Prentice Hall - Science Explorer - Cells and Heredity
Chapter 1- Cell structure and Function
Section 4- The Cell in its Environment
Questions - Comment - Key Words - Connections
Diffusion
Osmosis
Passive Transport
Active Transport
Main Ideas; Visuals + Predictions
Diffusion
* Diffusion is the main method by which small molecules move across the cell membrane.
Diffusion: The process by which molecules move from an area of higher concentration to an area of lower concentration.
What causes Diffusion? * When moving molecules bump into one another. Collisions cause the molecules to push away from one another and overtime the molecules of a substance will continue to spread out. Then, it will evenly spread throughout the area.
Diffusion of Oxygen * one celled organisms in pond water obtain the oxygen they need to survive from the water around them. And there is a higher concentration of oxygen molecules in the water than inside the cell. so, the oxygen molecules diffuse from the area of higher concentration—the pond water—through the cell membrane to the area of lower concentration—the inside of the cell.
Osmosis
Osmosis: The diffusion of water molecules through a selectively permeable membrane.
* Because cells cannot function properly without adequate water, many cellular processes depend on osmosis.
Osmosis and Diffusion * In osmosis, water molecules move by diffusion from an area where they are highly concentrated through the cell membrane to an area where they are less concentrated.
Effects of Osmosis
Active Transport
Passive transport: The movement of materials through a cell membrane without using energy. (releasing)
Active transport: The movement of materials through a cell membrane using cellular energy. (taking in)
* Active transport requires the cell to use its own energy, while passive transport does not.
*The image below shows active transport as it requires the cell membrane to use its cellular energy.
Transport of proteins * Transport proteins in the cell membrane “pick up” molecules outside the cell and carry them in or carry them out, using energy. * Some substances that are carried into and out of cells in this way include calcium, potassium, and sodium.
Transport by Engulfing * Engulfing is a form of active transport. * The cell membrane surrounds or encloses and engulfs a particle. Once the particle is engulfed, the cell membrane wraps around the particle and forms a vacuole within the cell.
Why are cells small? * cells are small because when a molecule enters the cell it is transported by the cytoplasm to its destination within the cell. So, it has to be small so that the cytoplasm won't take to long to bring the molecule. * Big cell = farther distance = longer time * small cell = shorter distance = shorter time
*so, a Large cell can’t quickly remove wastes or bring materials to all parts of the cell which enables it to grow.