Chapter+Five

Chapter Five Module Two

Definition Worksheet #5: Chapter 5 Define the following key terms. 1. Hydrophilic - water loving 2. Hydrophobic - affraid of water 3. Selective permeability - the membrane allows some substances to pass through but no others 4. Concentration gradient - a difference in concentration between two adjacent regions 5. Electrical gradient - a difference in electrical charge can affect the rate of diffusion. difference in electrical charge between two regions. 6. Pressure gradient - two regions with different pressures 7. Diffusion - movement of molecules down a concentration gradient 8. Facilitated diffusion - (passive transport) requires no energy 9. Passive transport - (facilitated diffusion) requires no energy 10. Active transport - requires energy to go against gradient 11. Osmosis - diffusion of water 12. Hypotonic solution - low concentration part of a solution 13. Hyptertonic solution - high concentration part of a solution 14. Isotonic solutions - equal concentration through out soultion 15. Hydrostatic pressure - pressure that a volume of fluid exerts against the cell wall 16. Osmotic pressure - the amount of hydrostatic pressure that can stop water from diffusing 17. Exocytosis - exits cell 18. Endocytosis - enters cell 19. Phagocytosis - phagocytic cells such as amoebas engulf microorganisms, cellular debris, or other particles. 20. Pinocytosis - the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane

1. Cell Membrane Structure: A. There are many different molecules including, phospholipids, glycolipids, cholesterol, proteins and glycoproteins in the cell membrane. This is why the membrane is often described as having a “mosaic” appearance. B. The most abundant part of the cell membrane isphospholipid __molecules that are arranged in two layers.__ __1. The central portion is composed of fatty acid tails and cholesterol and is__ __therefore “water fearing” (__ hydrophopic or non-polar) 2. The outer and inner surfaces have the “head” of the phospholipid molecules that contain a glycerol backbone (sugar), a phosphate group and hydroxyl groups that are all “water loving” ( hydrophillic or polar) C. The unsaturated phospholipid tails of the membrane have a slight bend that helps to keep the molecules from packing too tightly together, and helps keep it more “fluid-like”. D. The lipid molecule cholesterol is more rigid and helps to stabilize the “fluid-like” phospholipid bilayer at normal body temperature providing some stability and rigidity to the membrane. E. The many different protein molecules that are part of the cell membrane have just as many different functions (described below). F. The membrane is described as being SELECTIVELY PERMEABLE. What does this mean?
 * __ CHAPTER 5 __**** : Organization of the Cell Membrane **

1. **non-polar or lipid soluble molecules** cross directly through the phospholipid part of the membrane easily 2. **polar or water soluble molecules** can only cross through specific protein channels found in the phospholipid membrane G. The cell membrane is originally produced at the endoplasmic reticulum, portions “bud-off” to become transport vesicles that move to the Golgi body, where the protein molecules are further modified. Secretory vesicles then move to the cell membrane and fuse with it in a process called exocytosis. 2. The membrane proteins serve several different functions. Some of these were introduced in chapter four. A. ANCHORING or Adhering __Proteins: help cells of the same type stick together to form tissues. They serve as attachment points for the phospholipid membrane to the internal cytoskeleton and external fibers, or to neighboring cells. These are typically found in tissues that must be able to **stretch** as an organ fills, such as in the walls of the stomach, heart, and urinary bladder.__ __B. COMMUNICATING or__ Gap Junction Proteins: form an open channel between two cells allowing chemicals and “messages” to pass quickly from cell to cell so they may function more effectively as a group. These are especially common in the walls of the heart.

