biology

• Magnifying power


  The ability of a microscope to make an object appear larger
• Resolving power


  The ability of a microscope to distinguish between two closely spaced objects
• Light microscopes have lower magnifying and resolving power compared to electron microscopes
• Calculating magnification


  Magnification = Diameter of image / Diameter of object
• When labelling an image from a microscope, make it clear what magnification you used
• Light microscope


  • Typical magnification range: x4 to x1000
  • Typical resolving power: 0.2 micrometres
• Electron microscope


  • Typical magnification range: x2000 to x2000000
  • Typical resolving power: 0.2 nanometres
• The actual size of the image depends on the magnification used
• Animal and plant cells

  Structures and functions
• Plant cells can make their own food, they do not move the whole body about, and they are generally larger than animal cells
• Plant cells contain chloroplasts, which are not found in animal cells
• The presence of chloroplasts and vacuoles


  Are important differences between plant and animal cells
• Chloroplasts are found in many plant cells but not all of them
• Eukaryotic cells


  Contain membrane-bound organelles and genetic material enclosed within a nucleus
• Prokaryotic cells


  Lack membrane-bound organelles and have a simpler structure, with genetic material not enclosed within a nucleus
• Prokaryotes are generally smaller and simpler in structure than eukaryotes
• Prokaryotes have a cell wall around the outside of the cell membrane
• Prokaryotes have circular DNA and many have plasmids
• The genetic material in eukaryotes is enclosed within a nucleus


  While in prokaryotes it is not enclosed
• Animal and plant cells are both eukaryotic
• Specialised animal cells


  • Have a structure adapted to their specific function within an organism
• Specialised plant cells


  • Have a structure adapted to their specific function within a plant
• Muscle cells are adapted for contraction and movement
• Photosynthetic cells in plants contain chloroplasts for photosynthesis
• Phloem cells in plants transport sugars and other nutrients
• Xylem cells in plants transport water and minerals
• The structure of a specialised plant cell


  Is adapted to carry out its particular function
• Diffusion


  The movement of particles from an area of high concentration to an area of low concentration
• Diffusion occurs down a concentration gradient
• Diffusion is affected by temperature, with particles moving more rapidly at higher temperatures</b>
• Substances such as oxygen, carbon dioxide, water and glucose can move in and out of cells by diffusion
• Osmosis


  The diffusion of water molecules through a partially permeable membrane from an area of high water concentration to an area of low water concentration
• Osmosis is important for maintaining the correct water balance in animal and plant cells
• Plant cells can be damaged if the water concentration outside the cell changes dramatically
• Active transport


  The movement of substances against a concentration gradient, requiring the input of energy
• Active transport allows plants to absorb mineral ions from very dilute solutions in the soil
• Active transport is important for the absorption of nutrients in the gut and the reabsorption of substances in the kidneys
• Some glands use active transport to produce very salty secretions
• Adaptations for exchanging materials

  • Increase the surface area to volume ratio
  • Provide a moist surface for diffusion
  • Improve blood/air contact
• Adaptations in plants


  • Thin cell walls
  • Many stomata
  • Large surface area of leaves