Chapter 4

Cellular Transport

Water, molecules, and ions move in and out of cells all of the time.

If the cells are surrounded by such a tough membrane, how can these particles move.

The cell membrane is not impermeable, but merely semi-permeable.

So some things, like small ions can move freely through the cell membrane.

Cellular Transport

Plasma Membrane

Plasma Membrane may be 1. Differentially permeable 2. Semi-permeable 3. Impermeable

If it allows the rapid entry of some molecules and the gradual or slow entry of some other molecules

If it allows some molecules to pass through and prevents other molecules from passing through.

When plasma membrane prevents the crossing of all molecules

Methods of Cellular Transport

1. Passive Transport 2. Active Transport 3. Bulk Transport

This passive process is called passive transport, it is the movement of materials across the membrane from region of greater concentration to region of lower concentration

When ions and molecules are moving up the concentration gradient, from and area of low concentration to an area of high concentration, then energy is needed.

This allows the passage of large molecules like proteins, lipids or microorganism.

Diffusion The process of diffusion is very simple,

and operates on each separate molecule drifting in the air, or in water based upon it concentration.

Diffusion is the process of molecules moving from areas of high concentration to areas of lower concentrations.

Dialysis and osmosis are examples of passive diffusion

Osmosis

This is the same process that move ions through cell membranes. But in this case, we call it osmosis.

Osmosis is simply the process of diffusion, except that the particles are moving through a semi-permeable membrane.

OSMOSIS

OSMOSIS

Physiological Solution

Salt Solution – 0.85% NaCl Sugar Solution – 0.3 M soln

There are three possible relationships that cells can encounter when placed into a

water solution. The concentration of solute in the solution can be

equal to the concentration of solute in the cells. The cell is in an isotonic solution. (iso = same as normal)

The concentration of solute in the solution can be greater than the concentration of solute in the cells. The cell is in an hypertonic solution. (hyper = more than normal)

The concentration of solute in the solution can be less than the concentration of solute in the cells. The cell is in an hypotonic solution. hypo = less than normal

Plasmoptysis is when a cell bursts because it has taken in too much water as a result of being place in a hypotonic environment.

Plasmolysis is cell shrinkage due to water loss as a result of being placed in a hypertonic environment. 

Cytolysis is caused by excessive osmosis, or movement of water, towards the inside of a cell. Cytolysis does not occur in plant cell.

Equal movement of water into and out of cell

net water movement out of cell

net water movement into the cell

George in Hypertonic Solution

George in Isotonic Solution

George in Hypotonic Solution

SPLATSPLAT

AAARRGHH!AAARRGHH!

Uh...Oh!Uh...Oh!

Summary

Active Transport

When ions and molecules are moving up the concentration gradient, from and area of low concentration to an area of high concentration, then energy is needed.

This process is called active transport, and it needs ATP.

Bulk Transport

Phagocytosis – eating - solid molecules are engulfed by the cell Pinocytosis – drinking - liquid molecules are

engulfed by the cell

End of Presentation

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