C. Recognition Proteins: serve as a kind of “identification tag” for a cell, allowing antibodies and white blood cells to detect who “belongs” and who must be “destroyed” because they do not belong in the body. These also are responsible for the various blood types (A, B, AB, etc.) D. Receptor Proteins: serve as binding sites for signaling molecules (hormones) that will trigger a change in the activities of the cell. This is why some cells respond to a specific chemical (hormone) while others do not. E. __ENZYME__ Proteins: assist the cell by speeding up essential chemical reactions. They are generally found attached to either the outer or inner surface of the membrane. F. Transport __Proteins: help move water and water soluble (polar) substances across the phospholipids membrane. These protein molecules have an internal channel and tend to be very specific (selective) for the substance moving through them. There are two main types of these proteins:__ __1. Passive__ __Transporters: do not require energy for activation__ __2.__ Active __Transporters: do require energy for activation__ __3. There are several “driving forces” that influence the movement of substances across the cell membrane:__ __A.Concentration__ of a Solution: this is defined as the density of a particular substance in a given area (volume). Tonicity is defined as the comparative solute concentration of two solutions on either side of a selectively permeable membrane. 1. There are essentially three “types” of solutions when discussing the movement of substances across a membrane: Out, or in? || Solution OUTSIDE is_ to solution INSIDE membrane. || Solution INSIDE is _ to solution OUTSIDE the membrane. ||
 * Solution outside membrane || Solution inside membrane || Where will water go?
 * 2% || 8% || in || hypotonic || hypertonic ||
 * 8% || 8% || stays the same || isotonic || isotonic ||
 * 8% || 2% || out || hypotonic || hypertonic ||

2. Because the cell membrane is selectively permeable, there is a tendency for some molecules to have a greater concentration on one side of the membrane than the other. The composition of the intracellular fluid is quite different from the composition of the extracellular fluid surrounding the cells in the body. For most cells in the body, there is a higher concentration of protein molecules, ATP and potassium ions (K+1) inside the cell than outside the cell. There is also a higher concentration of everything else outside the cell, especially sodium ions (Na+1) and chloride ions (Cl-1).

3. The difference in composition on each side of a cell membrane is called a __Concentration GRADIENT. There is a natural tendency for__ __molecules to move down__ __from the side of the membrane with a high__ __concentration and__ to __the side of the membrane with a low concentration (DOWN their concentration gradient) if at all possible.__ __B. Because there are many ions in solution, one side of the membrane will often be more positive and one side more negative, which creates an unequal charge distribution. Thcharge differences also tend to influence the movement of ions across the membrane. Remember that ions that have the same charge tend to__ __REPEL each other while those with opposite charges tend to__ __ATTRACT each other. Differences in electrical charges on each side of__ __a cell membrane is called an ELECTRICAL__ GRADIENT. C. Because there are numerous gases dissolved in the body (especially O2 and CO2) there is typically a gradient that influences the movement of gases across membranes throughout the body, especially between the lungs and the blood vessels within the lungs. As the concentration of a gas in solution increases, so does the pressure of the gas. Differences in gas pressure on each side of a membrane is called a PRESSURE __GRADIENT.__ __4. Substances move across a cell membrane by two main processes:__ __A. ACTIVE TRANSPORT involves the movement of molecules or ions across a__ __membrane from the side with a__ low __concentration to the side with__ __a__ high concentration. In other words, the molecules are moving __AGAINST their concentration gradients. This process requires that the cell use energy (ATP) to accomplish this action and the substance is described as being “pumped” across the membrane.__ __1. If the transporter protein “pumps” two substances at the same time and in the same direction, they are called SYMPORTERS.__ __2. If the transporter protein “pumps” two substances at the same time in opposite directions, they are called ANTIPORTERS. The most common example of this type is the sodium-potassium pump (found in nerve and muscle cells).__ __B. PASSIVE TRANSPORT involves the movement of molecules and ions across a__ __membrane from the side with a__ HIGH concentration to the side with a __LOWconcentration, or in other words, the molecules are moving WITH__ __ their concentration or pressure gradients. This process does not __ __need the cell to supply additional__ ENERGY (ATP) to move the substance across the membrane.

