Chapter 4: Cells and Their Environment

Transcription

1 Chapter 4: Cells and Their Environment

2 Objectives for the Chapter: 1. Relate concentration gradi equilibrium. 2. Predict the direction of wat of cells. 3. Describe the importance o transport. 4. Identify the role of carrier p diffusion. 5. Compare active transport w 6. Describe the importance o pump. 7. Distinguish between endoc 8. Identify 3 ways receptor pr activity of a cell.

3 ent, diffusion, and er movement into and out f ion channels in passive roteins in facilitated ith passive transport. f the sodium-potassium ytosis and endocytosis. oteins can change the

4 Vocabulary Passive transport Concentration gradient Equilibrium Diffusion Osmosis Hypertonic solution Hypotonic solution Isotonic solution Ion channel Carrier protein Facilitated diffusion Active transport Sodium-potassium pump Endocytosis Exocytosis Receptor protein Second messenger

5 Assignment: Answer the following question and submit answer on MBC under Schoolwork. It is called Chapter 4, Assignment 1. Using the figure on the cover of this chapter, hypothesize what this chapter will cover. Why do you think that? 10 points

6 Passive Transport Movement across the cell membrane that does not require any energy from the cell is called passive transport. To better understand passive transport, imagine 2 rooms of equal size separated by a wall with a closed door. Suppose you release 100 bouncy balls into the first room. The balls move randomly, bouncing of the walls, the floor, and the ceiling. Also suppose the balls can bounce forever without slowing down. Eventually the balls will become evenly distributed in the first room. Now, open the door to the second room. What happens? Some of the balls from the first room bounce through the doorway into the second room by the natural bouncing motion of the balls. Occasionally a ball will bounce back into the first room from the second room. After a long while, both rooms will reach equilibrium, meaning they will have them same amount of bouncy balls in each room bouncing back and forth between the two rooms. In passive transport, molecules cross the cell membrane randomly, without energy. The movement of those molecules is always from a higher concentration to a lower concentration, passing through a barrier (the wall in the example) which is known as the concentration gradient.

7 Types of Passive Transport Diffusion The movement of any substance, except water, from a high concentration to a low concentration. Osmosis The movement of water from a high concentration to a low concentration.

8 Types of Solutions Isotonic solution - molecules move in and out of the cell at the same rate causing the cell to stay the same shape and size. Hypertonic solution - molecules move from inside the cell to the outside causing the cells to shrink. Hypotonic solution - molecules move from the outside to the inside causing the cells to swell.

9 Diffusion through Ion Channels Ions such as potassium, calcium, sodium, and chloride play major roles in the functioning of cells. In order to get those ions into the cell, ion channels are used. An ion channel is a transport protein, located within the cell membrane, that opens and closes like a gate allowing ions to pass. The gates of the ion channel opens and closes in response to chemical and electrical stimuli. The movement of a substance across the cell membrane is generally determined by the concentration gradient. The movement of a charged particle (ion) is also influenced by its positive or negative charge. Typically, the inside of a cell is negative. Thus, a positively charged ion will be allowed to move into the cell and negatively charged ions will be allowed to move out of the cell.

10 Facilitated Diffusion Most cells also have a kind of transport protein that can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side. Such proteins are called carrier proteins. When these proteins are used to transport amino acids and sugars down the concentration gradient (from high to low) then it is called facilitated diffusion.

11 Assignment: Answer the following questions and submit answers to MBC under Schoolwork. It is called Chapter 4, Assignment Distinguish between diffusion and osmosis. 2. Describe how diffusion of ions across a cell membrane differs from the diffusion of nonpolar molecules across the cell membrane. 3. Explain how some substances cross the cell membrane by facilitated diffusion. 10 points

12 Active Transport The transportation of a substance across a cell membrane against (low to high) its concentration gradient is called active transport. Unlike passive transport which requires no energy, active transport requires the cell the give up ATP in order for the process to occur. Some active transports will use carrier proteins to "pump" the substances across the cell membrane. For this reason, carrier proteins are sometimes referred to as membrane pumps. Active transport works much like this ball and pump. As the air pump uses energy (from you) the air is moved against the concentration gradient into the ball.

13 Types of Active Transport Sodium-Potassium Pump One of the most important membrane pumps in an animal cell is the sodium-potassium pump. This is for 2 reasons: (1) prevents sodium ions from building up in the cell which could cause a hypotonic solution in our cells, (2) helps maintain the concentration gradient.

14 Movement in Vesicles Endocytosis The movement into a cell by using a vesicle is called endocytosis. Exocytosis The movement out of a cell using vesicles is called exocytosis.

15 Membrane Receptor Proteins There is a vast amount of information In the form of chemical signals coming into and out of your cells at all times. Somehow, our cells have to find a way to filter out the unimportant information and respond to the important information. They do this by using receptor proteins. Receptor proteins are proteins, imbedded in the cell membrane, that binds to a specific signal molecule. Those signal molecules are chemical messages. When a receptor protein and it's complementary signal molecule bind together, it causes a change in the cell. The change can occur in one of three ways. 1) change permeability of the cell membrane, 2) triggering second messengers inside the cell which amplifies the signal, 3) activating enzymes within the cell.

16 Assignment: Answer the following questions and submit answers to MBC under Schoolwork. it is called Chapter 4, Assignment Distinguish between active and passive transport. 2. Describe how the sodiumpotassium pump helps prevent animal cells from bursting. 3. List 3 ways that the binding of a signal molecule to a receptor protein causes change in the receiving cell. 4. Compare endocytosis with exocytosis. 10 points

17 End of Chapter 4

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