Title: Chapter 5 Homeostasis and Cell Transport
1Chapter 5 Homeostasis and Cell Transport
- Section 1 Passive Transport
2Passive Transport
- Substances cross the cell membrane without any
input of energy - Ex. diffusion
Red dye diffusing into water
3Diffusion
- The movement of molecules from an area of high
concentration to an area of lower concentration
4Diffusion occurs until equilibrium is reached
- the concentration of molecules is the same
throughout a space
5Diffusion Across Membranes
- Called simple diffusion- cell membranes only
allow certain substances to pass through
Cell membranes are semi-permeable
6Materials that enter the cell through simple
diffusion
- 1) carbon dioxide
- 2) oxygen
Earthworms breathe through their skin!
7Osmosis- a form of passive transport concerning
water
- The movement of water from an area of high
concentration to an area of low concentration
8The direction of osmosis
Water moves out- cell shrivels
Water moves in-cells may burst
Same amt. of water moves in and out
9What is the fate of the cell in each condition???
Isotonic-nothing its normal
Hypertonic-shrivel/shrink
10Hypotonic (Hippo-)
11For red blood cells, this is fatal
- Hypotonic ? isotonic ?
hypertonic
12How 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
13Section 1 cont.
- Turgor pressure- the pressure that water
molecules exert against the cell wall - Do the cells of this plant have turgor pressure?
14- Plasymolysis- when a plant doesnt receive enough
water and the cell membrane shrinks from the cell
wall turgor pressure is not maintained
15Facilitated 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
16Facilitated diffusion uses a carrier protein.
17Facilitated Diffusion
What might this molecule be?
- Molecule attaches to protein.
- Protein changes shape.
- Molecule is released to other side.
- Protein returns to original shape.
18Ion Channels
- Membrane proteins move Na, K, Ca2, Cl- across
the cell membrane
19Three kinds of stimuli determine whether gates
are open
- 1) stretching of the cell membrane
- 2) electrical signals
- 3) chemical signals