Download
1 / 21
220 likes | 399 Vues
Cell membranes and transport. The need to control movement. Waste products need to be removed Nutrients need to be received Requirements for respiration Oxygen, Carbon dioxide. Phospholipids. Polar structure Hydrophobic tails (water hating) Hydrophilic head (water liking). Cell membrane.
E N D
The need to control movement • Waste products need to be removed • Nutrients need to be received • Requirements for respiration • Oxygen, Carbon dioxide
Phospholipids • Polar structure • Hydrophobic tails (water hating) • Hydrophilic head (water liking)
Cell membrane • Phosophlipidbylayer visible at x100 000 (7nm) • Fluid mosaic ie the phospholipids are free to move around. • Hydrophobic tails point inwards in the cell • Some proteins float between the two membrane layers, which can assist with active transport • Cholesterol helps regulate the rigidity and fluidity of this layer.
Proteins • Transport proteins act as a hydrophylic pathway through the membrane. • Glycolipids and glycoproteins have a carbohydrate chain attached. They can act as receptors for particular chemicals and hormones.
Movement in and out of cells • Diffusion- the spreading of molecules from a high concentration to low concentration (down gradient) until evenly distributed. • Factors affecting rate of diffusion: • Steepness of gradient • Temperature (kinetic energy) • Surface area for movement • Molecule size • Facilitated diffusion (hydrophilic protein channels) is used for large molecules.
Osmosis • Diffusion of water molecules across a semi permeable membrane • Water moves from regions of high water potential to low water potential. The presence of solutes on one side of the membrane affects the water potential
Solute plus solvent = Solution • Addingsolute to water lowers the water potential. • Pure water has a water potential of zero • Addingsomesolutewillgive the water a negative value for water potential • (The amountthat a solutewill do thisiscalledsolutepotential)
Osmosis in plant cells Plasmolysis, Turgidity
Answer SAQ 4.3 • Page 56
Active transport • Active transport involvesmovement of ions UP the concentration gradient. Transport proteinsform ‘kissinggates’ which open and close to move substances. This process uses energy (ATP)
Bulk transport • Some processes exsist to move substances on a larger (non molecular scale) • Phagocytosis involves the cell ‘eating up’ substances by engulfing them through the membrane. This is carried out by cells called phagocytes, which typically exsist in the immune system. • Pinoscytosis is the similar proccess where cells may take in liquids. • Removing substances from the cells in this way is called exocytosis
Exchange surfaces • In many instances WHOLE ORGANISMS need to beinvolved in the transfer of substances. • Lungs are one suchexample in gas exchange. Alveolicreate a structure with a huge surface area wherebloodispassedveryclosely to gassesfrom the outsideenvironment. (total lung surface area of an adultis 70m2) • Lungsallow CO2 fromblood to diffuse down concentration gradient intolungs, and O2 down concentration gradient intoblood.
Plant roots • Plant root hair cells give the plant an enormous surface area for the uptake of mineral ions. • Plants can reduce their water potential trough transpiration, which causes the roots to draw up more water from the soil by osmosis. • Plants may use facilitated diffusion with water movement to gain mineral ions. • Active transport will more often be used when the concentration of ions is much higher in the root than the soil.
