Biology 1.3 (Part 2)

Membrane transport

Goal

inside contents of the cell to reach equilibrium with outside enviroment

The concentration gradient

• cell membrane allows the transport of substances in and out

• It’s based on the difference in concentrations

Diffusion

defined as the net movement of molecules from an area of greater concentration to an area of of lesser concentration without using energy.

Facilitated diffusion

• type of diffusion that uses specialised proteins to move molecules across the cell membrane

• Molecules move down a concentration gradient (high to low)

• Doesn’t require energy (passive)

• Involves channel proteins and carrier proteins

Carrier proteins

• Selectively bind and allow specific molecules to move across the membrane.

• Moves larger, hydrophilic molecules

Channel proteins

• form small pores that are selectively opened and closed

• moves charged atoms and molecules

Osmosis

• diffusion of water across a semi permeable membrane

• Water moves from an area of lower solute concentration to an area of higher solute concentration

Tonicty

ability of the extra cellular solution to make water move into or out of the cell by osmosis

Hypotonic

solution that has a lower solute concentration compared to the solution. Water moves into the cell, causing cell to burst or swell.

• hypo=low

Hypertonic

solution that has a higher solute concentration compared to the solution. Water moves out the cell, causing cell to shrink

• hyper=high

Isotonic

solution that has the same solute concentration compared to the solution. Nothing happens.

Active transport

• movement against concentration gradient

• requires input of cellular energy (ATP)

  • requires a carrier protein to facilitate the movement

Bulk transport

• movement of large amount of material across a membrane

• there are 2 types of bulk transport: endocytosis and exocytosis (both active therefore requires energy)

Bulk transport 1: Endocytosis

• movement of large materials into a cell

• cell membrane extends around material.

• Breaks off into a membrane bound package known as a vesicle

Bulk Transport 2:

• movement of large materials out of a cell

• material is packaged into a vesicle which moves to the cell membrane