The Cell and Its Environment

Diffusion I. Diffusion Molecules are not stationary, instead they are constantly moving about Molecules have energy of motion (kinetic energy) Collisions between moving molecules will spread the molecules apart until the molecules are evenly distributed throughout the available space

Diffusion The movement of molecules from an area of high concentration to an area of low concentration is called diffusion. Ex. Perfume diffusing through the air Food coloring diffusing in water

Hey, sponges are permeable too!! Permeablility II.Permeability A material is permeable if it allows molecules to pass through. The cell membrane (plasma membrane) is permeable. Hey, sponges are permeable too!!

Osmosis III. Osmosis Osmosis is the diffusion of water molecules across a permeable membrane. In osmosis, like diffusion, water molecules move from an area of high concentration to low.

Osmosis Hypotonic solutions- Solutions which contain a lower concentration of dissolved substances than a solution to which it is being compared. In a hypotonic solution the cell swells or possibly explodes Red blood cell placed in distilled water

Osmosis Hypertonic Solution Solutions which contain a higher concentration of dissolved substances than the solution to which it is being compared In hypertonic solutions the cell shrinks Red blood cell placed in salt water solution

Osmosis Isotonic solutions When the solution inside the membrane is the same concentration as the solution outside the membrane. An isotonic solution is at equilibrium In an isotonic solution there is no change in the cell Red blood cell in an isotonic solution

Osmosis D A B C E Which is the most hypertonic solution? Which is the most hypotonic solution? Which solution is isotonic?

Turgor Pressure Osmosis is one way that plants take in water through their root cells. Plant cells use osmosis to build up a large positive internal pressure, the turgor pressure. Turgor pressure determines the rigidity and stability of plant tissues. Plants that lose turgor pressure wilt.

Turgor Pressure

Passive Transport Both Osmosis and Diffusion are types of passive transport. Passive transport requires no input of energy from the cell.

Cellular Transport

Passive Transport Passive Transport: requires no energy. Examples of passive transport: 1. diffusion: movement of molecules from high concentration to low concentration. 2. osmosis: movement of water across a permeable membrane from an area of high concentration to low concentration.

Passive Transport BUT: There are some molecules that are too large to pass through the phospholipid bilayer. Therefore, some molecules must undergo passive transport by means of transport proteins. This is called:FACILITATED DIFFUSION

Transport Proteins There are two types of transport proteins:   1. channel proteins 2. carrier proteins

Transport Proteins Channel proteins are tube like and provide openings through which particles can diffuse.

Transport Proteins Carrier proteins have a specific shape that fits a specific molecule. When the proper molecule combines with the protein, it changes shape and moves the molecule across the membrane.

Passive Transport Facilitated diffusion is passive and requires no energy.

Active Transport Can a cell ever move particles from a region of lesser concentration to a region of greater concentration?   Yes, but energy must counteract the tendency of the molecules to move in the opposite direction.

Active Transport The transport of materials against a concentration gradient requires energy (ATP) and is called ACTIVE TRANSPORT.

Active Transport First a transport protein binds with the substance to be transported. Energy from the cell is used to change the shape of the proteins so that the particle is released on the other side of the membrane. Once the particle is released, the protein regains its’ original shape.

Active Transport Some cells can take in large molecules, groups of molecules, or even whole cells through ENDOCYTOSIS.

Active Transport The reverse process of endocytosis is EXOCYTOSIS. Cells use this to expel wastes, and secrete cellular products.

                                                                   

Review PASSIVE TRANSPORT: 1. no energy 2. movement of molecules from high concentration to low concentration. 3. Examples: diffusion, osmosis, facilitated diffusion ACTIVE TRANSPORT: 1. requires energy 2. movement of molecules from low concentration to high concentration. 3. use of transport proteins 4.exocytosis and endocytosis are active transport for large molecules, wastes, and cellular products. 

The Cell and Its Environment Reflection Questions The diffusion of water molecules across a permeable membrane is called ________. The movement of molecules from an area of high concentration to an area of low concentration is called ___________. Describe each of the following solutions: hypotonic, hypertonic, and isotonic solutions. What is turgor pressure and why is it important for plants? Both osmosis and diffusion are examples of ___________ transport.

Cellular Transport Reflection Questions 1.What is passive transport? 2. List and describe the different types of passive transport. 3. What is active transport? 4. List and describe the different types of active transport. 5. List the two types of transport proteins. When the transport proteins are used, is it active or passive transport?