Active Transport

Lesson 11

February 3rd, 2011

Active transport

• After eating a meal food is broken down in the stomach and travels to the small intestine, where most of the nutrient molecules are absorbed into cells.

• If the nutrients were absorbed by simple diffusion only around half of all the nutrients would be absorbed because the net movement of molecules would stop when both sides had equal concentrations.

Active transport

• This would leave the other half of the nutrients to leave as waste.

• To maximize the amount of absorption of nutrient, glucose is pumped though cell membranes.

• This is done by special protein carriers that use ATP (energy) to move the molecules across the chemical gradient in a process called active transport.

Active Transport • There are other types of active transport pumps that

are found in membranes of other types of cells. • Sodium-potassium pumps are found in nerve and

muscle cells. – Without these pumps, we would not be able to use our

muscles or send an action potential down a nerve.

http://www.youtube.com/watch?v=_bmp2_T0c7k&feature=related

• There are several other types of pumps designed to pump vitamins, amino acids, and hydrogen ions. All of these pumps require energy and are thus active transport.

Bulk Transport

• Diffusion and active transport are responsible for moving large amounts of material though cell membranes. These methods can only move dissolved particles that are at the size of atoms, ions and small molecules. Sometimes cells need to move large quantities of materials (bulk) into or out of their cytoplasm all at once. A process called Bulk Transport can accomplish this.

• There are two types of bulk transport, both of which require energy making active transport.

Bulk Transport

• There are two types of bulk transport, both of which require energy making active transport.

1. Endocytosis

Endocytosis is the form of bulk transport used to bring large amounts of material into the cell from the extracellular fluid. There are two ways this can be done.

1. Phagocytosis (cell eating)

2. Pinocytosis (cell drinking)

Phagocytosis

• A solid particle comes in contact with plasma membrane of a cell.

• Pseudopods surround and enclose the particle in a vesicle that is within the cell’s cytoplasm.

• Digestive enzymes break down the particles

• This is how white blood cells kill invading bacteria

http://www.youtube.com/watch?v=S9QGJ3JN8Kw

Pinocytosis

• Extracellular fluid is engulfed in a process similar to Phagocytosis

2 Exocytosis

• Cells remove large amounts of materials out of their cytoplasm by a process that is essentially the reverse of Endocytosis

– This can be done to export hormones or enzymes

http://www.youtube.com/watch?v=U9pvm_4-bHg

Questions:

1. What is the main difference between Passive transport and Active transport?

2. Why is it beneficial for the body to use active transport in the small intestine?

3. What are the two types of Endocytosis?

4. Where are sodium potassium pumps found? Why are they important?

5. Why would a cell remove large amounts of materials? (Exocytosis)