SB1 bio edexcel

• Osmosis


  The diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a selectively permeable membrane
• Selectively permeable membrane


  • Allows some small substances to pass through but prevents larger substances doing the same
• The cell wall is totally permeable and has no role in controlling what enters and leaves a cell
• Cell wall


  A rigid structure that provides a plant cell with support and keeps non-woody plants upright
• Osmosis is the diffusion of water molecules down the concentration gradient
• Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration.
• Diffusion occurs in gases like air and liquids like water because their particles can move around and collide with each other randomly.
• the hotter the gas or liquid, the faster diffusion happens. This is because the particles have more energy and move faster at higher temperatures.
• • substances diffuse more quickly through gases than through liquids. This is because the particles in a gas are more spread out and move faster than the particles in a liquid.
• The nucleus is the control centre of the cell, containing genetic material (DNA) that determines its characteristics.
• Animal cell


  • Nucleus - stores genetic information
  • Cell membrane - controls what enters and exits
  • Mitochondria - responsible for respiration
  • Ribosomes - make essential proteins
  • Cytoplasm - where chemical reactions happen
• Plant cell


  • Cell wall - gives extra strength and protection
  • Vacuole - stores cell sap
  • Chloroplasts - for photosynthesis
• Bacteria cell


  • Flagellum - acts like a 'tail' for movement
  • DNA floats loose in cytoplasm
  • Plasmid loops - extra DNA
• Prokaryotic cells


  Smaller, simpler, no nucleus
• Eukaryotic cells


  Bigger, more complex, have a nucleus
• Cell differentiation


  Cells switch particular genes on/off to become specialized
• Sperm and egg cells

  • Haploid nucleus - half the normal number of chromosomes
  • Egg cell has lots of nutrients in cytoplasm
• Ciliated epithelial cell


  • Has hair-like cilia to help move substances along
• Light microscope


  Invented in 1500s, uses light beams, relatively low resolution, can view living cells
• Electron microscope


  Invented in 1930s, uses electron beams, higher resolution, cannot view living cells
• Total magnification


  Eyepiece lens magnification x Objective lens magnification
• Enzymes

  Biological catalysts made by living things, speed up reactions
• Enzyme active site


  Place where substrate fits in, highly specific
• Enzyme breakdown


  Larger molecules broken down into smaller molecules
• Enzyme synthesis


  Smaller molecules joined together to form larger molecules
• As temperature increases


  Enzyme activity increases until optimum, then quickly denatures
• As pH changes from optimum


  Enzyme begins to denature
• As substrate concentration increases

  Enzyme activity increases until all active sites are full
• Benedict's test for reducing sugars

  1. Add Benedict's reagent

  2. Heat gently

  3. Blue = low sugar, orange-red = high sugar
• Biuret test for proteins

  1. Add potassium hydroxide

  2. Add copper sulfate

  3. Purple colour indicates positive
• Emulsion test for lipids

  1. Add ethanol, shake, pour into water

  2. Milky water indicates positive
• Iodine test for starch

  1. Add iodine

  2. Blue-black colour indicates positive
• Calorimetry to measure food energy


  1. Set up apparatus

  2. Burn food sample

  3. Measure temperature rise in water

  4. Calculate energy using specific heat capacity
• Diffusion


  Passive movement of particles from high to low concentration
• Active transport


  Movement of particles from low to high concentration, requires energy
• Osmosis


  Diffusion of water molecules from high to low concentration through a partially permeable membrane