I hope that you found this WebQuest activity useful to expand and reinforce your knowledge of how life works!

Types of soultions (Diffusion and Osmosis)

What is a Solution?

A solution is a combination of solute (a solid) that has been dissolved in a solvent (a liquid like water).

-There are three kinds of solutions:

a. isotonic solution - is a solution where the solute concentration of the solution that the cell is in is the same as the solute concentration of the cell's cytoplasm.b. hypotonic solution - is a solution where the solute concentration of the solution that the cell is in is lower than the solute concentration of a cell's cytoplasmc. hypertonic solution - is a solution where the solute concentration of the solution that the cell is in is higher than the solute concentration of a cell's cytoplasm3. What happens when cells are place in different kinds of solutions?

a. Hypertonic solutions
The cells shrink or shrivel due to water leaving the cell. If a cell is placed in a hypertonic solution (higher solute concentration outside the cell) water will leave the cell, the net movement of water is from the inside to the outside of the cell. If blood cells are placed in a salt solution, the cell will shrink or "crenate". When this occurs in a plant cell it is said to plasmolyze.

b. Hypotonic solutions
The cells will swell due to water entering the cell. If a cell is placed in a hypotonic solution (lower solute concentration outside the cell) water will enter the cell, the net movement of water is from the outside to the inside of the cell. If blood cells are placed in a distilled water solution, the will swell or burst. This is called hemolysis in blood cells and lysis in non blood cells. In plant cells it is called turgor pressure because the plant cell wall prevents the cell from bursting.


c. Isotonic solutions
When a cell is placed in a solution where the solute concentration is the same on both sides of the cell membrane, the cell will neither shrink nor swell. 0.9% sodium chloride (salt) is isotonic to blood cells.

http://www.abbysenior.com/biology/transport_across_membranes.htm

Transport Across Membranes

Cell Transport

How material moves in and out of the cell ?

PASSIVE TRANSPORT (does not require energy)
a. Diffusion - Diffusion is the movement of molecules, other than water, from an area of high concentration to an area of low concentration. No ATP energy is used. eg. Perfume filling a whole room. -Molecules move like this naturally, so no chemical or cellular energy is needed.

How does the size of molecules, temperature and concentration gradient affect diffusion?
- Size of the molecules, temperature, and the size of the concentration gradient affects the speed of diffusion. Large molecules diffuse slower that small ones, the greater the concentration difference the faster the rate of diffusion and increased temperature speeds up diffusion. The reason diffusion takes place faster is because of the increased number of collisions of the particles. When you heat up something the particles vibrate faster, collide more often and spread out faster. When the concentration is high, there is a greater number of particles in the solution. With a greater number of particles, there is a greater chance of collision and thus spreading out. Large molecules need more energy to begin moving and thus diffuse slower.-Lipid-soluble molecules can diffuse through the membrane easily. Oxygen and carbon dioxide pass through easily. Water passes through easily even though it is lipid insoluble. (see protein lined pores)

b. Osmosis - Flow of water from a high concentration to a low concentration across a selectively permeable membrane. Ex. Water moving from the large intestine into the blood.

c. Facilitated transport - is also the movement of molecules from a high concentration to a low concentration. Lipid insoluble substances such as glucose and amino acids are taken across by "carrier proteins". These carrier proteins are embedded in the plasma membrane and will pick up, carry and regulate the rate that specific molecules move into the cell. No chemical energy is required in this process .eg. amino acids, glucose and other breakdown products of food are absorbed by the small intestine.d. Active Transport - It is the movement of molecules across a living membrane from an area of low concentration to an area of high concentration with the aid of a carrier protein and using energy or ATP.
The diagram below represents the sodium/potassium pump a kind of active transport.

ACTIVE TRANSPORT (requires energy)
§ Two kinds of active transport:
1. Endocytosis - Surrounding a substance with the cell membrane and the subsequent formation of a vesicle to bring these substances into the cell. Energy is used.

There are two kinds of Endocytosis:

a. Phagocytosis - involves the ingestion of large food particles or cellular debris

b. Pinocytosis - involves the ingestion of fluids or dissolved particles.