5. There are three main mechanisms that use the passive transport process: A. **DIFFUSION** __: the natural tendency for particles to spread out from an area of high concentration to an area of low concentration.__ __1. Remember that the cell membrane is selectively permeable. Lipid soluble__ __(**NON POLAR**__ or hydrophobic) molecules can pass directly through the cell membrane as though it is not there. This is also how fat soluble vitamins and dissolved gases like oxygen (O2) and carbon dioxide (CO2) cross the cell membrane. 2. There are several factors that will increase diffusion rates across cell membranes or other membranes in the body: a. Greater the difference in concentration of solutes on each side of the membrane, **FASTER** the rate of diffusion b. Warmer the temperature of a solution, the **MORE** __molecules are moving about in the solution__ __c. Larger the size of the molecules, the **SLOWER**__ they move d. Ions of opposite charges (+ and -) **ATTRACT** each other, whereas those that have the same charges **REPEL** each other. e. An increase in pressure of a gas on one side of a membrane causes molecules to try to move to an area with less pressure. f. Larger surface area available for diffusion will **SLOW** the rate of diffusion. This is especially important in the lungs and intestines. g. The shorter the distance to diffuse, the **FASTER** diffusion occurs. This doesn’t apply to cell membranes as they are all the same thickness (phospholipid __bi-layer__), however when the lungs fill with fluid, it is harder for the oxygen to diffuse into the blood because it must move through the liquid as well as through the membrane. B. **FACILITATED** __DIFFUSION: the movement of water molecules__ __and water soluble (polar or__ **HYDROPHILIC**__) particles from the side of a selectively permeable membrane with a higher concentration of the molecule that is moving to the other side with the assistance (help) of a membrane protein.__ __1. Some of these protein channels are always open (leakage channels), but only allow specific molecules to pass through. Many animal and plant cells have__ __channels called aquaporins that are always open and allow **WATER**__ to cross the membrane easily to help maintain a proper fluid balance. 2. Some channels must change their **SHAPE** to allow a molecule to pass through and therefore can regulate when and if a substance gets through or not. These proteins are said to be “**GATED**” and can open or close in response to stimuli like a specific chemical, pressure or changes in membrane electrical gradients.

C.**OSMOSIS** __: the diffusion of water across a selectively permeable__ __membrane. Water like any other substance diffuses from an area of__ **HIGH** water concentration to an area of **LOW** water concentration. 1. The direction of movement of water across a membrane is sometimes difficult to keep straight because solutions are described by the concentration (amount) of the solutes dissolved in the water, not by the amount of the water. 2. Water molecules move across a selectively permeable membrane from the solution that is **HYPO**__TONIC to the solution that is__ **HYPER**TONIC. A hypotonic solution has relatively __more water__ compared to a hypertonic solution, and water moves from the solution where there is “more of it” to the solution where there is “less of it”.
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Hypotonic Hypertonic Isotonic Solution Solution Solution

6. There area several additional forces that influence the movement of WATER across membranes: A. **HYDROSTATIC** PRESSURE: is the force generated by the flow of a fluid against a membrane. In the circulatory system the heart pumps blood, which when under pressure tends to push the fluid through openings in membranes, carrying with it all small substances dissolved in the blood. This is the driving force behind how the kidneys filter the blood B. **​OSMOTIC** __PRESSURE: is the force needed to prevent water from flowing across a membrane, down the concentration gradient for the water. This is the driving force behind how the capillaries (very small blood vessels) “pull” tissue fluid back into the circulatory system.__

__7. There are several process that are used to move large quantities of substances or molecules or substances that are too “large” to cross the cell membrane through the protein channels:__ __A.__ ___: this is the process the cell uses to expel or export large molecules produced inside the cell. Transport vesicles fuse with the membrane and the contents “spill out” of the cell. This is also the way the membrane is replaced with a “new and improved” membrane each time a substance is exported from the cell.__
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B. _: this is the process the cell uses to take in large molecules for use by the cell or to be destroyed by the cell in the case of white blood cells. This is also the way worn-out membrane is repaired by the cell as sections are pulled into the cell and broken down by fusing with lysosomes. .
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There are three basic forms of Endocytosis: 1. _ __ENDOCYTOSIS: receptors on the surface of the cell membrane bind to__ very specific __substances (hormone, vitamin, mineral, etc.), then the membrane folds in on itself forming a vesicle.__ __2.__ _: this is the process the cell uses to “engulf” large microorganisms or “food particles” that happen to be in the extracellular fluid. This process is also thought of as “cellular eating” 3. ENDOCYTOSIS: this process is much less selective and is used primarily to remove excess membrane that forms as exocytosis occurs, or to remove sections of worn-out membrane. This process is sometimes known as PINOCYTOSIS or is thought of as “cellular drinking”, as some of the extracellular fluid is brought into the cell in the process.

