I'm Etalie, I'm currently studying for my AS levels and will (hopefully) be posting revision entries on psychology and sociology.
I previously uploaded posts on GCSE revision. If it helps you then great! But I'm not an expert on anything AT ALL so don't rely on everything I post.
(Also, I'm not taking credit for any of the pictures or info here, it's all off google images, notes from BBC bitesize and CGP revision guides, textbooks etc)

(NB - GCSE: italics in the science subjects are things that are only in paper 2!)

Tuesday, 29 April 2014

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS

Diffusion
  • The gradual movement of particles from a high concentration to a lower concentration 
  • Happens in liquids and gases - particles free to move about 
  • eg: perfume in air

Cell membranes -
  • Hold cell together and control substances entering/exiting 
  • Substances move in and out of cells by osmosis, diffusion and active transport 
  • Only small molecules can dissolve through (eg: glucose, amino acids, water, oxygen) 
  • Large molecules (eg: starch, proteins etc.) can't diffuse through cell membranes  

Diffusion experiment (non-living system) - 
- Phenolphthalein - pH indicator, pink in alkaline, colourless in acidic solution
  1. Make agar jelly with phenolphthalein and dilute sodium hydroxide (jelly will be pink) 
  2. Fill beaker with dilute hydrochloric acid 
  3. Use a scalpel to cut out cubes of jelly - put them in the beaker (use different size cubes and a timer to investigate surface area and diffusion)
  4. leave cubes - turn colourless (acid diffuses into agar jelly, neutralises sodium hydroxide)
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