unit 2 topics 6,7 & 9 - permeability

what are the types of transport across a membrane?

• passive

• active

define passive transport

• transport of a molecule that does not require energy from the cell because a solute is moving with its concentration or electrochemical gradient

• involved in the import of materials and the export of waste

what are the types of passive transport?

• diffusion

• osmosis

• facilitated diffusion

define diffusion

• spontaneous process resulting from the constant motion of molecules

• substances move from a high to low concentration

• molecules diffuse directly across the membrane

• different rates of diffusion for different molecules

define osmosis

• the diffusion of water down its concentrated gradient across a selectively permeable membrane

• can also be thought of as the diffusion of water from areas of low solute concentration (high water - hypotonic) to areas of high solute concentration (low water - hypertonic)

define facilitated diffusion

• diffusion of molecules through the membrane via transport proteins

what does facilitated diffusion increase rate of diffusion for?

• small ions, water, carbohydrates

what are the types of transport proteins?

• channel

• carrier

• each transport protein is specific for substances that it can facilitate movement for

why is facilitated diffusion passive transport?

• because the substances that the proteins are helping to move are moving down their concentration gradient and no energy is required

define channel proteins

• provide a channel for molecules and ions to pass

what is a characteristic of channel proteins?

• hydrophilic

• many are gated

  • only allow passage when there is a stimulus

define aquaporins

• specific channel protein for water

• always active when water imbalances in the cell

what is the function of carrier proteins?

• undergo conformational changes for substances to pass