Chapter 5 Homeostasis and Cell Transport Section 1 Passive Transport

Passive Transport Substances cross the cell membrane without any input of energy Ex. diffusion Red dye diffusing into water

Diffusion The movement of molecules from an area of high concentration to an area of lower concentration

Diffusion occurs until equilibrium is reached… …the concentration of molecules is the same throughout a space

Diffusion Across Membranes Called simple diffusion- cell membranes only allow certain substances to pass through Cell membranes are semi-permeable

Materials that enter the cell through simple diffusion… 1) carbon dioxide 2) oxygen Earthworms “breathe” through their skin!

Osmosis- a form of passive transport concerning water The movement of water from an area of high concentration to an area of low concentration

The direction of osmosis… Water moves out- cell shrivels Water moves in-cells may burst Same amt. of water moves in and out

What is the fate of the cell in each condition??? Isotonic-nothing; it’s normal Hypertonic-shrivel/shrink Hypotonic- burst

Hypotonic (Hippo-) The cell gets bigger.

For red blood cells, this is fatal… Hypotonic  isotonic  hypertonic

How Cells deal with Osmosis For unicellular freshwater organisms, this is a problem. Some of them have special organs for removing water. Ex. Paramecia have pumps called contractile vacuoles that constantly remove water from their bodies

Do the cells of this plant have turgor pressure? Section 1 cont. Turgor pressure- the pressure that water molecules exert against the cell wall Do the cells of this plant have turgor pressure?

Plasymolysis- when a plant doesn’t receive enough water and the cell membrane shrinks from the cell wall; turgor pressure is not maintained

Facilitated Diffusion A type of passive transport that is used for 1) molecules too large to pass through the cell membrane 2) molecules that do not dissolve in lipids

Facilitated diffusion uses a carrier protein.

Facilitated Diffusion What might this molecule be? Molecule attaches to protein. Protein changes shape. Molecule is released to other side. Protein returns to original shape.

Ion Channels Membrane proteins move Na+, K+, Ca+2, Cl- across the cell membrane

Three kinds of stimuli determine whether “gates” are open: 1) stretching of the cell membrane 2) electrical signals 3) chemical signals