8. Hydrophilic (polar) substances cross the cell membrane with the assistance of transport proteins. For each of the following, choose one of the mechanisms of protein-mediated transport listed. Some descriptions below require active transport, some indicate passive transport is required, while other descriptions do not provide enough information to definitively chose one or the other, so may apply to either active or passive transport. A. active transport B. passive transport C. may apply to either active or passive transport 1. The calcium channel pump uses this method to transport calcium 2. Involves a transport protein that is not energized 4. A transport protein is specific to only one type of substance 5. Solute molecules move across the membrane from the side with a higher concentration to the side with a lower concentration of the solute molecule 6. The transport protein must receive an energy boost, usually from ATP. 7. Binding of ATP to a transporter protein leads to changes in protein shape 8. The sodium-potassium pump uses this mechanism of transport 9. Net movement of solutes will be down the solute’s concentration gradient using this method of transport. 10. A solute is pumped across the cell membrane //against// its concentration gradient. 11. The solute binding site improves when ATP donates energy to the transport protein to allow a better chemical fit. 12. Passive two-way transport will continue until solute concentrations become equal on both sides of the membrane. 13. _ Movement is through a transport membrane protein, with a solute’s concentration gradient.

9. Osmosis is an important process that has many effects on living things. Test your understanding of osmosis by predicting in each of the following cases whether water will enter the cell (In) or leave the cell (Out), or whether there will be no net movement of water (None). Assume that the plasma membrane is permeable to water but not to the solutes.

_ 1. A cell is exposed to a hypertonic solution. _ 2. A cell is placed in a salt solution whose concentration is greater than that of the cell contents. _ 3. Due to disease, the solute concentration of the body fluid outside the cell is less than the solute concentration of the cytoplasm. _ 4. The cell is in an isotonic solution. _ 5. A single-celled organism is placed in drop of pure water for examination under microscope. _ 6. A cell is immersed in solution of sucrose and glucose whose combined concentration is greater than the concentration of solutes in the cytoplasm. _ 7. The solute concentration of the cell cytoplasm is greater than the solute concentration of fluid surrounding the cell. _ 8. A cell is exposed to a hypotonic solution. _ 9. The concentration of solutes in the cytoplasm is equal to the solute concentration of the extracellular fluid. _ 10. The cytoplasm of a cell is more dilute than the surrounding solution = =

10. Choose the most appropriate answer for each.

2. _ osmosis 3. _ tonicity 4. _ hypotonic solution 5. _ hypertonic solution 6. _ isotonic solutions 7. _ hydrostatic pressure 8. _ osmotic pressure 9. _ plasmolysis || A. Refers to the relative solute concentrations of two fluids B. Having the same solute concentrations C. Mass movement of one or more substances in response to pressure, gravity, or other external force D. The amount of force that prevents further increase in a solution’s volume E. The fluid on one side of a membrane that contains more solutes than the fluid on the other side of the membrane F. The diffusion of water in response to a water concentration gradient between two regions separated by a selectively permeable membrane G. Osmotically induced swellingh of a cell until it ruptures H. The fluid on one side of a membrane that contains fewer solutes than the fluid on the other side of the membrane I. A fluid force exerted against a cell wall and/or membrane enclosing the fluid || = = 11. If the statement is true, write a T in the blank. If the statement is false, make it correct by changing the underlined word(s) and writing the correct word(s) in the answer blank.
 * 1. _ bulk flow

_ __1. Because membrane exhibits selective permeability, concentrations of dissolved substances can__ increase __on one side of the membrane or the other.__ _ 2. A water concentration gradient is influenced by the number of __solute__ molecules present on both sides of the membrane. _ __3. The relative concentrations of solutes in two fluids are referred to as__ tonicity__.__ _ 4. An animal cell placed in a __hypertonic__ solution would swell and perhaps burst. _ __5. Physiological saline is 0.9 percent NaCl; red blood cells placed in such a solution will not gain or lose water; therefore, one could state that the fluid in red blood cells is__ hypertonic__.__ _ 6. A solution of 80 percent water, 20 percent solute is __more__ concentrated than a solution of 70 percent water, 30 percent solute. _ __7. The mass movement of one or more substances in response to pressure, gravity, or some other external force is called__ osmosis__.__ _ 8. Animal cells placed in a __hypotonic__ solution will swell. 12. Review the function of cell membranes by matching each of the phrases on the right with the appropriate mechanisms from the list on the left. Answers may be used more than once and some questions require more than one answer.

