Transcript Notes 3-4
Notes 3-4 The Cell in Its Environment Cell Membrane • Provides protection for the cell • Chooses what comes in and out of cell • It is selectively permeable, which means it lets some substances pass through the membrane, and other substances cannot Cell Membrane • Here is the cell membrane magnified • Remember it surrounds the entire cell • Notice it is made up of lipids, proteins, and carbs (3 of the organic molecules from section 3-3) Passive Vs. Active Transport Passive Transport: • Movement of materials through cell membrane WITHOUT energy • Materials move from a high concentration of the material to a lower concentration of material • Its like rolling down a hill (no energy is needed) Active Transport: • Movement of materials through cell membrane WITH energy • Materials move from a low concentration of the material to a higher concentration of material • Its like trying to roll up a hill (imagine how hard that would be and how much of your energy it would take) Passive and Active Transport • Passive and active transport are two processes by which materials pass through the cell membrane. Active transport requires the cell to use its own energy, while passive transport does not. • When looking at the images, pay attention to what is meant by low concentration of materials versus high concentration of materials. Diffusion • Molecules move across cell membrane without energy (passive transport) • Move from high concentration to low concentration • Molecules continue to pass through membrane until there are equal amounts of molecules inside the cell as outside the cell • Remember, Molecules can only diffuse through the membrane if the membrane is permeable to it (if the membrane chooses to let it in!) Diffusion • In diffusion, molecules move from an area of higher concentration to an area of lower concentration. Osmosis • Special example of diffusion- Osmosis is the diffusion of WATER! • Passive transport, no energy required • Water will move from a high concentration of water to an area of low concentration of water until amount of water is equal inside and outside the cell • If too much water moves out of cell, the cell will shrivel (not good) • If too much water moves into cell, cell will burst (not good) • Cell needs to maintain a balance to function properly Osmosis Notice how the different concentrations of water choose whether water moves into or out of cell A selectively permeable membrane separates the 2 sides of the solution. The arrow shows that water is moving towards the right side. WHY? Water is moving from an area where water is high to an area where water is low, and the membrane is permeable to water. Why are the sugar molecules not moving across the membrane? The membrane must not be permeable to sugar (otherwise the sugar would be moving to the left side, from high to low concentrations of sugar) Transport Proteins • There are proteins embedded in the cell membrane that pick up materials and bring them into cell or carry them out of cell • Active transport, so requires energy • Brings materials from low concentration to high concentration • Each protein recognizes and carries a specific molecule such as calcium, potassium, or sodium. Transport Proteins: Why does this process require energy (ATP)? • This proton pump is a transport protein. • ATP is the energy its using. • Notice its pumping Hydrogen Ions out of the cell (from low concentration to high concentration) Because it is using active transport (it is transporting materials from low to high concentration). Engulfing • Cell extends its cytoplasm and cell membrane, surrounds molecule, and engulfs it (encloses it) • A vacuole is formed around molecule in this process • Process known as endocytosis (meaning inside cell) • A form of active transport, requires energy Cell Size • Cells must be small in order to function properly • If cells were too big, it would take too long for molecules to pass from one side of the cell to the other • Also, if cells were too big, it would take too long for wastes to be removed Let’s Review • Passive transport requires energy- True or False? False! Active transport does! Think of it like this… you need energy to be active! • Does diffusion require energy? No, because it is an example of passive transport. Let’s Review • What are some examples of active transport? • Osmosis is the diffusion of _________? WATER Engulfing (or endocytosis) and transport proteins