b1

• image size = real object x magnification
• size of 1 cell = diameter of field view ➗ number of cells across diameter
• higher resolution = better because it gives a sharper image
• microscope rpa

  1. drop water using pipette on microscope slide
  2. peel thin layer of epidermal tissue
  3. use forceps to place layer on slide
  4. add 2 drops of iodine using pipette
  5. lower coverslip
  6. place slide on stage
  7. lowest power objective lens
  8. turn coarse adjustment knob for distance
  9. turn fine adjustment for focus
  10. make clear labelled drawing of cells
• coarse adjustment knob - changes the distance between the objective lens and the slide
• fine adjustment knob - brings image into focus
• iodine - stains highlight object in a cell by adding colour to them
• osmosis - the movement of water molecules from a region of high water concentration to a region of low water concentration cross a partially permeable membrane from a dilute solution
• active transport - movement of molecules from a low concentration to a high concentration through a membrane
• diffusion - the net movement of particles from an area of high concentration to an area of low concentration
• osmosis rpa

  1. cork borer to cut 5 potato cylinders of same diameter
  2. trim length of cylinders to 3cm
  3. dry potato carefully by blotting it with a paper towel
  4. accurately measure and record mass and length of each potato
  5. measure 10cm³ of 1.0m, 0.75m, 0.5m and 0.25m of sugar solution into boiling tubes (label)
  6. 5th boiling tube should have just water to act as a control
  7. add one potato into each boiling tube
  8. leave overnight
  9. remove and dry
  10. remeasure length and mass
  11. calculate % change
• eukaryotic cells - have a nucleus with DNA and membrane bound organelles
• prokaryotic cells - no nucleus, free DNA, plasmids
• differentiation - the process by which a cell becomes specialised for its function
• diffusion - the net movement of particles from an area of high concentration to an area of low concentration
• osmosis - the movement of water molecules from a region of high water concentration to a region of low water concentration through a partially permeable membrane
• active transport - movement of molecules from a low concentration to a high concentration against the concentration gradient, requires energy from respiration
• examples of active transport:

  • root hair cells: take up minerals ions (for growth), it has a higher concentration of minerals in the root hair cell than in the soil so requires energy from respiration for active transport
  • in the gut: glucose and amino acids from food move from the gut to the bloodstream - sometimes a lower concentration of sugar/nutrients in the gut than the blood so the concentration gradient is wrong way, diffusion cannot take place, active transport allows nutrients to be taken into the blood
• water always moves into the more concentrated solution

  • so drinking high salt content means that there's a lower water concentration in your blood and tissue fluid than your cells - so the water is sucked out via osmosis and the cells shrivel up and die
• external solution more dilute = water molecules move into cells causing it to burst

  external solution less dilute = water molecules move out of cells causing it to be shrivelled up
• examples of diffusion in the body:

  • oxygen moves through structures in the lungs called alveoli into red blood cells and then into cells across the body for respiration
  • urea (waste product) moves from liver cells into blood plasma to be transported to the kidney for excretion
• alveoli are specialised to maximise diffusion rate:

  • large surface area
  • thin walls
  • moist lining
  • good blood supply
  • covered in cappillaries
• single-celled organisms have a large surface area to volume ratio so enough substances can be diffused across the membrane to supply the volume of the cell
• multicellular organisms have a smaller surface area to volume ratio so need an exchange surface because not enough substances can diffuse across to supply the cells entire volume
• exchange surfaces (in multicellular organisms) are adapted to maximise effectiveness:

  • thin membrane - substances have a short distance to diffuse
  • large surface area to volume ratio so lots of substances can diffuse at once
  • lots of blood vessels to get substances in and out the blood quickly
• Villi provides a large surface area inside the small intestine so more digested food is absorbed quickly into the blood

  they have:

  • single layer of surface cells
  • good blood supply to assist quick absorption

  moves by both diffusion and active transport depending on concentration of nutrients in blood and gut
• water vapour evaporates from inside the cells inside the leaf - it then escapes via diffusion because there's lots of it inside the leaf and less of it in the air outside the leaf
• leaves have a large surface area (flat shape) so that more co2 enters leaves for photosynthesis and can absorb more sunlight. Airspaces inside the leaf create more surface area
• thin membrane provides a short diffusion pathway eg in lungs, capillary and alveoli walls are thin and in the small intestine, villi have a single layer of surface cell
• having a good blood supply creates a steep concentration gradient so diffusion occurs faster eg in lungs supply oxygen to alveoli where gas exchange takes place so blood becomes oxygenated and waste co2 is removed, this is a constant process so concentration gradient is always steep.
• Two ways bacteria can be grown


  • Nutrient broth
  • colonies on agar plate
• stem cells

  take stem cells from patient bone marrow remove the faulty gene create embryo using these stem cells remove stem cells from embryo allow them to divide / differentiate into another cell