To stay alive, a cell must exchange materials such as food and waste with its environment. These materials must cross the cell membrane.
Passive Transport Does not require the cell to use energy Diffusion Osmosis Facilitated diffusion
SimpleDiffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. (down its concentration gradient) concentration gradient - the difference in the concentration of molecules across a space http://www.biologycorner.com/bio1/diffusion.html Driven by kinetic energy energy of motion
Diffusion causes the concentration of molecules to be the same throughout space When molecules are dispersed evenly, there is no longer any diffusion because there is no longer a concentration gradient. a state of equilibrium exists (balance) http://www.brainpop.com/search/?keyword=diffusion
Rate of Diffusion molecules diffuse faster at higher temperatures than at lower temperatures smaller molecules diffuse faster than larger molecules Type of molecule
Water and Diffusion The diffusion of water across a semipermeable membrane is called osmosis. Osmosis occurs in response to the concentration of solutes dissolved in water.
Hypertonic Solution In a hypertonic solution, the concentration of solute molecules outside the cell is higher than inside the cell. What direction will the water diffuse?
Water diffuses out of the cell until equilibrium is reached.
What do you think will happen if the cell loses too much water? The cell will shrink and shrivel. plasmolysis
Hypotonic Solution In a hypotonic solution, the concentration of solutes outside the cell is lower than the concentration of solutes inside the cell. What direction will the water diffuse?
Water diffuses into the cell until equilibrium is reached.
How does this affect the cell? The cell will swell and possibly burst. Cytolysis
Isotonic Solution In an isotonic solution, the concentration of solutes outside and inside the cell are equal. How will the water diffuse across the cellular membrane?
Water will diffuse in and out of the cell at equal rates.
Red Blood Cell in different Solutions http://www.coolschool.ca/lor/BI12/unit4/U04L06/rbc.html http://www2.nl.edu/jste/osmosis.htm#Osmosis http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm http://bcs.whfreeman.com/thelifewire/content/chp05/0502001.html
Think: Apply what you have learned! In plants, cells that transport water against the concentration gradient are found to contain many more mitochondria than do some other plant cells. Give a possible explanation for this?