A-LEVEL NOTES
  • Home
  • Biology
    • AQA
    • OCR
  • Chemistry
    • AQA
    • OCR
  • Home
  • Biology
    • AQA
    • OCR
  • Chemistry
    • AQA
    • OCR
A-LEVEL NOTES

A-LEVEL BIOLOGY AQA NOTES 
transport across cell membranes


Picture
DOWNLOAD PDF
Made with ❤️by snaprevise.co.uk

Cell Membranes
  • Cell membranes act as barriers and can control what passes into and out of cells and organelles
  • ​The cell membrane is composed of phospholipids, proteins, glycoproteins, glycolipids and cholesterol.
Picture
  • Cholesterol has a hydrophilic end and a hydrophobic end & regulates membrane fluidity by intercalating between the phospholipids

​Passive Transport
  • Passive transport involves exchange of substances without requiring metabolic energy from the cell
  • Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration (down their concentration gradient).
  • Facilitated diffusion is the net movement of particles down their concentration gradient across a partially permeable cell membrane via carrier or channel proteins
Picture
Picture
  • Water potential is a measure of the tendency of water molecules to move from one area to another area and describes the pressure created by these water molecules; the more dilute a solution, the higher (less negative) the water potential (Ѱ).
  • Osmosis is the net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane.
  • The rate of diffusion can be increased by increasing the number of channel & carrier proteins, the surface area of the cell membrane, reducing the diffusion distance and creating a steeper concentration gradient. 

​Active Transport

Active transport is the movement of particles from an area of low concentration to an area of high concentration (against their concentration gradient) across a cell membrane, using ATP and carrier proteins.
  • Co-transport occurs when the transport of one substance is coupled with the transport of another substance across a membrane.
  • ​Glucose & sodium are co-transported in the ileum:
Picture

A-LEVEL BIOLoGY

A-level AQA Biology
A-level OCR Biology
A-level Edexcel Biology

A-LEVEL CHEMISTRY

A-level AQA Chemistry
A-level OCR Chemistry
​A-level Edexcel Chemistry