2.4 Understand what is meant by passive and active transport, endocytosis and exocytosis

What is meant by passive transport

Transport of molecules across a cell membrane without the use of energy.

It occurs along the concentration gradient, from high to low concentration

What are three examples of passive transport

• Diffusion

• Facilitated Diffusion

• Osmosis

What is diffusion

Transport of dry molecules from an area of high to low concentration without the use of energy

What is facilitated diffusion

Transport of dry molecules from an area of high to low concentration without the use of energy and with the use of a carrier or channel protein as they are large molecules or are ions

What is the role of a carrier protein

• Moves large molecules in and out of a cell

• Carrier proteins are specific to the molecule they are transporting

!EXAM Q! What is the process of transport using a carrier protein (2 marks)

1. The large molecule attaches to a carrier protein in the membrane

2. The protein then changes shape and releases the molecule to the opposite side of the membrane

What is the role of a channel protein

• Moves ions (charged particles) in and out of the cell

• Channel proteins are specific to the molecule they are transporting

!EXAM Q! What is the process of transport using a channel protein (2 marks)

1. The channel proteins form pores on the cell membrane

2. This allows charged particles to diffuse along the concentration gradient into the other side of the membrane

What is Active Transport

Transport of molecules and ions across plasma membranes with the use of energy (ATP) and a carrier protein

!EXAM Q! Give a reason and explain as to why molecules would use Active Transport to exit the cell (4 marks)

1. The molecule has a charge and therefore cannot directly diffuse out of the cell

2. The molecule attaches to the carrier protein at a binding site

3. The protein then changes shape

4. This moves the molecule across the membrane where it is released on the other side

Where does the energy come from in Active Transport

ATP

• ATP is produced in respiration

• It acts as an immediate source of energy in the cell

• When ATP is hydrolysed (broken down), energy is released

• This energy allows the molecule to move against the concentration gradient

What is the process called where cells take in molecules that are too large to be transported by carrier proteins

Endocytosis

Give some examples of molecules that require endocytosis

• Proteins

• Lipids

• Some carbohydrates

What is the process of endocytosis

1. The membrane forms a vesicle

2. This vesicle ingests the substance and brings it through the membrane into the cell

Does endocytosis require energy?

Yes, it requires energy in the form of ATP

What is the process called where substances that are produced by the cell are released

Exocytosis

Give examples of molecules that require exocytosis

• Digestive enzymes

• Hormones

• Lipids

What is the process of exocytosis

1. A vesicle containing the substance pinch off the sacs of the Golgi Apparatus and moves towards the cell membrane

2. The vesicle fuses with the cell membrane and releases its contents out of the cell

What substances are not released outside of the cell but instead are inserted straight into the cell membrane

• Membrane proteins

Does exocytosis require energy

Yes, it requires energy in the form of ATP