cell membrane

• Cell membrane encloses the cytoplasm of the cell and controls what enters and exists the cell.
• Cell membrane is made of a phospholipid bilayer, which is made up of hydrophobic tails made of fatty acids and hydrophilic heads made of phosphate.
• Cell membrane is a selectively permeable barrier, as some small substances can move through the membrane very easily.
• The chemical structure of the cell membrane is based on the 'fluid mosaic model'.
• Outside the cell membrane, there are extrinsic proteins.
• Inside the phospholipid bilayer of the cell membrane, there are intrinsic proteins.
• Carbohydrates are organic molecules made up of carbon, hydrogen, and oxygen atoms, and are a great source of energy.
• Lipids are a group of organic compounds with an oily, greasy, and waxy consistence, and their role is for biological fuel, hormones, and structural components of membranes.
• The plasma membrane is a selectively permeable membrane that allows certain substances to go in and out, and its structure is described by the fluid mosaic model.
• The plasma membrane consists of two layers of phospholipid molecules, and has important functions in cell recognition and communication with other cells.
• Glycolipids act as surface receptors and stabilise the membrane, helping cells to aggregate in the formation of tissues.
• Glycoproteins are involved in cellular recognition and immune response, and help to stabilise membrane structure.
• Passive transport does not require energy, while active transport requires energy and involves the active movement of molecules across the membrane against a concentration gradient.
• Simple diffusion is a process where a substance moves down the concentration gradient, moving from a region of high concentration to low concentration.
• Facilitated diffusion is a process where diffusion is assisted by proteins in the membrane, selectively increasing the diffusion rate of specific molecules, and does not require energy because it’s going down its concentration gradient.
• Channel mediated diffusion is a process where small polar molecules and ions diffuse by channel mediated facilitated diffusion.
• When a cell is placed in a hypertonic solution, the cell becomes flaccid (plasmolysis).
• Diffusion rates will be higher when there is a greater difference in concentration between 2 regions.
• Active transport is used to actively transport molecules across a membrane.
• Pores in a barrier enhance diffusion.
• Energy is released when ATP is hydrolysed forming ADP.
• Thick barriers slow the rate of diffusion.
• ATP binds to a transport protein during active transport.
• The rate of diffusion is greater when there is a large surface area across which diffusion can occur.
• Osmotic pressure is the pressure that causes free water molecules to move along a concentration gradient across a semi-permeable membrane.
• Facilitated diffusion by carriers shows saturation.
• Isotonic solution: The solution being compared have equal concentration of solutes.
• The transport protein goes back to its original position after transporting the molecule.
• The energy of active transport comes from ATP.
• A molecule to be transported binds to the transport protein during active transport.
• Uses pores to allow substances to go through.
• Hypertonic solution: The solution with a higher concentration of solute; hence lower concentration of free water molecules.
• Osmotic gradient is a difference in the concentration of a solute on each side of a semi-permeable membrane.
• The molecule transported inside during active transport is moved to its final destination.
• ATP is hydrolysed or broken down during active transport.
• Transport of glucose into red blood cells or skeletal muscle cells is an example of active transport.
• Carrier mediated diffusion is the process where lipid-insoluble molecules are aided across the membrane by a transmembrane carrier protein.
• Net diffusion of water occurs through a semi-permeable membrane from a diluted to a concentrated solution along its own concentration gradient.
• Diffusion over shorter distances occurs at a greater rate than diffusion over larger distances.
• When a cell is placed in a hypotonic solution, the cell bursts.