Cell biology

• Light microscopes

  • developed in 17th century
  • uses light and lenses to form a magnified image of a specimen
  • scientists use it to see individual cells and their large subcellular structures e.g. nuclei
• Electron microscopes

  • developed in first half of 20th century
  • used beams of electrons instead of light
  • has a higher magnification and resolving power as they have a much smaller wavelength
  • scuentists use it to see cells in much more detail e.g. internal structures of mitochondria
• Equation for magnification 


  magnification = image size/actual size
• diffusion

  • the net movement of particles from an area of high concentration to low concentration
  • e.g. oxygen and carbon dioxide diffuse in and out of cells during gas exchange
• rate of diffusion

  • temperature
  • concentration
  • pressure
  • surface area
• osmosis

  • the net movement of water across a partially permeable membrane, from an area of high water concentration to low concentration
  • e.g. water will diffuse into a sugar solution and dilute it as it has low water concentration
• active transport

  • allows substance to travel from an area of low concentration to high concentration (against concentration gradient)
  • because of this it requires a lot of energy from respiration
• example of active transport

  • root hair cells are specialised cells which create an exchange surface with soil
  • they use energy from repsiration to actively transport the ions from the soil to the cell
• prokaryotic cells

  • e.g. bacterial cell
  • no nucleus
  • single-celled
  • simpler and smaller than eukaryotic cells
• eukaryotic cells

  • e.g. plant and animal cells
  • has a nucleus
  • multicellular (made up of many cells)
• the difference in plant cells to animal cells

  • vacuole
  • cell wall
  • chloroplast
• mitochondria


  releases energy for respiration
• ribosomes


  used for protein synthesis
• cytoplasm


  where chemical reactions take place
• cell wall


  made of cellulose to provide structure and support to the cell
• bacterial cell structure

  • single strand of DNA
  • small rings of DNA called plasmids
  • no chloroplast or mitochondria
  • has cell wall, cell membrane, cytoplasm