2. Exocytosis - is the opposite of endocytosis. Materials are surrounded by a vesicle in the cytoplasm of the cell and released from the cell as the vesicle merges with the plasma membrane. Materials such as waste, useless cellular debris, or useful hormones for other cells are released in this manner. Energy is used.

http://www.abbysenior.com/biology/transport_across_membranes.htm

Structure and Function of the Plasma Membrane

The Structure and Function of the Cell Membrane
The cell membrane is a fluid mosaic of lipids, proteins, and carbohydrates. In this tutorial we will describe these three structures and how they function in the cell membrane. This topic provides another example of the relationship between structure and function.
The Structure of Lipids Lipids are the one class of large biological molecules that does not include polymers. They are grouped together because they share one important chemical property: they have little or no affinity for water. The hydrophobic behavior of lipids is based on their molecular structure. Although they may have some polar bonds associated with oxygen, lipids consist mostly of hydrocarbons. Smaller than true (polymeric) macromolecules, lipids are a highly varied group in both form and function, and include such things as waxes and certain pigments. In this tutorial we will focus on three classes of lipids: the fats, steroids, and phospholipids.

http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/

CELL ORGANELLES

Eucaryotic Cell Organelles

• Nucleus: The nucleus is the most obvious organelle in any eukaryotic cell. It is enclosed in a double membrane and communicates with the surrounding cytosol via numerous nuclear pores. Within the nucleus is the DNA responsible for providing the cell with its unique characteristics. The DNA is similar in every cell of the body, but depending on the specific cell type, some genes may be turned on or off - that's why a liver cell is different from a muscle cell, and a muscle cell is different from a fat cell. When a cell is dividing, the nuclear chromatin (DNA and surrounding protein) condenses into chromosomes that are easily seen by microscopy.

• Nucleolus: The prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus and take positions on the rough endoplasmic reticulum where they are critical in protein synthesis.



• Cytosol : Cytosol is the "soup" within which all the other cell organelles reside and where most of the cellular metabolism occurs. Though mostly water, the cytosol is full of proteins that control cell metabolism including signal transduction pathways, glycolysis, intracellular receptors, and transcription factors.



• Cytoplasm: This is a collective term for the cytosol plus the organelles suspended within the cytosol.



• Centrosome: The centrosome, or MICROTUBULE ORGANIZING CENTER (MTOC), is an area in the cell where microtubles are produced. Plant and animal cell centrosomes play similar roles in cell division, and both include collections of microtubules, but the plant cell centrosome is simpler and does not have centrioles.
  During animal cell division, the centrioles replicate (make new copies) and the centrosome divides. The result is two centrosomes, each with its own pair of centrioles. The two centrosomes move to opposite ends of the nucleus, and from each centrosome, microtubules grow into a "spindle" which is responsible for separating replicated chromosomes into the two daughter cells.
  



• Centriole (animal cells only): Each centriole is a ring of nine groups of fused microtubules. There are three microtubules in each group. Microtubules (and centrioles) are part of the cytoskeleton. In the complete animal cell centrosome, the two centrioles are arranged such that one is perpendicular to the other.

• Golgi apparatus: The Golgi apparatus is a membrane-bound structure with a single membrane. It is actually a stack of membrane-bound vesicles that are important in packaging macromolecules for transport elsewhere in the cell. The stack of larger vesicles is surrounded by numerous smaller vesicles containing those packaged macromolecules. The enzymatic or hormonal contents of lysosomes, peroxisomes and secretory vesicles are packaged in membrane-bound vesicles at the periphery of the Golgi apparatus.

• Lysosome: Lysosomes contain hydrolytic enzymes necessary for intracellular digestion. They are common in animal cells, but rare in plant cells. Hydrolytic enzymes of plant cells are more often found in the vacuole.
  



• Peroxisome: Peroxisomes are membrane-bound packets of oxidative enzymes. In plant cells, peroxisomes play a variety of roles including converting fatty acids to sugar and assisting chloroplasts in photorespiration. In animal cells, peroxisomes protect the cell from its own production of toxic hydrogen peroxide. As an example, white blood cells produce hydrogen peroxide to kill bacteria. The oxidative enzymes in peroxisomes break down the hydrogen peroxide into water and oxygen.