B. Active transport C. Osmosis D. Phagocytosis E. Passive transport F. Facilitated diffusion G. Pinocytosis H. Receptor-mediated endocytosis I. Exocytosis || _ 1. Movement of substances across a biological membrane directly through the phospholipids bilayer _ 2. Moves solutes against concentration gradient _ 3. Any spread of molecules from area of higher concentration to area of lower concentration _ 4. Movement of substances across a membrane down the concentration gradient with the help of a transport protein _ 5. Three types of endocytosis where substances enter the cell and are contained within vesicles. _ 6. Engulfing of fluid in membrane vesicles _ 7. Diffusion of water across selectively permeable membrane, from hypotonic to hypertonic solution _ 8. Transport molecules use ATP to function better _ 9. Enables cell to engulf bulk quantities of very specific large molecules that bind to surface proteins _ 10. How oxygen and carbon dioxide enter and leave cells _ 11. Two examples of passive transport through a protein channel in the membrane _ 12. Engulfing of large particle in membrane vesicle _ 13. Fusion of membrane-bound vesicle with membrane, and dumping of contents outside cell _ 14. How a cell might capture a bacterium _15. A general term used to represent the movement of substances down their concentration gradient through a protein channel without the use of ATP energy. ||
 * A. Diffusion


 * //Sample Test Questions for Chapter 5://**

1. The cell membrane consists mostly of a a. protein bilayer with phospholipids scattered throughout the membrane b. carbohydrate bilayer with proteins scattered throughout the membrane c. phospholipid bilayer with proteins scattered throughout the membrane d. protein bilayer with carbohydrates scattered throughout the membrane

2. The phospholipids molecules of most membranes have a. a hydrophobic head and a hydrophilic tail b. a hydrophobic head and a hydrophobic tail c. a hydrophilic head and two hydrophilic tails d. a hydrophilic head and two hydrophobic tails

3. In an attempt to describe the membrane as a “fluid mosaic model”, we would describe the as floating in a sea of __.__ __a. lipid…….protein__ __b. phospholipids………carbohydrates__ __c. proteins……….phospholipids__ __d. lipids……….water__

__4. Oxygen and carbon dioxide pass through the membrane by which of the following processes?__ __a. osmosis__ __b. diffusion__ __c. active transport__ __d. facilitated diffusion__ __e. receptor mediated endocytosis__

__5. Movement of molecules against their concentration gradient occurs by which of the following processes?__ __a. osmosis__ __b. diffusion__ __c. active transport__ __d. facilitated diffusion__ __e. receptor mediated endocytosis__

__6. A red blood cell placed in a hypotonic solution would__ __a. shrink__ __b. swell__ __c. stay the same size__ __d. become a substrate__

__7. Osmosis is similar to passive transport in that both:__ __a. always involve the diffusion of water__ __b. do not require the cell to expend ATP energy__ __c. involve diffusion down the concentration gradient__ __d. rely on transport proteins__ __e. both B and C__

__8. A cell that neither gains nor loses water when it is immersed in a solution is__ __a. isotonic to its environment__ __b. hypertonic to its environment__ __c. hypotonic to its environment__ __d. metabolically inactive__

__9. Which of the following pieces of evidence would prove that a substance enters a cell by active transport rather than passive transport?__ __a. the substance is moved across the cell membrane by a carrier protein__ __b. the substance enters the cell when its concentration is higher outside the cell than inside__ __c. the breakdown of ATP is needed for the transport to occur__ __d. all of the above__ __e. both A and C only__

__10. Phagocytosis is to eating as__ is to drinking. a. osmosis b. exocytosis c. pinocytosis d. diffusion