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Transport
All living cells and organisms must transport a variety of materials in and out.
Eg. Sugar, oxygen, carbon dioxide and water
How does this movement occur?
Diffusion
Osmosis
Active transport
Diffusion:
an idea developed by physicists and chemists.
It is based on the following:
all matter is made up of very small particles – atoms & molecules
these particles are in constant motion
this movement is random
the random movement gradually moves the particles from an area of
high concentration to an area of low concentration
5. Eventually the particles will be evenly distributed
6. In this way, particles and entire molecules can get into and out of cells
1.
2.
3.
4.
Diffusion: example one
1. What happens when you place dye into a beaker of water? Draw three diagrams to
show how the dye reacts with the water.
Remember: molecules move from an area of high concentration to an area of low
concentration. This continues until the molecules are evenly spread out.
Example two:
2. The following shows a cell and the movement of oxygen. More oxygen is outside
the cell so it diffuses into the cell
Example three
3. Cells are surrounded by a semi-permeable membrane. This means that some
material will be able to pass through it and other materials will not.
Osmosis
Since water is a vital ingredient for all life processes, it has a special name for the process
by which it moves into and out of cells.
The diffusion of water through a semi-permeable membrane is known as osmosis.
Example: if an animal cell has a concentration of 3% salt and 97% water and is placed
into an environment of 6% salt and 94% water, what will happen?
The concentration of water is higher inside the cell, therefore the water will
diffuse out of the cell and the cell will become dehydrated.. Some salt molecules will also
diffuse into the cell, but not as easily as water.
Example: The same animal cell as above is placed into distilled water, what will happen?
The concentration of water is higher outside the cell, therefore water will diffuse
into the cell. The cell will expand with water and as it only has a cell membrane around
it, the cell will eventually burst. Some salt molecules will diffuse out of the cell, but this
happens much more slowly that the diffusion of water.
Example: What happens if we take a plant cell with the same concentrations as the
animal cell (3% salt and 97% water) and place it in salt water? (6% salt and 94% water)
The concentration of water is higher inside the cell, so water will diffuse from the
cell into the environment. Because the plant cell has a more rigid cell wall around the
outside of it, the cell will not collapse, but the cell will become dehydrated causing the
membrane to pull away from the cell wall.
Example: Place the plant cell into distilled water, what will happen?
The concentration of water is higher outside the cell, so water will diffuse into the
cell. Again, because the plant cell has the rigid cell wall, the cell will not burst like the
animal cell, but the cell membrane will expand and push up against the cell wall causing
turgor pressure.
Types of Solutions:
Hypotonic: solutions that contain low concentration of salt, high concentration of water
when compared to the cell.
Isotonic: Solutions which contain equal concentrations of salt and water when compared
to the cell.
Hypertonic: Solutions which contain a high concentration of salt and a low concentration
of water when compared to the cell.
Diffusion and osmosis are both examples of passive transport, because they do not
require any expenditure of energy by the cell. There are times however, when the cell
requires transport of a material against the concentration gradient (from low to high) and
this requires active transport. There are different types of active transport, but all of
them require an input of energy from the cell.
Active Transport – the movement of materials from an area of low concentration to
an area of high concentration. This requires energy from the cell.
1. one type of active transport involves the protein molecules in the cell
membrane. These protein molecules can receive an energy boost and then
capture molecules and move them either into or out of the cell. The exact
mechanism is not known but there are several theories. (see page 45)
2. endocytosis – cells engulf large molecules and extend the cytoplasm around
them, trapping them within a vacuole inside the cytoplasm
a. pinocytosis – engulfing liquids
b. phagocytosis – engulfing solid particles
3. Exocytosis – process in which large molecules inside the cell are transported
out of the cell. Golgi Apparatus creates a vesicle around the molecule, which then
break off and move to the cell membrane. The vesicle then fuse to the cell
membrane and release the molecule outside the cell. Eg wastes, proteins