• Secretory Vesicle: Cell secretions - e.g. hormones, neurotransmitters - are packaged in secretory vesicles at the Golgi apparatus. The secretory vesicles are then transported to the cell surface for release.

• Cell Membrane: Every cell is enclosed in a membrane, a double layer of phospholipids (lipid bilayer). The exposed heads of the bilayer are "hydrophilic" (water loving), meaning that they are compatible with water both within the cytosol and outside of the cell. However, the hidden tails of the phosopholipids are "hydrophobic" (water fearing), so the cell membrane acts as a protective barrier to the uncontrolled flow of water. The membrane is made more complex by the presence of numerous proteins that are crucial to cell activity. These proteins include receptors for odors, tastes and hormones, as well as pores responsible for the controlled entry and exit of ions like sodium (Na+) potassium (K+), calcium (Ca++) and chloride (Cl-).

• Mitochondria: Mitochondria provide the energy a cell needs to move, divide, produce secretory products, contract - in short, they are the power centers of the cell. They are about the size of bacteria but may have different shapes depending on the cell type. Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. The outer membrane is fairly smooth. But the inner membrane is highly convoluted, forming folds (cristae) as seen in the cross-section, above. The cristae greatly increase the inner membrane's surface area. It is on these cristae that food (sugar) is combined with oxygen to produce ATP - the primary energy source for the cell.

• Vacuole: A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In animal cells, vacuoles are generally small. Vacuoles tend to be large in plant cells and play several roles: storing nutrients and waste products, helping increase cell size during growth, and even acting much like lysosomes of animal cells. The plant cell vacuole also regulates turgor pressure in the cell. Water collects in cell vacuoles, pressing outward against the cell wall and producing rigidity in the plant. Without sufficient water, turgor pressure drops and the plant wilts.

• Cell Wall (plant cells only): Plant cells have a rigid, protective cell wall made up of polysaccharides. In higher plant cells, that polysaccharide is usually cellulose. The cell wall provides and maintains the shape of these cells and serves as a protective barrier. Fluid collects in the plant cell vacuole and pushes out against the cell wall. This turgor pressure is responsible for the crispness of fresh vegetables.

• Chloroplast (plant cells only): Chloroplasts are specialized organelles found in all higher plant cells. These organelles contain the plant cell's chlorophyll responsible for the plant's green color. Chloroplasts have a double outer membrane. Within the stroma are other membrane structures - the thylakoids. Thylakoids appear in stacks called "grana" (singular = granum).

• Smooth Endoplasmic Reticulum: Throughout the eukaryotic cell, especially those responsible for the production of hormones and other secretory products, is a vast network of membrane-bound vesicles and tubules called the endoplasmic reticulum, or ER for short. The ER is a continuation of the outer nuclear membrane and its varied functions suggest the complexity of the eukaryotic cell.The smooth endoplasmic reticulum is so named because it appears smooth by electron microscopy. Smooth ER plays different functions depending on the specific cell type including lipid and steroid hormone synthesis, breakdown of lipid-soluble toxins in liver cells, and control of calcium release in muscle cell contraction.

• Rough Endoplasmic Reticulum: Rough endoplasmic reticulum appears "pebbled" by electron microscopy due to the presence of numerous ribosomes on its surface. Proteins synthesized on these ribosomes collect in the endoplasmic reticulum for transport throughout the cell.

• Ribosomes: Ribosomes are packets of RNA and protein that play a crucial role in both prokaryotic and eukaryotic cells. They are the site of protein synthesis. Each ribosome comprises two parts, a large subunit and a small subunit. Messenger RNA from the cell nucleus is moved systematically along the ribosome where transfer RNA adds individual amino acid molecules to the lengthening protein chain.

• Cytoskeleton: As its name implies, the cytoskeleton helps to maintain cell shape. But the primary importance of the cytoskeleton is in cell motility. The internal movement of cell organelles, as well as cell locomotion and muscle fiber contraction could not take place without the cytoskeleton. The cytoskeleton is an organized network of three primary protein filaments:
  - microtubules- actin filaments (microfilaments)- intermediate fibers