Bio chap 3

• Permeable


  Allow molecules to freely pass through it
• Semi-permeable


  Allow certain molecules/ions can pass through it by diffusion
• Ions


  Have charge
• Molecules


  No charge
• Rate of passage depends on the concentration, temperature, and permeability of the membrane
• Plasma membrane


  • Permeable to non-polar, small, uncharged molecules (e.g. O2, CO2, water)
  • Not permeable to charged ions, polar molecules (e.g. glucose, starch)
• Plasma membrane is a phospholipid bilayer with hydrophilic tails
• Passive transport


  Allow molecules to pass through plasma membrane down a concentration gradient without requiring cellular energy
• Active transport


  Pumps molecules through the plasma membrane against a concentration gradient, utilising cellular energy (ATP)
• • Passive transport includes diffusion, facilitated diffusion, osmosis
  • Active transport includes sodium-potassium pump, secretion of substances into bloodstream
• Diffusion


  Net movement of molecules or ions from a region of high concentration to a region of low concentration, no energy needed
• Factors affecting rate of diffusion

  • Temperature
  • Concentration gradient
  • Distance
  • Surface area
• Osmosis


  Diffusion of water molecules across a semi-permeable membrane down the concentration gradient, no energy needed
• Water has high water potential in regions with low solute concentration, and low water potential in regions with high solute concentration
• Experiment


  1. Fill visking tube with starch solution

  2. Suspend in water (control)

  3. Fill visking tube with starch and amylase solution, suspend in water (experiment)

  4. Add Benedict's solution to both

  5. Leave for 5 minutes

  6. Record colour change
• Amylase will digest starch into maltose, which can diffuse out through the tubing</b>
• Dependent variable


  Presence of glucose/maltose inside and outside the tubing
• Independent variable


  Presence of amylase
• Control variables


  Quantities of solutions, time, temperature, Benedict's and iodine solutions
• Plant cell


  • Turgid - swollen, firm
  • Flaccid - soft
  • Turgor pressure from water pushing outwards on cell wall
  • Cell wall is made of cellulose, outside the cell membrane, fully permeable
• Plasmolysis


  Plant cell placed in concentrated solution loses water by osmosis, cell contents shrink and pull away from cell wall
• Active transport


  Movement of molecules/ions from low to high concentration, requires cellular energy (ATP) and carrier proteins
• Active transport is important for uptake of molecules like ions, amino acids by root hairs against concentration gradient
• Carrier proteins change shape to take molecules/ions through cell membrane against concentration gradient
• Starch


  A complex carbohydrate made up of long chains of glucose molecules bonded together.
• Glucose


  A simple sugar (monosaccharide) that is a building block for more complex carbohydrates and is absorbed directly into the bloodstream during digestion.
• Amylase


  An enzyme that breaks down complex carbohydrates, such as starch, into simpler sugars that can be absorbed and used for energy by the body.
• Maltose


  A disaccharide made up of two glucose molecules bonded together. It is formed when the enzyme amylase breaks down starch during digestion.